China, People’s Republic
Study on Temper Embrittlement and Hydrogen Embrittlement of a Hydrogenation Reactor by Small Punch Test
Jun 2017
Publication
The study on temper embrittlement and hydrogen embrittlement of a test block from a 3Cr1Mo1/4V hydrogenation reactor after ten years of service was carried out by small punch test (SPT) at different temperatures. The SPT fracture energy Esp (derived from integrating the load-displacement curve) divided by the maximum load (Fm) of SPT was used to fit the Esp/Fm versus-temperature curve to determine the energy transition temperature (Tsp) which corresponded to the ductile-brittle transition temperature of the Charpy impact test. The results indicated that the ratio of Esp/Fm could better represent the energy of transition in SPT compared with Esp. The ductile-to-brittle transition temperature of the four different types of materials was measured using the hydrogen charging test by SPT. These four types of materials included the base metal and the weld metal in the as-received state and the base metal and the weld metal in the de-embrittled state. The results showed that there was a degree of temper embrittlement in the base metal and the weld metal after ten years of service at 390 °C. The specimens became slightly more brittle but this was not obvious after hydrogen charging. Because the toughness of the material of the hydrogenation reactor was very good the flat samples of SPT could not characterize the energy transition temperature within the liquid nitrogen temperature. Additionally there was no synergetic effect of temper embrittlement and hydrogen embrittlement found in 3Cr1Mo1/4V steel.
Assessment of a Fuel Cell Based-hybrid Energy System to Generate and Store Electrical Energy
Jan 2022
Publication
Solid oxide fuel cells (SOFC) have significant applications and performance and their integration into coupled and cascading energy systems can improve the overall performance of the process. Furthermore due to the constant time performance of the fuel cell the problem of fuel starvation may arise by changing the amount of load which can adversely affect the overall performance of the process. In the present study the excess heat of the SOFC is converted into electrical energy in two stages using different heat generators. The coupled energy system in the present article has a new configuration in which the relationship of its components is different from the systems reported in the literature. Furthermore since the use of an energy storage system can improve the overall reliability the energy produced by the coupled energy cycle is stored by a storage technology for peak consumption times. The introduced system can generate approximately 580 W of electrical power with an efficiency of 80%. The highest and lowest share in power generation is related to fuel cell with 82% and thermoelectric generator with 5%. The rest of the system power (i.e. 13%) is produced by thermionic generator. In addition the system requires 0.025 kg per hour of hydrogen fuel. It was also found that to operate the system for 5 h a day requires a storage system with a size of 3.3 m3 . Moreover two key issues to enhance the storage system performance are: adjusting the initial pressure of the system to values close to the peak (optimal) value and using turbines and/or pumps with higher efficiencies. With the aim of supplying 5 kWh of electrical energy five different scenarios based on the design of various effective parameters have been presented.
A Fundamental Viewpoint on the Hydrogen Spillover Phenomenon of Electrocatalytic Hydrogen Evolution
Jun 2021
Publication
Hydrogen spillover phenomenon of metal-supported electrocatalysts can significantly impact their activity in hydrogen evolution reaction (HER). However design of active electrocatalysts faces grand challenges due to the insufficient understandings on how to overcome this thermodynamically and kinetically adverse process. Here we theoretically profile that the interfacial charge accumulation induces by the large work function difference between metal and support (∆Φ) and sequentially strong interfacial proton adsorption construct a high energy barrier for hydrogen transfer. Theoretical simulations and control experiments rationalize that small ∆Φ induces interfacial charge dilution and relocation thereby weakening interfacial proton adsorption and enabling efficient hydrogen spillover for HER. Experimentally a series of Pt alloys-CoP catalysts with tailorable ∆Φ show a strong ∆Φ-dependent HER activity in which PtIr/CoP with the smallest ∆Φ = 0.02 eV delivers the best HER performance. These findings have conclusively identified ∆Φ as the criterion in guiding the design of hydrogen spillover-based binary HER electrocatalysts
Thermodynamic Analysis of the Gasification of Municipal Solid Waste
May 2017
Publication
This work aims to understand the gasification performance of municipal solid waste (MSW) by means of thermodynamic analysis. Thermodynamic analysis is based on the assumption that the gasification reactions take place at the thermodynamic equilibrium condition without regard to the reactor and process characteristics. First model components of MSW including food green wastes paper textiles rubber chlorine-free plastic and polyvinyl chloride were chosen as the feedstock of a steam gasification process with the steam temperature ranging from 973 K to 2273 K and the steam-to-MSW ratio (STMR) ranging from 1 to 5. It was found that the effect of the STMR on the gasification performance was almost the same as that of the steam temperature. All the differences among the seven types of MSW were caused by the variation of their compositions. Next the gasification of actual MSW was analyzed using this thermodynamic equilibrium model. It was possible to count the inorganic components of actual MSW as silicon dioxide or aluminum oxide for the purpose of simplification due to the fact that the inorganic components mainly affected the reactor temperature. A detailed comparison was made of the composition of the gaseous products obtained using steam hydrogen and air gasifying agents to provide basic knowledge regarding the appropriate choice of gasifying agent in MSW treatment upon demand.
Hydrogen Embrittlement and Improved Resistance of Al Addition in Twinning-Induced Plasticity Steel: First-Principles Study
Apr 2019
Publication
Understanding the mechanism of hydrogen embrittlement (HE) of austenitic steels and developing an effective strategy to improve resistance to HE are of great concern but challenging. In this work first-principles studies were performed to investigate the HE mechanism and the improved resistance of Al-containing austenite to HE. Our results demonstrate that interstitial hydrogen atoms have different site preferences in Al-free and Al-containing austenites. The calculated binding energies and diffusion barriers of interstitial hydrogen atoms in Al-containing austenite are remarkably higher than those in Al-free austenite indicating that the presence of Al is more favorable for reducing hydrogen mobility. In Al-free austenite interstitial hydrogen atoms caused a remarkable increase in lattice compressive stress and a distinct decrease in bulk shear and Young’s moduli. Whereas in Al-containing austenite the lattice compressive stress and the mechanical deterioration induced by interstitial hydrogen atoms were effectively suppressed.
3D Quantitative Risk Assessment on a Hydrogen Refuelling Station in Shanghai
Sep 2019
Publication
The number of hydrogen refuelling stations worldwide is growing rapidly in recent years. The first large capacity hydrogen refuelling station in China is under construction. A 3D quantitative risk assessment QRA)is conducted for this station. Hazards associated with hydrogen systems are identified. Leakage frequency of hydrogen equipment are analyzed. Jet flame explosion scenarios and corresponding accident consequences are simulated. Risk acceptance criteria for hydrogen refuelling stations are discussed. The results show that the risk of this refuelling station is acceptable. And the maximum lethality frequency is 6.3*10-6. The area around compressors has the greatest risk. People should be avoided as far as possible from the compressor when the compressor does not need to be maintained. With 3D QRA the visualization of the evaluation results will help stakeholders to observe the hazardous areas of the hydrogen refuelling station at a glance.
Modulating Electronic Structure of Metal-organic Frameworks by Introducing Atomically Dispersed Ru for Efficient Hydrogen Evolution
Mar 2021
Publication
Developing high-performance electrocatalysts toward hydrogen evolution reaction is important for clean and sustainable hydrogen energy yet still challenging. Herein we report a single-atom strategy to construct excellent metal-organic frameworks (MOFs) hydrogen evolution reaction electrocatalyst (NiRu0.13-BDC) by introducing atomically dispersed Ru. Significantly the obtained NiRu0.13-BDC exhibits outstanding hydrogen evolution activity in all pH especially with a low overpotential of 36 mV at a current density of 10 mA cm−2 in 1 M phosphate buffered saline solution which is comparable to commercial Pt/C. X-ray absorption fine structures and the density functional theory calculations reveal that introducing Ru single-atom can modulate electronic structure of metal center in the MOF leading to the optimization of binding strength for H2O and H* and the enhancement of HER performance. This work establishes single-atom strategy as an efficient approach to modulate electronic structure of MOFs for catalyst design.
Magnesium Based Materials for Hydrogen Based Energy Storage: Past, Present and Future
Jan 2019
Publication
Volodymyr A. Yartys,
Mykhaylo V. Lototskyy,
Etsuo Akiba,
Rene Albert,
V. E. Antonov,
Jose-Ramón Ares,
Marcello Baricco,
Natacha Bourgeois,
Craig Buckley,
José Bellosta von Colbe,
Jean-Claude Crivello,
Fermin Cuevas,
Roman V. Denys,
Martin Dornheim,
Michael Felderhoff,
David M. Grant,
Bjørn Christian Hauback,
Terry D. Humphries,
Isaac Jacob,
Petra E. de Jongh,
Jean-Marc Joubert,
Mikhail A. Kuzovnikov,
Michel Latroche,
Mark Paskevicius,
Luca Pasquini,
L. Popilevsky,
Vladimir M. Skripnyuk,
Eugene I. Rabkin,
M. Veronica Sofianos,
Alastair D. Stuart,
Gavin Walker,
Hui Wang,
Colin Webb,
Min Zhu and
Torben R. Jensen
Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures kinetics and thermodynamics of the systems based on MgH2 nanostructuring new Mg-based compounds and novel composites and catalysis in the Mg based H storage systems. Finally thermal energy storage and upscaled H storage systems accommodating MgH2 are presented.
Investigation of the Influence of Pre-Charged Hydrogen on Fracture Toughness of As-Received 2.25Cr1Mo0.25V Steel and Weld
Jun 2018
Publication
Fracture failure caused by hydrogen embrittlement (HE) is a major concern for the system reliability and safety of hydrogen storage vessels which are generally made of 2.25Cr1Mo0.25V steel. Thus study of the influence of pre-charged hydrogen on fracture toughness of as-received 2.25Cr1Mo0.25V steel and weld is of significant importance. In the current work the influence of hydrogen on fracture toughness of as-received 2.25Cr1Mo0.25V steel and weld was systematically studied. Base metal (BM) and weld metal (WM) specimens under both hydrogen-free and hydrogen-charged conditions were tested using three-point bending tests. Hydrogen was pre-charged inside specimens by the immersion charging method. The J-integral values were calculated for quantitatively evaluating the fracture toughness. In order to investigate the HE mechanisms optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure of BM and WM specimens. The results revealed that the presence of pre-charged hydrogen caused a significant decrease of the fracture toughness for both BM and WM specimens. Moreover the pre-charged hydrogen led to a remarkable transition of fracture mode from ductile to brittle pattern in 2.25Cr1Mo0.25V steel.
Development and Comparison of the Test Methods Proposed in the Chinese Test Specifications for Fuel Cell Electric Vehicles
Feb 2022
Publication
Fuel cell electric vehicles are generally considered to have broad development prospects due to their high efficiency and zero emissions. The governments of the United States Japan the European Union and China are taking action to promote the development of the industry. In 2020 China launched a fuel cell electric vehicle demonstration project and there will be 30∼50 thousand FCEVs included in this project by the end of 2025. How to standardize the consistency of data and develop a unified and accurate evaluation method is an important topic. The difficulty is how to keep balance among scientificity neutrality and feasibility in the evaluation method. In order to evaluate the performance of vehicles in demonstration operation projects China has issued the "Fuel Cell Electric Vehicle Test Specifications" which is an important guide for the future development of fuel cell electric vehicles in China. This paper compares the test methods for critical parameters in this specifications with those used in the United States and Japan. It explains China’s technical considerations in detail including fuel cell system rated power the volume power density of the fuel cell stack fuel cell system specific power fuel cell system sub-zero cold start and fuel cell electric vehicle range contributed by hydrogen. For the volume power density of the fuel cell stack as an example both the US Department of Energy and Japan’s New Energy and Industrial Technology Development Organization have proposed technical goals. However the lack of specific and detailed test methods has confused the industry. We propose a new test method using bipolar plate measurement based on scientificity feasibility and neutrality This is the first time to define the measuring method of the volume and specific power density of the fuel cell stack. For sub-zero cold start we put forward a feasible scheme for sub-zero cold start at the system level. For range contributed by hydrogen we propose a new test method that can distinguish the contributing of electric and hydrogen energy. Furthermore a hydrogen-to-electric conversion formula is proposed to calculate the equivalent hydrogen consumption which makes it possible to compare the energy consumption between plug-in and non-plug-in vehicles. At the same time this approach is significant in helping fuel cell-related enterprises to understand the formulation of China’s “Fuel Cell Electric Vehicle Test Specifications”. It should also be helpful for guiding product design and predicting fuel cell electric vehicle policy direction in China.
Holistic Energy Efficiency and Environmental Friendliness Model for Short-Sea Vessels with Alternative Power Systems Considering Realistic Fuel Pathways and Workloads
Apr 2022
Publication
Energy requirements push the shipping industry towards more energy-efficient ships while environmental regulations influence the development of environmentally friendly ships by replacing fossil fuels with alternatives. Current mathematical models for ship energy efficiency which set the analysis boundaries at the level of the ship power system are not able to consider alternative fuels as a powering option. In this paper the energy efficiency and emissions index are formulated for ships with alternative power systems considering three different impacts on the environment (global warming acidification and eutrophication) and realistic fuel pathways and workloads. Besides diesel applications of alternative powering options such as electricity methanol liquefied natural gas hydrogen and ammonia are considered. By extending the analysis boundaries from the ship power system to the complete fuel cycle it is possible to compare different ships within the considered fleet or a whole shipping sector from the viewpoint of energy efficiency and environmental friendliness. The applicability of the model is illustrated on the Croatian ro-ro passenger fleet. A technical measure of implementation of alternative fuels in combination with an operational measure of speed reduction results in an even greater emissions reduction and an increase in energy efficiency. Analysis of the impact of voluntary speed reduction for ships with different power systems resulted in the identification of the optimal combination of alternative fuel and speed reduction by a specific percentage from the ship design speed.
Economic and Technical Analysis of Power to Gas Factory Taking Karamay as an Example
May 2022
Publication
Power to gas (PTG) refers to the technology of converting power into energy-storage gas which can absorb excess power when there is excess power and release energy-storage gas when needed. Based on the carbon dioxide (CO2 ) emission of Karamay City in Northwest China this study designed a process flow of the CO2 absorption process and the hydrogen and CO2 methanation process in PTG technology. The results show that the efficiency of the CO2 absorption process was 91.5% and the methanation efficiency was 77.5%. The heat recovery module was set during the process and the total heat recovered was 17.85 MW. The cost of producing synthetic natural gas (SNG) in the PTG factory was 1782 USD/ton. In terms of cost the cost of hydrogen production from electrolyzed water accounted for the largest proportion. In terms of product profit the sale of pure oxygen was the largest part of the profit. At present the carbon emission reduction index profit brought by SNG production accounted for a small proportion. In the future with technological progress industrial upgrading and the improvement in the carbon trading market PTG technology is expected to become one of the ways to achieve carbon-emission-reduction targets.
Artificial Neural Network Based Optimization of a Six-step Two-bed Pressure Swing Adsorption System for Hydrogen Purification
Apr 2021
Publication
The pressure swing adsorption (PSA) system is widely applied to separate and purify hydrogen from gaseous mixtures. The extended Langmuir equation fitted from the extended Langmuir-Freundlich isotherm has been used to predict the adsorption isothermal of hydrogen and methane on the zeolite 5A adsorbent bed. A six-step two-bed PSA model for hydrogen purification is developed and validated by comparing its simulation results with other works. The effects of the adsorption pressure the P/F ratio the adsorption step time and the pressure equalization time on the performance of the hydrogen purification system are studied. A four-step two-bed PSA model is taken into consideration and the six-step PSA system shows higher about 13% hydrogen recovery than the four-step PSA system. The performance of the vacuum pressure swing adsorption (VPSA) system is compared with that of the PSA system the VPSA system shows higher hydrogen purity than the PSA system. Based on the validated PSA model a dataset has been produced to train the artificial neural network (ANN) model. The effects of the number of neurons in the hidden layer and the number of samples used for training ANN model on the predicted performance of ANN model are investigated. Then the well-trained ANN model with 6 neurons in the hidden layer is applied to predict the performance of the PSA system for hydrogen purification. Multi-objective optimization of hydrogen purification system is performed based on the trained ANN model. The artificial neural network can be considered as a very effective method for predicting and optimizing the performance of the PSA system for hydrogen purification.
Optimization of Geothermal- and Solar-driven Clean Electricity and Hydrogen Production Multi-generation Systems to Address the Energy Nexus
Jan 2022
Publication
Given the limited sources of fossil fuels mankind should find new ways to meet its energy demands. In this regard geothermal and solar energy are acknowledged as reliable safe promising and clean means for this purpose. In this research study a comparative analysis is applied on geothermal and solar-driven multi-generation systems for clean electricity and hydrogen production through energy and exergy assessments. The system consists of an organic Rankine cycle a proton electrolyte membrane electrolyzer and a thermoelectric generator subsystem. The Engineering Equation Solver software has been utilized in order to model the system and obtain the output contours sensitivity analysis and exergy destruction. The results were calculated considering the ambient temperature of Bandar Abbas city as a case study considering the geothermal system due to better performance in comparison to the solar system. According to the sensitivity analysis the turbine efficiency evaporator inlet temperature thermoelectric generator suitability criterion pump efficiency and evaporator inlet mass flow rate are the most influential parameters. Also the exergy analysis showed that the utmost system's exergy destruction is pertinent to the evaporator and the least is related to the pump. In addition the system produces 352816 kWh and 174.913 kg of electrical power and hydrogen during one year.
Recent Development of Hydrogen and Fuel Cell Technologies: A Review
Aug 2021
Publication
Hydrogen has emerged as a new energy vector beyond its usual role as an industrial feedstock primarily for the production of ammonia methanol and petroleum refining. In addition to environmental sustainability issues energy-scarce developed countries such as Japan and Korea are also facing an energy security issue and hydrogen or hydrogen carriers such as ammonia and methylcyclohexane seem to be options to address these long-term energy availability issues. China has been eagerly developing renewable energy and hydrogen infrastructure to meet their sustainability goals and the growing energy demand. In this review we focus on hydrogen electrification through proton-exchange membrane fuel cells (PEMFCs) which are widely believed to be commercially suitable for automotive applications particularly for vehicles requiring minimal hydrogen infrastructure support such as fleets of taxies buses and logistic vehicles. This review covers all the key components of PEMFCs thermal and water management and related characterization techniques. A special consideration of PEMFCs in automotive applications is the highlight of this work leading to the infrastructure development for hydrogen generation storage and transportation. Furthermore national strategies toward the use of hydrogen are reviewed thereby setting the rationale for the hydrogen economy.
Comparison of Two Energy Management Strategies Considering Power System Durability for PEMFC-LIB Hybrid Logistics Vehicle
Jun 2021
Publication
For commercial applications the durability and economy of the fuel cell hybrid system have become obstacles to be overcome which are not only affected by the performance of core materials and components but also closely related to the energy management strategy (EMS). This paper takes the 7.9 t fuel cell logistics vehicle as the research object and designed the EMS from two levels of qualitative and quantitative analysis which are the composite fuzzy control strategy optimized by genetic algorithm and Pontryagin’s minimum principle (PMP) optimized by objective function respectively. The cost function was constructed and used as the optimization objective to prolong the life of the power system as much as possible on the premise of ensuring the fuel economy. The results indicate that the optimized PMP showed a comprehensive optimal performance the hydrogen consumption was 3.481 kg/100 km and the cost was 13.042 $/h. The major contribution lies in that this paper presents a method to evaluate the effect of different strategies on vehicle performance including fuel economy and durability of the fuel cell and battery. The comparison between the two totally different strategies helps to find a better and effective solution to reduce the lifetime cost.
Hollow CdS-Based Photocatalysts
Oct 2020
Publication
In recent years photocatalytic technology driven by solar energy has been extensively investigated to ease energy crisis and environmental pollution. Nevertheless efficiency and stability of photocatalysts are still unsatisfactory. To address these issues design of advanced photocatalysts is important. Cadmium sulphide (CdS) nanomaterials are one of the promising photocatalysts. Among them hollow-structured CdS featured with enhanced light absorption ability large surface area abundant active sites for redox reactions and reduced diffusion distance of photogenerated carriers reveals a broad application prospect. Herein main synthetic strategies and formation mechanism of hollow CdS photocatalysts are summarized. Besides we comprehensively discuss the current development of hollow-structured CdS nanomaterials in photocatalytic applications including H2 production CO2 reduction and pollutant degradation. Finally brief conclusions and perspectives on the challenges and future directions for hollow CdS photocatalysts are proposed.
Research on Carbide Characteristics and Their Influence on the Properties of Welding Joints for 2.25Cr1Mo0.25V Steel
Feb 2021
Publication
The carbide characteristics of 2.25Cr1Mo0.25V steel have an extremely important influence on the mechanical properties of welding joints. In addition hydrogen resistance behavior is crucial for steel applied in hydrogenation reactors. The carbide morphology was observed by scanning electron microscopy (SEM) and the carbide microstructure was characterized by transmission electron microscopy (TEM). Tensile and impact tests were carried out and the influence of carbides on properties was studied. A hydrogen diffusion test was carried out and the hydrogen brittleness resistance of welding metal and base metal was studied by tensile testing of hydrogenated samples to evaluate the influence of hydrogen on the mechanical properties. The research results show that the strength of the welding metal was slightly higher and the Charpy impact value was significantly lower compared to the base metal. The hydrogen embrittlement resistance of the welding metal was stronger than that of the base metal. The presence of more carbides and inclusions was the main cause of the decreased impact property and hydrogen brittleness resistance of the welding metal. These conclusions have certain reference value for designing and manufacturing hydrogenation reactors. View Full-Text
Effect of α′ Martensite Content Induced by Tensile Plastic Prestrain on Hydrogen Transport and Hydrogen Embrittlement of 304L Austenitic Stainless Steel
Aug 2018
Publication
Effects of microstructural changes induced by prestraining on hydrogen transport and hydrogen embrittlement (HE) of austenitic stainless steels were studied by hydrogen precharging and tensile testing. Prestrains higher than 20% at 20 °C significantly enhance the HE of 304L steel as they induce severe α′ martensite transformation accelerating hydrogen transport and hydrogen entry during subsequent hydrogen exposure. In contrast 304L steel prestrained at 50 and 80 °C and 316L steel prestrained at 20 °C exhibit less HE due to less α′ after prestraining. The increase of dislocations after prestraining has a negligible influence on apparent hydrogen diffusivity compared with pre-existing α′. The deformation twins in heavily prestrained 304L steel can modify HE mechanism by assisting intergranular (IG) fracture. Regardless of temperature and prestrain level HE and apparent diffusivity ( Dapp ) increase monotonously with α′ volume fraction ( fα′ ). Dapp can be described as log Dapp=log(Dα′sα′/sγ)+log[fα′/(1−fα′)] for 10%<fα′<90% with Dα′ is diffusivity in α′ sα′ and sγ are solubility in α′ and austenite respectively. The two equations can also be applied to these more typical duplex materials containing both BCC and FCC phases.
Synthetic Natural Gas Production from CO2 and Renewable H2: Towards Large-scale Production of Ni–Fe Alloy Catalysts for Commercialization
Apr 2020
Publication
Synthetic natural gas (SNG) is one of the promising energy carriers for the excessive electricity generated from variable renewable energy sources. SNG production from renewable H2 and CO2 via catalytic CO2 methanation has gained much attention since CO2 emissions could be simultaneously reduced. In this study Ni–Fe/(MgAl)Ox alloy catalysts for CO2 methanation were prepared via hydrotalcite precursors using a rapid coprecipitation method. The effect of total metal concentration on the physicochemical properties and catalytic behavior was investigated. Upon calcination the catalysts showed high specific surface area of above 230 m2 g−1. Small particle sizes of about 5 nm were obtained for all catalysts even though the produced catalyst amount was increased by 10 times. The catalysts exhibited excellent space-time yield under very high gas space velocity (34000 h−1) irrespective of the metal concentration. The CO2 conversions reached 73–79% at 300 °C and CH4 selectivities were at 93–95%. Therefore we demonstrated the potential of large-scale production of earth-abundant Ni–Fe based catalysts for CO2 methanation and the Power-to-Gas technology.
Synthesizing the High Surface Area g-C3N4 for Greatly Enhanced Hydrogen Production
Jul 2021
Publication
Adjusting the structure of g-C3N4 to significantly enhance its photocatalytic activity has attracted considerable attention. Herein a novel sponge-like g-C3N4 with a porous structure is prepared from the annealing of protonated melamine under N2/H2 atmosphere (PH-CN). Compared to bulk g-C3N4 via calcination of melamine under ambient atmosphere (B-CN) PH-CN displays thinner nanosheets and a higher surface area (150.1 m2/g) which is a benefit for shortening the diffusion distance of photoinduced carriers providing more active sites and finally favoring the enhancement of the photocatalytic activity. Moreover it can be clearly observed from the UV-vis spectrum that PH-CN displays better performance for harvesting light compared to B-CN. Additionally the PH-CN is prepared with a larger band gap of 2.88 eV with the Fermi level and conduction band potential increased and valence band potential decreased which could promote the water redox reaction. The application experiment results show that the hydrogen evolution rate on PH-CN was nearly 10 times higher than that of B-CN which was roughly 4104 μmol h−1 g−1. The method shown in this work provides an effective approach to adjust the structure of g-C3N4with considerable photocatalytic hydrogen evolution activity.
Self-Supported High-Entropy Alloy Electrocatalyst for Highly Efficient H2 Evolution in Acid Condition
Jul 2020
Publication
Developing non-precious catalysts as Pt substitutes for electrochemical hydrogen evolution reaction (HER) with superior stability in acidic electrolyte is of critical importance for large-scale low-cost hydrogen production from water. Herein we report a CoCrFeNiAl high-entropy alloy (HEA) electrocatalyst with self-supported structure synthesized by mechanical alloying and spark plasma sintering (SPS) consolidation. The HEA after HF treatment and in situ electrochemical activation for 4000 cycles of cyclic voltammetry (HF-HEAa2) presents favourable activity with overpotential of 73 mV to reach a current density of 10 mA cm−2 and a Tafel slope of 39.7 mV dec−1. The alloy effect of Al/Cr with Co/Fe/Ni at atomic level high-temperature crystallization as well as consolidation by SPS endow CoCrFeNiAl HEA with high stability in 0.5 M H2SO4 solution. The superior performance of HF-HEAa2 is related with the presence of metal hydroxides/oxides groups on HEA.
Physicochemical Properties of Proton-conducting SmNiO3 Epitaxial Films
Mar 2019
Publication
Proton conducting SmNiO3 (SNO) thin films were grown on (001) LaAlO3 substrates for systematically investigating the proton transport properties. X-ray Diffraction and Atomic Force Microscopy studies reveal that the as-grown SNO thin films have good single crystallinity and smooth surface morphology. The electrical conductivity measurements in air indicate a peak at 473 K in the temperature dependence of the resistance of the SNO films probably due to oxygen loss on heating. A Metal-Insulator-Transition occurs at 373 K for the films after annealing at 873 K in air. In a hydrogen atmosphere (3% H2/97% N2) an anomalous peak in the resistance is found at 685 K on the first heating cycle. Electrochemical Impedance Spectroscopy studies as a function of temperature indicate that the SNO films have a high ionic conductivity (0.030 S/cm at 773 K) in a hydrogen atmosphere. The activation energy for proton conductivity was determined to be 0.23 eV at 473–773 K and 0.37 eV at 773–973 K respectively. These findings demonstrate that SNO thin films have good proton conductivity and are good candidate electrolytes for low temperature proton-conducting Solid Oxide Fuel Cells.
Modeling and Statistical Analysis of the Three-side Membrane Reactor for the Optimization of Hydrocarbon Production from CO2 Hydrogenation
Feb 2020
Publication
Direct CO2 hydrogenation to hydrocarbons is a promising method of reducing CO2 emissions along with producing value-added products. However reactor design and performance have remained a challenging issue because of low olefin efficiency and high water production as a by-product. Accordingly a one-dimensional non-isothermal mathematical model is proposed to predict the membrane reactor performance and statistical analysis is used to assess the effects of important variables such as temperatures of reactor (Tr:A) shell (Ts:B) and tube (Tt:C) as well as sweep ratio (θ:D) and pressure ratio (φ:E) and their interactions on the products yields. In addition the optimized operating conditions are also obtained to achieve maximum olefin yields. Results reveal that interacting effects comprising AB (TrTs) AC (TrTt) AE (Trφ) BC (TsTt) CE (Ttφ) CD (Ttθ) and DE (θφ) play important roles on the product yields. It is concluded that higher temperatures at low sweep and pressure ratios can maximize the yields of olefins while simultaneously the yields of paraffins are minimized. In this regard optimized values for Tr Ts Tt θ and φ are determined as 325 °C 306.96 °C 325 °C 1 and 1 respectively.
Microwave Absorption of Aluminum/Hydrogen Treated Titanium Dioxide Nanoparticles
Dec 2018
Publication
Interactions between incident electromagnetic energy and matter are of critical importance for numerous civil and military applications such as photocatalysis solar cells optics radar detection communications information processing and transport et al. Traditional mechanisms for such interactions in the microwave frequency mainly rely on dipole rotations and magnetic domain resonance. In this study we present the first report of the microwave absorption of Al/H2 treated TiO2 nanoparticles where the Al/H2 treatment not only induces structural and optical property changes but also largely improves the microwave absorption performance of TiO2 nanoparticles. Moreover the frequency of the microwave absorption can be finely controlled with the treatment temperature and the absorption efficiency can reach optimal values with a careful temperature tuning. A large reflection loss of −58.02 dB has been demonstrated with 3.1 mm TiO2 coating when the treating temperature is 700 °C. The high efficiency of microwave absorption is most likely linked to the disordering-induced property changes in the materials. Along with the increased microwave absorption properties are largely increased visible-light and IR absorptions and enhanced electrical conductivity and reduced skin-depth which is likely related to the interfacial defects within the TiO2 nanoparticles caused by the Al/H2 treatment.
Overview of Biomass Conversion to Electricity and Hydrogen and Recent Developments in Low-Temperature Electrochemical Approaches
Nov 2020
Publication
Biomass is plant or animal material that stores both chemical and solar energies and that is widely used for heat production and various industrial processes. Biomass contains a large amount of the element hydrogen so it is an excellent source for hydrogen production. Therefore biomass is a sustainable source for electricity or hydrogen production. Although biomass power plants and reforming plants have been commercialized it remains a difficult challenge to develop more effective and economic technologies to further improve the conversion efficiency and reduce the environmental impacts in the conversion process. The use of biomass-based flow fuel cell technology to directly convert biomass to electricity and the use of electrolysis technology to convert biomass into hydrogen at a low temperature are two new research areas that have recently attracted interest. This paper first briefly introduces traditional technologies related to the conversion of biomass to electricity and hydrogen and then reviews the new developments in flow biomass fuel cells (FBFCs) and biomass electrolysis for hydrogen production (BEHP) in detail. Further challenges in these areas are discussed.
Analysis of Strategic Directions in Sustainable Hydrogen Investment Decisions
Jun 2020
Publication
This study seeks to find the appropriate strategies necessary to make sustainable and effective hydrogen energy investments. Within this scope nine different criteria are defined regarding social managerial and financial factors. A hesitant interval-valued intuitionistic fuzzy (IVIF) decision-making trial and evaluation laboratory (DEMATEL) methodology is considered to calculate the degree of importance of the criteria. Additionally impact relation maps are also generated to visualize the causality relationship between the factors. The findings indicate that the technical dimension has the greatest importance in comparison to managerial and financial factors. Furthermore it is also concluded that storage and logistics research and development and technological infrastructure are the most significant factors to be considered when defining hydrogen energy investment strategies. Hence before investing in hydrogen energy necessary actions should be taken to minimize the storage and logistic costs. Among them building the production site close to the usage area will contribute significantly to this purpose. In this way possible losses during the transportation of hydrogen can be minimized. Moreover it is essential to identify the lowest-cost hydrogen storage method by carrying out the necessary research and development activities thereby increasing the sustainability and effectiveness of hydrogen energy investment projects.
Combined Soft Templating with Thermal Exfoliation Toward Synthesis of Porous g-C3N4 Nanosheets for Improved Photocatalytic Hydrogen Evolution
Apr 2021
Publication
Insufficient active sites and fast charge carrier recombination are detrimental to photocatalytic activity of graphitic carbon nitride (g-C3N4). In this work a combination of pore creating with thermal exfoliation was employed to prepare porous g-C3N4 nanosheets for photocatalytic water splitting into hydrogen. Hexadecyl trimethyl ammonium chloride (CTAC) as the soft template promoted the formation of porous g-C3N4 during the thermal condensation of melamine. On further post-synthesis calcination the porous g-C3N4 aggregates were exfoliated into discrete nanosheets accompanied by an increase in specific surface area and defects. Optimal porous g-C3N4 nanosheets achieved 3.6 times the photocatalytic hydrogen evolution rate for bulk counterpart. The enhanced photocatalytic activity may be ascribed to TCN-1%CTAC has larger specific surface area stronger optical absorption intensity and higher photogenerated electron–hole separation efficiency. The external quantum efficiency of TCN-1%CTAC was measured to be 3.4% at 420 nm. This work provides a simple combinatorial strategy for the preparation of porous g-C3N4 nanosheets with low cost environmental friendliness and enhanced photocatalytic activity.
On-Board Liquid Hydrogen Cold Energy Utilization System for a Heavy-Duty Fuel Cell Hybrid Truck
Aug 2021
Publication
In this paper a kind of on-board liquid hydrogen (LH2 ) cold energy utilization system for a heavy-duty fuel cell hybrid truck is proposed. Through this system the cold energy of LH2 is used for cooling the inlet air of a compressor and the coolant of the accessories cooling system sequentially to reduce the parasitic power including the air compressor water pump and radiator fan power. To estimate the cold energy utilization ratio and parasitic power saving capabilities of this system a model based on AMESim software was established and simulated under different ambient temperatures and fuel cell stack loads. The simulation results show that cold energy utilization ratio can keep at a high level except under extremely low ambient temperature and light load. Compared to the original LH2 system without cold energy utilization the total parasitic power consumption can be saved by up to 15% (namely 1.8 kW).
Enhanced Hydrogen Storage of Alanates: Recent Progress and Future Perspectives
Feb 2021
Publication
The global energy crisis and environmental pollution have caused great concern. Hydrogen is a renewable and environmentally friendly source of energy and has potential to be a major alternative energy carrier in the future. Due to its high capacity and relatively low cost of raw materials alanate has been considered as one of the most promising candidates for hydrogen storage. Among them LiAlH4 and NaAlH4 as two representative metal alanates have attracted extensive attention. Unfortunately the high desorption temperature and sluggish kinetics restrict its practical application. In this paper the basic physical and chemical properties as well as the hydrogenation/dehydrogenation reaction mechanism of LiAlH4 and NaAlH4 are briefly reviewed. The recent progress on strategic optimizations toward tuning the thermodynamics and kinetics of the alanate including nanoscaling doping catalysts and compositing modification are emphatically discussed. Finally the coming challenges and the development prospects are also proposed in this review.
Microbial Fuel Cells: Technologically Advanced Devices and Approach for Sustainable/renewable Energy Development
Dec 2021
Publication
There is a huge quantity of energy needs/demands for multiple developmental and domestic activities in the modern era. And in this context consumption of more non-renewable energy is reported and created many problems or issues (availability of fossil fuel stocks in the future period causes a huge quantity of toxic gases or particles or climatic change effects) at the global level. And only sustainable or renewable fuel development can provide alternate fuel and we report from various biological agents processes including microbial biofuel cell applications for future energy needs only. These will not cause any interference in natural resources or services. Microbial biofuel cells utilize the living cell to produce bioelectricity via bioelectrochemical system. It can drive electricity or other energy generation currents via lived cell interaction. Microbial fuel cells (MFCs) and enzymatic biofuel cells with their advancement in design can improve sustainable bio-energy production by proving an efficient conversion system compared to chemical fuels into electric power. Different types of MFCs operation are reported in wastewater treatment with biogas biohydrogen and other biofuel/energy generation. Later biogas can convert into electric power. Hybrid microbial biofuel cell utility with photochemical reaction is found for electricity generation. Recent research and development in microbial biofuel design and its application will emphasize bioenergy for the future.
Efficient Renewable-to-Hydrogen Conversion via Decoupled Electrochemical Water Splitting
Aug 2020
Publication
Water electrolysis powered by renewables provides a green approach to hydrogen production to support the ‘‘hydrogen economy.’’ However the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are tightly coupled in both time and space in traditional water electrolysis which brings inherent operational challenges such as the mixture of H2/O2 and the limited HER rate caused by the sluggish kinetics of OER. Against this background decoupling H2 and O2 production in water electrolysis by using the auxiliary redox mediator was first proposed in 2013 in which O2 and H2 are produced at different times rates and/or locations. The decoupling strategy offers not only a new way to facilitate renewables to H2 but it can also be applied in other chemical or electrochemical processes. This review describes recent efforts to develop high-performance redox mediators optimized strategies in decoupled water electrolysis the design of electrolyzer configuration the challenges faced and the prospective directions.
Wittichenite Semiconductor of Cu3BiS3 Films for Efficient Hydrogen Evolution from Solar Driven Photoelectrochemical Water Splitting
Jun 2021
Publication
A highly efficient low-cost and environmentally friendly photocathode with long-term stability is the goal of practical solar hydrogen evolution applications. Here we found that the Cu3BiS3 film-based photocathode meets the abovementioned requirements. The Cu3BiS3-based photocathode presents a remarkable onset potential over 0.9 VRHE with excellent photoelectrochemical current densities (~7 mA/cm2 under 0 VRHE) and appreciable 10-hour long-term stability in neutral water solutions. This high onset potential of the Cu3BiS3-based photocathode directly results in a good unbiased operating photocurrent of ~1.6 mA/cm2 assisted by the BiVO4 photoanode. A tandem device of Cu3BiS3-BiVO4 with an unbiased solar-to-hydrogen conversion efficiency of 2.04% is presented. This tandem device also presents high stability over 20 hours. Ultimately a 5 × 5 cm2 large Cu3BiS3-BiVO4 tandem device module is fabricated for standalone overall solar water splitting with a long-term stability of 60 hours.
Integral Sliding Mode Control for Maximum Power Point Tracking in DFIG Based Floating Offshore Wind Turbine and Power to Gas
Jun 2021
Publication
This paper proposes a current decoupling controller for a Doubly-fed Induction Generator (DFIG) based on floating offshore wind turbine and power to gas. The proposed controller realizes Maximum Power Point Tracking (MPPT) through integral sliding mode compensation. By using the internal model control strategy an open-loop controller is designed to ensure that the system has good dynamic performance. Furthermore using the integral Sliding Mode Control (SMC) strategy a compensator is designed to eliminate the parameter perturbation and external disturbance of the open-loop control. The parameters of the designed controller are designed through Grey Wolf Optimization (GWO). Simulation results show that the proposed control strategy has better response speed and smaller steady-state error than the traditional control strategy. This research is expected to be applied to the field of hydrogen production by floating offshore wind power.
Comparison Between Hydrogen Production by Alkaline Water Electrolysis and Hydrogen Production by PEM Electrolysis
Sep 2021
Publication
Hydrogen is an ideal clean energy source that can be used as an energy storage medium for renewable energy sources. The water electrolysis hydrogen production technology which is one of the mainstream hydrogen production methods can be used to produce high-purity hydrogen and other energy sources can be converted into hydrogen storage by electrolysis. Hydrogen production by alkaline water electrolysis and hydrogen production by PEM electrolysis are all water electrolysis hydrogen production technologies that have been industrially applied. From the application point of view the paper compares the working principle of the two kinds of electrolyzers the process flow of hydrogen production equipment advantages and disadvantages. This article provides a reference for relevant researchers.
The Effect of Symmetrically Tilt Grain Boundary of Aluminum on Hydrogen Diffusion
Feb 2022
Publication
High-strength aluminum alloys are widely used in industry. Hydrogen embrittlement greatly reduces the performance and service safety of aluminum alloys. The hydrogen traps in aluminum profoundly affect the hydrogen embrittlement of aluminum. Here we took a coincidence-site lattice (CSL) symmetrically tilted grain boundary (STGB) Σ5(120)[001] as an example to carry out molecular dynamics (MD) simulations of hydrogen diffusion in aluminum at different temperatures and to obtain results and rules consistent with the experiment. At 700 K three groups of MD simulations with concentrations of 0.5 2.5 and 5 atomic % hydrogen (at. % H) were carried out for STGB models at different angles. By analyzing the simulation results and the MSD curves of hydrogen atoms we found that in the low hydrogen concentration of STGB models the grain boundaries captured hydrogen atoms and hindered their movement. In high-hydrogen-concentration models the diffusion rate of hydrogen atoms was not affected by the grain boundaries. The analysis of the simulation results showed that the diffusion of hydro-gen atoms at the grain boundary is anisotropic.
Effect of Cementite on the Hydrogen Diffusion/Trap Characteristics of 2.25Cr-1Mo-0.25V Steel with and without Annealing
May 2018
Publication
Hydrogen embrittlement (HE) is a critical issue that affects the reliability of hydrogenation reactors. The hydrogen diffusivity/trap characteristics of 2.25Cr-1Mo-0.25V steel are important parameters mainly used to study the HE mechanism of steel alloys. In this work the hydrogen diffusivity/trap characteristics of heat-treated (annealed) and untreated 2.25Cr-1Mo-0.25V steel were studied using an electrochemical permeation method. The microstructures of both 2.25Cr-1Mo-0.25V steels were investigated by metallurgical microscopy. The effect of cementite on the hydrogen diffusivity/trap mechanisms was studied using thermodynamics-based and Lennard–Jones potential theories. The results revealed that the cementite located at the grain boundaries and at the interfaces of lath ferrite served as a kind of hydrogen trap (i.e. an irreversible hydrogen trap). In addition hydrogen was transported from ferrite to cementite via up-hill diffusion thereby supporting the hypothesis of cementite acting as a hydrogen trap.
Effect of Deformation Microstructures on Hydrogen Embrittlement Sensitivity and Failure Mechanism of 304 Austenitic Stainless Steel: The Significant Role of Rolling Temperature
Feb 2022
Publication
Metastable austenitic stainless steels (ASSs) have excellent ductility but low strength so that their usage as load-bearing components is significantly limited. Rolling is an effective method of increasing strength whereas the effect of rolling temperature on microstructural evolution the hydrogen embrittlement (HE) sensitivity and fracture mechanisms is still unclear. In present study the effect of cold/warm rolling on detailed microstructural characteristics of 304 ASS was quantitatively investigated and the corresponding HE sensitivity was evaluated via slow strain rate test. The results suggest that cold-rolling led to high strength but poor plasticity and deteriorated HE sensitivity while warm-rolled samples provided combination of high strength and ductility and also superior HE resistance. Compared with 18% α′-martensite in cold -rolled steel warm-rolled specimens consisted of complete austenite less twins and lower dislocation density,moreover the favorable {112} ND and {110} ND textures replaced the harmful {001} ND texture. Based on in-situ EBSD observation during SSRT the HE sensitivity was governed by the combined effect of pre-deformation microstructures and the dynamic microstructural evolution. Advanced method of time-of-flight secondary ion mass spectrometry was used to observe the distribution of hydrogen and the hydrogen content of specimens was determined by the gas chromatograph thermal desorption analysis method. An exceedingly small amount of hydrogen entered the warm-rolled samples while a large amount of hydrogen was trapped at grain boundaries of cold-rolled sample leading to complete intergranular fracture. Therefore warm rolling is an effective pathway for obtaining high combination of strength and ductility together with excellent HE sensitivity.
Multi-Criteria Optimization of a Biomass-Based Hydrogen Production System Integrated With Organic Rankine Cycle
Oct 2020
Publication
Biomass-based gasification is an attractive and promising pathway for hydrogen production. In this work a biomass-based hydrogen production system integrated with organic Rankine cycle was designed and investigated to predict the performance of hydrogen production yield and electricity generation under various operating conditions. The modified equilibrium model presented desirable results for the produced syngas compositions compared with the experimental data. Hydrogen yields from four types of biomass (wood chips daily manure sorghum and grapevine pruning wastes) were compared under the same operating condition with wood chips exhibiting the maximum hydrogen yield of 11.59 mol/kg. The effects of gasification temperature equivalence ratio and steam-to-biomass ratio on the hydrogen yield and electricity generation were investigated by using the response surface method. Furthermore the system was optimized using a genetic algorithm based on the response surface model. A preferred optimal solution with a hydrogen yield of 39.31 mol/kg and an output power of 3558.08 kW (0.99 kW h/kg) was selected by the linear programming technique for multidimensional analysis of the preference method.
Study on Flake Formation Behavior and Its Influence Factors in Cr5 Steel
Apr 2018
Publication
A flake is a crack that is induced by trapped hydrogen within steel. To study its formation mechanism previous studies mostly focused on the formation process and magnitude of hydrogen pressure in hydrogen traps such as cavities and cracks. However according to recent studies the hydrogen leads to the decline of the mechanical properties of steel which is known as hydrogen embrittlement is another reason for flake formation. In addition the phenomenon of stress induced hydrogen uphill diffusion should not be neglected. All of the three behaviors are at work simultaneously. In order to further explore the formation mechanism of flakes in steel the process of flake initiation and growth were studied with the following three coupling factors: trap hydrogen pressure hydrogen embrittlement and stress induced hydrogen re-distribution. The analysis model was established using the finite element method and a crack whose radius is 0.5 mm was set in its center. The cohesive method and Bilinear Traction Separate Law (BTSL) were used to address the coupling effect. The results show that trap hydrogen pressure is the main driving force for flake formation. After the high hydrogen pressure was generated around the trap a stress field formed. In addition the trap is the center of stress concentration. Then hydrogen is concentrated in a distribution around this trap and most of the steel mechanical properties are reduced. The trap size is a key factor for defining the critical hydrogen content for flake formation and propagation. However when the trap size exceeds the specified value the critical hydrogen content does not change any more. As for the crack whose radius is 0.5 mm the critical hydrogen content of Cr5VMo steel is 2.2 ppm which is much closer to the maximum safe hydrogen concentration of 2.0 ppm used in China. The work presented in this article increases our understanding of flake formation and propagation mechanisms in steel.
Effect of Hydrogen on Very High Cycle Fatigue Behavior of a Low-strength Cr-Ni-Mo-V Steel Containing Micro-defects
Dec 2017
Publication
The role of hydrogen in fatigue failure of low strength steels is not as well understood as of high strength steels in very high cycle fatigue regime. In this work axially cyclic tests on a low strength Cr-Ni-Mo-V steel with charged hydrogen were carried out up to the very high cycle fatigue regime under ultrasonic frequency to examine the degradation of fatigue strength and associated failure mechanisms. Results show that the S-N curves show a continuously decreasing mode and hydrogen-charged specimens have lower fatigue strength and shorter fatigue lifetime as compared with as-received specimens. It is concluded that the hydrogen trapped by inclusions drives interior micro-defects as dominant crack initiation site and has a clear link to the initiation and early growth of interior fatigue cracks.
Study of the Co-production of Butanol and Hydrogen by Immobilizing Clostridium Acetobutylicum CICC8012
Mar 2019
Publication
Three kinds of carrier materials activated carbon bagasse and brick were used as immobilizing carriers during fermentation by Clostridium acetobutylicum CICC8012. Compared with cell suspended fermentation enhanced fermentation performance was achieved during immobilizing cell fermentation with shorter fermentation time required. During the experiments hydrogen and butanol appear to be competitive events. The best fermentation performance of butanol was obtained in the case of bagasse as immobilizing carrier (5.804g/L of butanol production 0.22g/g of yield and 0.44g/L/h of productivity) while the hydrogen yield was just 1.41 mol/mol. The highest hydrogen productivity (402mL/L/h) and yield (1.808mol/mol glucose) could be obtained in the case of brick as immobilizing carrier while the butanol yield was 0.18 g/g. The highest hydrogen concentration of 66.76 % was obtained in the case of activated carbon as immobilizing carrier.
A Host-guest Approach to Fabricate Metallic Cobalt Nanoparticles Embedded in Silk-derived N-doped Carbon Fibers for Efficient Hydrogen Evolution
Feb 2017
Publication
Hydrogen evolution reaction (HER) plays a key role in generating clean and renewable energy. As the most effective HER electrocatalysts Pt group catalysts suffer from severe problems such as high price and scarcity. It is highly desirable to design and synthesize sustainable HER electrocatalysts to replace the Pt group catalysts. Due to their low cost high abundance and high activities cobalt-incorporated N-doped nanocarbon hybrids are promising candidate electrocatalysts for HER. In this report we demonstrated a robust and eco-friendly host-guest approach to fabricate metallic cobalt nanoparticles embedded in N-doped carbon fibers derived from natural silk fibers. Benefiting from the one-dimensional nanostructure the well-dispersed metallic cobalt nanoparticles and the N-doped thin graphitized carbon layer coating the best Co-based electrocatalyst manifests low overpotential (61 mV@10 mA/cm2) HER activity that is comparable with commercial 20% Pt/C and good stability in acid. Our findings provide a novel and unique route to explore high-performance noble-metal-free HER electrocatalysts.
Acoustic Emission Characteristics of Used 70 MPa Type IV Hydrogen Storage Tanks During Hydrostatic Burst Tests
Sep 2019
Publication
Currently the periodic inspection of composite tanks is typically achieved via hydrostatic test combined with internal and external visual inspections. Acoustic emission (AE) technology demonstrates a promising non destructive testing method for damage mode identification and damage assessment. This study focuses on AE signals characteristics and evolution behaviours for used 70 MPa Type IV hydrogen storage tanks during hydrostatic burst tests. AE-based tensile tests for epoxy resin specimen and carbon fiber tow were implemented to obtain characteristics of matrix cracking and fiber breakage. Then broadband AE sensors were used to capture AE signals during multi-step loading tests and hydrostatic burst tests. K-means ++ algorithm and wavelet packet transform are performed to cluster AE signals and verify the validity. Combining with tensile tests three clusters are manifested via matrix cracking fiber/matrix debonding and fiber breakage according to amplitude duration counts and absolute energy. The number of three clustering signals increases with the increase of pressure showing accumulated and aggravated damage. The sudden appearance of a large number of fiber breakage signals during hydrostatic burst tests suggests that the composite tank structure is becoming mechanically unstable namely the impending burst failure of the tank.
Amorphous Iron-nickel Phosphide Nanocone Arrays as Efficient Bifunctional Electrodes for Overall Water Splitting
May 2020
Publication
The synthesis of low-cost and highly active electrodes for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for water splitting. In this work the novel amorphous iron-nickel phosphide (FeP-Ni) nanocone arrays as efficient bifunctional electrodes for overall water splitting have been in-situ assembled on conductive three-dimensional (3D) Ni foam via a facile and mild liquid deposition process. It is found that the FeP-Ni electrode demonstrates highly efficient electrocatalytic performance toward overall water splitting. In 1 M KOH electrolyte the optimal FeP-Ni electrode drives a current density of 10 mA/cm2 at an overpotential of 218 mV for the OER and 120 mV for the HER and can attain such current density for 25 h without performance regression. Moreover a two-electrode electrolyzer comprising the FeP-Ni electrodes can afford 10 mA/cm2 electrolysis current at a low cell voltage of 1.62 V and maintain long-term stability as well as superior to that of the coupled RuO2/NF‖Pt/C/NF cell. Detailed characterizations confirm that the excellent electrocatalytic performances for water splitting are attributed to the unique 3D morphology of nanocone arrays which could expose more surface active sites facilitate electrolyte diffusion benefit charge transfer and also favourable bubble detachment behaviour. Our work presents a facile and cost-effective pathway to design and develop active self-supported electrodes with novel 3D morphology for water electrolysis.
Spin Pinning Effect to Reconstructed Oxyhydroxide Layer on Ferromagnetic Oxides for Enhanced Water Oxidation
Jun 2021
Publication
Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER to manipulate the spin ordering of ferromagnetic OER catalysts (e.g. by magnetization) can reduce the kinetic barrier. However most active OER catalysts are not ferromagnetic which makes the spin manipulation challenging. In this work we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxideFM/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning simple magnetization further increases the spin alignment and thus the OER activity which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1st dehydrogenation to reduce the barrier for subsequent O-O coupling.
Design and Performance of a Compact Air-Breathing Jet Hybrid-Electric Engine Coupled With Solid Oxide Fuel Cells
Feb 2021
Publication
A compact air-breathing jet hybrid-electric engine coupled with solid oxide fuel cells (SOFC) is proposed to develop the propulsion system with high power-weight ratios and specific thrust. The heat exchanger for preheating air is integrated with nozzles. Therefore the exhaust in the nozzle expands during the heat exchange with compressed air. The nozzle inlet temperature is obviously improved. SOFCs can directly utilize the fuel of liquid natural gas after being heated. The performance parameters of the engine are acquired according to the built thermodynamic and mass models. The main conclusions are as follows. 1) The specific thrust of the engine is improved by 20.25% compared with that of the traditional jet engine. As pressure ratios rise the specific thrust increases up to 1.7 kN/(kg·s−1). Meanwhile the nozzle inlet temperature decreases. However the temperature increases for the traditional combustion engine. 2) The power-weight ratio of the engine is superior to that of internal combustion engines and inferior to that of turbine engines when the power density of SOFC would be assumed to be that predicted for 2030. 3) The total pressure recovery coefficients of SOFCs combustors and preheaters have an obvious influence on the specific thrust of the engine and the power-weight ratio of the engine is strongly affected by the power density of SOFCs.
Catalyst Engineering for Electrochemical Energy Conversion from Water to Water: Water Electrolysis and the Hydrogen Fuel Cell
May 2020
Publication
In the context of the current serious problems related to energy demand and climate change substantial progress has been made in developing a sustainable energy system. Electrochemical hydrogen–water conversion is an ideal energy system that can produce fuels via sustainable fossil-free pathways. However the energy conversion efficiency of two functioning technologies in this energy system—namely water electrolysis and the fuel cell—still has great scope for improvement. This review analyzes the energy dissipation of water electrolysis and the fuel cell in the hydrogen–water energy system and discusses the key barriers in the hydrogen- and oxygen-involving reactions that occur on the catalyst surface. By means of the scaling relations between reactive intermediates and their apparent catalytic performance this article summarizes the frameworks of the catalytic activity trends providing insights into the design of highly active electrocatalysts for the involved reactions. A series of structural engineering methodologies (including nanoarchitecture facet engineering polymorph engineering amorphization defect engineering element doping interface engineering and alloying) and their applications based on catalytic performance are then introduced with an emphasis on the rational guidance from previous theoretical and experimental studies. The key scientific problems in the electrochemical hydrogen–water conversion system are outlined and future directions are proposed for developing advanced catalysts for technologies with high energy-conversion efficiency.
An Investigation of Gaseous Hydrogen Storage Characterizations of Mg–Y–Ni–Cu Alloys Synthesized by Melt Spinning
Aug 2018
Publication
Melt spinning was successfully utilized to prepare Mg25−xYxNi9Cu (x = 0 1 3 5 7) alloys producing nanocrystalline and amorphous structures with improved hydrogenation and dehydrogenation performances. The influence of spinning rate on hydrogenation and dehydrogenation thermodynamics and kinetics was studied in detail. XRD and TEM were utilized to characterize the alloy structures. Hydrogenation and dehydrogenation performances were investigated by Sievert apparatus DSC and TGA connected to a H2 detector. Dehydrogenation activation energies were estimated using both Arrhenius and Kissinger methods. Results show that melt spinning significantly decreases thermodynamic parameters (ΔH and ΔS) and ameliorates desorption kinetics. Dehydrogenation activation energy markedly lowers with increase in spinning rate and is the real driver of amelioration of dehydrogenation kinetics caused by increasing Y content.
Comprehensive Performance Evaluation of Densified Liquid Hydrogen/Liquid Oxygen as Propulsion Fuel
Jan 2022
Publication
Densified liquid hydrogen/liquid oxygen is a promising propulsion fuel in the future. In order to systematically demonstrate the benefits and challenges of densified liquid hydrogen/liquid oxygen a transient thermodynamical model considering the heat leakage temperature rise engine thrust pressurization pressure of the tank and wall thickness of tank is developed in the present paper and the performance of densified liquid hydrogen/liquid oxygen as propulsion fuel is further evaluated in actual application. For liquid hydrogen/liquid oxygen tanks at different structural dimensions the effects of many factors such as temperature rise during propellant ground parking lift of engine thrust mass reduction of the tank structure and extension of spacecraft in‐orbit time are analyzed to demonstrate the comprehensive performance of liquid hydrogen/liquid oxygen after densification. Meanwhile the problem of subcooling combination matching of liquid hydro‐ gen/liquid oxygen is proposed for the first time. Combining the fuel consumption and engine thrust lifting the subcooling combination matching of liquid hydrogen/liquid oxygen at different mixing ratios and constant mixing ratios are discussed respectively. The results show that the relative engine thrust enhances by 6.96% compared with the normal boiling point state in the condition of slush hydrogen with 50% solid content and enough liquid oxygen. The in‐orbit time of spacecraft can extend about 2–6.5 days and 24–95 days for slush hydrogen with 50% solid content and liquid oxygen in the triple point state in different cryogenic tanks respectively. Due to temperature rise during parking the existing adiabatic storage scheme and filling scheme for densification LH2 need to be redesigned and for densification LO2 are suitable. It is found that there is an optimal subcooling matching relation after densification of liquid hydrogen/liquid oxygen as propulsion fuel. In other words the subcooling temperature of liquid hydrogen/liquid oxygen is not the lower the bet‐ ter but the matching relationship between LH2 subcooling degree and LO2 subcooling degree needs to be considered at the same time. It is necessary that the LO2 was cooled to 69.2 K and 54.5 K when the LH2 of 13.9 K and SH2 with 45% was adopted respectively. This research provides theoretical support for the promotion and application of densification cryogenic propellants.
No more items...