China, People’s Republic

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.

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.

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.

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.

Managing the concentration of atmospheric CO₂ requires a multifaceted engineering strategy which remains a highly challenging task. Reducing atmospheric CO₂ (CO2R) by converting it to value-added chemicals in a carbon neutral footprint manner must be the ultimate goal. The latest progress in CO2R through either abiotic (artificial catalysts) or biotic (natural enzymes) processes is reviewed herein. Abiotic CO2R can be conducted in the aqueous phase that usually leads to the formation of a mixture of CO formic acid and hydrogen. By contrast a wide spectrum of hydrocarbon species is often observed by abiotic CO2R in the gaseous phase. On the other hand biotic CO2R is often conducted in the aqueous phase and a wide spectrum of value-added chemicals are obtained. Key to the success of the abiotic process is understanding the surface chemistry of catalysts which significantly governs the reactivity and selectivity of CO2R. However in biotic CO2R operation conditions and reactor design are crucial to reaching a neutral carbon footprint. Future research needs to look toward neutral or even negative carbon footprint CO2R processes. Having a deep insight into the scientific and technological aspect of both abiotic and biotic CO2R would advance in designing efficient catalysts and microalgae farming systems. Integrating the abiotic and biotic CO2R such as microbial fuel cells further diversifies the spectrum of CO2R.

The current evidential effect of carbon emissions has become a societal challenge and the need to transition to cleaner energy sources/technologies has attracted wide research attention. Technologies that utilize low-grade heat like the organic Rankine cycle (ORC) and Kalina cycle have been proposed as viable approaches for fossil reduction/carbon mitigation. The development of renewable energy-based multigeneration systems is another alternative solution to this global challenge. Hence it is important to monitor the development of multigeneration energy systems based on low-grade heat. In this study a review of the ORC’s application in multigeneration systems is presented to highlight the recent development in ORC integrality/application. Beyond this a new ORC-CPVT (concentrated photovoltaic/thermal) integrated multigeneration system is also modeled and analyzed using the thermodynamics approach. Since most CPVT systems integrate hot water production in the thermal stem the proposed multigeneration system is designed to utilize part of the thermal energy to generate electricity and hydrogen. Although the CPVT system can achieve high energetic and exergetic efficiencies while producing thermal energy and electricity these efficiencies are 47.9% and 37.88% respectively for the CPVT-ORC multigeneration configuration. However it is noteworthy that the electricity generation from the CPVT-ORC configuration in this study is increased by 16%. In addition the hot water cooling effect and hydrogen generated from the multigeneration system are 0.4363 L/s 161 kW and 1.515 L/s respectively. The environmental analysis of the system also shows that the carbon emissions reduction potential is enormous.

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.

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.

The ever-increasing demand for energy coupled with dwindling fossil fuel resources make the establishment of a clean and sustainable energy system a compelling need. Hydrogen-based energy systems offer potential solutions. Although in the long-term the ultimate technological challenge is large-scale hydrogen production from renewable sources the pressing issue is how to store hydrogen efficiently on board hydrogen fuel-cell vehicles.

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.