Production & Supply Chain

The thermochemical conversion of methane (CH4) and water (H2O) to syngas and hydrogen via chemical looping using concentrated sunlight as a sustainable source of process heat attracts considerable attention. It is likewise a means of storing intermittent solar energy into chemical fuels. In this study solar chemical looping reforming of CH4 and H2O splitting over non-stoichiometric ceria (CeO2/CeO2−δ) redox cycle were experimentally investigated in a volumetric solar reactor prototype. The cycle consists of (i) the endothermic partial oxidation of CH4 and the simultaneous reduction of ceria and (ii) the subsequent exothermic splitting of H2O and the simultaneous oxidation of the reduced ceria under isothermal operation at ~1000°C enabling the elimination of sensible heat losses as compared to non-isothermal thermochemical cycles. Ceria-based reticulated porous ceramics with different sintering temperatures (1000 and 1400°C) were employed as oxygen carriers and tested with different methane flow rates (0.1–0.4 NL/min) and methane concentrations (50 and 100%). The impacts of operating conditions on the foam-averaged oxygen non-stoichiometry (reduction extent δ) syngas yield methane conversion solar-to-fuel energy conversion efficiency as well as the effects of transient solar conditions were demonstrated and emphasized. As a result clean syngas was successfully produced with H2/CO ratios approaching 2 during the first reduction step while high-purity H2 was subsequently generated during the oxidation step. Increasing methane flow rate and CH4 concentration promoted syngas yields up to 8.51 mmol/gCeO2 and δ up to 0.38 at the expense of enhanced methane cracking reaction and reduced CH4 conversion. Solar-to-fuel energy conversion efficiency namely the ratio of the calorific value of produced syngas to the total energy input (solar power and calorific value of converted methane) and CH4 conversion were achieved in the range of 2.9–5.6% and 40.1–68.5% respectively.

According to new findings the use of alternative energy sources such as wind energy is needed to supply the energy demand of future generations. On the other hand combined renewable energy systems can be more efficient than their stand-alone systems. Therefore clean energy-based hybrid energy systems can be a suitable solution for fossil fuels. However for their widespread commercialization more detailed and powerful studies are needed. On the other hand in order to attain sustainable development for the use of renewable energy sources due to their nature energy storage is required. The motivation of this study is introduce and examine a new energy system performance for the production of electricity and hydrogen fuel as well as energy storage. So this paper presents the energy and exergy operation of a hybrid wind turbine water electrolyzer and Pumped-hydro-compressed air system. The electricity produced by the wind turbine is used to produce hydrogen fuel in electrolyzer and the excess energy is stored using the storage system. It was found that the electrolyzer needed 512.6 W of electricity to generate 5 mol/h of hydrogen fuel which was supplied by a 10 kW-wind turbine. In such a context the efficiency of the process was 74.93%. Furthermore on average the isothermal process requires 17.53% less storage capacity than the isentropic process. The effect of key parameters such as rate of hydrogen fuel production operating pressures wind speed and components efficiency on the process operation is also examined.

Efficient hydrogen emission from ethanol with disperse graphene foam particles by using a continuous wave infrared laser diode is reported. The products of ethanol dissociation - hydrogen methane and carbon oxide were measured using mass spectrometry. It was found that the most efficient generation of hydrogen was observed when graphene particles were irradiated by a focused laser beam proceeded at the surface of ethanol solution. The process was assisted by intense white light emission resulting from the laser induced multiphoton ionization of graphene combined with the simultaneous emission of hot electrons. The hot electron emission enables the efficient dissociation of ethanol molecules located close to the solution surface with graphene foam particles.

Hydrogen is an economical source of clean energy that has been utilized by industry for decades. In recent years demand for hydrogen has risen significantly. Hydrogen sources include water electrolysis hydrocarbon steam reforming and fossil fuels which emit hazardous greenhouse gases and therefore have a negative impact on global warming. The increasing worldwide population has created much pressure on natural fuels with a growing gap between demand for renewable energy and its insufficient supply. As a result the environment has suffered from alarming increases in pollution levels. Biohydrogen is a sustainable energy form and a preferable substitute for fossil fuel. Anaerobic fermentation photo fermentation microbial and enzymatic photolysis or combinations of such techniques are new approaches for producing biohydrogen. For cost-effective biohydrogen production the substrate should be cheap and renewable. Substrates including algal biomass agriculture residue and wastewaters are readily available. Moreover substrates rich in starch and cellulose such as plant stalks or agricultural waste or food industry waste such as cheese whey are reported to support dark- and photo-fermentation. However their direct utilization as a substrate is not recommended due to their complex nature. Therefore they must be pretreated before use to release fermentable sugars. Various pretreatment technologies have been established and are still being developed. This article focuses on pretreatment techniques for biohydrogen production and discusses their efficiency and suitability including hybrid-treatment technology

Fuel cells are promising technologies for zero-emission energy conversion. They are used in several applications such as power plants cars and even submarines. Hydrogen supply is crucial for such systems and using Proton Exchange Membrane Fuel Cell in dead-end mode is a solution to save hydrogen. Since water and impurities accumulate inside the stack purging is necessary. However the importance of operating parameters is not well known for fuel cells working in closed environments. A Design of Experiment approach studying time between two purges and cell performance was conducted on an air-breathing stack in a closed environment. The most influential parameters on the time between two purges are the relative humidity and the current load. Convection in the closed environment can decrease the stability of the fuel cell. A linear model with interactions between these last three parameters was found to accurately describe the studied responses.

A technoeconomic analysis of photoelectrochemical (PEC) and photovoltaic-electrolytic (PV-E) solar-hydrogen production of 10 000 kg H₂ day⁻¹ (3.65 kilotons per year) was performed to assess the economics of each technology and to provide a basis for comparison between these technologies as well as within the broader energy landscape. Two PEC systems differentiated primarily by the extent of solar concentration (unconcentrated and 10× concentrated) and two PV-E systems differentiated by the degree of grid connectivity (unconnected and grid supplemented) were analyzed. In each case a base-case system that used established designs and materials was compared to prospective systems that might be envisioned and developed in the future with the goal of achieving substantially lower overall system costs. With identical overall plant efficiencies of 9.8% the unconcentrated PEC and non-grid connected PV-E system base-case capital expenses for the rated capacity of 3.65 kilotons H₂ per year were $205 MM ($293 per m² of solar collection area (m_S⁻²) $14.7 W_H2P⁻¹) and $260 MM ($371 mS−2 $18.8 W_H2P⁻¹) respectively. The untaxed plant-gate levelized costs for the hydrogen product (LCH) were $11.4 kg⁻¹ and $12.1 kg⁻¹ for the base-case PEC and PV-E systems respectively. The 10× concentrated PEC base-case system capital cost was $160 MM ($428 m_S−2 $11.5 WH₂P⁻¹) and for an efficiency of 20% the LCH was $9.2 kg−1. Likewise the grid supplemented base-case PV-E system capital cost was $66 MM ($441 _mS⁻² $11.5 W_H2P⁻¹) and with solar-to-hydrogen and grid electrolysis system efficiencies of 9.8% and 61% respectively the LCH was $6.1 kg⁻¹. As a benchmark a proton-exchange membrane (PEM) based grid-connected electrolysis system was analyzed. Assuming a system efficiency of 61% and a grid electricity cost of $0.07 kWh⁻¹ the LCH was $5.5 kg⁻¹. A sensitivity analysis indicated that relative to the base-case increases in the system efficiency could effect the greatest cost reductions for all systems due to the areal dependencies of many of the components. The balance-of-systems (BoS) costs were the largest factor in differentiating the PEC and PV-E systems. No single or combination of technical advancements based on currently demonstrated technology can provide sufficient cost reductions to allow solar hydrogen to directly compete on a levelized cost basis with hydrogen produced from fossil energy. Specifically a cost of CO₂ greater than ∼$800 (ton CO₂)−1 was estimated to be necessary for base-case PEC hydrogen to reach price parity with hydrogen derived from steam reforming of methane priced at $12 GJ⁻¹ ($1.39 (kg H₂)⁻¹). A comparison with low CO₂ and CO₂-neutral energy sources indicated that base-case PEC hydrogen is not currently cost-competitive with electrolysis using electricity supplied by nuclear power or from fossil-fuels in conjunction with carbon capture and storage. Solar electricity production and storage using either batteries or PEC hydrogen technologies are currently an order of magnitude greater in cost than electricity prices with no clear advantage to either battery or hydrogen storage as of yet. Significant advances in PEC technology performance and system cost reductions are necessary to enable cost-effective PEC-derived solar hydrogen for use in scalable grid-storage applications as well as for use as a chemical feedstock precursor to CO₂-neutral high energy-density transportation fuels. Hence such applications are an opportunity for foundational research to contribute to the development of disruptive approaches to solar fuels generation systems that can offer higher performance at much lower cost than is provided by current embodiments of solar fuels generators. Efforts to directly reduce CO₂ photoelectrochemically or electrochemically could potentially produce products with higher value than hydrogen but many as yet unmet challenges include catalytic efficiency and selectivity and CO₂ mass transport rates and feedstock cost. Major breakthroughs are required to obtain viable economic costs for solar hydrogen production but the barriers to achieve cost-competitiveness with existing large-scale thermochemical processes for CO₂ reduction are even greater.

Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets delivering low carbon heat and power decarbonising industry and more recently its ability to facilitate the net removal of CO₂ from the atmosphere. However despite this broad consensus and its technical maturity CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus in this paper we review the current state-of-the-art of CO₂ capture transport utilisation and storage from a multi-scale perspective moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS) and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

This paper presents the optimal design and operation of integrated wind-hydrogen-electricity networks using the general mixed integer linear programming energy network model STeMES (Samsatli and Samsatli 2015). The network comprises: wind turbines; electrolysers fuel cells compressors and expanders; pressurised vessels and underground storage for hydrogen storage; hydrogen pipelines and electricity overhead/underground transmission lines; and fuelling stations and distribution pipelines.<br/>The spatial distribution and temporal variability of energy demands and wind availability were considered in detail in the model. The suitable sites for wind turbines were identified using GIS by applying a total of 10 technical and environmental constraints (buffer distances from urban areas rivers roads airports woodland and so on) and used to determine the maximum number of new wind turbines that can be installed in each zone.<br/>The objective is the minimisation of the total cost of the network subject to satisfying all of the demands of the domestic transport sector in Great Britain. The model simultaneously determines the optimal number size and location of each technology whether to transmit the energy as electricity or hydrogen the structure of the transmission network the hourly operation of each technology and so on. The cost of distribution was estimated from the number of fuelling stations and length of the distribution pipelines which were determined from the demand density at the 1 km level.<br/>Results indicate that all of Britain's domestic transport demand can be met by on-shore wind through appropriately designed and operated hydrogen-electricity networks. Within the set of technologies considered the optimal solution is: to build a hydrogen pipeline network in the south of England and Wales; to supply the Midlands and Greater London with hydrogen from the pipeline network alone; to use Humbly Grove underground storage for seasonal storage and pressurised vessels at different locations for hourly balancing as well as seasonal storage; for Northern Wales Northern England and Scotland to be self-sufficient generating and storing all of the hydrogen locally. These results may change with the inclusion of more technologies such as electricity storage and electric vehicles.

The generation of hydrogen from water using light is currently one of the most promising alternative energy sources for humankind but faces significant barriers for large-scale applications due to the low efficiency of existing photo-catalysts. In this work we propose a new route to fabricate nano-hybrid materials able to deliver enhanced photo-catalytic hydrogen evolution combining within the same nanostructure a plasmonic antenna nanoparticle and semiconductor quantum dots (QDs). For each stage of our fabrication process we probed the chemical composition of the materials with nanometric spatial resolution allowing us to demonstrate that the final product is composed of a silver nanoparticle (AgNP) plasmonic core surrounded by satellite Pt decorated CdS QDs (CdS@Pt) separated by a spacer layer of SiO2 with well-controlled thickness. This new type of photoactive nanomaterial is capable of generating hydrogen when irradiated with visible light displaying efficiencies 300% higher than the constituting photo-active components. This work may open new avenues for the development of cleaner and more efficient energy sources based on photo-activated hydrogen generation.

Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H₂) from water namely the radical attack of H₂O and H₂O₂ and the free radicals recombination several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas i.e. N₂ O₂ Ar and air may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects i.e. dynamics of bubble oscillation and collapse events if any against indirect chemical effects i.e. the chemical reactions of free radicals formation and consequently hydrogen emergence it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera in the case of CO₂-saturated water where degassing bubbles are formed instead of transient cavitation.