Publications

Wind curtailment and weak inertia characteristics are two factors that shackle the permeability of wind power. An electric hydrogen production device consumes electricity to produce hydrogen under normal working conditions to solve the problem of abandoning wind. When participating in frequency regulation it serves as a load reduction method to assist the system to rebuild a power balance and improve the wind power permeability. However due to its own working characteristics an electric hydrogen production device cannot undertake the high-frequency component of the frequency regulation power command; therefore an energy storage device was selected to undertake a high-frequency power command to assist the electric hydrogen production device to complete the system frequency regulation. This paper first proposes and analyzes the architecture of a wind storage hydrogen-generating station for centralized hydrogen production with a distributed energy storage and proposes the virtual inertia and droop characteristic mechanism of the wind storage hydrogen-generating station to simulate a synchronous unit. Secondly an alkaline electrolysis cell suitable for large-scale engineering applications is selected as the research object and its mathematical model is established the matching between different energy storage devices and their cooperation in power grid frequency regulation is analyzed and a super capacitor is selected. A control strategy for the wind storage hydrogen-generating power station to participate in power grid frequency regulation with a wide time scale is then proposed. Using the first-order low-pass filter the low-frequency component of the frequency regulation power command is realized by an electric hydrogen production device load reduction and a high-frequency component is realized by the energy storage device. Finally the effectiveness and rationality of the proposed control strategy are verified by establishing the simulation model of the wind storage hydrogen-generating power station with different initial wind speed states comparing the system frequency dip values under the proposed multi-energy cooperative control strategy and a single energy device control strategy.

The effort to meet the ambitious targets of the Paris agreement is challenging many governments. The US and UK governments might have different approaches to achieving the targets but both will rely heavily on renewable energy sources such as wind and solar to power their economies. However these sources of power are unpredictable and ways will have to be developed to store renewable energy for hours days weeks seasons and maybe even years before it is used. As the disruptive and increasingly deadly impacts of climate change are being felt across the world the need to move to more sustainable sources of energy and to identify viable ways to store that energy has never been more important.<br/>This was the subject of the US–UK Science Forum on electrical storage in support of the grid which was held online from 17 – 18 March 2021. Co-organised by the Royal Society and the National Academy of Sciences it brought together a diverse group of 60 scientists policy makers industry leaders regulators and other key stakeholders for a wide-ranging discussion on all aspects of energy storage from the latest research in the field to the current status of deployment. It also considered the current national and international economic and policy contexts in which these developments are taking place. A number of key points emerged from the discussion. First it is clear that renewable energy will play an increasingly important role in the US and UK energy systems of the future and energy storage at a multi-terawatt hour scale has a vital role to play. Of course this will evolve differently to some extent in both countries and elsewhere according to the various geographical technological economic political social and regulatory environments. Second international collaboration is critical – no single nation will solve this problem alone. As two of the world’s leading scientific nations largest economies and per capita CO2 emitters with a long track record of collaboration the US and UK are well placed to play a vital role in addressing this critical challenge. As the discussion highlighted a wide range of energy storage technologies are now emerging and becoming increasingly available many of which have the potential to be critical components of a future net-zero energy system. A crucial next phase is in ensuring that these are technically developed as well as economically and political viable. This will require the support of a wide range of these potential solutions to ensure that their benefits remain widely available and to avoid costly ‘lock-in’. Scientists and science academies have a critical role to play in analysing technology options their combinations and their potential roles in future sustainable energy systems and in working with policymakers to incentivise investment and deployment.

Guidance on Sensor Placement remains one of the top priorities for the safe deployment of hydrogen and fuel cell equipment in the commercial marketplace. Building on the success of Phase l work reported at TCHS20l9 and published in TJHE this paper discusses the consecutive steps to further develop and validate such guidance for mechanically ventilated enclosures. The key step included a more in-depth analysis of sensitivity to variation of physical parameters in a small enclosure. and finally expansion of the developed approach to confined spaces in an outdoor environment.

Hydrogen blending into natural gas has attracted significant attention in domestic applications. The paper studied the effects of natural gas mixed with hydrogen at 0% (vol) 5% 10% 15% 20% and 25% on the performance of typical round-port gas stove (TRPGS) swirling strip-port gas stove (SSPGS) and radiant porous media gas stove (RPMGS). The experimental results show that flame length shortens with the increase of hydrogen proportion and the combustion remains stable when the hydrogen proportion is equal to or less than 25%. With increasing hydrogen proportion the measured heat inputs of the three types of domestic gas stoves decrease gradually and the average thermal efficiency of TRPGS and SSPGS increase by 0.82% and 1.18% respectively. In addition the average efficiency of the RPMGS first increases by 1.35% under a hydrogen proportion of 15% and then decreases by 1.36% under a hydrogen proportion of 25%. In terms of flue gas emission CO emission reduces significantly with increasing hydrogen proportion while NOX emissions remain almost unchanged.

A water electrolysis cell based on anion exchange membrane (AEM) and critical raw materials-free (CRM-free) electrocatalysts was developed. A NiFe-oxide electrocatalyst was used at the anode whereas a series of metallic electrocatalysts were investigated for the cathode such as Ni NiCu NiMo NiMo/KB. These were compared to a benchmark Pt/C cathode. CRMs-free anode and cathode catalysts were synthetized with a crystallite size of about 10 nm. The effect of recirculation through the cell of a diluted KOH solution was investigated. A concentration of 0.5–1 M KOH appeared necessary to achieve suitable performance at high current density. amongst the CRM-free cathodes the NiMo/KB catalyst showed the best performance in the AEM electrolysis cell achieving a current density of 1 A cm− 2 at about 1.7–1.8 V/cell when it was used in combination with a NiFe-oxide anode and a 50 µm thick Fumatech FAA-3–50® hydrocarbon membrane. Durability tests showed an initial decrease of cell voltage with time during 2000 h operation at 1 A cm− 2 until reaching a steady state performance with an energy efficiency close to 80%. An increase of reversible losses during start-up and shutdown cycles was observed. Appropriate stability was observed during cycled operation between 0.2 and 1 A cm− 2 ; however the voltage efficiency was slightly lower than in steady-state operation due to the occurrence of reversible losses during the cycles. Post operation analysis of electrocatalysts allowed getting a better comprehension of the phenomena occurring during the 2000 h durability test.

To achieve future emission targets for internal combustion engines the use of hydrogen gas generated by renewable energy sources (known as “green” hydrogen) instead of fossil fuels plays a key role in the development of new combustion-based engine concepts. For new hydrogen engine generations there are different challenges concerning the injector layout and functionality. Especially when talking about direct hydrogen injection the key challenge is to ensure a proper mixing between hydrogen and the combustion air—the mixing of gas with a gas is not trivial as shown in this article. In terms of injector functionality it must be ensured that the requested amount of hydrogen gas needs to be provided in time and on the other hand accurately metered to provide an appropriate mixing formation quality inside the combustion chamber. This contribution discusses deep injector analysis techniques with pneumatic and optical approaches for an improved overall understanding of functionality and effects caused by operation with a gaseous fuel. A metering technique for gas flow characterization and for test simplification a comparison of hydrogen with helium and nitrogen as possible surrogate gases indicate that helium and nitrogen can act as a substitute for hydrogen in functional testing. Furthermore this contribution focuses on the usability of helium instead of hydrogen for the determination of spray properties. This is shown by the comparison of spray propagation images that were observed with the Schlieren technique in a pressure vessel proving comparable spray properties. In a next step the usage of spray-guiding devices to improve the global gas distribution during the injection period is discussed. Here it turns out that the volume increase does obviously not depend on the nozzle design. Thus the advantage of multi-hole guiding-devices is based on its flexible gas-jet orientation.

Fuel cell electric vehicles (FCEV) are developing quickly from passenger vehicles to trucks or fork-lifts. Policymakers are supporting an ambitious strategy to deploy fuel cell electrical vehicles with infrastructure as hydrogen refueling stations (HRS) as the European Green deal for Europe. The hydrogen fuel quality according to international standard as ISO 14687 is critical to ensure the FCEV performance and that poor hydrogen quality may not cause FCEV loss of performance. However the sampling system is only available for nozzle sampling at HRS. If a FCEV may show a lack of performance there is currently no methodology to sample hydrogen fuel from a FCEV itself. It would support the investigation to determine if hydrogen fuel may have caused any performance loss. This article presents the first FCEV sampling system and its comparison with the hydrogen fuel sampling from the HRS nozzle (as requested by international standard ISO 14687). The results showed good agreement with the hydrogen fuel sample. The results demonstrate that the prototype developed provides representative samples from the FCEV and can be an alternative to determine hydrogen fuel quality. The prototype will require improvements and a larger sampling campaign.

During the fast-filling of a high-pressure hydrogen tank the temperature of hydrogen would rise significantly and may lead to failure of the tank. In addition the temperature rise also reduces hydrogen density in the tank which causes mass decrement into the tank. Therefore it is of practical significance to study the temperature rise and the amount of charging of hydrogen for hydrogen safety. In this paper the change of hydrogen temperature in the tank according to the pressure rise during the process of charging the high-pressure tank in the process of a 82-MPa hydrogen filling system the final temperature the amount of filling of hydrogen gas and the change of pressure of hydrogen through the pressure reducing valve and the performance of heat exchanger for cooling high-temperature hydrogen were analyzed by theoretical and numerical methods. When high-pressure filling began in the initial vacuum state the condition was called the “First cycle”. When the high-pressure charging process began in the remaining condition the process was called the “Second cycle”. As a result of the theoretical analysis the final temperatures of hydrogen gas were calculated to be 436.09 K for the first cycle of the high-pressure tank and 403.55 for the second cycle analysis. The internal temperature of the buffer tank increased by 345.69 K and 32.54 K in the first cycle and second cycles after high-pressure filling. In addition the final masses were calculated to be 11.58 kg and 12.26 kg for the first cycle and second cycle of the high-pressure tank respectively. The works of the paper can provide suggestions for the temperature rise of 82 MPa compressed hydrogen storage system and offer necessary theory and numerical methods for guiding safe operation and construction of a hydrogen filling system.

Renewable energy complementary hydrogen production can enhance the full consumption of renewable energy and reduce the abandonment of wind and solar power. The integration of renewable energy and hydrogen production equipment through existing multi-terminal DC systems can reduce new power lines construction and save investment in distribution equipment. For integrated renewable energy/hydrogen energy in an existing multi-terminal DC system this paper investigates its potential of hydrogen production based on renewable energy while ensuring the normal performance of the existing system being not affected. The typical structure and control strategy of the integrated renewable energy/hydrogen energy in multi-terminal DC system are firstly described. Then the state space model of the system is constructed and the key parameters affecting the hydrogen production capacity are studied by using the eigenvalues analysis method. Finally the corresponding system simulation model and test platform are built and the theoretical analysis results are verified and the potential of using multi-terminal DC system to enhance hydrogen production is quantitatively analyzed. The proposed scheme can enhance the hydrogen production potential from renewable energy meanwhile the normal performance of the existing system is not affected.

Extensive decarbonisation efforts result in major changes in energy demand for the extractive industry. In 2021 the extraction and primary processing of metals and minerals accounted for 4.5 Gt of CO2 eq. per year. The aluminium industry was responsible for 1.1 Gt CO2 eq. direct and indirect emissions. To reach the European milestone of zero emissions by 2050 a reduction of 3% annually is essential. To this end the industry needs to take a turn towards less impactful production practices coupling secondary production with green energy sources. The present work aims to comprehensively compare the lifecycle energy consumption and environmental performance of a secondary aluminium smelter employing alternative thermal and electricity sources. In this frame a comparative analysis of the environmental impact of different thermal energy sources namely natural gas light fuel oil liquified petroleum gas hydrogen and electricity for a secondary aluminium smelter is presented. The results show that H2 produced by renewables (green H2 ) is the most environmentally beneficial option accounting for −84.156 kg CO2 eq. By producing thermal energy as well as electricity on site H2 technologies also serve as a decentralized power station for green energy production. These technologies account for a reduction of 118% compared to conventionally used natural gas. The results offer a comprehensive overview to aid decision-makers in comparing environmental impacts caused by different energy sources.

This report sets out progress against our strategic framework for decarbonising aviation as well as the latest aviation emissions data and updated Jet Zero analysis.<br/>Among the significant milestones achieved since the Jet Zero strategy launch are the:<br/>- agreement at the International Civil Aviation Organization for a long-term aspirational goal for aviation of net zero 2050 carbon dioxide (CO2) emissions for international aviation<br/>- publication of the 2040 zero emissions airport target call for evidence<br/>significant progress on sustainable aviation fuels (SAF) including:<br/>- publishing the second SAF mandate consultation<br/>- launching a second round of the Advanced Fuels Fund<br/>- publishing the Philip New report and the government response on how to develop a UK SAF industry<br/>- publication of the government response to the UK ETS consultation setting out a range of commitments that will enhance the effectiveness of the UK Emissions Trading Scheme (ETS) for aviation<br/>- launch of the expressions of interest for 2 DfT- funded research projects into aviation’s non-CO2 impacts<br/>The report also acknowledges that big challenges remain and we need to continue to work across the aviation sector and with experts across the economy to ensure we continue to make progress on our path to decarbonise aviation.

To reduce greenhouse gases and air pollutants new technologies are emerging to reduce fossil fuel usage and to adopt more renewable energy sources. As the major aspects of fuel consumption power generation transportation and industrial applications have been given significant attention. The past few decades witnessed astonishing technological advancement in these energy sectors. In contrast the residential sector has had relatively little attention despite its significant utilization of fuels for a much longer period. However almost every energy transition in human history was initiated by the residential sector. For example the transition from fuelwood to cheap coal in the 1700s first took place in residential houses due to urbanization and industrialization. The present review demonstrates the energy transitions in the residential sector during the past two centuries while portending an upcoming energy transition and future energy structure for the residential sector. The feasibility of the 100% electrification of residential buildings is discussed based on current residential appliance adoption and the analysis indicates a hybrid residential energy structure is preferred over depending on a single energy source. Technical considerations and suggestions are given to help incorporate more renewable energy into the residential fuel supply system. Finally it is observed that compared to the numerous regulations on large energy-consumption aspects standards for residential appliances are scarce. Therefore it is concluded that establishing appropriate testing methods is a critical enabling step to facilitate the adoption of renewable fuels in future appliances.

In recent decades governments and society have been making increasing efforts to address and mitigate climate change by reducing emissions and decarbonising energy generation. Ireland has invested greatly in renewable electricity installing 4 GW of wind capacity since 2002 and has set assertive energy targets such as the aim to reduce overall emissions by 51% by 2030. Nonetheless considerable acceleration is needed in the decarbonisation of the country’s energy sector. This paper investigates the potential role hydrogen can play in Ireland’s energy transition proposing hydrogen as an energy vector and storage medium that may help the country achieve its targets and reduce greenhouse gas emissions. Through literature review research and from industry insights the current state of the Irish energy sector is analysed and recommendations are made as to how where and when hydrogen can be integrated into the decarbonisation of Ireland’s electricity heating and transport. It is concluded that; with significant effort from the government policymakers industry and organisations; the effective deployment of hydrogen technologies in Ireland could avoid up to 6.1 MtCO2eq of emissions annually reflecting a trend observed in many other developed countries in which hydrogen plays an important part in the path to a low-carbon future. Prospective roles for hydrogen in Ireland include renewable energy storage and grid balancing through the deployment of Power-to-Gas systems a replacement for fossil natural gas in the gas grid for backup electricity production as well as industry and heating requirements and the use of hydrogen as a fuel for heavy transport.

Sustainable Development Goals establish the main challenges humankind is called to tackle to assure equal comfort of living worldwide. Among these the access to affordable renewable energy and clean water are overriding especially in the context of developing economies. Reversible Solid Oxide Cells (rSOC) are a pivotal technology for their sector-coupling potential. This paper aims at studying the implementation of such a technology in new concept PV-hybrid energy storage mini-grids with close access to seawater. In such assets rSOCs have a double useful effect: charge/discharge of the bulk energy storage combined with seawater desalination. Based on the outcomes of an experimental proof-of-concept on a single cell operated with salty water the operation of the novel mini-grid is simulated throughout a solar year. Simulation results identify the fittest mini-grid configuration in order to achieve energy and environmental optimization hence scoring a renewable penetration of more than 95% marginal CO2 emissions (13 g/kWh) and almost complete coverage of load demand. Sector-coupling co-production rate (desalinated water versus electricity issued from the rSOC) is 0.29 L/kWh.

Power-to-gas (P2G) facilities use surplus electricity to convert to natural gas in integrated energy systems (IES) increasing the capacity of wind power to be consumed. However the capacity limitation of P2G and the antipeaking characteristic of wind power make the wind abandonment problem still exist. Meanwhile the oxygen generated by P2G electrolysis is not fully utilized. Therefore this study proposes a low-carbon economic dispatch model considering the utilization of hydrogen and oxygen energy. First the two-stage reaction model of P2G is established and the energy utilization paths of hydrogen blending and oxygen-rich deep peaking are proposed. Specifically hydrogen energy is blended into the gas grid to supply gas-fired units and oxygen assists oxygenrich units into deep peaking. Subsequently the stochastic optimization is used to deal with the uncertainty of the system and the objective function and constraints of the IES are given to establish a low-carbon dispatch model under the energy utilization model. Finally the effectiveness of the proposed method is verified based on the modified IEEE 39-node electric network 20-node gas network and 6-node heat network models.

In this paper a feasibility study was carried out to evaluate cyclic adsorption processes for capturing CO2 from either shifted synthesis gas or H2 PSA tail gas of an industrial-scale SMR-based hydrogen plant. It is expected that hydrogen is to be widely used in place of natural gas in various industrial sectors where electrification would be rather challenging. A SMR-based hydrogen plant is currently dominant in the market as it can produce hydrogen at scale in the most economical way. Its CO2 emission must be curtailed significantly by its integration with CCUS. Two Vacuum Pressure Swing Adsorption (VPSA) systems including a rinse step were designed to capture CO2 from an industrial-scale SMR-based hydrogen plant: one for the shifted synthesis gas and the other for the H2 PSA tail gas. Given the shapes of adsorption isotherms zeolite 13X and activated carbon were selected for tail gas and syngas capture options respectively. A simple Equilibrium Theory model developed for the limiting case of complete regeneration was taken to analyse the VPSA systems in this feasibility study. The process performances were compared to each other with respect to product recovery bed productivity and power consumption. It was found that CO2 could be captured more cost-effectively from the syngas than the tail gas unless the desorption pressure was too low. The energy consumption of the VPSA was comparable to those of the conventional MDEA processes.

Methanol is currently considered one of the most useful chemical products and is a promising building block for obtaining more complex chemical compounds such as acetic acid methyl tertiary butyl ether dimethyl ether methylamine etc. Methanol is the simplest alcohol appearing as a colorless liquid and with a distinctive smell and can be produced by converting CO2 and H2 with the further benefit of significantly reducing CO2 emissions in the atmosphere. Indeed methanol synthesis currently represents the second largest source of hydrogen consumption after ammonia production. Furthermore a wide range of literature is focused on methanol utilization as a convenient energy carrier for hydrogen production via steam and autothermal reforming partial oxidation methanol decomposition or methanol–water electrolysis reactions. Last but not least methanol supply for direct methanol fuel cells is a well-established technology for power production. The aim of this work is to propose an overview on the commonly used feedstocks (natural gas CO2 or char/biomass) and methanol production processes (from BASF—Badische Anilin und Soda Fabrik to ICI—Imperial Chemical Industries process) as well as on membrane reactor technology utilization for generating high grade hydrogen from the catalytic conversion of methanol reviewing the most updated state of the art in this field.

Currently renewable energy-based generators are considered worldwide to achieve net zero targets. However the stochastic nature of renewable energy systems leads to regulation and control challenges for power system operators especially in remote and regional grids with smaller footprints. A hybrid system (i.e. solar wind biomass energy storage) could minimise this issue. Nevertheless the hybrid system is not possible to develop in many islands due to the limited land area geographical conditions and others. Hydrogen as a carrier of clean energy can be used in locations where the installation of extensive or medium-scale renewable energy facilities is not permissible due to population density geographical constraints government policies and regulatory issues. This paper presents a techno-economic assessment of designing a green hydrogen-based microgrid for a remote island in North-east Australia. This research work determines the optimal sizing of microgrid components using green hydrogen technology. Due to the abovementioned constraints the green hydrogen production system and the microgrid proposed in this paper are located on two separate islands. The paper demonstrates three cost-effective scenarios for green hydrogen production transportation and electricity generation. This work has been done using Hybrid Optimisation Model for Multiple Energy Resources or HOMER Pro simulation platform. Simulation results show that the Levelized Cost of Energy using hydrogen technology can vary from AU$0.37/kWh to AU$1.08/kWh depending on the scenarios and the variation of key parameters. This offers the potential to provide lower-cost electricity to the remote community. Furthermore the CO2 emission could be reduced by 1760777 kg/year if the renewable energy system meets 100% of the electricity demand. Additionally the sensitivity analysis in this paper shows that the size of solar PV and wind used for green hydrogen production can further be reduced by 50%. The sensitivity analysis shows that the system could experience AU$0.03/kWh lower levelized cost if the undersea cable is used to transfer the generated electricity between islands instead of hydrogen transportation. However it would require environmental approval and policy changes as the islands are located in the Great Barrier Reef.

This paper explores the implications of siting a bioenergy with carbon capture and storage (BECCS) facility to carbon emission performances for three case-study supply chains using the Carbon Navigation System (CNS) model. The three case-study supply chains are a wheat straw derived BECCS-power a municipal solid waste derived BECCS-waste-to-energy and a sawmill residue derived BECCS-hydrogen. A BECCS facility needs to be carefully sited taking into consideration its local low carbon infrastructure available biomass and geography for successful deployment and achieving a favorable net-negative carbon balance. On average across the three supply chains a 10 km shift in the siting of the BECCS facility results in an 8.6–13.1% increase in spatially explicit supply chain emissions. BECCS facilities producing low purity CO2 at high yields have lower spatial emissions when located within the industrial clusters while those producing high purity CO2 at low yields perform better outside the clusters. A map is also generated identifying which of the three modeled supply chains delivers the lowest spatially explicit supply chain emission options for any given area of the UK at a 1 MtCO2/yr capture scale.

Understanding the political feasibility of transition pathways is a key issue in energy transitions. Policy changes are a significant source of uncertainty in energy system optimisation modelling. Energy system models are nevertheless continuously being updated to reflect policy signals as realistically as possible. Using the concept of transition pathways as a starting point this cross-disciplinary study combines energy system optimization modelling with political feasibility of different transition pathways. This combination generates insights into key political decision points in the ongoing energy transition. Resting on actor support structure and political feasibility of four main pathway categories (electrification hydrogen biomass and energy efficiency) we identify critical model assumptions that are politically significant and impact model outcome. Then by replacing the critical assumptions with technical limitations we model a scenario that is unrestrained by assumptions about policy we identify areas where political choices are key to model outcomes. The combination of actor preferences and modelled energy system consequences enables the identification of future key decision points. We find that there is considerable support for electrification as the main pathway to net-zero. The implications of widespread electrification in terms of energy production and grid capacity lead us to identify challenging policy decisions with implications for the energy transition.

This paper presents an eco-technoeconomic analysis (eTEA) of hydrogen production via solid oxide electrolysis cells (SOECs) aimed at identifying the economically optimal size and operating trajectories for these cells. Notably degradation effects were accounted by employing a data-driven degradationbased model previously developed by our group for the analysis of SOECs. This model enabled the identification of the optimal trajectories under which SOECs can be economically operated over extended periods of time with reduced degradation rate. The findings indicated that the levelized cost of hydrogen (LCOH) produced by SOECs (ranging from 2.78 to 11.67 $/kg H2) is higher compared to gray hydrogen generated via steam methane reforming (SMR) (varying from 1.03 to 2.16 $ per kg H2) which is currently the dominant commercial process for large-scale hydrogen production. Additionally SOECs generally had lower life cycle CO2 emissions per kilogram of produced hydrogen (from 1.62 to 3.6 kg CO2 per kg H2) compared to SMR (10.72–15.86 kg CO2 per kg H2). However SOEC life cycle CO2 emissions are highly dependent on the CO2 emissions produced by its power source as SOECs powered by high-CO2-emission sources can produce as much as 32.22 kg CO2 per kg H2. Finally the findings of a sensitivity analysis indicated that the price of electricity has a greater influence on the LCOH than the capital cost.

The consumption of hydrogen could increase by sixfold in 2050 compared to 2020 levels reaching about 530 Mt. Against this backdrop the proton exchange membrane fuel cell (PEMFC) has been a major research area in the field of energy engineering. Several reviews have been provided in the existing corpus of literature on PEMFC but questions related to their evolutionary nuances and research hotspots remain largely unanswered. To fill this gap the current review uses bibliometric analysis to analyze PEMFC articles indexed in the Scopus database that were published between 2000–2021. It has been revealed that the research field is growing at an annual average growth rate of 19.35% with publications from 2016 to 2012 alone making up 46% of the total articles available since 2000. As the two most energy-consuming economies in the world the contributions made towards the progress of PEMFC research have largely been from China and the US. From the research trend found in this investigation it is clear that the focus of the researchers in the field has largely been to improve the performance and efficiency of PEMFC and its components which is evident from dominating keywords or phrases such as ‘oxygen reduction reaction’ ‘electrocatalysis’ ‘proton exchange membrane’ ‘gas diffusion layer’ ‘water management’ ‘polybenzimidazole’ ‘durability’ and ‘bipolar plate’. We anticipate that the provision of the research themes that have emerged in the PEMFC field in the last two decades from the scientific mapping technique will guide existing and prospective researchers in the field going forward.

Hydrogen energy is considered one of the cleanest and most promising alternatives to fossil fuel because the only combustion product is water. The development of water splitting electrocatalysts with Earth abundance cost-efficiency and high performance for large current density industrial applications is vital for H2 production. However most of the reported catalysts are usually tested within relatively small current densities (< 100 mA cm−2 ) which is far from satisfactory for industrial applications. In this minireview we summarize the latest progress of effective non-noble electrocatalysts for large current density hydrogen evolution reaction (HER) whose performance is comparable to that of noble metal-based catalysts. Then the design strategy of intrinsic activities and architecture design are discussed including self-supporting electrodes to avoid the detachment of active materials the superaerophobicity and superhydrophilicity to release H2 bubble in time and the mechanical properties to resist destructive stress. Finally some views on the further development of high current density HER electrocatalysts are proposed such as scale up of the synthesis process in situ characterization to reveal the micro mechanism and the implementation of catalysts into practical electrolyzers for the commercial application of as-developed catalysts. This review aimed to guide HER catalyst design and make large-scale hydrogen production one step further.

The paper is a review of the opportunities and challenges of cryogenic power devices of electric aircraft and the ongoing research and development efforts of the government agencies and the industry. Liquid Hydrogen (LH2) and Liquefied Natural Gas (LNG) are compared to support high temperature superconducting (HTS) and normal metal devices respectively. The power devices were assumed to operate at the normal boiling point of the fuel used. The efficiencies of the electrical devices are estimated based on state-of-the-art technology. The mass flow rates and total fuel requirements for both the cryogenic fuels required to maintain the operating temperatures of the devices were simulated using thermal network models. A twin-aisle 300 passenger aircraft with a 5.5 h flight duration was used for the models. The results show that the required masses of LH2 and LNG are 744 kg and 13638 kg respectively for the cooling requirement. The corresponding volumes of LH2 and LNG required are 9760 and 30300 L respectively. In both cases the estimated mass of the fuel needed for the aircraft is more than what is needed to maintain the cryogenic environment of the power devices. It was concluded that an electric aircraft with LNG cooled normal metal devices is feasible. However an aircraft with HTS devices and cooled with LH2 is more attractive if the ongoing R&D efforts on HTS devices and LH2 infrastructure are successful. The emission reductions would be substantially higher with LH2 particularly when H2 is produced using renewable energy sources.

Green hydrogen produced from surplus electricity during peak production can be injected into subsurface reservoirs and retrieved during high-demand periods. In this study X-ray tomography was employed to examine hysteresis resulting from repeated hydrogen injection and withdrawal. An unsteady state experiment was performed to evaluate the distribution of hydrogen and brine after drainage and imbibition cycles: images of the pore-space configuration of fluids were taken immediately once injection had stopped and after waiting for a period of 16 h with no flow. A Bentheimer sandstone sample with a length of 60 mm and diameter of 12.8 mm was used and hydrogen was injected at ambient temperature and a pore pressure of 1 MPa. The gas flow rate was decreased from 2 ml/min to 0.08 ml/min over three cycles of gas injection followed by water flooding while the brine injection rate was kept constant. The results showed the presence of capillary pressure hysteresis and hydrogen migration through Ostwald ripening due to the diffusion of gas dissolved in the brine. These phenomena were characterized through analysis of interfacial curvature area connectivity and pore occupancy. The hydrogen tended to reside in the larger pore spaces consistent with water-wet conditions. 16 h after flow had stopped the hydrogen aggregated into larger ganglia with a single large connected ganglion dominating the volume. Moreover the Euler characteristic decreased after 16 h indicating an improvement in connectivity. The work implies that Ostwald ripening – mass transport of dissolved gas – leads to less hysteresis and better connectivity than would be assumed ignoring this effect as done in assessments of hydrocarbon flow and trapping.