United States

Magnesium-based hydrogen storage alloys have attracted significant attention as promising materials for solid-state hydrogen storage due to their high hydrogen storage capacity abundant reserves low cost and reversibility. However the widespread application of these alloys is hindered by several challenges including slow hydrogen absorption/desorption kinetics high thermodynamic stability of magnesium hydride and limited cycle life. This comprehensive review provides an in-depth overview of the recent advances in magnesium-based hydrogen storage alloys covering their fundamental properties synthesis methods modification strategies hydrogen storage performance and potential applications. The review discusses the thermodynamic and kinetic properties of magnesium-based alloys as well as the effects of alloying nanostructuring and surface modification on their hydrogen storage performance. The hydrogen absorption/desorption properties of different magnesium-based alloy systems are compared and the influence of various modification strategies on these properties is examined. The review also explores the potential applications of magnesium-based hydrogen storage alloys including mobile and stationary hydrogen storage rechargeable batteries and thermal energy storage. Finally the current challenges and future research directions in this field are discussed highlighting the need for fundamental understanding of hydrogen storage mechanisms development of novel alloy compositions optimization of modification strategies integration of magnesium-based alloys into hydrogen storage systems and collaboration between academia and industry.

The NREL Hydrogen Sensor Laboratory is comprised of researchers dedicated to furthering hydrogen sensor technology and detection methodology. NREL has teamed up with researchers at Environment and Climate Change Canada (ECCC) and Transport Canada (TC) to conduct research to quantify hydrogen emissions from Fuel Cell Electric Vehicles (FCEV). Test protocols will have a large effect on monitoring and regulating the hydrogen emissions from FCEVs. How emissions are tested will play an important role when understanding the safety and environmental implications of using FCEVs. NREL Sensor Laboratory personnel have partnered with other entities to conduct multiple variations of emissions testing for FCEVs. This experimentation includes testing different models of FCEVs under various driving conditions while monitoring the hydrogen concentration of the exhaust using several different test methods and apparatus. Researchers look to support regulatory bodies by providing useful data that can support more consistent and relevant safety and environmental standards. We plan to present on the current test methods and results from recent emissions measurements at ECCC.

This paper intends to give an impression of new technologies and processes that are in development for application to achieve decarbonization and about which less or no experience on associated hazards exists in the process industry. More or less an exception is hydrogen technology because its hazards are relatively known and there is industry experience in handling it safely but problems will arise when it is produced stored and distributed on a large scale. So when its use spreads to communities and it becomes as common as natural gas now measures to control the risks will be needed. And even with hydrogen surprise findings have been shown lately e.g. its BLEVE behavior when in a liquified form stored in a vessel heated externally. Substitutes for hydrogen are not without hazard concern either. The paper will further consider the hazards of energy storage in batteries and the problems to get those hazards under control. Relatively much attention will be paid to the electrification of the process industry. Many new processes are being researched which given green energy will be beneficial to reduce greenhouse gases and enhance sustainability but of which hazards are rather unknown. Therefore as last chapter the developments with respect to the concept of hazard identification and scenario definition will be considered in quite detail. Improvements in that respect are also being possible due to the digitization of the industry and the availability of data and considering the entire life cycle all facilitated by the data model standard ISO 15926 with the scope of integration of life-cycle data for process plants including oil and gas production facilities. Conclusion is that the new technologies and processes entail new process and personal hazards and that much effort is going into renewal but safety analyses are scarce. Right in a period of process renewal attention should be focused on possibilities to implement inherently safer design.

The war in Ukraine caused Europe to more than double its imports of liquefied natural gas (LNG) in only one year. In addition imported LNG remains a crucial source of energy for resource-poor countries such as Japan where LNG imports satisfy about a quarter of the country’s primary energy demand. However an increasing number of countries are formulating stringent decarbonization plans. Liquefied hydrogen and liquefied ammonia coupled with carbon capture and storage (LH2-CCS LNH3-CCS) are emerging as the front runners in the search for low-carbon alternatives to LNG. Yet little is currently known about the full environmental profile of LH2-CCS and LNH3-CCS because several characteristics of the two alternatives have only been analyzed in isolation in previous work. Here we show that the potential of these fuels to reduce greenhouse gas (GHG) emissions throughout the supply chain is highly uncertain. Our best estimate is that LH2-CCS and LNH3-CCS can reduce GHG emissions by 25%–61% relative to LNG assuming a 100 year global warming potential. However directly coupling LNG with CCS would lead to substantial GHG reductions on the order of 74%. Further under certain conditions emissions from LH2-CCS and LNH3-CCS could exceed those of LNG by up to 44%. These results question the suitability of LH2-CCS and LNH3-CCS for stringent decarbonization purposes.

Integration of hydrogen into the existing natural gas infrastructure is considered a potential pathway that can accelerate the incorporation of hydrogen into the energy sector. While blending renewable hydrogen with natural gas offers advantages such as reduced carbon intensity and the ability to utilize existing infrastructure for hydrogen storage and transportation there are several concerns including leakage and associated issues. Un derstanding the behavior of hydrogen blended with natural gas in the existing infrastructure is crucial to ensure safe and efficient integration. In this study the leakage rates of mixtures of hydrogen and methane at different molar concentrations (5% 10% 20% and 50% hydrogen) through both precision machined orifices and com mon pipe fitting threads were investigated. The experiments showed that the leakage rates of these mixtures increased as the hydrogen content increased; however gas chromatography (GC) analysis showed that hydrogen did not leak preferentially at a greater rate than methane. The results indicate that mixing hydrogen with methane can increase the volume of gas leakage under the same pressure conditions. These findings suggest that mixing hydrogen with natural gas may result in increased volumetric flow rate of gas leaks but hydrogen alone does not leak preferentially to methane.

Hydrogen component reliability and the hazard associated with failure rates is a critical area of research for the successful implementation and growth of hydrogen technology across the globe. The research team has partnered to quantify system risk reduction through earlier detection of hydrogen component failures. A model of hydrogen dispersion in a hydrogen equipment enclosure has been developed utilizing experimentally quantified hydrogen component leak rates as inputs. This model provides insight into the impact of hydrogen safety sensors and ventilation on the flammable mass within a hydrogen equipment enclosure. This model also demonstrates the change in safety sensor response time due to detector placement under various leak scenarios. The team looks to improve overall hydrogen system safety through an improved understanding of hydrogen component reliability and risk mitigation methods. This collaboration fits under the work program of IEA Hydrogen Task 43 Subtask E Hydrogen System Safety.

Underground coal gasification (UCG) is an emerging clean energy technology with significant potential for enhanced hydrogen production especially when coupled with water injection. Previous lab-scale studies have explored this potential but the mechanisms driving water-assisted hydrogen enhancement in large-scale deep UCG settings remain unclear. This study addresses this gap using numerical simulations of a large-scale deep coal model designed for hydrogen-oriented UCG. We investigated single-point and multipoint water injection stra tegies to optimize hydrogen production. Additionally we developed a retractable water injection technique to ensure sustained hydrogen output and effective cavity control. Our results indicate that the water–gas shift re action is crucial for increasing hydrogen production. Multipoint injection has been proven to be more effective than single-point injection increasing hydrogen production by 11% with an equal amount of steam. The introduction of retractable injection allows for continuous and efficient hydrogen generation with daily hydrogen production rates of approximately five times that of a conventional injection scheme and an increase in cumulative hydrogen production of approximately 105% over the same time period. Importantly the mul tipoint injection method also helped limit vertical cavity growth mitigating the risk of aquifer contamination. These findings support the potential of UCG as a low-carbon energy source in the transition to a hydrogen economy

The large deployment of hydrogen technologies for new applications such as heat power mobility and other emerging industrial utilizations is essential to meet targets for CO2 reduction. This will lead to an increase in the number of hydrogen installations nearby local populations that will handle hydrogen technologies. Local regulations differ and provide different safety and/or separation distances in different geographies. The purpose of this work is to give an insight on different methodologies and recommendations developed for hydrogen (mainly) risk management and consequences assessment of accidental scenarios. The first objective is to review available methodologies and to identify the divergent points on the methodology. For this purpose a survey has been launched to obtain the needed inputs from the subtask participants. The current work presents the outcomes of this survey highlighting the gaps and suggesting the prioritization of the actions to take to bridge these gaps.

Hydrogen energy systems (HES) are increasingly recognized as pivotal in cutting global carbon dioxide (CO2) emissions especially in transportation power generation and industrial sectors. This paper offers a comprehensive review of HES emphasizing their diverse applications and economic viability. By 2030 hydrogen energy is expected to revolutionize various sectors significantly impacting CO2 abatement and energy demand. In electricity and power generation hydrogen could reduce CO2 emissions by 50–100 million tons annually requiring 10–20 million tons of hydrogen and an investment of $50–100 billion underscoring its role in grid stabilization. Additionally in the heating sector hydrogen could facilitate a CO2 abatement of 30–50 million tons. We examine the levelized cost of hydrogen (LCOH) production influenced by factors like production methods efficiency and infrastructure. While steam methane reforming is cost-effective it poses a larger environmental impact compared to electrolysis. The global life-cycle cost of hydrogen production decreases as production scales up with current costs ranging from $1–3 per kg for fossil-based sources to $3.4–7.5 per kg for electrolysis using low-emission electricity. These costs are projected to decrease especially for electrolytic hydrogen in regions with abundant solar energy. However despite the technical feasibility of decarbonization high production costs still pose challenges. A systematic and effective transition to a hydrogen economy requires comprehensive policy and financial support mechanisms including incentives subsidies tax measures and funding for research and development of pilot projects. Additionally the paper discusses hydrogen's role in advanced storage technologies such as hydrides and Japan's ENE-FARM solution for residential energy emphasizing the need for strategic investments across the hydrogen value chain to enhance HES competitiveness reduce LCOH and advance the learning rates of hydrogen production technologies.

Continuing from previous episodes about encouraging global investment in green hydrogen Patrick Molloy and Alicia Eastman speak with Ignacio de Calonje Chief Investment Officer IFC Global Infrastructure. Ignacio breaks down the role of the IFC and its relationship with other Multilateral Development Banks (MDBs) to encourage decarbonization and bespoke solutions for the Global South.

The podcast can be found on their website.

Electrifying ammonia production using renewable energy (RE) and water electrolysis is a critical step in the worldwide transition from fossil fuels to alternative energy sources. However the common requirement that the ammonia reactor operate at a steady production level harms the system’s economic feasibility due to the large hydrogen and battery storage required to overcome RE variability. In this study we examine the sensitivity of the plant storage capacity requirement to the flexibility of the ammonia reactor. We examine two aspects of ammonia reactor flexibility: ramping rate flexibility and the range of operation (turndown flexibility). We develop a storage dispatch and ammonia reactor scheduling optimization which computes the minimum storage requirement given a RE generation profile and set of reactor flexibility parameters. We optimize across a sweep of flexibility parameters for two locations in the United States. We find that turndown flexibility is the most important while ramping flexibility has little effect on the overall storage requirement. Further we see that seasonal variability in the RE generation profile is the primary driver of high storage capacity requirement. We find that with a turndown flexibility of 60% of the ammonia plants rated capacity which is understood to be achievable with existing ammonia reactor technology the storage capacity was reduced by 84 % in one of the locations we examined which resulted in a 22% decrease in the levelized cost of ammonia with pipe-based hydrogen storage.

Efforts to create a sustainable hydrogen economy are gaining momentum as governments all over the world are investing in hydrogen production storage distribution and delivery technologies to develop a hydrogen infrastructure. This involves transporting hydrogen in gaseous or liquid form or using carrier gases such as methane ammonia or mixtures of methane and hydrogen. Hydrogen is a colorless odorless gas and can easily leak into the atmosphere leading to economic loss and safety concerns. Therefore deployment of robust low-cost sensors for various scenarios involving hydrogen is of paramount importance. Here we review some recent developments in hydrogen sensors for applications such as leak detection safety process monitoring in production transport and use scenarios. The status of methane and ammonia sensors is covered due to their important role in hydrogen production and transportation using existing natural gas and ammonia infrastructure. This review further provides an overview of existing commercial hydrogen sensors and also addresses the potential for hydrogen as an interferent gas for currently used sensors. This review can help developers and users make informed decisions about how to drive hydrogen sensor technology forward and to incorporate hydrogen sensors into the various hydrogen deployment projects in the coming decade.

Quantitative Risk Assessments (QRA) is an important tool for enabling safe deployment of hydrogen technologies and is increasingly embedded in the permitting process. Following the framework developed in our companion paper we conducted a detailed QRA on the uncontrolled releases from a high-capacity hydrogen fueling station with liquid hydrogen (LH2) storage. We characterized gaseous and liquid hydrogen releases determined the causal pathways that led to them and the frequency of the potential hazardous outcomes. These hazardous scenarios were modeled to estimate their potential harm on station users. The analysis results reveal that the total frequency for a major hydrogen release is 1.48 × 10− 2 times per station-year. However considering the control barriers in the station the expected frequency of ignition events is reduced to 1.35 × 10− 5 ignition per stationyear. The expected fatality risk is within the tolerable limit for hydrogen fueling stations but still remains higher than that of conventional gasoline stations. The most severe scenario identified involves a high-pressure GH2 release leading to a jet fire with jet flames reaching up to 15 m in length. The most probable sources of GH2 releases are from the gaseous hydrogen filters while for LH2 releases cryogenic pumps are the primary contributors. To improve the accuracy of QRAs for LH2 systems we identified critical gaps including the need for improved reliability data that must be addressed.

Until recently electrified aircraft propulsion (EAP) technology development has been driven by the dual objectives of reducing greenhouse gas (GHG) emissions and addressing the depletion of fossil fuels. However the increasing severity of climate change posing a significant threat to all life forms has resulted in the global consensus of achieving net-zero GHG emissions by 2050. This major shift has alerted the aviation electrification industry to consider the following: What is the clear path forward for EAP technology development to support the net-zero GHG goals for large commercial transport aviation? The purpose of this paper is to answer this question. After identifying four types of GHG emissions that should be used as metrics to measure the effectiveness of each technology for GHG reduction the paper presents three significant categories of GHG reduction efforts regarding the engine evaluates the potential of EAP technologies within each category as well as combinations of technologies among the different categories using the identified metrics and thus determines the path forward to support the net-zero GHG objective. Specifically the paper underscores the need for the aviation electrification industry to adapt adjust and integrate its EAP technology development into the emerging new engine classes. These innovations and collaborations are crucial to accelerate net-zero GHG efforts effectively.

A unique hydrogen leak detection strategy is the use of powerless indicator wraps for fittings and other pneumatic elements within a hydrogen facility. One transduction mechanism of such indicators is a color change that is induced by a reaction between a pigment and released hydrogen. This is an effective way to detect hydrogen leaks and to identify their source before they become a safety event however this technology requires visual (manual) inspection to identify a color change or leak. One improvement in this strategy would be to improve the communication of the visual response to an end-user. Element One (E1) has previously developed and introduced DetecTape® a self-fusing silicone non-reversible hydrogen leak detecting tape for application to potential leak sites in hydrogen piping valves and fittings and it has been successfully commercialized with excellent feedback. Element One’s sensors can be fabricated using either pigments or thin films which both change color and conductivity. Neither change requires an external power source. The conductivity change may be communicated as a wireless transmission such as passive radio frequency identification devices (RFID) to an appropriate receiving system where it may be remotely monitored to achieve higher levels of safety and reliability at low cost. Element One will report on its recent progress in the commercial development of remotely monitored hydrogen leak detection using several wireless protocols including passive RFID.

Hydrogen is one of a handful of new low carbon solutions that will be critical for the transition to net zero. The upscaling of production and applications entails that hydrogen is likely to be stored in liquid phase (LH2) at cryogenic conditions to increase its energy density. Widespread LH2 use as an alternative fuel will require significant infrastructure upgrades to accommodate increased bulk transport storage and delivery. However current LH2 bulk storage separation distances are based on subjective expert recommendations rather than experimental observations or physical models. Experimental studies of large-scale LH2 release are challenging and costly. The existing large-scale tests are scarce and numerical studies are a viable option to investigate the existing knowledge gaps. Controlled or accidental releases of LH2 for hydrogen refueling infrastructure would result in high momentum two-phase jets or formation of liquid pools depending on release conditions. Both release scenarios lead to a flammable/explosive cloud posing a safety issue to the public.<br/>The manuscript reports exploratory study to numerically determine the safety zone resulting from cryogenic hydrogen releases related to LH2 storage and refueling using the in-house HyFOAM solver further modified for gaseous hydrogen releases at cryogenic conditions and the subsequent atmospheric dispersion and ignition within the platform of OpenFOAM V8.0. The current version of the solver neglects the flashing process by assuming that the temperature of the stored LH2 is equal to the boiling point at the atmospheric condition. Numerical simulations of dispersion and subsequent ignition of LH2 release scenarios with respect to different release orientations release rates release temperatures and weather conditions were performed. Both hydrogen concentration and temperature fields were predicted and the boundary of zones within the flammability limit was also defined. The study also considered the sensitivities of the consequences to the release orientation wind speed ambient temperature and release content etc. The effect of different barrier walls on the deflagration were also evaluated by changing the height and location.

Presented is an evaluation of the carbon footprint and costs associated with hydrogen production via the aluminum-water reaction (AWR) identifying an optimized scenario that achieves 1.45 kgCO2 equiv per kg of hydrogen produced. U.S.-based data are used to compare results with conventional production methods and to assess hydrogen use in fuel-cell passenger vehicles. In the optimized scenario major contributors include the use of recycled aluminum (0.38 kgCO2 equiv) aluminum processing (0.45 kgCO2 equiv) and alloy activator recovery (0.57 kgCO2 equiv). A cost analysis estimates hydrogen production at $9.2/kg when using scrap aluminum alloy recovery and recycling thermal energy aligning with current green hydrogen prices. Reselling reaction byproducts such as boehmite could generate revenue 5.6 times greater than input costs enhancing economic feasibility. The cradle-to-grave assessment suggests that aluminum fuel as an energy carrier for hydrogen distribution and fuel cell vehicle applications offers a low-emission and economically viable pathway for clean energy deployment.

Hydrogen is a zero-carbon energy carrier with potential to decarbonize industrial and transportation sectors but its life-cycle greenhouse gas (GHG) emissions depend on its energy supply chain and carbon management measures (e.g. carbon capture and storage). Global support for clean hydrogen production and use has recently intensified. In the United States Congress passed several laws that incentivize the production and use of renewable and low-carbon hydrogen such as the Bipartisan Infrastructure Law (BIL) in 2021 and the Inflation Reduction Act (IRA) in 2022 which provides tax credits of up to $3/kg depending on the carbon intensity of the produced hydrogen. A comprehensive life-cycle accounting of GHG emissions associated with hydrogen production is needed to determine the carbon intensity of hydrogen throughout its value chain. In the United States Argonne’s R&D GREET® (Greenhouse Gases Regulated emissions and Energy use in Technologies) model has been widely used for hydrogen carbon intensity calculations. This paper describes the major hydrogen technology pathways considered in the United States and provides data sources and carbon intensity results for each of the hydrogen production and delivery pathways using consistent system boundaries and most recent technology performance and supply chain data.

Introduction: Several cities in Malaysia have established plans to reduce their CO2 emissions in addition to Malaysia submitting a Nationally Determined Contribution to reduce its carbon intensity (against GDP) by 45% in 2030 compared to 2005. Meeting these emissions reduction goals will require ajoint effort between governments industries and corporations at different scales and across sectors.<br/>Methods: In collaboration with national and sub-national stakeholders we developed and used a global integrated assessment model to explore emissions mitigation pathways in Malaysia and Kuala Lumpur. Guided by current climate action plans we created a suite of scenarios to reflect uncertainties in policy ambition level of adoption and implementation for reaching carbon neutrality. Through iterative engagement with all parties we refined the scenarios and focus of the analysis to best meet the stakeholders’ needs.<br/>Results: We found that Malaysia can reduce its carbon intensity and reach carbon neutrality by 2050 and that action in Kuala Lumpur can play a significant role. Decarbonization of the power sector paired with extensive electrification energy efficiency improvements in buildings transportation and industry and the use of advanced technologies such as hydrogen and carbon capture and storage will be Major drivers to mitigate emissions with carbon dioxide removal strategies being key to eliminate residual emissions.<br/>Discussion: Our results suggest a hopeful future for Malaysia’s ability to meet its climate goals recognizing that there may be technological social and financial challenges along the way. This study highlights the participatory process in which stakeholders contributed to the development of the model and guided the analysis as well as insights into Malaysia’s decarbonization potential and the role of multilevel governance.

Hydrogen is increasingly recognized as a key contributor to a low-carbon energy future and machine learning (ML) is emerging as a valuable tool to optimize hydrogen production processes. This review presents a comprehensive analysis of ML applications across various hydrogen production pathways including gray blue and green hydrogen with additional insights into pink turquoise white and black/brown hydrogen. A total of 51 peer-reviewed studies published between 2012 and 2025 were systematically reviewed. Among these green hydrogen—particularly via water electrolysis and biomass gasification—received the most attention reflecting its central role in decarbonization strategies. ML algorithms such as artificial neural networks (ANNs) random forest (RF) and gradient boosting regression (GBR) have been widely applied to predict hydrogen yield optimize operational conditions reduce emissions and improve process efficiency. Despite promising results real-world deployment remains limited due to data sparsity model integration challenges and economic barriers. Nonetheless this review identifies significant opportunities for ML to accelerate innovation across the hydrogen value chain. By highlighting trends key methodologies and current gaps this study offers strategic guidance for future research and development in intelligent hydrogen systems aimed at achieving sustainable and cost-effective energy solutions.

Energy system optimization models offer insights into energy and emissions futures through least-cost optimization. However real-world energy systems often deviate from deterministic scenarios necessitating rigorous uncertainty exploration in macro-energy system modeling. This study uses modeling techniques to generate diverse near cost-optimal net-zero CO2 pathways for the United States’ energy system. Our findings reveal consistent trends across these pathways including rapid expansion of solar and wind power generation substantial petroleum use reductions near elimination of coal combustion and increased end-use electrification. We also observe varying deployment levels for natural gas hydrogen direct air capture of CO2 and synthetic fuels. Notably carbon-captured coal and synthetic fuels exhibit high adoption rates but only in select decarbonization pathways. By analyzing technology adoption correlations we uncover interconnected technologies. These results demonstrate that diverse pathways for decarbonization exist at comparable system-level costs and provide insights into technology portfolios that enable near cost-optimal net-zero CO2 futures.

The integration of wind and solar energy with green hydrogen technologies represents an innovative approach toward achieving sustainable energy solutions. This review examines state-ofthe-art strategies for synthesizing renewable energy sources aimed at improving the efficiency of hydrogen (H2 ) generation storage and utilization. The complementary characteristics of solar and wind energy where solar power typically peaks during daylight hours while wind energy becomes more accessible at night or during overcast conditions facilitate more reliable and stable hydrogen production. Quantitatively hybrid systems can realize a reduction in the levelized cost of hydrogen (LCOH) ranging from EUR 3.5 to EUR 8.9 per kilogram thereby maximizing the use of renewable resources but also minimizing the overall H2 production and infrastructure costs. Furthermore advancements such as enhanced electrolysis technologies with overall efficiencies rising from 6% in 2008 to over 20% in the near future illustrate significant progress in this domain. The review also addresses operational challenges including intermittency and scalability and introduces system topologies that enhance both efficiency and performance. However it is essential to consider these challenges carefully because they can significantly impact the overall effectiveness of hydrogen production systems. By providing a comprehensive assessment of these hybrid systems (which are gaining traction) this study highlights their potential to address the increasing global energy demands. However it also aims to support the transition toward a carbon-neutral future. This potential is significant because it aligns with both environmental goals and energy requirements. Although challenges remain the promise of these systems is evident.

Renewable hydrogen production from biomass thermochemical conversion is an emerging technology to reduce fossil fuel consumptions and carbon emissions. Biomass-derived hydrogen can be produced by pyrolysis gasification alkaline thermal treatment etc. However the removal of impurities from biomass thermochemical conversion products to improve hydrogen purity is currently technical bottleneck. It is important to assess and investigate the types and properties of impurities the difficulty of separation and the impact on downstream utilization of hydrogen in the biomass-derived hydrogen production process. The key objectives of this comprehensive review are: (1) to reveal the current status and necessity of developing biomass-derived hydrogen production; (2) to evaluate the types devices and impurities distribution of biomass thermochemical conversion; (3) to explore the formation pathways and removal technologies of typical impurities of tar CO2 sulfides and nitrides in hydrogen production process; and (4) to propose future insights on the separation technologies of typical impurities to promote the gradual substitution of biomass-derived hydrogen for fossil-derived energy.

As climate change intensifies determining a developing region’s role in achieving net-zero emissions worldwide is crucial. However regional efforts considering historical emissions remain underexplored. Here we assess energy system changes technology adoption and investments needed for developing regions including five major- and minor-emitting nations. Our analysis using an integrated assessment model shows a large gap in regional efforts toward global net-zero emissions stemming from the necessary shift of energy systems to low-carbon resources. The use of new technologies like electric vehicles hydrogen and carbon capture varies by region with the highest adoption required between 2020 and 2030. Financing this shift needs an average gross domestic product (GDP) investment rise of 0.464% in minor-emitting regions and up to 2.1% in major-emitting regions by 2085. Our results could guide policies and support setting quantifiable targets for developing nations. The findings are key to facilitating strategic technology use and finance mobilization to achieve a carbon-neutral future.

Water electrolysis is a promising technology for sustainable energy conversion and storage of intermittent and fluctuating renewable energy sources and production of high-purity hydrogen for fuel cells and various industrial applications. Low-temperature electrochemical water splitting technologies include alkaline proton exchange membrane and anion exchange membrane water electrolyses which normally consist of two coupled half reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Despite the advances over decades formidable challenges still exist and hinder the practical application of large-scale energy-efficient and economically viable water electrolysis including large energy penalty sluggish kinetics high cost of precious metal based electrocatalysts possible H2/O2 gas crossover difficulty in storage and distribution of H2. Herein we first briefly introduce the fundamentals of water electrolysis summarize the recommended standardized electrochemical characterization protocols and demonstrate the metrics and key performance indicators that are used to evaluate the performances of HER and OER electrocatalysts and electrolyser cells. Then we present six new strategies to mitigate the technical challenges in conventional water electrolysis. These emerging strategies for disruptive innovation of water electrolysis technology include overall water electrolysis based on bifunctional nonprecious electrocatalysts (or pre-catalysts) magnetic field-assisted water electrolysis decoupled water electrolysis hybrid water electrolysis acid/alkaline asymmetric electrolyte electrolysis and tandem water electrolysis. Finally the remaining challenges perspectives and future directions are discussed. This review will provide guidance and inspire more endeavours to deepen the mechanistic understanding and advance the development of water electrolysis.