NiMoO4@CoFe-LDH Anode Design to Improve Oxygen Bubble Transport in Dynamic Water Electrolysis.

Developing bifunctional catalysts for overall water splitting with high activity and durability at high current density remains a challenge. In an attempt to overcome this bottleneck, in this work, unique CoNiFe-layered double hydroxide nanoflowers are in situ grown on nickel-iron (NiFe) foam through a corrosive approach and following a chemical vapor deposition process to generate nitrogen-doped carbon nanotubes at the presence of melamine (CoNiFe@NCNTs). The coupling effects between various metal species act a key role in accelerating the reaction kinetics. Moreover, the in situ formed NCNTs also favor promoting electrocatalytic activity and stability. For oxygen evolution reaction it requires low overpotentials of 330 and 341 mV in 1M KOH and 1M KOH + seawater to drive 500 mA cm-2. Moreover, water electrolysis can be operated with CoNiFe@NCNTs as both anode and cathode with small voltages of 1.95 and 1.93V to achieve 500 mA cm-2 in 1M KOH and 1M KOH + seawater, respectively.

Water electrolysis is extensively researched as a next-generation energy storage method to overcome the intermittency of renewable energy. Electricity generated from renewable sources such as solar and wind power can be converted into pure green hydrogen through water electrolysis. Despite the potential of green hydrogen as a renewable energy storage/carrier medium, the high overpotential resulting from the slow kinetics of oxygen evolution reaction (OER) and the use of expensive noble metals make cost-competitive hydrogen production a significant challenge. Anion exchange membrane water electrolysis (AEMWE) is one method for hydrogen production, offering economic advantages over proton exchange membrane systems as it allows for the use of relatively inexpensive transition metal catalysts like Ni, Fe, and Co due to its alkaline environment.Nickel phosphide (Ni2P)-based catalysts have emerged as highly promising candidates to accelerate the electrocatalytic OER. In particular, the introduction of Fe into Ni2P has been found to induce charge transfer, optimizing the electronic structure and accelerating the OER process. OER catalysts based on transition metal phosphides often exhibit a core-shell structure with phosphide at the core and oxide at the shell during OER measurements. This core-shell structure enhances OER performance through the oxide shell, complementing the deficient electrical conductivity of the phosphide core, resulting in superior catalytic activity and durability. From this perspective, transition metal phosphates are also being studied as electrocatalysts for OER. Phosphates, such as PO3 -, not only promote oxygen adsorbate adsorption but also induce a distorted local metal center geometry that favors OH- adsorption and further oxidation.To address these challenges, this study develops a facile and scalable synthesis of iron-doped nickel phosphide-phosphate (Fe-doped Ni2P-POx) nano-hybrid system as a superior noble-metal free OER powder-catalyst. The utilization of self-filling and pyrolysis approaches facilitates economically viable production of the highly porous phosphide catalyst with a high specific surface area and rough surfaces. X-ray diffractometer, X-ray photoelectron spectroscopy, and electron paramagnetic resonance elucidates the electronic structure modulation, resulting in phosphide-phosphate nano-hybrid structures. Consequently, the catalyst demonstrates excellent OER activity in 1 M KOH, with a significantly low overpotential of 283 mV at 20 mA cm-2, a small Tafel slope of 28.4 mV dec-1, and a superior exchange current density of 8.22 mA cm-2, surpassing state-of-the-art PGM catalysts. Furthermore, its durability over 20 hours indicates its excellent stability, mass transport properties, and mechanical robustness in alkaline media, underscoring its potential as an efficient OER catalyst to facilitate electrocatalytic hydrogen production. Figure 1

While the dynamics of hydrogen bubbles during water electrolysis have been intensively studied in recent years, adequate insights into the dynamics of oxygen bubbles are still lacking. Therefore, this study presents a comparative analysis of hydrogen and oxygen bubble dynamics during potentiostatic water electrolysis in an acidic electrolyte. Complementary optical techniques, such as high-speed shadowgraphy, particle tracking velocimetry, and schlieren imaging are applied to measure geometric features of the evolving bubbles and the microscale Marangoni convection, as well as the refractive index field around the growing bubbles. Distinct differences between oxygen and hydrogen bubbles are found in the average current, in the Marangoni convection pattern, and in the degree of refractive index reduction at the bubble foot, suggesting a synergetic action of both thermal and solutal effects at oxygen bubbles.

Hydrogen from renewables: Is it always green? The Italian scenario

PurposeHydrogen has enormous decarbonization potential in the transportation sector. Heavy vehicles, maritime transport, aviation and railways are exploring hydrogen as a decarbonization solution. Hydrogen is important as a future mobility and transportation solution because global regulations for emissions reduction are becoming increasingly stringent. The European Green Deal aims to reduce greenhouse gas (GHG) emissions by 90% by 2050 compared to 1990 levels, affecting the mobility industry. Hydrogen will play a crucial role in achieving climate goals, especially in public transport and mobility. A rigorous statistical study of global hydrogen production capacities becomes essential in the context of the enormous decarbonization potential that hydrogen holds for transportation. The study analyzes the evolution of global annual hydrogen production capacity for mobility from 2009 to 2022. Until 2015, the main technology used was alkaline water electrolysis, while in 2016, polymer electrolyte membrane (PEM) electrolyzer technology became dominant. Alkaline water electrolysis technology has a 22% higher production capacity compared to PEM technology. It has been observed that Asia has the largest operational hydrogen production capacity at 43.3%, followed by Europe at 26.8%, the USA at 26.2%, Africa at 3.5% and Australia at 0.3%. The countries with the highest operational hydrogen production capacity for mobility are China at 41.7%, the USA at 25.7% and Germany at 7.4%.Design/methodology/approachThe study involved the analysis of data related to hydrogen production systems for use in mobility, conducted over an extended period from 2011 to 2022. It represents a detailed look at the evolution of this vital technology for the future of global sustainable mobility. Hydrogen production has seen significant development in recent years, driven by increasing awareness of the adverse impact of GHG emissions on the environment and the need for cleaner and more efficient solutions for transportation. In the study, we analyzed the evolution of hydrogen production capacity in each country, also tracking its development over time. Additionally, we investigated continental-level capacity, providing a comprehensive overview of progress and global potential in hydrogen production.FindingsGreen hydrogen represents a promising solution for decarbonizing the transportation industry. Its production using renewable energy sources such as solar and wind power can significantly reduce carbon emissions. Green hydrogen can be used in fuel cell vehicles to power zero-emission cars and transportation, contributing to the fight against climate change and the creation of a sustainable future for our mobility. The analysis highlighted that the development of hydrogen production capacities is highly dynamic. During the period from 2009 to 2015, the hydrogen production for mobility was approximately 1,570 cubic meters per hour (m3 H2/h). However, what becomes evident from the analysis is the impressive growth in hydrogen production capacity in this area. Between 2016 and 2020, production capacity increased significantly, reaching approximately 6,240 m3 H2/h, which represents roughly a fourfold increase compared to the previous period.Originality/valueA crucial factor that has spurred this growth is the increasing commitment to reducing carbon emissions and other pollutants from the transportation industry. The potential of hydrogen production systems has been recognized as a viable alternative due to their capacity to generate environmentally friendly hydrogen, commonly referred to as green hydrogen, through the utilization of renewable energy sources such as solar or wind power. Over recent years, researchers have made significant advancements in the field of hydrogen generation, specifically in the areas of water electrolysis and natural gas reforming. These approaches have played a crucial role in improving the efficiency of both green and gray hydrogen production. Green hydrogen is considered one of the most environmentally friendly energy sources because the carbon emissions associated with its production are minimal or even nonexistent.

Hydrogen is considered an ideal clean energy due to its high mass-energy density, and only water is generated after combustion. Water electrolysis is a sustainable method of obtaining a usable amount of pure hydrogen among the various hydrogen production methods. However, its development is still limited by applying expensive noble metal catalysts. Here, the dissolution-recrystallization process of TiO2 nanotube arrays in water with the hydrothermal reaction of a typical nickel-cobalt hydroxide synthesis process followed by phosphating to prepare a self-supported electrode with (NiCo)CO3/TiO2 heterostructure named P-(NiCo)CO3/TiO2/Ti electrode is combined. The electrode exhibits an ultra-low overpotential of 31mV at 10mA cm-2 with a Tafel slope of 46.2mVdec-1 in 1m KOH and maintained its stability after running for 500h in 1m KOH. The excellent catalytic activity can be attributed to the structure of nanotube arrays with high specific surface area, superhydrophilicity, and super aerophobicity on the electrode surface. In addition, the uniform (NiCo)CO3/TiO2 heterostructure also accelerates the electron transfer on the electrode surface. Finally, DFT calculations demonstrate that phosphating also improves the ΔGH* and ΔGH2O of the electrode. The synthesis strategy also promotes the exploration of catalysts for other necessary electrocatalytic fields.

Durability of NiFe-based oxygen evolution electrocatalysts in AEM water electrolyzer under fluctuating power supply.

In 2023, global hydrogen production reached 97 Mt (million tons), but low-emission hydrogen production technologies accounted for less than 1% of this total, resulting in an estimated 920 Mt of CO2 emissions. Green hydrogen or renewable hydrogen is produced by coupling water electrolysers to renewable energy systems. Among the water electrolyser technologies, the most advanced and widely deployed is the alkaline water electrolyser (AWE), which constitutes 60% of the global electrolyser capacity [1].To make hydrogen production via water electrolysis competitive with hydrocarbon-based hydrogen production methods, innovative strategies need to be developed, such as identifying more cost-effective and efficient electrodes and electrocatalysts like nickel (Ni)-based materials to minimize power losses through AWE sub-components and system modifications. AWEs operate at relatively low temperatures (compared to solid oxide electrolyser cells), leading to significant cell voltage and thus power losses caused by the formation of molecular hydrogen and oxygen gas bubbles (H₂ and O₂). These bubbles cover large portions of the electrode surface, acting like a “passivation layer” and thus reducing its electrocatalytic activity [2].Additionally, the gas release creates a bubble curtain near the surface, in turn lowering the electrolyte conductivity. Therefore, finding ways to remove these bubbles more efficiently is crucial for improving AWE efficiency. Two strategies can be applied, depending on the use of an external power source.In this study, we explore the combination of both methods—using a porous electrode (passive) and power ultrasound (active)—to enhance the removal of gas bubbles at the hydrogen electrode. The use of a porous electrode offers two key advantages: (i) it increases the electrochemically active surface area (ECSA), and (ii) it enhances the superaerophobicity of the surface [3]. These electrodes are fabricated through a two-step process: a first planar Ni layer is electrodeposited, followed by the creation of a porous Ni layer using the Dynamic Hydrogen Bubble Template method [4]. The process starts with the electrodeposition of a 1x1 cm² planar Ni layer on a copper (Cu) substrate for circa 20 minutes in a Ni Watts bath containing 1.33 M NiSO₄·6H₂O, 0.21 M NiCl₂·6H₂O, and 0.65 M H₃BO₃ at 60°C. Next, the porous layer is formed in an undisclosed electrolyte for 2 minutes at a current density of 1 A·cm⁻². Additionally, power ultrasound (20 and 580 kHz in the acoustic power range of 0 to 67 W) is known to significantly improve gas bubble removal from the electrode surface, aid in solution/electrolyte degassing, disrupt the Nernst diffusion layer thickness (d), enhance the mass transport of electroactive species through the double layer, and promote both the activation and cleaning of the electrode surface [5]. This study builds on previous studies involving ultrasonication of Ni electrode surfaces, as a pretreatment activation process [6].In our conditions, it was observed that the cathodic HER overpotential (η) at -10 mA.cm-2 (j) and Tafel slope (b) both decrease significantly from the planar to the porous electrode with a further reduction occurring upon the addition of ultrasound, depending on the acoustic power emitted by the sonotrode. However, erosion was observed during ultrasonication when the electrode was placed at pressure nodes, where mass transfer and performance are maximal. This study thus paves the way for further exploration of optimization strategies for sonoAWE.[1] U. Remme, Global Hydrogen Review 2024, (2024).[2] K. Zouhri, S. Lee, Evaluation and optimization of the alkaline water electrolysis ohmic polarization: Exergy study, Int. J. Hydrog. Energy 41 (2016) 7253–7263. https://doi.org/10.1016/j.ijhydene.2016.03.119.[3] R. Andaveh, Gh. Barati Darband, M. Maleki, A. Sabour Rouhaghdam, Superaerophobic/superhydrophilic surfaces as advanced electrocatalysts for the hydrogen evolution reaction: a comprehensive review, J. Mater. Chem. A 10 (2022) 5147–5173. https://doi.org/10.1039/D1TA10519A.[4] M. Hao, V. Charbonneau, N.N. Fomena, J. Gaudet, D.R. Bruce, S. Garbarino, D.A. Harrington, D. Guay, Hydrogen Bubble Templating of Fractal Ni Catalysts for Water Oxidation in Alkaline Media, ACS Appl. Energy Mater. 2 (2019) 5734–5743. https://doi.org/10.1021/acsaem.9b00860.[5] J. Hihn, F. Touyeras, M. Doche, C. Costa, B.G. Pollet, Sonoelectrodeposition: The Use of Ultrasound in Metallic Coatings Deposition, in: B.G. Pollet (Ed.), Power Ultrasound Electrochem., 1st ed., Wiley, 2012: pp. 169–214. https://doi.org/10.1002/9781119967392.ch6.[6] F. Foroughi, M. Tintor, A.Y. Faid, S. Sunde, G. Jerkiewicz, C. Coutanceau, B.G. Pollet, In Situ Sonoactivation of Polycrystalline Ni for the Hydrogen Evolution Reaction in Alkaline Media, ACS Appl. Energy Mater. 6 (2023) 4520–4529. https://doi.org/10.1021/acsaem.2c02443.

Alkaline water (H2O) electrolysis is currently a commercialized green hydrogen (H2) production technology, yet the unsatisfactory hydrogen evolution reaction (HER) performance severely limits its energy conversion efficiency and cost reduction. Herein, PtRu2.9Fe0.15Co1.5Ni1.3 high entropy alloys (HEAs) is synthesized and subsequently exploited electrochemically induced structural oxidation processes to construct self-reconfigurable HEAs, as an efficient alkaline HER catalyst. The optimized self-reconstructed PtRu2.9Fe0.15Co1.5Ni1.3 HEAs with the HEAs and cobalt rutheniate interface (HEAs-Co2RuO4) exhibits excellent alkaline HER performance, requiring just 11.8mV to obtain a current density (j) of 10 mA cm-2 in 1m KOH. And the j on HEAs-Co2RuO4 is 41.8 mA cm-2 at 0.07 VRHE, 2.0 and 6.1 times higher than PtRu2.9Fe0.15Co1.5Ni1.3 HEAs and 20% Pt/C. Mechanism studies reveal that the improved alkaline HER performance of HEAs-Co2RuO4 is due to the formation of HEAs-Co2RuO4, which significantly shrinks the Helmholtz layer, provides a new fast material transport channel, boosts H2O adsorption, and reduces hydrogen adsorption, and thus accelerates the alkaline HER. This research not only throws new light on the self-reconstruction of catalysts but also provides guidance for the rational design of efficient electrocatalysts.

All-solid-state batteries with nonflammable inorganic solid electrolytes, an alternative to conventional inflammable organic liquid electrolytes, are widely studied as next generation batteries with low risk of leakage and explosion. Bulk-type batteries use composite electrodes of active materials and solid electrolytes. Solid electrolytes play a role of delivering Li ions to active materials. Bulk-type batteries are capable of having high energy density by adding large amounts of active materials into composite electrodes. We have investigated the electrochemical performance of bulk-type all-solid-state cells using a LiCoO2 composite positive electrode and a Li2S-P2S5 solid electrolyte [1]. Composite electrodes can be fabricated by mixing LiCoO2 particles and solid electrolyte particles. There are many solid-solid interfaces in composite electrodes. It is important that electrochemical reactions at LiCoO2-electrolyte solid-solid interfaces are clarified to improve the cell performance. Raman microscopy is one of the useful methods for investigating the reactions because of its feature of high spatial resolution and surface sensitivity. Raman spectral changes of composite electrodes are closely related to the structural changes of active material during charge-discharge cycling. In this study, Raman spectroscopy was carried out for LiCoO2 composite positive electrodes in all-solid-state cells before and after the charge-discharge process. Moreover, Raman mapping was conducted to evaluate state-of-charge (SOC) distributions of each active material in the electrodes. The 75Li2S·25P2S5 (mol%) glass and indium foil were used as solid electrolyte and a negative electrode, respectively. A composite positive electrode was prepared by mixing LiCoO2 particles and 75Li2S·25P2S5 glass particles (80:20 wt.%). All-solid-state cells were charged and discharged with a cut-off voltage of 2.6-4.2 V (vs. Li+/Li) at 25 oC under a current density of 0.064 mA cm-2. Raman spectra were obtained for the surface part of composite positive electrodes prepared by an Ar ion-milling technique. There are two strong Raman peaks at 486 and 596 cm-1, originating from the E g and A 1g modes of oxygen vibration in LiCoO2, respectively. Those peaks shifted to the lower wavenumber side and their intensity decreased after the initial charging process. After the discharging process, those peaks returned to the original positions. Mapping images showed charge-discharge reactions did not proceed uniformly at the areas of insufficient contacts between LiCoO2 particles and solid electrolyte particles [2]. Our approaches to fabricate composite positive electrodes having uniform charge-discharge reactions will be demonstrated. Acknowledgement This research was financially supported by JST, ALCA-SPRING.

Hydrogen is one of the types of energy discovered in recent decades, which is based on the electrolysis of water in order to separate hydrogen from oxygen. These include grey hydrogen, black hydrogen, blue hydrogen, yellow hydrogen, turquoise hydrogen, and green hydrogen. Generally, hydrogen can be extracted from a variety of sources, including fossil fuels and biomass, water, or a combination of the two. Green hydrogen has the potential to be a critical enabler of the global transition to sustainable energy and zero-emissions economies. Worldwide, there is unprecedented momentum to realize hydrogen's long-standing potential as a clean energy solution. Green hydrogen is a carbon-free fuel and the source of its production is water, and the production processes witness the separation of its molecules from its oxygen counterpart in the water by electricity generated from renewable energy sources such as wind and solar energy. Green hydrogen is one of the most important sources of clean energy, which may be why it is called green hydrogen. It is a clean source of energy, and its generation is based on renewable energy sources, so no carbon gases are released during its production. Green hydrogen produced by water electrolysis becomes a promising and tangible solution for the storage of excess energy for power generation and grid balancing, as well as the production of decarbonized fuel for transportation, heating, and other applications, as we shift away from fossil fuels and toward renewable energies. Green hydrogen is being produced in countries all over the world because it is one of the solutions to reducing carbon emissions, and it is clean, environmentally friendly energy that is derived from clean renewable energy. However, due to the combination of renewable generation and low-carbon fuels, projects for the production of green hydrogen are very expensive. The goal of this review is to highlight the various types of hydrogen, with a focus on the more practical green hydrogen.

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been used mainly for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sector at various and increasing scale. The PEMWE technology is also considered as a key one in the frame of the ongoing energy transition if the process of hydrogen generation by means of WE is linked to renewable energy sources, such as wind, solar, etc.Among other existing water electrolysis technologies, such as alkaline, solid oxide, the technology based on proton-exchange membranes has received a great deal of interest in South Africa. One of the reasons is endowment of South Africa with its PGM resources, such as platinum (Pt) and iridium (Ir) that are used in PEM water electrolysis (WE) catalytic components. As it is known, PEMWE technology is very well suited to accommodate intermittency of energy supply associated with renewables. PEMWE technology can also deliver relatively high-pressure hydrogen gas of high purity. South Africa has also superior endowment of both onshore wind and solar. It is known thar renewable energy (RE) is one of the largest operational cost components in the production of green hydrogen. Other factors contributing to the interest in green hydrogen water electrolysis technology in South Africa that are not obvious, but important, include large tracts of sparsely populated land with little alternative use, which can be dedicated for RE production. South Africa also has a suitable geographical position with deep water ports for the potential export of large quantity of hydrogen and its derivatives such as ammonia.Approximately 15 years ago South African Government approved national program HySA: Hydrogen South Africa that resulted in developing expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include development of local IP at the components, stack and system levels. Recently, a number of “catalytic” projects have been identified in order to increase a demand in green hydrogen and stimulate investments.Recently, an international R&D project between South Africa and Japan was launched to develop further expertise in both green hydrogen and ammonia technologies [1]. Most recently, large companies, such as SASOL, made commitments to lead green hydrogen production at a large scale for the variety of applications, aiming at decarbonisation of mining and petrochemical sectors [2]. On the Governmental level, South Africa recently has approved its national hydrogen road map [3].This talk will provide a comprehensive update on the research, technology, and commercialisation activities in South Africa in the area of green hydrogen production.

A lot of efforts have been devoted to develop highly active noble-metal-free catalysts for hydrogen production by water electrolysis.1,2 Nevertheless, the stability of such catalysts, yet equally important, is rarely touched. NiMo alloy is an emerging catalyst for hydrogen evolution reaction (HER) in alkaline media.3 In the present work, we studied the stability of NiMo alloy for HER under alkaline (1M KOH, Fe-free) conditions as a model catalyst. Using electrodeposition at room temperature, we deposited NiMo alloy onto nickel foam substrates. A long-term (20h) stability test at a fixed current density of -100 mA cm-2 was carried out using chronopotentiometry. Electrochemical active surface area (ECSA) and HER polarization curves were determined prior and after this stability test. Here, obvious activity loss is observed. The ECSA of NiMo catalyst after chronopotentiometry test increases by 10%. Thus, an obvious increase in the overpotential is observed upon normalizing the catalytic current with ECSA (Figure 1a). As further stability test 100 CV cycles at a scan rate of 100 mV s-1 from 0 to –350 mV vs. RHE were carried out, the catalysts then hold for 30 min at open circuit potential and again 100 CV cycles carried out. A clear drop in activity during the second 100 cycles is also observed here and especially at the higher current density of 60 mA cm-2 (Figure 1b). In summary, we found that NiMo, though active initially, loses its activity with time under HER conditions in alkaline media.References Vesborg, P. C. K.; Seger, B.; Chorkendorff, I. Phys. Chem. Lett. 2015, 6, 951– 957.Zou, X. X.; Zhang, Y. Soc. Rev. 2015, 44, 5148– 5180.Kuznetsov, V. V.; Gamburg, Y. D.; Zhulikov, V. V.; Krutskikh, V. M.; Filatova, E. A.; Trigub, A. L.; Belyakova, O. A. Electrochim. Acta 2020, 354, 136610. Figure 1

Due to rising energy demand, renewable energy sources integrated processes have gained great interest in the recent years. Water electrolysis powered with renewable energy have potential to contribute to the development of sustainable hydrogen economy enormously. Despite the fact that “green” hydrogen is produced in the water electrolyzers with eco-friendly product O2, the excess energy input still hinders this technology to replace the fossil fuel-based technologies. Even with tremendous attempts and considerable contribution to the electrocatalyst development/optimization/improvement over last decades, there is a continued massive endeavor on the way of noble-metal based catalyst replacement for oxygen evolution reaction (OER) as well as for hydrogen evolution reaction (HER). From this point of view, transition metal-containing intermetallic compounds with well-defined electronic and crystal structures, are considered as promising electrocatalysts or precursors for them [1, 3]. Up to now, Mo-Ni and Mo-B systems have been explored for the hydrogen evolution reaction, and noticeable HER activities have been demonstrated for the binary compounds in these systems [4-6].The chemical behavior of ternary borides Mo2FeB2, Mo2CoB2 and Mo2NiB2 under hydrogen evolution (HER) reactions is investigated. Material synthesis and electrode manufacturing include the arc melting of elements in 2:1:2 atomic ratio, homogenization annealing at 1300-1400 °C and densification of grinded powder into cylindrically shaped electrodes via spark plasma sintering (SPS). The electrochemical measurements are carried out in 1M KOH and ambient conditions. Electrocatalytic activity and stability are monitored with cyclic voltammetry (CV) and 2-hour chronopotentiometry (CP) measurements performed at reducing current density of 10 mA cm-2, which are considered as conditions of standard benchmarking HER experiment. Furthermore, long-term stability of HER activity at elevated reducing current densities such as 50, 100, 200 mA cm-2 are essential to prove the preserved catalytic performance under harsh reaction conditions. For the comprehensive pre- and post-characterization of the electrode materials, bulk and surface-sensitive techniques are utilized.The pristine Mo2FeB2, Mo2CoB2 and Mo2NiB2 in HER region outperform their constituent TM components and indeed, their HER activity is close to that of the state-of-art Pt catalyst (Figure). During short-term CP experiment, Mo2NiB2 and Mo2FeB2 show continuing activation during the measurement, whereas Mo2CoB2 maintained its stability. Energy dispersive X-ray analysis (EDXS) of electrochemically treated areas indicate an enrichment in Fe, Co and Ni due to the noticeable leaching of Mo into electrolyte. Also, chemical analysis via ICP-OES reveals only Mo among all three constituent elements in the exploited electrolyte solution.As a conclusion, Mo2 TMB2 intermetallic compounds show outstanding HER activity and its stability over 2h of CP with respect to corresponding reference materials. Long-term chronopotentiometry in alkaline media were carried out and will be extensively presented. Figure. HER activity of Mo2 TMB2 (TM: Fe, Co, Ni) with respect to elemental references Fe, Co, Ni and state-of-art Pt. Inlets: Backscattered secondary electron images after 2h CP, including energy dispersive X-ray (EDXS) analysis results.

Green hydrogen (H2) is an essential component of global plans to reduce carbon emissions from hard-to-abate industries and heavy transport. However, challenges remain in the highly efficient H2 production from water electrolysis powered by renewable energies. The sluggish oxygen evolution restrains the H2 production from water splitting. Rational electrocatalyst designs for highly efficient H2 production and oxygen evolution are pivotal for water electrolysis. With the development of high-performance electrolyzers, the scale-up of H2 production to an industrial-level related activity can be achieved. This review summarizes recent advances in water electrolysis such as the proton exchange membrane water electrolyzer (PEMWE) and anion exchange membrane water electrolyzer (AEMWE). The critical challenges for PEMWE and AEMWE are the high cost of noble-metal catalysts and their durability, respectively. This review highlights the anode and cathode designs for improving the catalytic performance of electrocatalysts, the electrolyte and membrane engineering for membrane electrode assembly (MEA) optimizations, and stack systems for the most promising electrolyzers in water electrolysis. Besides, the advantages of integrating water electrolyzers, fuel cells (FC), and regenerative fuel cells (RFC) into the hydrogen ecosystem are introduced. Finally, the perspective of electrolyzer designs with superior performance is presented.