Classification and technical target of water electrolysis for hydrogen production

Continuous efforts are underway to reduce carbon emissions worldwide in response to global climate change.Water electrolysis technology,in conjunction with renewable energy,is considered the most feasible hydrogen production technology based on the viable possibility of large-scale hydrogen production and the zero-carbon-emission nature of the process.However,for hydrogen produced via water electrolysis systems to be utilized in various fields in practice,the unit cost of hydrogen production must be reduced to$1/kg H_(2).To achieve this unit cost,technical targets for water electrolysis have been suggested regarding components in the system.In this paper,the types of water electrolysis systems and the limitations of water electrolysis system components are explained.We suggest guideline with recent trend for achieving this technical target and insights for the potential utilization of water electrolysis technology.

Decoupled water electrolysis:Flexible strategy for pure hydrogen production with small voltage inputs

Hydrogen gas is widely regarded as an ideal green energy carrier and a potential alternative to fossil fuels for coping with the aggravating energy crisis and environmental pollution.Currently,the vast majority of the world's hydrogen is produced by reforming fossil fuels;however,this hydrogen-making technology is not sustainable or environmentally friendly because ofits high energy consumption and large carbon emissions.Renewables-driven water splitting(2H_(2)0-2H_(2)+0_(2))becomes an extensively studied scheme for sustain-able hydrogen production.Conventional water electrolysis requires an input voltage higher than 1.23 V and forms a gas mixture of H_(2)/O_(2),which results in high electricity consumption,potential safety hazards,and harmful reactive oxygen species.By virtue of the auxiliary redox mediators(RMs)as the robust H^(+)/e^(-)reservoir,decoupled electrolysis splits water at a much lower potential and evolves O_(2)(H_(2)O+RMS_(ox)-O_(2)+H-RMS_(red))and H_(2)(H-RMS_(red)-H_(2)+RMS_(ox))at separate times,rates,and spaces,thus pro-ducing the puretarget hydrogen gas safely.Decoupled electrolysis has accelerated the development ofwater electrolysis technology for H_(2) production.However,itis still lack of a comprehensive and in-depth review in this field based on different types of RMs.This review highlights the basic principles and critical progress of this emerging water electrolysis mode over the past decade.Several representative examples are then dis-played in detail according to the differences in the RMs.The rational choice and design of RMs have also been emphasized.Subsequently,novel applications of decoupled water splitting are briefly discussed,including the manufacture of valuable chemicals,Cl_(2) production,pollutant degradation,and other half-reactions in artificial photosynthesis.Finally,thekey characteristics and disadvantages of each type of mediator are sum-marized in depth.In addition,we present an outlook for future directions in decoupled water splitting.Thus,the flexibility in the design of mediators provides huge space for improving this electrochemical technology.@2024 Science Press and Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by ELSEVIER B.V.and Science Press.All rights reserved.

Pt nanoclusters modified porous g-C_(3)N_(4)nanosheets to significantly enhance hydrogen production by photocatalytic water reforming of methanol

For the use of green hydrogen energy,it is crucial to have efficient photocatalytic activity for hydrogen generation by water reforming of methanol under mild conditions.Much attention has been paid to gC_(3)N_(4)as a promising photocatalyst for the generation of hydrogen.To improve the separation of photogenerated charge,porous nanosheet g-C_(3)N_(4)was modified with Pt nanoclusters(Pt/g-C_(3)N_(4))through impregnation and following photo-induced reduction.This catalyst showed excellent photocatalytic activity of water reforming of methanol fo r hydrogen production with a 17.12 mmol·g^(-1)·h^(-1)rate at room temperature,which was 311 times higher than that of the unmodified g-C_(3)N_(4).The strong interactions of Pt-N in Pt/g-C_(3)N_(4)constructed effective electron transfer channels to promote the separation of photogenerated electrons and holes effectively.In addition,in-situ infrared spectroscopy was used to investigate the intermediates of the hydrogen production reaction,which proved that methanol and water eventually turn into H_(2)and CO_(2)via formaldehyde and formate.This study provides insights for understanding the photocatalytic hydrogen production in the water reforming of methanol.

Generation of input spectrum for electrolysis stack degradation test applied to wind power PEM hydrogen production

Hydrogen production by proton exchange membrane electrolysis has good fluctuation adaptability,making it suitable for hydrogen production by electrolysis in fluctuating power sources such as wind power.However,current research on the durability of proton exchange membrane electrolyzers is insufficient.Studying the typical operating conditions of wind power electrolysis for hydrogen production can provide boundary conditions for performance and degradation tests of electrolysis stacks.In this study,the operating condition spectrum of an electrolysis stack degradation test cycle was proposed.Based on the rate of change of the wind farm output power and the time-averaged peak-valley difference,a fluctuation output power sample set was formed.The characteristic quantities that played an important role in the degradation of the electrolysis stack were selected.Dimensionality reduction of the operating data was performed using principal component analysis.Clustering analysis of the data segments was completed using an improved Gaussian mixture clustering algorithm.Taking the annual output power data of wind farms in Northwest China with a sampling rate of 1 min as an example,the cyclic operating condition spectrum of the proton-exchange membrane electrolysis stack degradation test was constructed.After preliminary simulation analysis,the typical operating condition proposed in this paper effectively reflects the impact of the original curve on the performance degradation of the electrolysis stack.This study provides a method for evaluating the degradation characteristics and system efficiency of an electrolysis stack due to fluctuations in renewable energy.

Development of advanced anion exchange membrane from the view of the performance of water electrolysis cell

Green hydrogen produced by water electrolysis combined with renewable energy is a promising alternative to fossil fuels due to its high energy density with zero-carbon emissions.Among water electrolysis technologies,the anion exchange membrane(AEM) water electrolysis has gained intensive attention and is considered as the next-generation emerging technology due to its potential advantages,such as the use of low-cost non-noble metal catalysts,the relatively mature stack assembly process,etc.However,the AEM water electrolyzer is still in the early development stage of the kW-level stack,which is mainly attributed to severe performance decay caused by the core component,i.e.,AEM.Here,the review comprehensively presents the recent progress of advanced AEM from the view of the performance of water electrolysis cells.Herein,fundamental principles and critical components of AEM water electrolyzers are introduced,and work conditions of AEM water electrolyzers and AEM performance improvement strategies are discussed.The challenges and perspectives are also analyzed.

Recent advances and future prospects on Ni_(3)S_(2)-Based electrocatalysts for efficient alkaline water electrolysis

Green hydrogen(H_(2))produced by renewable energy powered alkaline water electrolysis is a promising alternative to fossil fuels due to its high energy density with zero-carbon emissions.However,efficient and economic H_(2) production by alkaline water electrolysis is hindered by the sluggish hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).Therefore,it is imperative to design and fabricate high-active and low-cost non-precious metal catalysts to improve the HER and OER performance,which affects the energy efficiency of alkaline water electrolysis.Ni_(3)S_(2) with the heazlewoodite structure is a potential electrocatalyst with near-metal conductivity due to the Ni–Ni metal network.Here,the review comprehensively presents the recent progress of Ni_(3)S_(2)-based electrocatalysts for alkaline water electrocatalysis.Herein,the HER and OER mechanisms,performance evaluation criteria,preparation methods,and strategies for performance improvement of Ni_(3)S_(2)-based electrocatalysts are discussed.The challenges and perspectives are also analyzed.

Production of Hydrogen by Electrolysis of Water: Effects of the Electrolyte Type on the Electrolysis Performances

The production of hydrogen, vector of energy, by electrolysis way and by using photovoltaic solar energy can be optimized by suitable choice of electrolytes. Distilled water, usually used, due to membrane presence may be substituted by wastewaters, which enters more in their treatment. Waste water such as those of the Cleansing National Office, and also of the factories such as those referring with ammonia, the margines, and even urines that make it possible to produce much more hydrogen as distilled or salted water, more especially as they do not even require an additive or membranes: conventional electrolysers with two electrodes. This study seeks to optimize the choice among waste water and this, by electrolysis in laboratory or over the sun according to produced hydrogen flow criteria, electrolysis efficiency and electric power consumption. The additive used is NaCl. The most significant results are on the one hand the significant increase in the produced hydrogen flow by the addition of the additive;on the other hand the advantage of gas liquor and urine compared to the others tested electrolytes.

Production of Green Hydrogen by Efficient and Economic Electrolysis of Water with Super-alloy Nanowire Type Electrocatalysts

Green hydrogen production from the electrolysis of water has good appli­cation prospect due to its renewability.The applied voltage of 1.6-2.2V is required in the traditional actual water electrolysis process although the the­oretical decomposition potential of electrolyzing water is 1.23V.The high overpotential in the electrode reaction results in the high energy-consuming for the water electrolysis processes.The overpotentials of the traditional Ru,Ir and Pt based electrocatalysts are respectively 0.3V,0.4V and 0.5V,furthermore use of the Pt,Ir and Ru precious metal catalysts also result in high cost of the water electrolysis process.For minimizing the overpoten­tials in water electrolysis,a novel super-alloy nanowire electrocatalysts have been discovered and developed for water splitting in the present pa­per.It is of significance that the overpotential for the water electrolysis on the super-alloy nanowire electrocatalyst is almost zero.The actual voltage required in the electrolysis process is reduced to 1.3V by using the novel electrocatalyst system with zero overpotential.The utilization of the su­per-alloy nanowire type electrocatalyst instead of the traditional Pt,Ir and Ru precious metal catalysts is the solution to reduce energy consumption and capital cost in water electrolysis to generate hydrogen and oxygen.

Next‑Generation Green Hydrogen: Progress and Perspective from Electricity, Catalyst to Electrolyte in Electrocatalytic Water Splitting

Green hydrogen from electrolysis of water has attracted widespread attention as a renewable power source.Among several hydrogen production methods,it has become the most promising technology.However,there is no large-scale renewable hydrogen production system currently that can compete with conventional fossil fuel hydrogen production.Renewable energy electrocatalytic water splitting is an ideal production technology with environmental cleanliness protection and good hydrogen purity,which meet the requirements of future development.This review summarizes and introduces the current status of hydrogen production by water splitting from three aspects:electricity,catalyst and electrolyte.In particular,the present situation and the latest progress of the key sources of power,catalytic materials and electrolyzers for electrocatalytic water splitting are introduced.Finally,the problems of hydrogen generation from electrolytic water splitting and directions of next-generation green hydrogen in the future are discussed and outlooked.It is expected that this review will have an important impact on the field of hydrogen production from water.

Towards high-performance and robust anion exchange membranes(AEMs)for water electrolysis:Super-acid-catalyzed synthesis of AEMs

The increasing demand for hydrogen energy to address environmental issues and achieve carbon neutrality has elevated interest in green hydrogen production,which does not rely on fossil fuels.Among various hydrogen production technologies,anion exchange membrane water electrolyzer(AEMWE)has emerged as a next-generation technology known for its high hydrogen production efficiency and its ability to use non-metal catalysts.However,this technology faces significant challenges,particularly in terms of the membrane durability and low ionic conductivity.To address these challenges,research efforts have focused on developing membranes with a new backbone structure and anion exchange groups to enhance durability and ionic conductivity.Notably,the super-acid-catalyzed condensation(SACC)synthesis method stands out due to its user convenience,the ability to create high molecular weight(MW)polymers,and the use of oxygen-tolerant organic catalysts.Although the synthesis of anion exchange membranes(AEMs)using the SACC method began in 2015,and despite growing interest in this synthesis approach,there remains a scarcity of review papers focusing on AEMs synthesized using the SACC method.The review covers the basics of SACC synthesis,presents various polymers synthesized using this method,and summarizes the development of these polymers,particularly their building blocks including aryl,ketone,and anion exchange groups.We systematically describe the effects of changes in the molecular structure of each polymer component,conducted by various research groups,on the mechanical properties,conductivity,and operational stability of the membrane.This review will provide insights into the development of AEMs with superior performance and operational stability suitable for water electrolysis applications.

Progress in manipulating spin polarization for solar hydrogen production

Photocatalytic and photoelectrochemical water splitting using semiconductor materials are effective approaches for converting solar energy into hydrogen fuel.In the past few years,a series of photocatalysts/photoelectrocatalysts have been developed and optimized to achieve efficient solar hydrogen production.Among various optimization strategies,the regulation of spin polarization can tailor the intrinsic optoelectronic properties for retarding charge recombination and enhancing surface reactions,thus improving the solar-to-hydrogen(STH)efficiency.This review presents recent advances in the regulation of spin polarization to enhance spin polarized-dependent solar hydrogen evolution activity.Specifically,spin polarization manipulation strategies of several typical photocatalysts/photoelectrocatalysts(e.g.,metallic oxides,metallic sulfides,non-metallic semiconductors,ferroelectric materials,and chiral molecules)are described.In the end,the critical challenges and perspectives of spin polarization regulation towards future solar energy conversion are briefly provided.

Ultralow-voltage hydrogen production and simultaneous Rhodamine B beneficiation in neutral wastewater

Electrocatalytic water splitting for hydrogen production is hampered by the sluggish oxygen evolution reaction(OER)and large power consumption and replacing the OER with thermodynamically favourable reactions can improve the energy conversion efficiency.Since iron corrodes easily and even self-corrodes to form magnetic iron oxide species and generate corrosion currents,a novel strategy to integrate the hydrogen evolution reaction(HER)with waste Fe upgrading reaction(FUR)is proposed and demonstrated for energy-efficient hydrogen production in neutral media.The heterostructured MoSe_(2)/MoO_(2) grown on carbon cloth(MSM/CC)shows superior HER performance to that of commercial Pt/C at high current densities.By replacing conventional OER with FUR,the potential required to afford the anodic current density of 10 m A cm^(-2)decreases by 95%.The HER/FUR overall reaction shows an ultralow voltage of 0.68 V for 10 m A cm^(-2)with a power equivalent of 2.69 k Wh per m^(3)H_(2).Additionally,the Fe species formed at the anode extract the Rhodamine B(Rh B)pollutant by flocculation and also produce nanosized magnetic powder and beneficiated Rh B for value-adding applications.This work demonstrates both energy-saving hydrogen production and pollutant recycling without carbon emission by a single system and reveals a new direction to integrate hydrogen production with environmental recovery to achieve carbon neutrality.

Water electrolysis based on renewable energy for hydrogen production

As an energy storage medium,hydrogen has drawn the attention of research institutions and industry over the past decade,motivated in part by developments in renewable energy,which have led to unused surplus wind and photovoltaic power.Hydrogen production from water electrolysis is a good option to make full use of the surplus renewable energy.Among various technologies for producing hydrogen,water electrolysis using electricity from renewable power sources shows greatpromise.To investigate the prospects of water electrolysis for hydrogen production,this review compares different water electrolysis processes,i.e.,alkaline water electrolysis,proton exchange membrane water electrolysis,solid oxide water electrolysis,and alkaline anion exchange membrane water electrolysis.The ion transfer mechanisms,operating characteristics,energy consumption,and industrial products of different water electrolysis apparatus are introduced in this review.Prospects for new water electrolysis technologies are discussed.

Hydrogen production by glycerol reforming in supercritical water over Ni/MgO-ZrO_2 catalyst

Nano ZrO2 and MgO-ZrO2 were prepared by a self-assembly route and were employed as the support for Ni catalysts used in hydrogen production from glycerol reforming in supercritical water （SCW）. The reforming experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 600-800 ℃. The influences of process variables such as temperature, contact time, and water to glycerol ratio on hydrogen yield were investigated and the catalysts were charactered by ICP, BET, XRD and SEM. The results showed that high hydrogen yield was obtained from glycerol by reforming in supercritical water over the Ni/MgO-ZrO2 catalysts in a short contact time. The MgO in the catalyst showed significant promotion effect for hydrogen production likely due to the formation of the alkaline active site. Even when the glycerol feed concentration was up to 45 wt%, glycerol was completely gasified and transfered to the gas products containing hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At a diluted feed concentration of 5 wt%, near theoretical yield of 7 mole of H2/mol of glycerol could be obtained.

Reducing Energy Costs during Hydrogen Production from Water Electrolysis by Coupling Small Molecule Oxidation: From Molecular Catalysis to Industrial Exploration

Hydrogen energy has garnered significant attention in recent years as a solution to address the global energy crisis and environmental pollution.While water electrolysis stands out as the most promising method to produce green hydrogen,the sluggish reaction kinetics of the oxygen evolution reaction(OER)on the anode increases the cost of hydrogen production.One potential solution to this challenge is replace OER with the thermodynamically more favorable oxidation of small molecules,which can efficiently reduce the energy cost while simultaneously yielding high-value chemicals.Up to now,various organic oxidation reactions have been reported to couple with hydrogen evolution,including alcohol oxidation,biomass platform molecule upgrading,and sacrificial reagents oxidation associated with wastewater treatments.This review concentrates on the recent advancements in the mechanism,catalyst,reactor,and process in this field,with a discussion on its prospects for commercialization.

Study on Hydrogen Production System by Coupling with DSSCs

The consumption of dye-sensitized solar cells (DSSCs) used to produce hydrogen, compared with the traditional water-splitting energy, is much less. First of all it is because of DSSCs’ low cost, easy fabrication process, high conversion efficiency and good stability;secondly it also solves the problem of serious corrosion of the electrode, for the entire solar system is in the air. We use three tandem dye-sensitized photovoltaic cells as a source of power;the open circuit voltage of photoelectric unit shows the feasibility of using dye-sensitized photovoltaic cell decomposition of water to produce hydrogen.

Emerging trends of electrocatalytic technologies for renewable hydrogen energy from seawater:Recent advances,challenges,and techno-feasible assessment

Hydrogen has been regarded as a promising renewable and green energy source to meet energy needs and attain net-zero carbon emissions.The electrolysis of seawater to make hydrogen is one of the fascinating developments of the twenty-first century.This method uses abundant and relatively inexpensive seawater,as opposed to freshwater,which is rare and can be prohibitively expensive.In recent years,significant research and advancements have been made in direct seawater electrolysis technology for hydrogen production.However,producing highly effective and efficient electrocatalysts with long-term viability under harsh corrosive conditions remains a challenging and severe topic for large-scale seawater electrolysis technology.There is still a large accomplishment gap in understanding how to improve seawater electrolysis to increase hydrogen yields and prolong stability.It is,therefore,crucial to have a condensed knowledge of the tunable and inherent interactions between various electrocatalysts,covering electrolyzer types and paying particular attention to those with high efficiency,chemical stability,and conductivity.The extensive discussion is structured into a progression from noble metals to base metal compounds such as oxides,alloys,phosphides,chalcogenides,hydroxides,and nitrides,MXene-based complexes with a concise examination of hybrid electrocatalysts.In addition,proton exchange membranes,anion exchange membranes,alkaline water electrolyzers,and high-temperature water electrolyzers were potential contributors to seawater’s electrolysis.An extensive assessment of the techno-feasibility,economic insights,and future suggestions was done to commercialize the most efficient electrocatalytic systems for hydrogen production.This review is anticipated to provide academics,environmentalists,and industrial researchers with valuable ideas for constructing and modifying seawater-based electrocatalysts.

For more and purer hydrogen-the progress and challenges in water gas shift reaction

The water gas shift(WGS) reaction is a standard reaction that is widely used in industrial hydrogen production and removal of carbon monoxide. The improved catalytic performance of WGS reaction also contributes to ammonia synthesis and other reactions. Advanced catalysts have been developed for both high and low-temperature reactions and are widely used in industry. In recent years, supported metal nanoparticle catalysts have been researched due to their high metal utilization. Low-temperature catalysts have shown promising results, including high selectivity, high shift rates, and higher activity potential. Additionally, significant progress has been made in removing trace CO through the redox reaction in electrolytic cell. This paper reviews the development of WGS reaction catalysts, including the reaction mechanism, catalyst design, and innovative research methods. The catalyst plays a crucial role in the WGS reaction, and this paper provides an instant of catalyst design under different conditions. The progress of catalysts is closely related to the development of advanced characterization techniques.Furthermore, modifying the catalyst surface to enhance activity and significantly increase reaction kinetics is a current research direction. This review goals to stimulate a better understanding of catalyst design, performance optimization, and driving mechanisms, leading to further progress in this field.

Bifunctional PdPt bimetallenes for formate oxidation-boosted water electrolysis

Small-molecule electrooxidation-boosted water electrolysis(WE)is an energy-saving method for hydrogen(H2)production.Herein,PdPt bimetallenes(PdPt BMLs)are obtained through the simple galvanic replacement reaction.PdPt BMLs reveal 2.93-fold enhancement in intrinsic electroactivity and 4.53-fold enhancement in mass electroactivity for the formate oxidation reaction(FOR)with respect to Pd metallenes(Pd MLs)at 0.50 V potential due to the synergistic effect.Meanwhile,the introduction of Pt atoms also considerably increases the electroactivity of PdPt BMLs for hydrogen evolution reaction(HER)with respect to Pd MLs in an alkaline medium,which even exceeds that with the use of commercial Pt nanocrystals.Inspired by the outstanding FOR and HER electroactivity of bifunctional PdPt BMLs,a two-electrode FOR-boosted WE system(FOR-WE)is constructed by using PdPt BMLs as the cathode and the anode.The FOR-WE system only requires an operational voltage of 0.31 V to achieve H2 production,which is 1.48 V lower than that(ca.1.79 V)with the use of the traditional WE system.