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.

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.

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.

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.

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.

Hydrogen production at intermediate temperatures with proton conducting ceramic cells:Electrocatalytic activity,durability and energy efficiency

Proton conducting ceramic cells(PCCs)are an attractive emerging technology operating in the intermediate temperature range of 500 to 700℃.In this work,we evaluate the production of hydrogen at intermediate temperatures by proton conducting ceramic cell electrolysis(PCCEL).We demonstrate a highperformance steam electrolysis owing to a composite positrode based on BaGd_(0.8)La_(0.2)Co_(2)O_(6-δ)(BGLC1082)and BaZr0.5Ce0.4Y0.1O3-δ(BZCY541).The high reliability of PCCEL is demonstrated for 1680 h at a current density as high as-0.8 A cm^(-2)close to the thermoneutral cell voltage at 600℃.The electrolysis cell showed a specific energy consumption ranging from 54 to 66 kW h kg^(-1)that is comparable to state-of-the-art low temperature electrolysis technologies,while showing hydrogen production rates systematically higher than commercial solid oxide ceramic cells(SOCs).Compared to SOCs,the results verified the higher performances of PCCs at the relevant operating temperatures,due to the lower activation energy for proton transfer comparing with oxygen ion conduction.However,because of the p-type electronic conduction in protonic ceramics,the energy conversion rate of PCCs is relatively lower in steam electrolysis.The faradaic efficiency of the PCC in electrolysis mode can be increased at lower operating temperatures and in endothermic conditions,making PCCEL a technology of choice to valorize high temperature waste heat from industrial processes into hydrogen.To increase the faradaic efficiency by optimizing the materials,the cell design,or the operating strategy is a key challenge to address for future developments of PCCEL in order to achieve even more superior techno-economic merits.

Tri-profit electrolysis for energy-efficient production of benzoic acid and H_(2)

Electrosynthesis has recently attracted intensive research attentions and holds great potential in implementing scalable green synthesis thanks to more and more readily accessible renewable electric energy.

Pre-combustion mercury removal with co-production of hydrogen via coal electrolysis

Pre-combustion mercury removal via coal electrolysis was performed and investigated on a bench-scale coal electrolytic cell(CEC)systemically,and factorial design was used to determine the effect of different operating conditions(coal particle size,operating temperature,operating cell voltage,and flow rate of slurry)on the percentage of mercury removal,percentage of ash removal,and dry heating value change.The results showed that the operating cell voltage,as well as the interaction between operating cell voltage and coal particle size,are significant factors in the percentage of mercury removal.There is no significant factor in the percentage of ash removal and the dry heating value change,but the coal could be purified while keeping the dry heating value almost constant after electrolysis.A co-product of hydrogen could be produced during coal electrolysis with 50%lower energy consumption compared with water electrolysis.Meanwhile,a mechanism for mercury removal in coal was proposed.The facts indicate that coal electrolysis is a promising method for precombustion mercury removal.

Green hydrogen production by intermediate-temperature protonic solid oxide electrolysis cells:Advances,challenges,and perspectives

Protonic solid oxide electrolysis cells(P-SOECs)operating at intermediate temperatures,which have low costs,low environmental impact,and high theoretical electrolysis efficiency,are considered promising next-generation energy conversion devices for green hydrogen production.However,the developments and applications of P-SOECs are restricted by numerous material-and interface-related issues,including carrier mismatch between the anode and electrolyte,current leakage in the electrolyte,poor interfacial contact,and chemical stability.Over the past few decades,considerable attempts have been made to address these issues by improving the properties of P-SOECs.This review comprehensively explores the recent advances in the mechanisms governing steam electrolysis in P-SOECs,optimization strategies,specially designed components,electrochemical performance,and durability.In particular,given that the lack of suitable anode materials has significantly impeded P-SOEC development,the relationships between the transferred carriers and the cell performance,reaction models,and surface decoration approaches are meticulously probed.Finally,the challenges hindering P-SOEC development are discussed and recommendations for future research directions,including theoretical calculations and simulations,structural modification approaches,and large-scale single-cell fabrication,are proposed to stimulate research on P-SOECs and thereby realize efficient electricity-to-hydrogen conversion.

Strong electronic coupling of CoNi and N-doped-carbon for efficient urea-assisted H2 production at a large current density

Exploiting efficient urea oxidation reaction(UOR)and hydrogen evolution reaction(HER)catalysts are significant for energy-saving H2 production through urea-assisted water electrolysis,but it is still challenging.Herein,carbon-encapsulated CoNi coupled with CoNiMoO(CoNi@CN-CoNiMoO)is prepared by solvothermal method and calcination to enhance the activity/stability of urea-assisted water electrolysis at large current density.It exhibits good activity for UOR(E10/1,000=1.29/1.40 V)and HER(E-10/-1000=-45/-245 mV)in 1.0 M KOH+0.5 M urea solution.For the UOR||HER system,CoNi@CN-CoNiMoO only needs 1.58 V at 500 mA cm-2 and shows good stability.Density functional theory calculation suggests that the strong electronic interaction at the interface between NiCo alloy and N-doping-carbon layers can optimize the adsorption/desorption energy of UOR/HER intermediates and accelerate the water dissociation,which can expedite urea decomposition and Volmer step,thus increasing the UOR and HER activity,respectively.This work provides a new solution to design UOR/HER catalysts for H2 production through urea-assisted water electrolysis.

Hydrogen generation with acid/alkaline amphoteric water electrolysis

To reduce the energy consumption of the electrolytic hydrogen generation process, we propose a novel approach to generate hydrogen with acidic/alkaline amphoteric water electrolysis, wherein hydrogen is produced inside an acidic solution and oxygen evolved under alkaline condition, and a membrane is employed in the middle of the electrolyzer to restrain neutralization. The electrode polarization is greatly reduced due to the specific arrangement of the acidic/alkaline amphoteric electrolyzer. The rate of hydrogen production achieves over four times higher than that of the alkaline aqueous solution at 2.2 V, and the energy consumption is reduced approximately 30% under the current density of 200 m A/cm ^2. The investigation of transmembrane potential drop indicates water splitting on the membrane surfaces, which compensates for acid or alkaline loss on-site and maintains the concentration approximately constant during electrolysis process. The acidic/alkaline amphoteric water electrolysis is promising as an energy saving, clean and sustainable hydrogen production technology.

Progress and Prospects of Hydrogen Production: Opportunities and Challenges

This study presents an overview of the current status of hydrogen production in relation to the global requirement for energy and resources.Subsequently,it symmetrically outlines the advantages and disadvantages of various production routes including fossil fuel/biomass conversion,water electrolysis,microbial fermentation,and photocatalysis(PC),in terms of their technologies,economy,energy consumption,and costs.Considering the characteristics of hydrogen energy and the current infrastructure issues,it highlights that onsite production is indispensable and convenient for some special occasions.Finally,it briefly summarizes the current industrialization situation and presents future development and research directions,such as theoretical research strengthening,renewable raw material development,process coupling,and sustainable energy use.

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.

Electrocatalytic Performance of Carbon Layer and Spherical Carbon/Carbon Cloth Composites Towards Hydrogen Evolution from the Direct Electrolysis of Bunsen Reaction Product

A composite material comprising a carbon layer and spherical carbon/carbon cloth(C-SC/CC)was fabricated using a hydrothermal-pyrolysis method,employing carbon cloth as the substrate and glucose as the carbon source.The C-SC/CC electrode was evaluated as an electrocatalytic electrode for hydrogen production by electrolysis of Bunsen reaction products.The electrode prepared with 4 g of glucose and annealed at 800°C showed excellent electrocatalytic activity.It requires only a potential of 185 mV(vs.SCE)to achieve a current density of 10 mA/cm2.Furthermore,the electrode demonstrated good stability with a 6%loss in current density after 1000 cycles of scanning from 0.2 V to 1.2 V.These results indicate the potential of the SC/CC electrode as an efficient and durable electrocatalyst for the electrolysis of H2SO4 and HI.

Design and optimization of electrochemical cell potential for hydrogen gas production

This study deals with the optimization of best working conditions in molten melt for the production of hydrogen(H2) gas.Limited research has been carried out on how electrochemical process occurs through steam splitting via molten hydroxide.54 combinations of cathode,anode,temperature and voltage have been investigated for the optimization of best working conditions with molten hydroxide for hydrogen gas production.All these electrochemical investigations were carried out at 225 to 300℃ temperature and 1.5 to 2.5 V applied voltage values.The current efficiency of 90.5,80.0 and 68.6% has been achieved using stainless steel anodic cell with nickel,stainless steel and platinum working cathode respectively.For nickel cathode,an increase in the current directly affected the hydrogen gas flow rate at cathode.It can be hypothesized from the noted results that increase in current is directly proportional to operating temperature and applied voltage.Higher values were noted when the applied voltages increased from 1.5 to 2.5 V at 300℃,the flow rate of hydrogen gas increased from 1.5 to 11.3 cm^(3) min^(-1),1.0 to 13 cm^(3) min^(-1) in case of electrolysis@stainless steel and@graphite anode respectively.It is observed that the current efficiency of stainless steel anodic cell was higher than the graphite anodic cell.Therefore,steam splitting with the help of molten salts has shown an encouraging alternate to current methodology for H2 fuel production.

Renewable Methanol Production Using Captured Carbon Dioxide and Hydrogen Generated through Water-Splitting

The global warming issues associated with fossil fuels have forced the world to shift towards environment-friendly alternatives. The studies on the capture and storage of CO2 have gained significant research attention, and to attract the world towards CO2 capturing and storing, it is necessary to find suitable applications for this captured CO2. Methanol is one of the products which can be produced by utilizing the captured CO2 and hydrogen that can be produced by water splitting. Keeping in view both these green fuel production processes, this study proposes a combined application of both these technologies for the production of methanol, which is an important chemical used in manufacturing industries. This review paper presents a brief study of both carbon capture and hydrogen production technologies. It also provides research trends, economic aspects, and methods of incorporating both these technologies to produce methanol. Additionally, the prospects of the approach in Oman have also been presented.

Recent advances in hybrid water electrolysis for energy-saving hydrogen production

Electricity-driven water splitting to convert water into hydrogen(H_(2)has been widely regarded as an efficient approach for H_(2)production.Nevertheless,the energy conversion efficiency of it is greatly limited due to the disadvantage of the sluggish kinetic of oxidation evolution reaction(OER).To effectively address the issue,a novel concept of hybrid water electrolysis has been developed for energy–saving H_(2)production.This strategy aims to replace the sluggish kinetics of OER by utilizing thermodynamically favorable organics oxidation reaction to replace OER.Herein,recent advances in such water splitting system for boosting H_(2)evolution under low cell voltage are systematically summarized.Some notable progress of different organics oxidation reactions coupled with hydrogen evolution reaction(HER)are discussed in detail.To facilitate the development of hybrid water electrolysis,the major challenges and perspectives are also proposed.

Synergistically enhanced activity and stability of bifunctional nickel phosphide/sulfide heterointerface electrodes for direct alkaline seawater electrolysis

Direct electrolysis of seawater to generate hydrogen is an attractive but challenging renewable energy storage technology.Reasonable design of seawater electrolysis catalysts should integrate high activity for hydrogen evolution reaction(HER)/oxygen evolution reaction(OER)and enhanced physical/electrochemical stability in seawater.Herein,we demonstrate the development of a Ni foam(NF)supported interfacial heterogeneous nickel phosphide/sulfide(Ni_(2)P/NiS_(2))microsphere electrocatalyst(NiPS/NF)through a facile electrodeposition and subsequent phosphorization/sulfuration process.After NiS_(2)modification,a charge redistribution on the heterointerface is demonstrated and a more advantageous covalent nature of the Ni-P bond is obtained for more easily adsorption of H*and H_(2)O.The NiPS/NF thus yields an impressive electrocatalytic performance in 1.0 M KOH,requiring small overpotentials of 169 and 320 mV for HER and OER to obtain a high current density of 100 m A cm^(-2),respectively.The NiPS/NF can also work efficiently in alkaline seawater with negligible activity degradation,requiring overpotentials of only 188 and 344 mV for a current density of 100 m A cm^(-2)for HER and OER,respectively.A synergistically enhanced physical/electrochemical long-term stability NiPS/NF in saline water is also demonstrated.

Ternary layered double hydroxide oxygen evolution reaction electrocatalyst for anion exchange membrane alkaline seawater electrolysis

Anion exchange membrane(AEM)water electrolyzers are promising energy devices for the production of clean hydrogen from seawater.However,the lack of active and robust electrocatalysts for the oxygen evolution reaction(OER)severely impedes the development of this technology.In this study,a ternary layered double hydroxide(LDH)OER electrocatalyst(NiFeCo-LDH)is developed for high-performance AEM alkaline seawater electrolyzers.The AEM alkaline seawater electrolyzer catalyzed by the NiFeCo LDH shows high seawater electrolysis performance(0.84 A/cm^(2)at 1.7 Vcell)and high hydrogen production efficiency(77.6%at 0.5 A/cm^(2)),thus outperforming an electrolyzer catalyzed by a benchmark IrO_(2)electrocatalyst.The NiFeCo-LDH electrocatalyst greatly improves the kinetics of the AEM alkaline seawater electrolyzer,consequently reducing its activation loss and leading to high performance.Based on the results,this NiFeCo-LDH-catalyzed AEM alkaline seawater electrolyzer can likely surpass the energy conversion targets of the US Department of Energy.

Towards high-performance tubular-type protonic ceramic electrolysis cells with all-Ni-based functional electrodes

Protonic ceramic electrolysis cells(PCECs),which permit high-temperature electrolysis of water,exhibit various advantages over conventional solid oxide electrolysis cells(SOECs),including cost-effectiveness and the potential to operate at low-/intermediate-temperature ranges with high performance and efficiency.Although many efforts have been made in recent years to improve the electrochemical characteristics of PCECs,certain challenges involved in scaling them up remain unresolved.In the present work,we present a twin approach of combining the tape-calendering method with all-Ni-based functional electrodes with the aim of fabricating a tubular-designed PCEC having an enlarged electrode area(4.6 cm^2).This cell,based on a 25μm-thick BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting electrolyte,a nickelbased cermet and a Pr1.95Ba0.05NiO4+δ oxygen electrode,demonstrates a high hydrogen production rate(19 m L min^-1 at 600℃),which surpasses the majority of results reported for traditional button-or planar-type PCECs.These findings increase the scope for scaling up solid oxide electrochemical cells and maintaining their operability at reducing temperatures.