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.

Engineering oxygen vacancies on Tb-doped ceria supported Pt catalyst for hydrogen production through steam reforming of long-chain hydrocarbon fuels

Steam reforming of long-chain hydrocarbon fuels for hydrogen production has received great attention for thermal management of the hypersonic vehicle and fuel-cell application.In this work,Pt catalysts supported on CeO_(2)and Tb-doped CeO_(2)were prepared by a precipitation method.The physical structure and chemical properties of the as-prepared catalysts were characterized by powder X-ray diffraction,scanning electron microscopy,transmission electron microscopy,Raman spectroscopy,H_(2)temperature programmed reduction,and X-ray photoelectron spectroscopy.The results show that Tb-doped CeO_(2)supported Pt possesses abundant surface oxygen vacancies,good inhibition of ceria sintering,and strong metal-support interaction compared with CeO_(2)supported Pt.The catalytic performance of hydrogen production via steam reforming of long-chain hydrocarbon fuels(n-dodecane)was tested.Compared with 2Pt/CeO_(2),2Pt/Ce_(0.9)Tb_(0.1)O_(2),and 2Pt/Ce_(0.5)Tb_(0.5)O_(2),the 2Pt/Ce_(0.7)Tb_(0.3)O_(2)has higher activity and stability for hydrogen production,on which the conversion of n-dodecane was maintained at about 53.2%after 600 min reaction under 700℃at liquid space velocity of 9 ml·g^(-1)·h^(-1).2Pt/CeO_(2)rapidly deactivated,the conversion of n-dodecane was reduced to only 41.6%after 600 min.

Amorphous Iridium Oxide-Integrated Anode Electrodes with Ultrahigh Material Utilization for Hydrogen Production at Industrial Current Densities

Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily scalable electrodeposition at room temperature.Combined with a Nafion 117 membrane,the IrO_(x)-integrated electrode with an ultralow loading of 0.075 mg cm^(-2)delivers a high cell efficiency of about 90%,achieving more than 96%catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane(2 mg cm^(-2)).Additionally,the IrO_(x)electrode demonstrates superior performance,higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported anodes.Notably,the remarkable performance could be mainly due to the amorphous phase property,sufficient Ir^(3+)content,and rich surface hydroxide groups in catalysts.Overall,due to the high activity,high cell efficiency,an economical,greatly simplified and easily scalable fabrication process,and ultrahigh material utilization,the IrO_(x)electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution.

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.

Economic analysis of hydrogen production from electrolyzed water technology by provinces in China

A novel model for measuring the economics of hydrogen generation via electrolytic water projects was constructed.The model overcomes the current problem of incomplete and inaccurate assessments of the price of producing hydrogen via water,which are caused by ignoring the indirect carbon costs of different power generation sources in the process of determining the cost of producing hydrogen via water.The model was used to analyze the price of producing hydrogen via water electrolysis and its sensitivity to the electricity costs of hydrogen production and carbon prices in various provinces of China.With the continuing increase in the penetration of novel energy in China’s power system and the gradual decline in electricity prices,the price of producing hydrogen via electrolytic water is expected to be close to or even lower than that of producing hydrogen via coal in the future.Geographical differences also have a significant impact on the price of producing hydrogen,which is typically higher in the southeastern coastal region than in the western region,because of the local price of electricity and the composition of the energy sources.Provinces that have been effective in developing novel energy sources,such as Qinghai,Sichuan,and others,have been effective in the hydrogen energy industry.Sichuan and other provinces with significant new energy development have a clear advantage in the hydrogen industry.Because provinces with low hydrogen production costs can transport hydrogen to provinces with high hydrogen production costs through pipelines,hydrogen pipelines are planned from Shaanxi to Henan and from Xinjiang to Nei Mongol.These study results reveal the relative economic advantages of producing hydrogen via water electrolysis under various energy and electricity price policies and provide new perspectives on China’s energy strategy and the growth of the hydrogen energy sector.

Ethanol steam reforming over Ni/ZSM-5 nanosheet for hydrogen production

Compared to reforming reactions using hydrocarbons,ethanol steam reforming(ESR)is a sustainable alternative for hydrogen(H_(2))production since ethanol can be produced sustainably using biomass.This work explores the catalyst design strategies for preparing the Ni supported on ZSM-5 zeolite catalysts to promote ESR.Specifically,two-dimensional ZSM-5 nanosheet and conventional ZSM-5 crystal were used as the catalyst carriers and two synthesis strategies,i.e.,in situ encapsulation and wet impregnation method,were employed to prepare the catalysts.Based on the comparative characterization of the catalysts and comparative catalytic assessments,it was found that the combination of the in situ encapsulation synthesis and the ZSM-5 nanosheet carrier was the effective strategy to develop catalysts for promoting H_(2) production via ESR due to the improved mass transfer(through the 2-D structure of ZSM-5 nanosheet)and formation of confined small Ni nanoparticles(resulted via the in situ encapsulation synthesis).In addition,the resulting ZSM-5 nanosheet supported Ni catalyst also showed high Ni dispersion and high accessibility to Ni sites by the reactants,being able to improve the activity and stability of catalysts and suppress metal sintering and coking during ESR at high reaction temperatures.Thus,the Ni supported on ZSM-5 nanosheet catalyst prepared by encapsulation showed the stable performance with~88% ethanol conversion and~65% H_(2) yield achieved during a 48-h longevity test at 550-C.

In-situ photodeposition of co-catalyst Ni_(2)P on CdS for photocatalytic conversion of ethanol for synergistic hydrogen production

In this study,Ni_(2)P/CdS composites were constructed by depositing non-precious metal co-catalyst Ni_(2)P on a one-dimensional network of CdS using a simple in-situ photodeposition method.The prepared photocatalysts promoted the decomposition of ethanol into high-value-added products while generating hydrogen.The composite photoanodes loaded with the Ni_(2)P co-catalysts showed significantly higher ethanol conversion and hydrogen production in the visible light region,which was almost three times higher than that of pure CdS.The main products of photocatalytic ethanol production are acetaldehyde(AA)and 2,3-butanediol(2,3-BDA).Compared with CdS,the selectivity of the composite photocatalysts for converting ethanol to acetaldehyde was significantly improved(62% to 78%).Characterization of the prepared photocatalysts confirmed that the loading of Ni_(2)P co-catalysts on CdS not only broadened the optical region of the catalysts for trapping light but also effectively promoted the separation and transfer of charge carriers,which significantly improved the photocatalytic efficiency of ethanol conversion and hydrogen production in the catalysts.It has been proven through Electron Paramagnetic Resonance testing that loading a Ni_(2)P co-catalyst on CdS is beneficial for the adsorption of hydroxyethyl radicals(*CH(OH)CH_(3)),thereby further improving the selectivity of acetaldehyde.This study plays an important role in the rational design of composite catalyst structures and the introduction of co-catalysts to improve catalyst performance,promote green chemistry,advocate a low-carbon society,and promote sustainable development.

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.

Asymmetric orbital hybridization in Zn-doped antiperovskite Cu_(1-x)Zn_(x)NMn_(3)enables highly efficient electrocatalytic hydrogen production

Rational design of efficient and robust earth-abundant alkaline hydrogen evolution reaction(HER)catalysts is a key factor for developing energy conversion technologies.Currently,antiperovskite nitride CuNMn_(3)has garnered significant interest due to its remarkable properties such as negative/zero thermal expansion and magnetocaloric effects.However,when utilized as hydrogen evolution catalysts,it encounters large challenge resulting from excessively strong/weak interactions with adsorbed H on Mn/Cu active sites,which leads to low HER activity.In this study,we introduce an asymmetric orbital hybridization strategy in Zn-doped Cu_(1-x)Zn_(x)NMn_(3)by leveraging the localization of Zn electronic states to reconfigure the electronic structures of Cu and Mn,thereby reducing the energy barrier for water dissociation and optimizing Cu and Mn active sites for hydrogen adsorption and H_(2)production.Electrochemical evaluations reveal that Cu_(0.85)Zn_(0.15)NMn_(3)with x=0.15 demonstrates exceptional electrocatalytic activity in alkaline electrolytes.A low overpotential of 52 mV at 10 mA cm^(-2)and outstanding stability over a 150-h test period are achieved,surpassing commercial Pt/C.This research offers a novel strategy for enhancing HER performance by modulating asymmetric hybridization of electron orbitals between multiple metal atoms within a material structure.

Unveiling the chemistry behind the electrolytic production of hydrogen peroxide by oxygenated carbon

Oxygenated carbon materials exhibit outstanding electrocatalytic performance in the production of hydrogen peroxide(H2O2)through a two-electron oxygen reduction reaction.The nature of the active functional group and underlying reaction mechanism,however,remain unclear.Here,a comprehensive workflow was established to identify the active sites from the numerous possible structures.The common hydroxyl group at the notched edge demonstrates a key role in the two-electron process.The local chemical environment weakens the binding of OOH intermediate to substrate while enhancing interaction with solution,thereby promoting the H_(2)O_(2)production.With increasing pH,the intramolecular hydrogen bond between OOH intermediate and hydroxyl decreases,facilitating OOH desorption.Furthermore,the rise in selectivity with increasing potential stems from the suppression of the four-electron process.The active site was further validated through experiments.Guided by theoretical understanding,optimal performance was achieved with high selectivity(>95%)and current density(2.06 mA/cm^(2))in experiment.

Research on typical operating conditions of hydrogen production system with off-grid wind power considering the characteristics of proton exchange membrane electrolysis cell

Hydrogen energy,with its abundant reserves,green and low-carbon characteristic,high energy density,diverse sources,and wide applications,is gradually becoming an important carrier in the global energy transformation and development.In this paper,the off-grid wind power hydrogen production system is considered as the research object,and the operating characteristics of a proton exchange membrane(PEM)electrolysis cell,including underload,overload,variable load,and start-stop are analyzed.On this basis,the characteristic extraction of wind power output data after noise reduction is carried out,and then the self-organizing mapping neural network algorithm is used for clustering to extract typical wind power output scenarios and perform weight distribution based on the statistical probability.The trend and fluctuation components are superimposed to generate the typical operating conditions of an off-grid PEM electrolytic hydrogen production system.The historical output data of an actual wind farm are used for the case study,and the results confirm the feasibility of the method proposed in this study for obtaining the typical conditions of off-grid wind power hydrogen production.The results provide a basis for studying the dynamic operation characteristics of PEM electrolytic hydrogen production systems,and the performance degradation mechanism of PEM electrolysis cells under fluctuating inputs.

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.

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.

Marrying luminescent metal nanoclusters to C_(3)N_(4) for efficient photocatalytic hydrogen peroxide production

Photocatalytic oxygen(O_(2))reduction has been considered a promising method for hydrogen peroxide(H_(2)O_(2))production.However,the poor visible light harvesting and low-efficient separation and generation of charge carriers of conventional photocatalysts strongly limited their photocatalytic H_(2)O_(2) generation performance.Herein,we design a highly efficient photocatalyst in this work by marrying luminescent gold-silver nanoclusters(AuAg NCs)to polyethyleneimine(PEI)modified C_(3)N_(4)(C3N4-PEI).The key design in this work is the utilization of highly luminescent AuAg NCs as photosensitizers to promote the generation and separation of charge carriers of C_(3)N_(4)-PEI,thereby ultimately producing abundant e−for O_(2) reduction under visible light illumination(λ≥400 nm).As a result,the as-designed photocatalyst(C3N4-PEI-AuAg NCs)exhibits excellent photocatalytic activity with an H_(2)O_(2) production capability of 82μM in pure water,which is 3.5 times higher than pristine C_(3)N_(4)(23μM).This interesting design provides a paradigm in developing other high-efficient photocatalysts for visible-light-driven H_(2)O_(2) production.

Biohydrogen production with anaerobic sludge immobilized by granular activated carbon in a continuous stirred-tank

A continuous stirred-tank reactor （CSTR） process with granular activated carbon （GAC） was developed for fermentation hydrogen production from molasses-containing wastewater by mixed microbial cultures. Operation at 35℃, an initial biomass of 17.74 g·L^-1 and hydraulic retention time （HRT） of 6 h, the CSTR reactor presented a continuous hydrogen production ability of 5.9 L·d^-1 and the biogas was free of methane throughout the experiment. Dissolved fermehtation products were predominated by ethanol and acetate acid, with smaller quantities of propionic acid, butyric acid and valeric acid. It was found that GAC could make the immobilized system durable and stable in response to organic load impacting and low pH value. When the organic loading rate （OLR） ranged from 8 kgCOD/（m^3d） to 4 kgCOD/（m^3d）, stable ethanol-type fermentation was formed, and the ethanol and acetate concentrations account for 89% of the total liquid products.

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.

Effects of thermally pretreated temperature on bio-hydrogen production from sewage sludge

Hydrogen can be obtained by anaerobic fermentation of sewage sludge. Therefore, in this paper the effects of thermally pretreated temperatures on hydrogen production from sewage sludge were investigated under different pre-treatment conditions. In the thermal pretreatment, some microbial matters of sludge were converted into soluble matters from insoluble ones. As a result, the suspended solid（SS） and volatile suspended solid（VSS） of sludge decreased and the concentration of soluble COD（SCOD） increased, including soluble carbohydrates and proteins. The experimental results showed that all of those pretreated sludge could produce hydrogen by anaerobic fermentation and the hydrogen yields under the temperatures of 121℃ and 50℃ were 12.23 ml/g VS（most） and 1.17 ml/g VS （least）, respectively. It illuminated that the hydrogen yield of sludge was affected by the thermally pretreated temperatures. Additionally, the endurance of high hydrogen yield depended on the translation of microbial matters and inhibition of methanogens in the sludge. The temperatures of 100℃ and 121℃ （treated time, 30 min） could kill or inhibit completely the methanogens while the others could not. To produce hydrogen and save energy, 100℃ was chosen as the optimal temperature for thermal pretrcatment. The composition changes in liquid phase in the fermentation process were also discussed. The SCOD of sludge increased, which was affected by the pretreatment temperature. The production of volatile fatty acids in the anaerobic fermentation increased with the pretreatment temperature.

In situ construction of protonated g-C3N4/Ti3C2 MXene Schottky heterojunctions for efficient photocatalytic hydrogen production

Converting sustainable solar energy into hydrogen energy over semiconductor-based photocatalytic materials provides an alternative to fossil fuel consumption.However,efficient photocatalytic splitting of water to realize carbon-free hydrogen production remains a challenge.Heterojunction photocatalysts with well-defined dimensionality and perfectly matched interfaces are promising for achieving highly efficient solar-to-hydrogen conversion.Herein,we report the fabrication of a novel type of protonated graphitic carbon nitride(PCN)/Ti3C2 MXene heterojunctions with strong interfacial interactions.As expected,the two-dimensional(2D)PCN/2D Ti3C2 MXene interface heterojunction achieves a highly improved hydrogen evolution rate(2181μmol∙g‒1)in comparison with bulk g-C3N4(393μmol∙g‒1)and protonated g-C3N4(816μmol∙g‒1).The charge-regulated surfaces of PCN and the accelerated charge transport at the face-to-face 2D/2D Schottky heterojunction interface are the major contributors to the excellent hydrogen evolution performance of the composite photocatalyst.

Nanoheterostructured photocatalysts for improving photocatalytic hydrogen production

Rapid industrialization has accordingly increased the demand for energy.This has resulted in the increasingly severe energy and environmental crises.Hydrogen production,based on the photocatalytic water splitting driven by sunlight,is able to directly convert solar energy into a usable or storable energy resource,which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution.Unfortunately,the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements.The construction of heterostructured photocatalyst systems,which are comprised of multiple components or multiple phases,is an efficient method to facilitate the separation of electron‐hole pairs to minimize the energy‐waste,provide more electrons,enhance their redox ability,and hence improve the photocatalytic activity.We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts.The heterojunction photocatalytic hydrogen generation systems can be divided into type‐I,type‐II,pn‐junction and Z‐scheme junction,according to the differences in the transfer of the photogenerated electrons and holes.Finally,a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.

Ni-P cluster modified carbon nitride toward efficient photocatalytic hydrogen production

Exploring low-cost cocatalyst to take over noble metal cocatalyst is still challenging in the field of photocatalytic proton reduction.Herein,Ni-P alloy clusters are anchored onto the surface of polymeric carbon nitride through a chemical plating method and serve as highly efficient and stable cocatalyst toward photocatalytic proton reduction.An effective role in promoting the charge separation and migration of the photocatalytic system is demonstrated for Ni-P clusters,which essentially enhance the photocatalytic H2-production rate to a value of 1506μmol h^–1 g^–1.This performance is comparable to that of the benchmark of Pt-modified carbon nitride.This work highlights that the Ni-P alloy could be a potential alternative to noble metal cocatalyst in the photocatalytic reactions.