Ionic liquid derived electrocatalysts for electrochemical water splitting

Hydrogen production from electrochemical water splitting is a promising strategy to generate green energy,which requires the development of efficient and stable electrocatalysts for the hydrogen evolution reaction and the oxygen evolution reaction(HER and OER).Ionic liquids(ILs)or poly(ionic liquids)(PILs),containing heteroatoms,metal-based anions,and various structures,have been frequently involved as precursors to prepare electrocatalysts for water splitting.Moreover,ILs/PILs possess high conductivity,wide electrochemical windows,and high thermal and chemical stability,which can be directly applied in the electrocatalysis process with high durability.In this review,we focus on the studies of ILs/PILs-derived electrocatalysts for HER and OER,where ILs/PILs are applied as heteroatom dopants and metal precursors to prepare catalysts or are directly utilized as the electrocatalysts.Due to those attractive properties,IL/PIL-derived electrocatalysts exhibit excellent performance for electrochemical water splitting.All these accomplishments and developments are systematically summarized and thoughtfully discussed.Then,the overall perspectives for the current challenges and future developments of ILs/PILs-derived electrocatalysts are provided.

Electrochemical Water Splitting:Bridging the Gaps Between Fundamental Research and Industrial Applications

Electrochemical water splitting represents one of the most promising technologies to produce green hydrogen,which can help to realize the goal of achieving carbon neutrality.While substantial efforts on a laboratory scale have been made for understanding fundamental catalysis and developing high-performance electrocatalysts for the two half-reactions involved in water electrocatalysis,much less attention has been paid to doing relevant research on a larger scale.For example,few such researches have been done on an industrial scale.Herein,we review the very recent endeavors to bridge the gaps between fundamental research and industrial applications for water electrolysis.We begin by introducing the fundamentals of electrochemical water splitting and then present comparisons of testing protocol,figure of merit,catalyst of interest,and manufacturing cost for laboratory and industry-based water-electrolysis research.Special attention is paid to tracking the surface reconstruction process and identifying real catalytic species under different testing conditions,which highlight the significant distinctions of corresponding electrochemical reconstruction mechanisms.Advances in catalyst designs for industry-relevant water electrolysis are also summarized,which reveal the progress of moving the practical applications forward and accelerating synergies between material science and engineering.Perspectives and challenges of electrocatalyst design strategies are proposed finally to further bridge the gaps between lab-scale research and large-scale electrocatalysis applications.

Advanced electrocatalysts with unusual active sites for electrochemical water splitting

Electrochemical water splitting represents a promising technology for green hydrogen production.To design advanced electrocatalysts,it is crucial to identify their active sites and interpret the relationship between their structures and performance.Materials extensively studied as electrocatalysts include noble-metal-based(e.g.,Ru,Ir,and Pt)and non-noble-metal-based(e.g.,3d transition metals)compounds.Recently,advancements in characterization techniques and theoretical calculations have revealed novel and unusual active sites.The present review highlights the latest achievements in the discovery and identification of various unconventional active sites for electrochemical water splitting,with a focus on state-of-the-art strategies for determining true active sites and establishing structure–activity relationships.Furthermore,we discuss the remaining challenges and future perspectives for the development of next-generation electrocatalysts with unusual active sites.By presenting a fresh perspective on the unconventional reaction sites involved in electrochemical water splitting,this review aims to provide valuable guidance for the future study of electrocatalysts in industrial applications.

Vanadium metal-organic framework-derived multifunctional fibers for asymmetric supercapacitor,piezoresistive sensor,and electrochemical water splitting

Fiber-shaped integrated devices are highly desirable for wearable and portable smart electronics,owing to their merits of lightweight,high flexibility,and wearability.However,how to effectively employ multifunctional fibers in one integrated device that can simultaneously achieve energy storage and utilization is a major challenge.Herein,a set of multifunctional fibers all derived from vanadium metal-organic framework nanowires grown on carbon nanotube fiber(V-MOF NWs@CNT fiber)is demonstrated,which can be used for various energy storage and utilization applications.First,a fiber-shaped asymmetric supercapacitor(FASC)is fabricated based on the CoNi-layered double hydroxide nanosheets@vanadium oxide NWs@CNT fiber(CoNi-LDH NSs@V2O5 NWs@CNT fiber)as the positive electrode and vanadium nitride(VN)NWs@CNT fiber as the negative electrode.Benefiting from the outstanding compatibility of the functional materials,the FASC with a maximum working voltage of 1.7 V delivers a high-stack volumetric energy density of 11.27 mW·h/cm3.Then,a fiber-shaped integrated device is assembled by twisting a fiber-shaped piezoresistive sensor(FPS;VN NWs@CNT fiber also served as the highly sensitive material)and a FASC together,where the highperformance FASC can provide a stable and continuous output power for the FPS.Finally,the S-VOx NWs@CNT fiber(sulfur-doped vanadium oxide)electrode shows promising electrocatalytic performance for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),which is further constructed into a self-driven water-splitting unit with the integration of the FASCs.The present work demonstrates that the V-MOF NWs@CNTderived fibers have great potential for constructing wearable multifunctional integrated devices.

Recent developments in the use of single-atom catalysts for water splitting

Electrochemical water splitting is regarded as the most promising approach to produce hydrogen.However,the sluggish electrochemical reactions occurring at the anode and cathode,namely,the oxygen evolution reaction(OER)and the hydrogen evolution reaction(HER),respectively,consume a tremendous amount of energy,seriously hampering its wide application.Recently,single-atom catalysts(SACs)have been proposed to effectively enhance the kinetics of these two reactions.In this minireview,we focus on the recent progress in SACs for OER and HER applications.Three classes of SACs have been reviewed,i.e.,alloy-based SACs,carbon-based SACs and SACs supported on other compounds.Different factors affecting the activities of SACs are also highlighted,including the inherent element property,the coordination environment,the geometric structure and the loading amount of metal atoms.Finally,we summarize the current problems and directions for future development in SACs.

Tuning the electronic structure of the earth-abundant electrocatalysts for oxygen evolution reaction(OER)to achieve efficient alkaline water splitting-A review

Tuning the electronic structure of the electrocatalysts for oxygen evolution reaction(OER)is a promising way to achieve efficient alkaline water splitting for clean energy production(H2).At first,this paper introduces the significance of the tuning of electronic structure,where modifying the electronic structure of the electrocatalysts could generate active sites having optimal adsorption energy with OER intermediates,and that could diminish the energy barrier for OER,and that could improve the activity for OER.Later,this paper reviews the tuning of electronic structure along with catalytic performances,synthetic methodologies,chemical properties,and DFT calculations on various nanostructured earth-abundant electrocatalysts for OER in alkaline environment.Further,this review discusses the tuning of the electronic structure of the several nanostructured earth-abundant electrocatalysts including oxide,(oxy)hydroxide,layered double hydroxide,alloy,metal phosphide/phosphate,nitride,sulfide,selenide,carbon containing materials,MOF,core-shell/hetero/hollow structured materials,and materials with vacancies/defects for OER in alkaline environment(including activity:overpotential(η)of ≤200 mV at10 m A cm^(-2);stability:≥100 h;durability:≥5000 cycles).Then,this review discusses the robust stability of the electrocatalysts for OER towards practical application.Moreover,this review discusses the in situ formation of thin layer on the catalyst surface during OER.In addition,this review discusses the influence of the adsorption energy of the OER intermediates on OER performance of the catalysts.Finally,this review summarizes the various promising strategies for tuning the electronic structure of the electrocatalysts to achieve enhanced performance for OER in alkaline environment.

Solar‑Driven Sustainability:Ⅲ–ⅤSemiconductor for Green Energy Production Technologies

Long-term societal prosperity depends on addressing the world’s energy and environmental problems,and photocatalysis has emerged as a viable remedy.Improving the efficiency of photocatalytic processes is fundamentally achieved by optimizing the effective utilization of solar energy and enhancing the efficient separation of photogenerated charges.It has been demonstrated that the fabrication ofⅢ–Ⅴsemiconductor-based photocatalysts is effective in increasing solar light absorption,long-term stability,large-scale production and promoting charge transfer.This focused review explores on the current developments inⅢ–Ⅴsemiconductor materials for solar-powered photocatalytic systems.The review explores on various subjects,including the advancement ofⅢ–Ⅴsemiconductors,photocatalytic mechanisms,and their uses in H2 conversion,CO_(2)reduction,environmental remediation,and photocatalytic oxidation and reduction reactions.In order to design heterostructures,the review delves into basic concepts including solar light absorption and effective charge separation.It also highlights significant advancements in green energy systems for water splitting,emphasizing the significance of establishing eco-friendly systems for CO_(2)reduction and hydrogen production.The main purpose is to produce hydrogen through sustainable and ecologically friendly energy conversion.The review intends to foster the development of greener and more sustainable energy source by encouraging researchers and developers to focus on practical applications and advancements in solar-powered photocatalysis.

Hollow cobalt-nickel phosphide nanocages for efficient electrochemical overall water splitting

A low-cost,highly efficient and strong durable bifunctional electrocatalyst is crucial for electrochemical overall water splitting.In this paper,a self-templated strategy combined with in-situ phosphorization is applied to construct hollow structured bimetallic cobalt-nickel phosphide(CoNiP_(x))nanocages.Owing to their unique hollow structure and bimetallic synergistic effects,the as-synthesized CoNiP_(x)hollow nanocages exhibit a high electrocatalytic activity and stability towards hydrogen evolution reaction in all-pH electrolyte and a remarkable electrochemical performance for oxygen evolution reaction in 1.0 mol L^(-1)KOH.Meanwhile,with the bifunctional electrocatalyst in both anode and cathode for overall water splitting,a low voltage of 1.61 V and superior stability are achieved at a current density of 20 mA cm^(-2).

Engineering Ruthenium-Based Electrocatalysts for Effective Hydrogen Evolution Reaction

The investigation of highly effective,durable,and cost-effective electrocatalysts for the hydrogen evolution reaction(HER)is a prerequisite for the upcoming hydrogen energy society.To establish a new hydrogen energy system and gradually replace the traditional fossil-based energy,electrochemical water-splitting is considered the most promising,environmentally friendly,and efficient way to produce pure hydrogen.Compared with the commonly used platinum(Pt)-based catalysts,ruthenium(Ru)is expected to be a good alternative because of its similar hydrogen bonding energy,lower water decomposition barrier,and considerably lower price.Analyzing and revealing the HER mechanisms,as well as identifying a rational design of Ru-based HER catalysts with desirable activity and stability is indispensable.In this review,the research progress on HER electrocatalysts and the relevant describing parameters for HER performance are briefly introduced.Moreover,four major strategies to improve the performance of Ru-based electrocatalysts,including electronic effect modulation,support engineering,structure design,and maximum utilization(single atom)are discussed.Finally,the challenges,solutions and prospects are highlighted to prompt the practical applications of Rubased electrocatalysts for HER.

Design of efficient electrocatalysts for hydrogen evolution reaction based on 2D MXenes

The growing energy concern all over the world has recognized hydrogen energy as the most promising renewable energy sources.Recently,electrocatalytic hydrogen evolution reaction(HER)by water splitting has been extensively studied with a focus on developing efficient electrocatalysts that can afford HER at overpotential with minimum power consumption.The two-dimensional transition metal carbides and nitride,also known as MXenes,are becoming the rising star in developing efficient electrocatalysts for HER,owing to their integrated chemical and electronic properties,e.g.,metallic conductivity,variety of redox-active transition metals,high hydrophilicity,and tunable surface functionalities.In this review,the recent progress about the fundamental understanding and materials engineering of MXenes-based electrocatalysts is summarized in concern with two aspects:i)the regulation of the intrinsic properties of MXenes,which include the composition,surface functionality,and defects;and ii)MXenes-based composites for HER process.In the end,we summarize the present challenges concerning the efficiency of MXenes-based HER electrocatalysts and propose the directions of future research efforts.

Application of in situ/operando characterization techniques in heterostructure catalysts toward water electrolysis

The key to achieving the breakthrough of hydrogen energy from marginal energy sources in large scale applications lies in the development and design of efficient electrocatalysts for the electrochemical oxidation and reduction of water.The unique heterostructure endows the catalyst with a mass of functional interfaces that are decisive for the enhancement of catalyst activity,stability,and reaction kinetics.Although some cutting-edge reviews have focused on the synthesis strategies,constitution,and applications of heterostructure catalysts,the field still lacks a detailed discussion of the actual reaction processes occurring at the interface,which is detrimental to the understanding of the true catalytic mechanism.Relying on advanced in situ/operando characterization techniques to understand the working mechanism of heterostructure catalysts is essential for rational design of advanced catalysts.In this review,we first present the advantages of heterostructure catalysts applied to electrolyzing water.Subsequently,the application of in situ/operando techniques in probing three aspects of heterostructure catalyst surface reconstruction,reaction mechanism,and the role of each component is highlighted with classical case studies.Finally,the current challenges and prospects for the design of heterostructure electrocatalysts are discussed in detail.

Urea electrooxidation-boosted hydrogen production on nitrogen-doped porous carbon nanorod-supported nickel phosphide nanoparticles

Urea electro-oxidation reaction(UEOR)-boosted water electrolysis can supplant the kinetics-restricted oxygen evolution reaction(OER)and provide an energy-saving method of hydrogen generation.However,low UEOR activity and the poisoning issue of the catalyst limit its practical application.Herein,a simple coordination reaction is used to synthesize the dimethylglyoxime-NiⅡcomplex(DMGNiⅡ),which efficiently serves as the initial precursor to synthesize nitrogen-doped carbon nanorodsupported nickel phosphide nanoparticle(Ni_(2)P/N-C)nanocomposites.The density functional theory calculations and electrochemical results reveal that nitrogen doping can weaken the adsorption of hydrogen and the generated CO_(2)resulting in an enhancement of hydrogen evolution reaction(HER)and UEOR activity.In addition,N-doping can also promote the generation of Ni,which can further promote the UEOR and HER performance.Concretely,the overpotential for the HER on Ni_(2)P/N-C-2h nanocomposites is only 201 m V at 10 mA cm,and the onset potential of the UEOR on NiP/NC-2h nanocomposites is only 1.34 V.Additionally,the Ni_(2)P/N-Cnanocomposites also show excellent long-term stability due to the introduction of nitrogen-doped carbon material.Consequently,the symmetric Ni_(2)P/N-C-2h||Ni_(2)P/N-C-2h urea electrolyzer requires 1.41 V of electrolysis voltage for urea electrolysis,which can be applied in energy-saving H_(2) production and environment purification.

Ultrasonication-assisted and gram-scale synthesis of Co-LDH nanosheet aggregates for oxygen evolution reaction

Electrochemical water splitting(EWS)is a highly clean and efficient method for high-purity hydrogen production.Unfortunately,EWS suffers from the sluggish and complex oxygen evolution reaction(OER)kinetics at anode.At present,the efficient,stable,and low-cost non-precious metal based OER electrocatalyst is still a great and long-term challenge for the future industrial application of EWS technology.Herein,we develop a simple and fast approach for gram-scale synthesis of flower-like cobalt-based layered double hydroxides nanosheet aggregates by ultrasonic synthesis,which show outstanding electrocatalytic performance for the oxygen evolution reaction in alkaline media,such as preeminent stability,small overpotential of 300 mV at 10 mA·cm^−2 and small Tafel slope of 110 mV·dec^−1.