A robust & weak-nucleophilicity electrocatalyst with an inert response for chlorine ion oxidation in large-current seawater electrolysis

Seawater splitting into hydrogen,a promising technology,is seriously limited by the durability and tolerance of electrocatalysts for chlorine ions in seawater at large current densities due to chloride oxidation and corrosion.Here,we present a robust and weak-nucleophilicity nickel-iron hydroxide electrocatalyst with excellent selectivity for oxygen evolution and an inert response for chlorine ion oxidation which are key and highly desired for efficient seawater electrolysis.Such a weak-nucleophilicity electrocatalyst can well match with strong-nucleophilicity OH-compared with the weak-nucleophilicity Cl^(-),resultantly,the oxidation of OH-in electrolyte can be more easily achieved relative to chlorine ion oxidation,confirmed by ethylenediaminetetraacetic acid disodium probing test.Further,no strongly corrosive hypochlorite is produced when the operating voltage reaches about 2.1 V vs.RHE,a potential that is far beyond the thermodynamic potential of chlorine ion oxidatio n.This concept and approach to reasonably designing weaknucleophilicity electrocatalysts that can greatly avoid chlorine ion oxidation under alkaline seawater environments can push forward the seawater electrolysis technology and also accelerate the development of green hydrogen technique.

Electrochemical reconstruction of non-noble metal-based heterostructure nanorod arrays electrodes for highly stable anion exchange membrane seawater electrolysis

Direct seawater electrolysis for hydrogen production has been regarded as a viable route to utilize surplus renewable energy and address the climate crisis.However,the harsh electrochemical environment of seawater,particularly the presence of aggressive Cl^(-),has been proven to be prone to parasitic chloride ion oxidation and corrosion reactions,thus restricting seawater electrolyzer lifetime.Herein,hierarchical structure(Ni,Fe)O(OH)@NiCoS nanorod arrays(NAs)catalysts with heterointerfaces and localized oxygen vacancies were synthesized at nickel foam substrates via the combination of hydrothermal and annealing methods to boost seawater dissociation.The hiera rchical nanostructure of NiCoS NAs enhanced electrode charge transfer rate and active surface area to accelerate oxygen evolution reaction(OER)and generated sulfate gradient layers to repulsive aggressive Cl^(-).The fabricated heterostructure and vacancies of(Ni,Fe)O(OH)tuned catalyst electronic structure into an electrophilic state to enhance the binding affinity of hydroxyl intermediates and facilitate the structural transformation into amorphousγ-NiFeOOH for promoting OER.Furthermore,through operando electrochemistry techniques,we found that theγ-NiFeOOH possessing an unsaturated coordination environment and lattice-oxygen-participated OER mechanism can minimize electrode Cl^(-)corrosion enabled by stabilizing the adsorption of OH*intermediates,making it one of the best OER catalysts in the seawater medium reported to date.Consequently,these catalysts can deliver current densities of 100 and 500 mA cm-2for boosting OER at minimal overpotentials of 245and 316 mV,respectively,and thus prevent chloride ion oxidation simultaneously.Impressively,a highly stable anion exchange membrane(AEM)seawater electrolyzer based on the non-noble metal heterostructure electrodes reached a record low degradation rate under 100μV h-1at constant industrial current densities of 400 and 600 mA cm-2over 300 h,which exhibits a promising future for the nonprecious and stable AEMWE in the direct seawater electrolysis industry.

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.

Ni Single Atoms and Ni Phosphate Clusters Synergistically Triggered Surface-Functionalized MoS_(2)Nanosheets for High-performance Freshwater and Seawater Electrolysis

Two-dimensional metal dichalcogenides have been evidenced as potential electrocatalysts for hydrogen evolution reaction(HER);however,their application is limited by a poor oxygen evolution reaction(OER)activity due to insufficient number/types of multi-integrated active sites.In this study,we report a novel bifunctional catalyst developed by simultaneous engineering of single nickel atoms(Ni_(SA)) and nickel phosphate clusters(Ni_(Pi)) to synergistically trigger surface-functionalized MoS_(2) nanosheets(NSs)resulting in high reactivities for both HER and OER.The Ni_(SA)-Ni_(Pi)/MoS_(2)NSs material exhibits a fairly Pt-like HER behavior with an overpotential of 94.0 mV and a small OER overpotential of 314.0 mV to reach 10 mA cm^(-2) in freshwater containing 1.0 M KOH.Experimental results of the catalyst are well supported by theoretical study,which reveals the significant modulation of electronic structure and enrichment of electroactive site number/types with their reasonably adjusted free adsorption energy.For evaluating practicability,the Ni_(SA)-Ni_(Pi)/MoS_(2)NSs-based electrolyzer delivers effective operation voltage of 1.62,1.52,and 1.66 V at 10 mA cm^(-2) and superior long-term stability as compared to Pt/C//RuO_(2) system in freshwater,mimic seawater,and natural seawater,respectively.The present study indicates that the catalyst is a promising candidate for the practical production of green hydrogen via water electrolysis.

Design of highly active and durable oxygen evolution catalyst with intrinsic chlorine inhibition property for seawater electrolysis

High-efficiency seawater electrolysis is impeded by the low activity and low durability of oxygen evolution catalysts due to the complex composition and competitive side reactions in seawater.Herein,a heterogeneousstructured catalyst is constructed by depositing NiFe-layered double hydroxides(NiFe-LDH)on the substrate of MXene(V_(2)CT_(x))modified Ni foam(NF),and abbreviated as NiFe-LDH/V_(2)CT_(x)/NF.As demonstrated,owing to the intrinsic negative charge characteristic of V_(2)CT_(x),chlorine ions are denied entry to the interface between NiFeLDH and V_(2)CT_(x)/NF substrate,thus endowing NiFe-LDH/V_(2)CT_(x)/NF catalyst with high corrosion resistance and durable stability for 110 h at 500 mA cm^(-2).Meanwhile,the two-dimensional structure and high electrical conductivity of V_(2)CT_(x) can respectively enlarge the electrochemical active surface area and guarantee fast charge transfer,thereby synergistically promoting the catalytic performance of NiFe-LDH/V_(2)CT_(x)/NF in both deionized water electrolyte(261 m V at 100 m A cm^(-2))and simulated seawater electrolyte(241 mV at 100 mA cm^(-2)).This work can guide the preparation of oxygen evolution catalysts and accelerate the industrialization of seawater electrolysis.

A comprehensive review on catalysts for seawater electrolysis

Seawater electrolysis is a sustainable energy conversion technology that generates clean energy by splitting seawater into hydrogen and oxygen.However,the catalysts used in seawater electrolysis often face significant stability challenges because of the high concentration of salt ions and other impurities present in seawater.This review aims to discern the pivotal factors influencing catalyst stability in seawater electrolysis,elucidate the corrosion and electrochemical degradation mechanisms,and delve into the various strategies employed to enhance catalyst stability.These strategies encompass catalyst material selection,surface modification techniques,catalyst support materials,and catalyst design strategies.By gaining deeper insights into the obstacles and innovations concerning catalyst stability in seawater electrolysis,this review strives to expedite progress toward the commercialization and widespread adoption of this technology as a renewable and feasible approach for hydrogen production.Ultimately,the goal is to foster a cleaner and more sustainable future by enabling the efficient and enduring generation of hydrogen from seawater.

Highly anti-corrosive NiFe LDHs–NiFe alloy hybrid enables long-term stable alkaline seawater electrolysis

Owing to the significant potential of alkalin seawater electrolysis for converting surplus power into eco friendly hydrogen fuel,we developed bifunctional elec trodes that integrate low-crystalline NiFe LDHs and amorphous NiFe alloy on a Ni foam(NF)substrate to enhance this process.Driven by the battery-like charac teristics of NiFe LDHs,an anti-corrosive and active oute layer of NiFe^(vac)OOH continuously forms over time in th hybrid on the anode for the oxygen evolution reaction(OER),effectively mitigating powder shedding caused by corrosion induced by multiple anions in seawater.Mean while,the strong bond between the hybrid and the NF substrate maintains intact hybrid coatings to ensure a rel atively high overall conductivity of the electrodes,signif icantly reducing the negative effects of structura degradation during the OER and hydrogen evolution reaction(HER),as well as the accumulation of contami nants on the electrode surfaces.In long-term tests,thes bifunctionalhybridelectrodesmaintained stable performance,even at a high current density o500 mA·cm^(-2).The cell voltage increased by only 88 m V over 1000 h to 1.970 V during saline electrolysis and by103 mV over 500 h to 2.062 V during seawater electroly sis.Hence,this study provides valuable insights into efficient and stable seawater electrolysis using NiFe LDHs–NiFe alloy hybrids.

Challenges and strategies of chlorine inhibition in anode systems for seawater electrolysis

Seawater electrolysis for green hydrogen production is one of the key technologies for achieving carbon neutrality.However,in anode systems,the chloride ions(Cl^(-))in seawater will trigger an undesired chlorine evolution reaction(CER)that competes with an oxygen evolution reaction(OER),resulting in inferior OER activity and selectivity.Besides,the corrosive Cl^(-)and its derivative products will corrode anodes during seawater electrolysis,leading to poor stability.Therefore,great efforts have been devoted to developing efficient strategies for chlorine inhibition to improve the activity,selectivity,and stability of anode materials.Herein,focusing on chlorine inhibition,we present a mini review to comprehensively and concisely summarize the recent progress in anode systems for boosting seawater electrolysis.In particular,two strategies of physical and chemical regulation to inhibit Cl^(-)are summarized in some representative cases.Finally,some challenges and future opportunities in anode systems for seawater electrolysis are prospected.This mini review aims to shed light on designing highly efficient anode materials for seawater electrolysis.

Introducing sulfur to nickel-iron selenide for high-efficiency alkaline seawater electrolysis

Seawater electrolysis is an effective way to obtain hydrogen(H_(2))in a sustainable manner.However,the lack of electrocatalysts with high activity,stability,and selectivity for oxygen evolution reaction(OER)severely hinders the development of seawater electrolysis technology.Herein,sulfur-doped nickel-iron selenide nanosheets(S-NiFeSe_(2))were prepared by an ion-exchange strategy and served as highly active OER electrocatalyst for alkaline seawater electrolysis.The overpotential is 367 m V,and it can run stably for over 50 h at 100 m A cm^(-2).Excitingly,the S-NiFeSe_(2)||Pt/C pair exhibits cell voltage of 1.54 V at 10 m A cm^(-2)under alkaline seawater conditions,which can run smoothly for 100 h without decay,and the efficiency of electricity-tohydrogen(ETH)energy conversion reaches more than 80%.Such electrode,with abundant accessible reactive sites and good corrosion resistance,is a good candidate for seawater electrolysis.Moreover,density functional theory calculations reveal that the surface sulfur atoms can activate the adjacent Ni sites and decrease the free energy changes of the associated intermediates at the adjacent Ni sites for OER,and the step of~*OH→~*O is the potential rate-limiting step.In this work,the true reactive site in nickel-iron selenides is the Ni sites,but not the Fe sites as commonly believed.

Constructing an OH−-enriched microenvironment on the electrode surface for natural seawater electrolysis

Powered by clean energy, the hydrogen fuel production from seawater electrolysis is a sustainable green hydrogen technology, however, chlorine corrosion and correlative oxidation reactions severely erode the catalysts. Our previous work demonstrates that direct seawater electrolysis without a desalination process and strong alkali addition can be realized by introducing a hard Lewis acid oxide on the catalyst surface to capture OH−. However, the criteria for selecting Lewis acid oxides and the origin of OH− enrichment in chlorine chemistry inhibition on the catalyst surface remain unexplored. Here, we compare the ability of a series of Lewis acid oxides with different acidity constants (pKa), including MnO_(2), Fe_(2)O_(3), and Cr_(2)O_(3), to enrich OH− on the Co3O4 anode catalyst surface. Comprehensive analyses suggest that the lower pKa value of the Lewis acid oxide, the higher concentration of OH− enriched on Co3O4 surface, and the lower Cl− concentration. As established correlation among pKa of Lewis acid oxide, OH− enrichment and Cl− repulsion provide direct guidance for future design of highly active, selective and durable catalysts for natural seawater electrolysis.

Epitaxially Grown Ru Clusters-Nickel Nitride Heterostructure Advances Water Electrolysis Kinetics in Alkaline and Seawater Media

The epitaxial heterostructure can be rationally designed based on the in situ growth of two compatible phases with lattice similarity,in which the modulated electronic states and tuned adsorption behaviors are conducive to the enhancement of electrocatalytic activity.Herein,theoretical simulations first disclose the charge transfer trend and reinforced inherent electron conduction around the epitaxial heterointerface between Ru clusters and Ni_(3)N substrate(cRu-Ni_(3)N),thus leading to the optimized adsorption behaviors and reduced activation energy barriers.Subsequently,the defectrich nanosheets with the epitaxially grown cRu-Ni_(3)N heterointerface are successfully constructed.Impressively,by virtue of the superiority of intrinsic activity and reaction kinetics,such unique epitaxial heterostructure exhibits remarkable bifunctional catalytic activity toward electrocatalytic OER(226 mV@20 mA cm^(−2))and HER(32 mV@10 mA cm^(−2))in alkaline media.Furthermore,it also shows great application prospect in alkaline freshwater and seawater splitting,as well as solar-to-hydrogen integrated system.This work could provide beneficial enlightenment for the establishment of advanced electrocatalysts with epitaxial heterointerfaces.

P-Ni_(4)Mo Catalyst for Seawater Electrolysis with High Current Density and Durability

Rational design of highly efficient and durable electrocatalysts with low cost to replace noblemetal based catalysts for seawater electrolysis is extremely desirable,but challenging.In this work,we demonstrate a rapid electrodeposition method by growing P-Ni_(4)Mo on the surface of the copper foam(CF)substrate to synthesize an efficient seawater electrolysis catalyst(P-Ni_(4)Mo/CF).The catalyst exhibited considerable HER performance and stability in alkaline seawater,with the overpotential as low as 260 mV at a current density of 100 mA cm^(-2).The P-Ni_(4)Mo/CF is capable of achieving 1.0 A cm^(-2) with an overpotential of 551 mV,which is slightly worse than that of the Pt/C catalyst(453 mV).Moreover,P-Ni_(4)Mo/CF demonstrates robust durability,with almost no activity loss after the durability test for more than 200 h.This work not only reports a new catalyst for seawater electrolysis,but also presents a strategy for the performance enhancement of seawater electrolysis.

Research prospects of graphene-based catalyst for seawater electrolysis

Seawater has obvious resource reserve advantages compared to fresh water,and so the huge potential advantages for large-scale electrolysis of hydrogen production has been paid more attention to;but at the same time,electrolysis of seawater requires more stable and active catalysts to deal with seawater corrosion problems.Graphene-based materials are very suitable as composite supports for catalysts due to their high electrical conductivity,specific surface area,and porosity.Therefore,the review introduces the problems faced by seawater electrolysis for hydrogen production and the various catalysts performance.Among them,the advantages of catalysis of graphene-based catalysts and the methods of enhancement the catalytic performance of graphene are emphasized.Finally,the development direction of composite catalysts is prospected,hoping to provide guidance for the preparation of more efficient electrocatalysts for seawater electrolysis.

Advancements in Seawater Electrolysis:Progressing from Fundamental Research to Applied Electrolyzer Application

Seawater electrolysis(SWE)provides a promising and efficient pathway to produce green hydrogen.However,the current SWE technology confronts a lot of challenges,such as the sluggish reaction kinetics on the anode side,and a lot of impurities and ions in seawater that poison the active sites of the catalyst and block membrane pores.In addition,the existence of chloride ions(Cl−)in seawater will strongly compete with oxygen evolution reaction(OER)by the chlorine oxidation/evolution reaction(ClOR/ClER)on the anode side as a result of the extremely similar thermodynamic potentials.Thus,to move SWE much closer to commercialization,it is highly desirable to enhance not only the activity of electrocatalysts but also the selectivity and stability of efficient OER to restrain ClOR/ClER.At the same time,the additive of electrolytes and the unique structural design of the electrolyzer also promote the development of SWE.In this review,the fundamental mechanisms for SWE and water electrolysis are first introduced and compared.Then,the design principles of efficient catalysts,electrolytes,surface/interface engineering,and novelty reaction device are critically,comprehensively summarized and analyzed.Finally,perspectives,challenges,and opportunities to develop and boost SWE technologies are proposed.

In situ generation of oxyanions-decorated cobalt(nickel)oxyhydroxide catalyst with high corrosion resistance for stable and efficient seawater oxidation

The development of efficient and robust anode materials for stable alkaline seawater electrolysis is severely limited by chlorine evolution reaction and chloride corrosion.Here,the sulfur-doped cobalt-nickel bimetallic phosphides(CoNiPS)are specifically designed as a pre-catalyst for navigating a surface reconstruction to fabricate the anions(PO^(3-)_(4) and SO^(2-)_(4))-decorated Co(Ni)OOH catalyst(R-CoNiPS)with exceptional durability and high activity for stable alkaline seawater oxidation(ASO).Various experiment techniques together with theoretical simulations both demonstrate that the in situ-generated PO^(3-)_(4) and SO^(2-)_(4) anions on catalyst surface can improve the oxygen evolution reaction(OER)activity,regulating and stabilizing the catalytic active species Co(Ni)OOH,as well as make a critical role in inhibiting the adsorp-tion of chloride ions and extending the service life of electrode.Therefore,this R-CoNiPS electrode exhi-bits superb OER activity toward AsO and stands out among the non-precious ASO electrocatalysts reported recently,requiring low overpotentials of 420 and 440 mV to attain large current densities of 500 and 1000 mA cm^(-2) in an alkaline natural seawater electrolyte,respectively.Particularly,the catalyst displays a negligible chloride corrosion at room temperature during ASO operation(>200 h)at 500 mA cm^(-2).This work opens up a new viewpoint for designing high-activity and durable electrocata-lystsforseawaterelectrolysis.

High-precision regulation synthesis of Fe-doped Co_(2)P nanorod bundles as efficient electrocatalysts for hydrogen evolution in all-pH range and seawater

The hydrogen evolution reaction(HER)via water electrolysis has gained immense research attention.Seawater electrolysis provides great opportunities for sustainable energy production,but is extremely challenging.Transition metal phosphides are promising candidate electrocatalysts.Herein,we prepared a novel Fe-Co_(2)P bundle of nanorods(BNRs)for catalyzing the HER in seawater electrolysis and over the entire p H range.Cobalt phosphides with different crystal phases and morphologies were obtained by varying the Fe doping amount.The Co:Fe molar ratio of 1:0.5 was found to be optimum.The Fe doping improved the HER performance of Co_(2)P over the entire p H range by providing favorable electronic properties and morphology,lattice distortion,and special coordination environment.The Fe-Co_(2)P BNRs showed higher catalytic activity than 20%Pt/C in seawater at high potentials.The density functional theory calculations revealed that the Fe doping reduced the hydrogen binding strength of Co_(2)P to efficiently accelerate the HER kinetics and produce a favorable charge density.This study provides valuable insights into the design and development of high-efficiency HER catalysts for large-scale seawater electrolysis.

Hierarchical Interconnected NiMoN with Large Specific Surface Area and High Mechanical Strength for Efficient and Stable Alkaline Water/Seawater Hydrogen Evolution

NiMo-based nanostructures are among the most active hydrogen evolution reaction(HER)catalysts under an alkaline environment due to their strong water dissociation ability.However,these nanostructures are vulnerable to the destructive effects of H_(2) production,especially at industry-standard current densities.Therefore,developing a strategy to improve their mechanical strength while maintaining or even further increasing the activity of these nanocatalysts is of great interest to both the research and industrial communities.Here,a hierarchical interconnected NiMoN(HW-NiMoN-2h)with a nanorod-nanowire morphology was synthesized based on a rational combination of hydrothermal and water bath processes.HW-NiMoN-2h is found to exhibit excellent HER activity due to the accomodation of abundant active sites on its hierarchical morphology,in which nanowires con-nect free-standing nanorods,concurrently strengthening its structural stability to withstand H_(2) production at 1 A cm^(−2).Seawater is an attractive feedstock for water electrolysis since H_(2) generation and water desalination can be addressed simultaneously in a single process.The HER performance of HW-NiMoN-2h in alkaline seawater suggests that the presence of Na+ions interferes with the reation kinetics,thus lowering its activity slightly.However,benefiting from its hierarchical and interconnected characteristics,HW-NiMoN-2h is found to deliver outstanding HER activity of 1 A cm^(−2) at 130 mV overpotential and to exhibit excellent stability at 1 A cm^(−2) over 70 h in 1 M KOH seawater.

Modulation of d-orbital to realize enriched electronic cobalt sites in cobalt sulfide for enhanced hydrogen evolution in electrocatalytic water/seawater splitting

Herein,a novel single-atomic Pt doping and interface-rich CoS/Co(OH)_(2)(Pt-CoS/Co(OH)_(2)/C)electrocatalyst has been successfully prepared.Benefiting from precise regulation of d-orbital electronic structure modulation on Co site,Pt-CoS/Co(OH)_(2)/C exhibited remarkable HER activity and high stability for hydrogen evolution in splitting both water(73 mV@10 mA·cm^(−2)) and seawater(87 mV@10 mA·cm^(−2)).Notably,atomic Pt doping was introduced into CoS/Co(OH)_(2),which could produce local unbalanced Coulombic force and significantly increased the number of S vacancies,and then expose abundant Co sites.Meantime,Co(OH)_(2) in Pt-CoS/Co(OH)_(2)/C could act as the adsorption sites for H_(2)O in hydrogen evolution reaction process.Density functional theory results also proved that atomic Pt doping,S vacancies and Co(OH)_(2) coupling could result in the formation of enriched electronic Co sites and optimize d_(z2) orbital electronic structure,and then realize the depth upward shift of d-band center and enhance the adsorption of H*on Co sites.

An amorphous FeMoO_(4) nanorod array enabled high-efficiency oxygen evolution electrocatalysis in alkaline seawater

The development of highly efficient and durable oxygen evolution reaction(OER)catalysts for seawater electrolysis is of great importance for applications.Here,an amorphous FeMoO_(4) nanorod array on Ni foam is reported as a highly active OER electrocatalyst in alkaline seawater,requiring only overpotentials of 303 and 332 mV to achieve 100 and 300 mA·cm^(-2),respectively.Moreover,it shows strong long-term electrochemical durability for at least 50 h.