Defects and morphology engineering for constructing V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S nanotube heterojunction arrays toward efficient bifunctional electrocatalyst for overall water splitting

The development of highly active,stable and inexpensive electrocatalysts for hydrogen production by defects and morphology engineering remains a great challenge.Herein,S vacancies-rich Ni_(3)S_(2)@Cu_(2)S nan-otube heterojunction arrays were in-situ grown on copper foam(V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF)for efficient electrocatalytic overall water splitting.With the merits of nanotube arrays and efficient electronic mod-ulation drived by the OD vacancy defect and 2D heterojunction defect,the resultant V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF electrocatalyst exhibits excellent electrocatalytic activity with a low overpotential of 47 mV for the hydrogen evolution reaction(HER)at 10 mA cm^(-2) current density,and 263 mV for the oxygen evolution reaction(OER)at 50 mA cm^(-2) current density,as well as a cell voltage of 1.48 V at 10 mA cm^(-2).Moreover,the nanotube heterojunction arrays endows V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF with outstanding stability in long-term catalytic processes,as confirmed by the continuous chronopotentiom-etry tests at current densities of 10 mA cm^(-2) for 100 h.

In-situ building of multiscale porous NiFeZn/NiZn-Ni heterojunction for superior overall water splitting

The development of efficient nonprecious bifunctional electrocatalysts for water electrolysis is crucial to enhance the sluggish kinetics of the oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).A self-supporting,multiscale porous NiFeZn/NiZn-Ni catalyst with a triple interface heterojunction on nickel foam(NF)(NiFeZn/NiZn-Ni/NF)was in-situ fabricated using an electroplating-annealing-etching strategy.The unique multiinterface engineering and three-dimensional porous scaffold significantly modify the mass transport and electron interaction,resulting in superior bifunctional electrocatalytic performance for water splitting.The NiFeZn/NiZn-Ni/NF catalyst demonstrates low overpotentials of 187 m V for HER and 320 mV for OER at a current density of 600 mA/cm^(2),along with high durability over 150 h in alkaline solution.Furthermore,an electrolytic cell assembled with NiFeZn/NiZn-Ni/NF as both the cathode and anode achieves the current densities of 600 and 1000 m A/cm^(2) at cell voltages of 1.796 and 1.901 V,respectively,maintaining the high stability at 50 mA/cm^(2) for over 100 h.These findings highlight the potential of NiFeZn/NiZn-Ni/NF as a cost-effective and highly efficient bifunctional electrocatalyst for overall water splitting.

Self-derivation and reconstruction of silver nanoparticle reinforced cobalt-nickel bimetallic hydroxides through interface engineering for overall water splitting

Designing efficient and long-lasting non-metal electrocatalysts is an urgent task for addressing the issue of kinetic hysteresis in electrochemical oxidation reactions.The bimetallic hydroxides,catalyzing the oxygen evolution reaction(OER),have significant research potential because hydroxide reconstruction to generate an active phase is a remarkable advantage.Herein,the complete reconstruction of ultrathin CoNi(OH)_(2) nanosheets was achieved by embedding Ag nanoparticles into the hydroxide to induce a spontaneous redox reaction(SRR),forming heterojunction Ag@CoNi(OH)_(2) for bifunctional hydrolysis.Theoretical calculations and in situ Raman and ex situ characterizations revealed that the inductive effect of the Ag cation redistributed the charge to promote phase transformation to highly activate Ag-modified hydroxides.The Co-Ni dual sites in Co/NiOOH serve as novel active sites for optimizing the intermediates,thereby weakening the barrier formed by OOH^*.Ag@CoNi(OH)_(2) required a potential of 1.55 V to drive water splitting at a current density of 10 mA cm^(-2),with nearly 98.6% Faraday efficiency.Through ion induction and triggering of electron regulation in the OER via the synergistic action of the heterogeneous interface and surface reconstruction,this strategic design can overcome the limited capacity of bimetallic hydroxides and bridge the gap between the basic theory and industrialization of water decomposition.

Co_(3)S_(4)-pyrolysis lotus fiber flexible textile as a hybrid electrocatalyst for overall water splitting

Electrocatalytic overall water splitting(OWS),a pivotal approach in addressing the global energy crisis,aims to produce hydrogen and oxygen.However,most of the catalysts in powder form are adhesively bounding to the electrodes,resulting in catalyst detachment by bubble generation and other uncertain interference,and eventually reducing the OWS performance.To surmount this challenge,we synthesized a hybrid material of Co_(3)S_(4)-pyrolysis lotus fiber(labeled as Co_(3)S_(4)-p LF)textile by hydrothermal and hightemperature pyrolysis processes for electrocatalytic OWS.Owing to the natural LF textile exposing the uniformly distributed functional groups(AOH,ANH_(2),etc.)to anchor Co_(3)S_(4)nanoparticles with hierarchical porous structure and outstanding hydrophily,the hybrid Co_(3)S_(4)-p LF catalyst shows low overpotentials at 10 m A cm^(-2)(η_(10,HER)=100 m Vη_(10,OER)=240 mV)alongside prolonged operational stability during electrocatalytic reactions.Theoretical calculations reveal that the electron transfer from p LF to Co_(3)S_(4)in the hybrid Co_(3)S_(4)-p LF is beneficial to the electrocatalytic process.This work will shed light on the development of nature-inspired carbon-based materials in hybrid electrocatalysts for OWS.

MOF-Derived Iron-Cobalt Phosphide Nanoframe as Bifunctional Electrocatalysts for Overall Water Splitting

Transition metal phosphides(TMPs)have emerged as an alternative to precious metals as efficient and low-cost catalysts for water electrolysis.Elemental doping and morphology control are effective approaches to further improve the performance of TMPs.Herein,Fe-doped CoP nanoframes(Fe-CoP NFs)with specific open cage configuration were designed and synthesized.The unique nano-framework structured Fe-CoP material shows overpotentials of only 255 and 122 mV at 10 mA cm^(−2)for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER),respectively,overwhelming most transition metal phosphides.For overall water splitting,the cell voltage is 1.65 V for Fe-CoP NFs at a current density of 10 mA cm^(−2),much superior to what is observed for the classical nanocubic structures.Fe-CoP NFs show no activity degradation up to 100 h which contrasts sharply with the rapidly decaying performance of noble metal catalyst reference.The superior electrocatalytic performance of Fe-CoP NFs due to abundant accessible active sites,reduced kinetic energy barrier,and preferable*O-containing intermediate adsorption is demonstrated through experimental observations and theoretical calculations.Our findings could provide a potential method for the preparation of multifunctional material with hollow structures and offer more hopeful prospects for obtaining efficient earth-abundant catalysts for water splitting.

High-throughput calculation-based rational design of Fe-doped MoS_(2) nanosheets for electrocatalytic p H-universal overall water splitting

Electrocatalytic water splitting is crucial for H2generation via hydrogen evolution reaction(HER)but subject to the sluggish dynamics of oxygen evolution reaction(OER).In this work,single Fe atomdoped MoS_(2)nanosheets(SFe-DMNs)were prepared based on the high-throughput density functional theory(DFT)calculation screening.Due to the synergistic effect between Fe atom and MoS_(2)and optimized intermediate binding energy,the SFe-DMNs could deliver outstanding activity for both HER and OER.When assembled into a two-electrode electrolytic cell,the SFe-DMNs could achieve the current density of 50 mA cm^(-2)at a low cell voltage of 1.55 V under neutral condition.These results not only confirmed the effectiveness of high-throughput screening,but also revealed the excellent activity and thus the potential applications in fuel cells of SFe-DMNs.

Duplex Interpenetrating-Phase FeNiZn and FeNi_(3)Heterostructure with Low-Gibbs Free Energy Interface Coupling for Highly Efficient Overall Water Splitting

The sluggish kinetics of both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)generate the large overpotential in water electrolysis and thus high-cost hydrogen production.Here,multidimensional nanoporous interpenetrating-phase FeNiZn alloy and FeNi_(3)intermetallic heterostructure is in situ constructed on NiFe foam(FeNiZn/FeNi_(3)@NiFe)by dealloying protocol.Coupling with the eminent synergism among specific constituents and the highly efficient mass transport from integrated porous backbone,FeNiZn/FeNi_(3)@NiFe depicts exceptional bifunctional activities for water splitting with extremely low overpotentials toward OER and HER(η_(1000)=367/245 mV)as well as the robust durability during the 400 h testing in alkaline solution.The as-built water electrolyzer with FeNiZn/FeNi_(3)@NiFe as both anode and cathode exhibits record-high performances for sustainable hydrogen output in terms of much lower cell voltage of 1.759 and 1.919 V to deliver the current density of 500 and 1000 mA cm^(-2)as well long working lives.Density functional theory calculations disclose that the interface interaction between FeNiZn alloy and FeNi_(3)intermetallic generates the modulated electron structure state and optimized intermediate chemisorption,thus diminishing the energy barriers for hydrogen production in water splitting.With the merits of fine performances,scalable fabrication,and low cost,FeNiZn/FeNi_(3)@NiFe holds prospective application potential as the bifunctional electrocatalyst for water splitting.

Design of p-n homojunctions in metal-free carbon nitride photocatalyst for overall water splitting

Two-dimensional(2D)carbon nitride(CN)photocatalysts are attracting extensive attention owing to their excellent photocatalytic properties.In this study,we successfully prepared CN materials with heterogeneous structures via hydrothermal treatment,high-temperature roasting,ball milling,sintering,and other processes.Benefitting from interface interactions in hybrid architectures,the CN photocatalysts exhibited high photocatalytic activity.The rate of hydrogen production using these CN photocatalysts reached 17028.82μmol h^(−1)g^(−1),and the apparent quantum efficiency was 11.2%at 420 nm.The ns-level time-resolved photoluminescence(PL)spectra provided information about the time-averaged lifetime of fluorescence charge carriers;the lifetime of the charge carriers causing the fluorescence of CN reached 9.99 ns.Significantly,the CN photocatalysts displayed satisfactory results in overall water splitting without the addition of sacrificial agents.The average hydrogen and oxygen production rates were 270.95μmol h^(−1)g^(−1)and 115.21μmol h^(−1)g^(−1)in 7 h,respectively,which were promising results for the applications of the catalysts in overall water splitting processes.We investigated the high efficiency of the prepared CN photocatalysts via a series of tests(UV-vis diffuse reflectance spectroscopy,photocurrent response measurements,PL emission spectroscopy,time-resolved PL spectroscopy,and Brunauer-Emmett-Teller analysis).Furthermore,the Mott-Schottky plot and current-voltage curve were acquired via electrochemical tests.The fabricated CN photocatalyst had a small p-n junction in its heterogeneous structure,which further enhanced its photocatalytic efficiency.Therefore,this work can promote the development of CN photocatalysts.

Electric-Field-Treated Ni/Co_(3)O_(4) Film as High-Performance Bifunctional Electrocatalysts for Efficient Overall Water Splitting

Rational design of bifunctional electrocatalysts for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)with excellent activity and stability is of great significance,since overall water splitting is a promising technology for sustainable conversion of clean energy.However,most electrocatalysts do not simultaneously possess optimal HER/OER activities and their electrical conductivities are intrinsically low,which limit the development of overall water splitting.In this paper,a strategy of electric field treatment is proposed and applied to Ni/Co_(3)O_(4) film to develop a novel bifunctional electrocatalyst.After treated by electric field,the conductive channels consisting of oxygen vacancies are formed in the Co_(3)O_(4) film,which remarkably reduces the resistance of the system by almost 2×10^(4) times.Meanwhile,the surface Ni metal electrode is partially oxidized to nickel oxide,which enhances the catalytic activity.The electric-field-treated Ni/Co_(3)O_(4) material exhibits super outstanding performance of HER,OER,and overall water splitting,and the catalytic activity is significantly superior to the state-of-the-art noble metal catalysts(Pt/C,RuO_(2),and RuO_(2)‖Pt/C couple).This work provides an effective and feasible method for the development of novel and efficient bifunctional electrocatalyst,which is also promising for wide use in the field of catalysis.

Electron-Deficient Zn-N_(6) Configuration Enabling Polymeric Carbon Nitride for Visible-Light Photocatalytic Overall Water Splitting

Despite of suitable band structures for harvesting solar light and driving water redox reactions,polymeric carbon nitride(PCN)has suffered from poor charge transfer ability and sluggish surface reaction kinetics,which limit its photocatalytic activity for water splitting.Herein,atomically dispersed Zn-coordinated three-dimensional(3D)sponge-like PCN(Zn-PCN)is synthesized through a novel intermediate coordination strategy.Advanced characterizations and theoretical calculations well evidence that Zn single atoms are coordinated and stabilized on PCN in the form of Zn-N_(6) configura-tion featured with an electron-deficient state.Such an electronic configuration has been demonstrated contributive to promoted electron excitation,accelerated charge separation and transfer as well as reduced water redox barriers.Further benefited from the abundant surface active sites derived from the 3D porous structure,Zn-PCN realizes visible-light photocatalysis for overall water splitting with H_(2) and O_(2) simultaneously evolved at a stoichiometric ratio of 2:1.This work brings new insights into the design of novel single-atom photocatalysts by deepening the understanding of electronic configurations and reactive sites favorable to excellent photocatalysis for water splitting and related solar energy conversion reactions.

Optimizing band structure of CoP nanoparticles via rich-defect carbon shell toward bifunctional electrocatalysts for overall water splitting

Transition-metal phosphides(TMPs)with high catalytic activity are widely used in the design of electrodes for water splitting.However,a major challenge is how to achieve the trade-off between activity and stability of TMPs.Herein,a novel method for synthesizing CoP nanoparticles encapsu-lated in a rich-defect carbon shell(CoP/DCS)is developed through the self-assembly of modified polycyclic aromatic molecules.The graft and removal of high-activity C-N bonds of aromatic molecules render the controllable design of crystallite defects of carbon shell.The density functional theory calculation indicates that the carbon defects with unpaired electrons could effectively tailor the band structure of CoP.Benefiting from the improved activity and corrosion resistance,the CoP/DCS delivers outstanding difunctional hydrogen evolution reaction(88 mV)and oxygen evolution reaction(251 mV)performances at 10 mA cm^(−2)current density.Furthermore,the coupled water electrolyzer with CoP/DCS as both the cathode and anode presents ultralow cell voltages of 1.49 V to achieve 10 mA cm^(−2)with long-time stability.This strategy to improve TMPs electrocatalyst with rich-DCS and heterogeneous structure will inspire the design of other transition metal compound electrocatalysts for water splitting.

Fabrication strategies of porous precious-metal-free bifunctional electrocatalysts for overall water splitting:Recent advances

Electrocatalytic water splitting using power generated from renewable energy to produce hydrogen has been considered as one of the more attractive approach to alleviate the problems of energy crisis and environmental pollution.One of the biggest challenges for the large-scale application of water electrolysis is the searching of the low cost electrocatalysts with high and stable activity toward both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The well-developed porous features of materials synthesized from the earth abundant elements endow them with the enhanced mass transfer and improved electronic interconnection during electrochemical reactions,resulting in the excellent electrocatalytic performance for both OER and HER.Herein,this review focuses on the recent development of innovation strategies for the fabrication of porous non-noble-metal materials including heteroatom-doped carbon-based and transition metal(mainly Co,Ni,and Fe)-based materials as efficient electrocatalysts for overall water splitting.Specially,a detailed discussion of the structure–activity correlation gives an insight on the origin of the high electrocatalytic performance of porous materials obtained from different strategies,and provides guidance for future design and preparation of highly efficient electocatalysts based on non-precious carbon or metal materials for overall water splitting.

Self-supporting and hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as a bifunctional electrocatalyst for fluctuating overall water splitting

Stable non-noble metal bifunctional electrocatalysts are one of the challenges to the fluctuating overall water splitting driven by re-newable energy.Herein,a novel self-supporting hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as bifunctional electrocatalyst was constructed based on porous Ni-Fe electrodeposition on three-dimensional(3D)carbon fiber cloth,in situ oxidation,and chemical sulfuration.Results showed that the Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure with a large specific surface area exhibits good bifunctional activity and stability for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)because of the abundance of active sites,synergistic effect of the heterostructure,superhydrophilic surface,and stable,self-supporting structure.The results further confirmed that the Ni_(x)Fe-S phase in the heterostructure is transformed into metal oxides/hydroxides and Ni_(3)S_(2) during OER.Compared with the commercial 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer,the self-supporting Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) electrolyzer exhibits better stability and lower cell voltage in the fluctu-ating current density range of 10-500 mA/cm^(2).Particularly,the cell voltage of Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) is only approximately 3.91 V at an industrial current density of 500 mA/cm^(2),which is lower than that of the 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer(i.e.,approximately 4.79 V).This work provides a promising strategy to develop excellent bifunctional electrocatalysts for fluctuating overall water splitting.

Abundant heterointerfaces in MOF-derived hollow CoS_(2)-MoS_(2) nanosheet array electrocatalysts for overall water splitting

Rational coupling of hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) catalysts is extremely important for practical overall water splitting,but it is still challenging to construct such bifunctional heterostructures.Herein,we present a metal-organic framework(MOF)-etching strategy to design free-standing and hierarchical hollow CoS_(2)-MoS_(2) heteronanosheet arrays for both HER and OER.Resulting from the controllable etching of MOF by MoO_(4)^(2-) and in-situ sulfuration,the obtained CoS_(2)-MoS_(2) possesses abundant heterointerfaces with modulated local charge distribution,which promote water dissociation and rapid electrocatalytic kinetics.Moreover,the two-dimensional hollow array architecture can not only afford rich surface-active sites,but also facilitate the penetration of electrolytes and the release of evolved H_(2)/O_(2) bubbles.Consequently,the engineered CoS_(2)-MoS_(2) heterostructure exhibits small overpotentials of 82 mV for HER and 266 mV for OER at 10 mA cm^(-2).The corresponding alkaline electrolyzer affords a cell voltage of 1.56 V at 10 mA cm^(-2) to boost overall water splitting,along with robust durability over 24 h, even surpassing the benchmark electrode couple composed of IrO_(2) and Pt/C The present work may provide valuable insights for developing MOF-derived heterogeneous electrocatalysts with tailored interface/surface structure for widespread application in catalysis and other energyrelated areas.

Coupled cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes supported on nickel foam as a binder-free electrode for overall water splitting

In an attempt to develop low-cost,non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media,cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate.Benefiting from the optimized electronic structure and enhanced mass and charge transport,as well as the 3D conducting pathway,MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in an alkaline medium.The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs,which reveals a current density of 10 mA cm^-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER,respectively,and a relatively low cell voltage(1.63 V)for the overall water electrolysis.The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.

Rational design of hollow oxygen deficiency-enriched NiFe_(2)O_(4)@N/rGO as bifunctional electrocatalysts for overall water splitting

Bimetallic metal organic framework(MOF)as a precursor to prepare catalysts with bifunctional catalytic activity of oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)attracts more and more attention.Herein,hollow oxygen deficiency-enriched NiFe_(2)O_(4) is synthesized by pyrolytic FeNi bimetallic MOF.The defects of rGO during carbonization can act as nucleation sites for FeNi particles.After nucleation and N doping,the FeNi particles were served as catalysts for the deposition of dissolved carbon in the defects of the N/rGO.These deposited carbon,like a bridge,connect N/rGO and hollow oxygen deficiency-enriched NiFe_(2)O_(4) together,which giving full play to the advantages of N/rGO in fast electron transfer,thereby improving its catalytic activity.The resultant NiFe_(2)O_(4)@N/rGO-800 exhibits a low overpotential of 252 mV at 20 mA cm^(-2) for OER and 157 mV at 10 mA cm^(-2) for HER in 1 M KOH,respectively.When used as bifunctional electrodes for overall water splitting,it also shows low cell voltage of 1.60 V and 1.67 V at 10 and 20 mA cm^(-2),respectively.

Hollow FeCo-FeCoP@C nanocubes embedded in nitrogen-doped carbon nanocages for efficient overall water splitting

Designing readily available and highly active electrocatalysts for water splitting is essential for renewable energy technologies.Here we present the construction of FeCo-FeCoP@C hollow nanocubes encapsulated in nitrogen-doped carbon nanocages(FeCo-FeCoP@C@NCCs) through controlled carbonization and subsequent phosphorization of a Prussian blue analogue.With stronger electronic interaction and hollow structure,the as-obtained FeCo-FeCoP@C@NCCs material requires small overpotentials of 91 mV and280 mV to deliver 10 mA cm^(-2) in 1 M KOH toward hydrogen and oxygen evolution,respectively.More importantly,applying this material for overall water splitting,it only requires 1.64 V to afford10 mA cm^(-2) and exhibits impressively durability over 40 h without obvious performance decay.The present approach inspires potentials for the controllable synthesis of multi-component catalysts for practical applications.

Facile synthesis of free-standing nickel chalcogenide electrodes for overall water splitting

Developing high-performance noble metal-free and free-standing catalytic electrodes are crucial for overall water splitting. Here, nickel sulfide（NiS） and nickel selenide（Ni Se） are synthesized on nickel foam（NF） with a one-pot solvothermal method and directly used as free-standing electrodes for efficiently catalyzing hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline solution.In virtue of abundant active sites, the NiS/NF and the NiS e/NF electrodes can deliver a current density of 10 m A cmat only 123 m V, 137 m V for HER and 222 m V, 271 m V for OER. Both of the hierarchical NiS/NF and Ni Se/NF electrodes can serve as anodes and cathodes in electrocatalytic overall watersplitting and can achieve a current density of 10 m A cmwith an applied voltage of.59 V and 1.69 V,respectively. The performance of as-obtained NiS/NF||NiS/NF is even close to that of the noble metalbased Pt/C/NF||IrO/NF system.

In-situ pressure-induced BiVO_(4)/Bi_(0.6)Y_(0.4)VO_(4) S-scheme heterojunction for enhanced photocatalytic overall water splitting activity

Step-scheme(S-scheme)heterojunctions in photocatalysts can provide novel and practical insight on promoting photogenerated carrier separation.The latter is critical in controlling the overall efficiency in one-step photoexcitation systems.In this study,a nanosized BiVO4/Bi0.6Y0.4VO4 solid solution was prepared by a coprecipitation method following with hydrothermal or calcination processes.The S-scheme heterojunction was fabricated by in-situ pressure-induced transformations of bismuth vanadate from the tetragonal zircon phase to the monoclinic scheelite phase,which led to the formation of BiVO4 nanoparticles with a diameter of approximately 5 nm on the surface of BiVO_(4)/Bi_(0.6)Y_(0.4)VO_(4)/Bi_(0.6)Y_(0.4)VO_(4) with S-scheme heterojunctions showed significantly enhanced photocatalytic overall water splitting activity compared with using bare BiVO_(4)/Bi_(0.6)Y_(0.4)VO_(4).Characterization of the carrier dynamics demonstrated that a superior carrier separation through S-type heterojunctions might have caused the enhanced overall water splitting(OWS)activity.Surface photovoltage spectra and the results of selective photodeposition experiments indicated that the photogenerated holes mainly migrated to the BiVO4 nanoparticles in the heterojunction.This confirmed that the charge transfer route corresponds to an S-scheme rather than a type-II heterojunction mechanism under light illumination.This study presents a facile and efficient strategy to construct S-scheme heterojunctions through a pressure-induced phase transition.The results demonstrated that S-scheme junctions composed of different crystalline phases can boost the carrier separation capacity and eventually improve the photocatalytic OWS activity.

La-doped NiFe-LDH coupled with hierarchical vertically aligned MXene frameworks for efficient overall water splitting

The development of stable electrocatalysts with high hydrogen and oxygen evolution reactions (HER and OER) activity in alkaline electrolytes is critical to renewable energy conversion technologies,such as electrochemical water splitting.In this work,a novel strategy for engineering water splitting electrocatalysts in alkaline electrolyte was developed by synergistically coupling La-doped Ni Fe-layered double hydroxides (Ni Fe-LDH) nanosheets onto three-dimensional (3D) vertically aligned MXene nanosheets on macroporous nickel foam (NF) substrates (Ni Fe La-LDH/v-MXene/NF).The electrocatalytic performance of the prepared Ni Fe La-LDH/v-MXene/NF is enhanced by the synergy of strong electronic interaction among multiple metal centers and unique vertically aligned porous MXene with increased active surface area,accelerated reaction kinetics and improved water adsorption and dissociation ability.To reach the commercially required current density (500 m A cm^(-2)),the Ni Fe La-LDH/v-MXene/NF exhibits greatly reduced overpotentials of 233 and 255 m V for HER and OER,respectively,along with excellent durability.Moreover,an alkaline electrolyzer driven by Ni Fe La-LDH/v-MXene/NF delivers a lower cell voltage(1.71 V) compared with that of Pt/C-RuO_(2) couple to achieve the current density of 500 m A cm^(-2).