Templated synthesis of transition metal phosphide electrocatalysts for oxygen and hydrogen evolution reactions

Transition metal phosphides(TMPs)have been regarded as alternative hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)catalysts owing to their comparable activity to those of noble metal-based catalysts.TMPs have been produced in various morphologies,including hollow and porous nanostructures,which are features deemed desirable for electrocatalytic materials.Templated synthesis routes are often responsible for such morphologies.This paper reviews the latest advances and existing challenges in the synthesis of TMP-based OER and HER catalysts through templated methods.A comprehensive review of the structure-property-performance of TMP-based HER and OER catalysts prepared using different templates is presented.The discussion proceeds according to application,first by HER and further divided among the types of templates used-from hard templates,sacrificial templates,and soft templates to the emerging dynamic hydrogen bubble template.OER catalysts are then reviewed and grouped according to their morphology.Finally,prospective research directions for the synthesis of hollow and porous TMP-based catalysts,such as improvements on both activity and stability of TMPs,design of environmentally benign templates and processes,and analysis of the reaction mechanism through advanced material characterization techniques and theoretical calculations,are suggested.

Recent advances in transition metal phosphide materials:Synthesis and applications in supercapacitors

Supercapacitors(SCs)are considered promising energy storge systems because of their outstanding power density,fast charge and discharge rate and long-term cycling stability.The exploitation of cheap and efficient electrode materials is the key to improve the performance of supercapacitors.As the battery-type materials,transition metal phosphides(TMPs)possess high theoretical specific capacity,good electrical conductivity and superior structural stability,which have been extensively studied to be electrode materials for supercapacitors.In this review,we summarize the up-to-date progress on TMPs materials from diversified synthetic methods,diverse nanostructures and several prominent TMPs and their composites in application of supercapacitors.In the end,we also propose the remaining challenges toward the rational discovery and synthesis of high-performance TMP electrodes materials for energy storage.

Multicomponent transition metal phosphide for oxygen evolution

Transition metal phosphides(TMPs)have exhibited decent performance in an oxygen evolution reaction(OER),which is a kinetic bottleneck in many energy storages and conversion systems.Most reported catalysts are composed of three or fewer metallic components.The inherent complexity of multicomponent TMPs with more than four metallic components hinders their investigation in rationally designing the structure and,more importantly,comprehending the component-activity correlation.Through hydrothermal growth and subsequent phosphor-ization,we reported a facile strategy for combining TMPs with tunable elemental compositions(Ni,Fe,Mn,Co,Cu)on a two-dimensional ti-tanium carbide(MXene)flake.The obtained TMPs/MXene hybrid nanostructures demonstrate homogeneously distributed elements.They ex-hibit high electrical conductivity and strong interfacial interaction,resulting in an accelerated reaction kinetics and long-term stability.The res-ults of different component catalysts’OER performance show that NiFeMnCoP/MXene is the most active catalyst,with a low overpotential of 240 mV at 10 mA·cm−2,a small Tafel slope of 41.43 mV·dec−1,and a robust long-term electrochemical stability.According to the electrocata-lytic mechanism investigation,the enhanced NiFeMnCoP/MXene OER performance is due to the strong synergistic effect of the multi-ele-mental composition.Our work,therefore,provides a scalable synthesis route for multi-elemental TMPs and a valuable guideline for efficient MXene-supported catalysts design.

Metal-organic frameworks derived transition metal phosphides for electrocatalytic water splitting

It is critical to synthesize high-efficiency electrocatalysts to boost the performance of water splitting to meet the requirements of industrial applications. Metal-organic frameworks(MOFs) can function as ideal molecular platforms for the design of highly reactive transition metal phosphides(TMPs), a kind of candidates for high-efficiently electrocatalytic water splitting. The intrinsic activity of the electrocatalysts can be greatly improved via modulating the electronic structure of the catalytic center through the MOF precursors/templates. Moreover, the carbon layer converted in-situ by the organic ligands can not only protect the TMPs from being degraded in the harsh electrochemical environments, but also avoid agglomeration of the catalysts, thereby promoting their activities and stabilities. Furthermore,heteroatom-containing ligands can incorporate N, S or P, etc. atoms into the carbon matrixes after conversion, regulating the coordination microenvironments of the active centers as well as their electronic structures. In this review, we first summarized the latest developments in MOF-derived TMPs by the unique advantages in metal, organic ligand, and morphology regulations for electrocatalytic water splitting. Secondly, we concluded the critical scientific issues currently facing for designing state-of-the-art TMP-based electrocatalysts. Finally, we presented an outlook on this research area, encompassing electrocatalyst construction, catalytic mechanism research, etc.

Thioetherification of isoprene and butanethiol on transition metal phosphides

Thioetherification between mercaptan and diolefin is an efficient process to remove mercaptans in FCC gasoline at mild condition, during which the selective hydrogenation of diolefin to monoolefin is also expected. Here, Si O2 supported transition metal（Fe, Co, Ni, Mo and W） phosphides were tested for the thioetherification of isoprene and butanethiol on a fixed-bed reactor at 120℃ and 1.5 MPa H2, and their structure before and after reaction was characterized by means of XRD, HRTEM, N2 sorption, CO chemisorption, NH3-TPD, XPS and TG. It was found that, among different metal phosphides, Mo P/Si O2 showed the best performance, and the optimal nominal Mo P loading was 25%. Apart from the nature of metal, the density of metal and acid sites determined the catalyst performance. Metal site was mainly responsible for hydrogenation of isoprene, while acid site dominantly contributed to the thioetherification and the polymerization of olefins. Moreover, a balance between metallic and acidic functions is required to arrive at a desired performance. Excessive metal sites or acid sites led to the over-hydrogenation of isoprene or the severe polymerization of olefins, respectively. 25%Mo P/Si O2 was tested for 37 h time on stream, and butanethiol conversion maintained at 100%; although isoprene conversion remarkably decreased, the selectivity to isopentenes exceeded 80% after reaction for 11 h. We suggest that the deactivation of Mo P/Si O2 is mainly ascribed to the butanethiol poisoning and the carbonaceous deposit, especially the former.

A new insight into the promoting effects of transition metal phosphides in methanol electrooxidation

The construction of highly active catalysts for methanol oxidation reaction(MOR)is central to direct methanol fuel cells.Tremendous progress has been made in transition metal phosphides(TMPs)based catalysts.However,TMPs would be partially damaged and transformed into new substances(e.g.,Pt-M-P composite,where M represents a second transition metal)during Pt deposition process.This would pose a large obstacle to the cognition of the real promoting effects of TMPs in MOR.Herein,Co_(2)P co-catalysts(Pt-P/Co_(2)P@NPC,where NPC stands for N and P co-doped carbon)and Pt-Co-P composite catalysts(Pt-CoP/NPC)were controllably synthesized.Electrocatalysis tests show that the Pt-Co-P/NPC exhibits superior MOR activity as high as 1016 m A/mg_(Pt),significantly exceeding that of Pt-P/Co_(2)P@NPC(345 m A/mg_(Pt)).This result indicates that the promoting effect is ascribed primarily to the resultant Pt-Co-P composite,in sharply contrast to previous viewpoint that Co_(2)P itself improves the activity.Further mechanistic studies reveal that Pt-Co-P/NPC exhibits much stronger electron interaction and thus manifesting a remarkably weaker CO absorption than Pt-P/Co_(2)P@NPC and Pt/C.Moreover,Pt-Co-P is also more capable of producing oxygen-containing adsorbate and thus accelerating the removal of surface-bonded CO^(*),ultimately boosting the MOR performance.

A revisiting of transition metal phosphide(Cu_(3)P and FeP)nanozymes for two sugar-related reactions

Transition metal phosphides(TMPs)are essential catalysts for some general catalytic reactions.However,their potentials for biological catalysis have seldom been explored.Herein,we investigated the enzyme-like properties of four TMPs(FeP,CoP,Ni_(2)P,and Cu_(3)P)towards two sugar-related reactions.Among the four TMPs,Cu_(3)P nanoparticles(NPs)efficiently catalyzed the hydrolysis of glycosidic bonds as glycoside hydrolase mimics,and FeP NPs possessed both glucose oxidase-like(GOx-like)and peroxidase-like activities,which combined into a cascade reaction for glucose’s simple and one-step colorimetric biosensor without GOx.Cu_(3)P and FeP NPs with distinctive enzyme-like activities have shown unique biological catalysis potentials for further applications with an attractive and challenging goal of developing nanomaterials to mimic natural enzymes,which encourages more efforts to reveal TMP’s capabilities towards biocatalysis.

Synthesis and application of transition metal phosphides as electrocatalyst for water splitting

With continuous research on photocatalytic water splitting, searching for efficient catalyst for hydrogen evolution reaction(HER) becomes popular topic in addition to main catalyst research. Transition metal phosphides are receiving intense attention due to its abundance in the Earth's crust and comparable catalytic properties to noble metals. In this review, the synthesis approaches, HER reaction mechanism,photocatalytic activity, approaches to improve the activity of transition metal phosphides were reviewed and discussed. It was showed that the transition metal phosphides have great potential to reduce the cost of photocatalyst and promising application on water splitting. The stability problem and participation of poisonous reactant and product in its synthesis reaction limit its application and developing in a certain extent, but with the continuous efforts on the development and improvement of the synthesis methods,transition metal phosphides will find wide application in water splitting.

Self-supported transition metal phosphide based electrodes as high-efficient water splitting cathodes

Electrolytic water splitting has been considered as a promising technology to produce highly pure H2 by using electrical power produced from wind, solar energy or other fitful renewable energy resources. Combining novel self-supporting structure and high-performance transition metal phosphides （TMP） shows substantial promise for practical application in water splitting. In this review, we try to provide a comprehensive analysis of the design and fabrication of various self-supported TMP electrodes for hydrogen evolution reaction, which are divided into three categories： catalysts growing on carbon-based substrates, catalysts growing on metal-based substrates and free- standing catalyst films. The material structures together with catalytic performances of self-supported electrodes are presented and discussed. We also show the specific strategies to further improve the catalytic performance by elemental doping or incorporation of nanocarbons. The simple and one-step methods to fabricate self-supported TMP electrodes are also highlighted. Finally, the chal- lenges and perspectives for self-supported TMP electrodes in water splitting application are briefly discussed.

Heterostructured bimetallic phosphide nanowire arrays with latticetorsion interfaces for efficient overall water splitting

Designing cost-effective and high-efficiency electrocatalysts is critical to the water splitting performance during hydrogen generation.Herein,we have developed Fe_(2)P-Co_(2)P heterostructure nanowire arrays with excellent lattice torsions and grain boundaries for highly efficient water splitting.According to the microstructural investigations and theoretical calculations,the lattice torsion interface not only contributes to the exposure of more active sites but also effectively tunes the adsorption energy of hydrogen/oxygen intermediates via the accumulation of charge redistribution.As a result,the Fe_(2)P-Co_(2)P heterostructure nanowire array exhibits exceptional bifunctional catalytic activity with overpotentials of 65 and 198 mV at 10 mA cm^(-2) for hydrogen and oxygen evolution reactions,respectively.Moreover,the Fe_(2)P-Co_(2)P/NF-assembled electrolyzer can deliver 10 mA cm^(-2) at an ultralow voltage of1.51 V while resulting in a high solar-to-hydrogen conversion efficiency of 19.8%in the solar-driven water electrolysis cell.

Trimetallic synergistic optimization of 0D NiCoFe-P QDs anchoring on 2D porous carbon for efficient electrocatalysis and high-energy supercapacitor

Developing multi-functional and low-cost noble-metal-free catalysts such as transition metal phosphides(TMPs)to replace noble-metal is of practical significance for energy conversion and storage.However,the low-durability and the agglomeration phenomenon during the electrochemical process limit their practical applications.Herein,using metal–organic frameworks(MOFs)as the precursor and a combined strategy of gradient temperature calcination and thermal phosphorization,a 0D/2D heterostructure of NiCoFe-P quantum dots(QDs)anchored on porous carbon was successfully developed as highly efficient electrode materials for overall water splitting and supercapacitors.Owing to this distinctive 0D/2D heterostructure and the synergistic effect of multi-metallic TMPs,the NiCoFe-P/C exhibits excellent electrocatalytic activity and durability of HER(87 mV at 10 mA cm^(-2))and OER(257 mV at 100 mA cm^(-2))in the KOH electrolyte.When NiCoFe-P/C is used as the two electrodes of electrolyzed water,only 1.55 V can drive the current density to 10 m A cm^(-2).At the same time,our NiCoFe-P/C possessed extraordinary property for charge storage.In particular,an ultra-high energy density of 100.8 Wh kg^(-1) was achieved at a power density of 900.0 W kg^(-1) for our assembled hybrid supercapacitor device NiCoFe-P/C(2:1)//activated carbon(AC).This work may open a potential way for the design of 0D/2D hybrid multifunctional nanomaterials based on TMPs QDs.

Interfacial electronic coupling of V-doped Co_(2)P with high-entropy MXene reduces kinetic energy barrier for efficient overall water splitting

Developing efficient,low-cost non-noble metal-based bifunctional catalysts to achieve excellent hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)kinetics in alkaline media is challenging but very meaningful.However,improving the electronic structure of the catalyst to optimize the adsorption of intermediates and reduce the reaction energy barrier is the key to improve the reaction efficiency.Herein,a V-doped Co_(2)P coupled with high-entropy MXene heterostructure catalyst(V-Co_(2)P@HE)was prepared by a two-step electrodeposition and controlled phosphorization process.The analyses of X-ray absorption spectroscopy,X-ray photoelectron spectroscopy and theoretical calculations jointly show that the introduction of V and the strong electron coupling between the two components optimize the adsorption energy of water molecules and reaction intermediates.Benefiting from the abundant active sites and optimizing intermediate adsorption energy and heterogeneous interface electronic structure,V-Co_(2)P@HE has excellent HER and OER activity and long-term stability under alkaline condition.In particular,when assembled as cathode and anode,the bifunctional V-Co_(2)P@HE catalyst can drive a current density of 10 mA cm^(-2)with only 1.53 V.This work provides new strategies for the application of highentropy MXene and the design of novel non-noble metal-based bifunctional electrolytic water catalysts.

Highly efficient and stable electrocatalyst for hydrogen evolution by molybdenum doped Ni-Co phosphide nanoneedles at high current density

There is an increasingly urgent need to develop cost-effective electrocatalysts with high catalytic activity and stability as alternatives to the traditional Pt/C in catalysts in water electrolysis.In this study,microspheres composed of Mo-doped NiCoP nanoneedles supported on nickel foam were prepared to address this challenge.The results show that the nanoneedles provide sufficient active sites for efficient electron transfer;the small-sized effect and the micro-scale roughness enhance the entry of reactants and the release of hydrogen bubbles;the Mo doping effectively improves the electrocatalytic performance of NiCoP in alkaline media.The catalyst exhibits low hydrogen evolution overpotentials of 38.5 and 217.5 mV at a current density of 10 mA·cm^(-2) and high current density of 500 mA·cm^(-2),respectively,and only 1.978 V is required to achieve a current density of 1000 mA·cm^(-2) for overall water splitting.Density functional theory(DFT)calculations show that the improved hydrogen evolution performance can be explained as a result of the Mo doping,which serves to reduce the interaction between NiCoP and intermediates,optimize the Gibbs free energy of hydrogen adsorption(△G_(*H)),and accelerate the desorption rate of *OH.This study provides a promising solution to the ongoing challenge of designing efficient electrocatalysts for high-current-density hydrogen production.

Electron engineering of nickel phosphide for Ni^(δ+) in electrochemical nitrate reduction to ammonia

The electrochemical reduction of nitrate to ammonia(ENRA)provides an efficient approach to remove nitrate pollution and achieve ammonia production simultaneously.Herein,inspired by bio-enzyme in denitrifying bacteria,a carbon-coated nickel phosphide(NiPC)nanosheet derived from metal-organic frameworks(MOFs)is proposed as an efficient catalyst for ENRA.Through electron engineering,controllable Ni^(δ+)in nickel phosphide is achieved by regulating the degree of phosphating,which enhances its activity for the hydrogenation of nitrate.As the result,Niδ+becomes one of dominating factors determining the efficiency of the ENRA reaction in nickel phosphide.The optimal NiPC catalyst exhibits impressive property toward ENRA:NH_(4)^(+)Faraday efficiency of 96.68%,NH4+selectivity of 99.04%,and nitrate conversion rate of 90.43%under low nitrate concentration(200 mg·L^(−1)).This work opens a new avenue for the design of next-generation catalysts through electron engineering for ENRA.

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.

Rational design of three-dimensional branched NiCo-P@CoNiMo-P core/shell nanowire heterostructures for high-performance hybrid supercapacitor

Owing to the dramatically enhanced charge-mass transport and abundant electrochemically active sites,transition metal compound electrodes are increasingly attractive for achieving high-performance supercapacitors(SCs).Here,we report the fabrication of nickel foam supported three-dimensional(3 D)branched nickel-cobalt phosphides@tri-metal cobalt-nickel-molybdenum phosphides core/shell nanowire heterostructures(denoted as NiCo-P@CoNiMo-P)as high-performance electrode materials for hybrid supercapacitors.The presence of multiple valences of the cations in such NiCo-P@CoNiMo-P enables rich redox reactions and promoted synergy effects.Benefiting from their collective effects,the resulting electrode demonstrates high specific capacity of 1366 C g^(-1) at 2 A g^(-1)(2.03 C cm^(-2) at2 mA cm^(-2))and 922 C g^(-1) at 10 A g^(-1),as well as good cycling stability(retaining~94%of the initial capacity after 6000 cycles at 15 A g^(-1)).A hybrid SC using the NiCo-P@CoNiMo-P as the positive electrode and N-doped rGOs as the negative electrode exhibits a high energy density of 81.4 Wh kg^(-1) at a power density of 1213 W kg^(-1) and a capacity retention of 132%even after 6000 cycles at 10 A g^(-1).Our findings can facilitate the material design for boosting the performance of transition metal compounds based materials for fast energy storage.

Electronic modulation of sprout-shaped NiCoP nanoarrays by N and Ce doping for efficient overall water splitting

Bifunctional catalysts for hydrogen/oxygen evolution reactions(HER/OER)are urgently needed given the bright future of water splitting hydrogen production technology.Here,the self-supporting N and Ce dual-doped NiCoP nanoarrays(denoted N,Ce-NiCoP/NF)grown on Ni foam are successfully constructed.When the N,Ce-NiCoP/NF simultaneously acts as the HER and OER electrodes,the voltages of 1.54 and 2.14 V are obtained for driving 10 and 500 mA·cm^(-2)with a robust durability,and demonstrate its significant potential for practical water electrolysis.According to both experiments and calculations,the electronic structure of NiCoP may be significantly altered by strategically incorporating N and Ce into the lattice,which in turn optimizes the Gibbs free energy of HER/OER intermediates and speeds up the water splitting kinetics.Moreover,the sprout-shaped morphology significantly increases the exposure of active sites and facilitates charge/mass transfer,thereby augmenting catalyst performance.This study offers a potentially effective approach involving the regulation of anion and cation double doping,as well as architectural engineering,for the purpose of designing and optimizing innovative electrocatalysts.

B and Fe co-doped Co_(2)P hollow nanocubes for nitrate electroreduction to ammonia

Nitrate(NO_(3)^(−))electroreduction reaction(NO_(3)^(−)RR)provides an attractive and sustainable route for NO_(3)^(−)pollution mitigation or energy-saved ammonia(NH3)synthesis.In this work,high-quality B and Fe co-doped Co_(2) P hollow nanocubes(B/Fe-Co_(2) P HNCs)are successfully synthesized though simultaneous boronation-phosphorization treatment,which reveal outstanding selectivity,activity,stability for the NO_(3)^(−)to NH_(3) conversion in neutral electrolyte because of big surface area,fast mass transport,superhydrophilic surface,and optimized electronic structure.B/Fe-Co_(2) P HNCs can achieve the high NH3 yield rate(22.67 mg h^(−1) mg_(cat)^(−1))as well as Faradaic efficiency(97.54%)for NO_(3)^(−)RR,greatly outperforming most of non-precious metal based NO_(3)^(−)RR electrocatalysts.

Synergistic phosphorized NiFeCo and MXene interaction inspired the formation of high-valence metal sites for efficient oxygen evolution

Exploring low-cost,high-performance,and stable electrocatalysts toward the oxygen evolution reaction(OER)is highly desired but remains challenging.Transition metal hydroxide has been wildly utilized as a promising candidate,but practical implementation is impeded by insufficient catalytic activity,easy agglomeration,and poor conductivity.Here,we report that both phosphorization and combination with MXnene can improve the catalysts’intrinsic activity and conductivity.Besides,MXene also prevents the agglomeration of the nanoparticles,resulting in the enhanced exposure of active sites.Experimental char-acterizing and density functional theory simulations revealed that P species can attract electrons to pro-mote the formation of high-valence states of adjacent metal atoms,and coupling MXene support can effectively modulate the electronic structure and optimize the d-band center,which boosts the OER per-formance.Consequently,the optimized NiFeCoP/Mxene catalyst exhibits a low overpotential of 240 mV at a current density of 10 mA cm^(−2),a small Tafel slope of 55 mV dec^(−1),and superior long-term stability of 40 h in 1 M KOH electrolyte,which is superior to other counterparts.

Phase-mediated cobalt phosphide with unique core-shell architecture serving as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction

Hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR)have been considered as two critical processes in the field of electrocatalytic water-splitting for hydrogen production and fuel cells.However,the sluggish reaction kinetics of HER and ORR required efficient electrocatalyst such as Pt to promote such process.Transition metal phosphides(TMPs)exhibit great potential to replace noble metal electrocatalysts to accelerate HER and ORR due to their high activity and easy availability.Herein,a highly-efficient bifunctional CoP electrocatalyst for HER and ORR,featuring a unique core-shell structure decorated on nitrogen-doped carbon matrix was designed and constructed via etching a cobalt-based zeolitic imidazolate framework(ZIF-67)with phytic acid(PA)followed by pyrolysis treatment(PA-ZIF-67-900).Experimental results revealed that the pure-phase single-crystalline Co P exhibited outstanding electrocatalytic performance in HER and ORR,superior to Co(PO_(3))_(2) in PA-ZIF-67-700,hybrid phase of Co(PO_(3))_(2) and CoP in PA-ZIF-67-800 and Co_(2)P-doped CoP in PA-ZIF-67-1000.To reach the current density of 10 mA/cm^(2)the as-synthesized Co P required an overpotential of 120 m V for HER in 1 mol/L KOH and half-wave potential of 0.85 V in O_(2)-saturated 0.1 mol/L KOH.This work present new clue for construction of efficient and bifunctional electrocatalyst in the field of energy conversion and storage.