Synthesis And Electrocatalytic Water Splitting Performance Of MOF-derived Transition Metal Sulfide And Phosphide

The energy crisis and environmental pollution caused by the excessive use of fossil fuels hinder the sustainable development of today’s society and economy.Developing renewable clean energy is key to solve the two urgent problems.Hydrogen energy is a kind of renewable energy with high energy density,which is widely regarded as one of the alternative energies of petroleum fuel in the future.It has prominent advantages such as no carbon emission in preparation and combustion process,good environmental compatibility,wide source and application,abundant reserves,etc.,which has attracted extensive attention.Overall water splitting（OWS）can be divided into oxygen evolution reaction（OER）at the anode and hydrogen evolution reaction（HER）at the cathode,which is a method to produce high purity hydrogen with low cost and no emission of polluting gases.These two half reactions usually require efficient electrocatalysts to overcome high overpotential and slow reaction kinetics.As known to all,precious metals and their compounds have significant electrocatalytic activity（for example,Ru O₂ for OER and platinum（Pt）for HER）,but they are limited by high prices and low reserves to achieve large-scale industrial production.Over the past few decades,researchers have developed many cost-effective catalysts for HER and OER,such as transition metal phosphates,sulfides,nitrides,oxides,and hydroxides.Metal organic frameworks（MOFs）and its derivatives have been the focus of research in the field of materials and energy in recent years,but still have some problems e.g.low stability,low conductivity and low activity.Ideally,constructing efficient bifunctional catalysts to produce both hydrogen and oxygen in the same p H electrolyte is an effective strategy to simplify the electrolytic water system and save the total cost.In this paper,the synthesis of novel materials can be realized by analyzing the relationship between the structure and the properties of materials,optimizing the synthesis conditions,adjusting the morphology and composition of materials or directly growing electrode materials on the conductive substrate.1.MOF-derived V-Co_xP@NC nanoarchitectures for highly enhanced electrocatalytic water splitting through electronical tuningIn this work,V-doped Co P and Co₂P nanoparticles coated with N-doped carbon shell（V-Co_xP@NC）were synthesized by simple room temperature reaction and one-step low-temperature phosphorization process,which were used to electrocatalytic overall water splitting in 1.0 M KOH solution.The material composition and morphology were determined by a series of characterization methods.The excellent performance of the material was revealed by electrochemical tests.Under the protection of the carbon skeleton derived from MOF,the material has good stability.The incorporation of vanadium and the mixture of Co P and Co₂P nanoparticles could scatter the positive charges of Co to further improve the electrocatalytic capacity.The expermental results show more outstanding performance of MOF-derived V-Co_xP@NC NPs than many reported heteroatomic doping and transition metal phosphides electrocatalysts synthesized with ZIF-67 as the precursor,which strongly proves that the uniform nanoparticles promote the diffusion of electrolyte and rapid electron transfer,and enrich active sites.This work proves that V-Co_xP@NC is an effective catalyst for electrocatalytic water splitting and provides some effective strategies to improve performance of catalysts.2.Semi-sacrificial template growth of Fe S/Fe₂O₃/IF heterogeneous nanosheet for efficient oxygen evolution reaction.Fe S/Fe₂O₃/IF nanosheets with heterogeneous interface was synthesized with iron foam（IF）as substrate and raw material by two-step solvent heat method.The composition and electrocatalytic performance of Fe S/Fe₂O₃/IF were determined by a series of characterization and electrochemical tests.Electrocatalytic materials grow on conductive porous materials directly without polymer binder,which is beneficial to improve the conductivity and stability of materials.Nanosheets growing vertically on the substrate increases the contact area between the electrolyte and the catalyst surface,facilitating electrolyte diffusion and charge transfer,thereby helping to accelerate electrocatalytic OER rates.The existence of heterogeneous interfaces of Fe S/Fe₂O₃/IF adjusts electronic structure and exposes more defects as active sites,resulting in greatly improve catalytic activity.It is worth mentioning that,compared with the more common nickel foam as the substrate,iron as the second most abundant metal in the crust is much cheaper and easier to obtain.Inexpensive and readily available metal sources,easy and operable method,excellent electrocatalytic OER activity and strong stability under high current density prove that Fe S/Fe₂O₃/IF is expected to be used as the anode material of electrocatalytic water splitting in practical production.