Preparation And Electrocatalytic Water Splitting Study Of Transition Metal Phosphosulphides

With the continuous development and progress of human society,the over-exploitation and use of fossil energy materials with limited reserves has caused serious energy crisis and environmental problems.Facing these problems,it is urgent to develop new renewable energy by using environmental protection technology.Because of its high energy density,hydrogen is the most potential alternative energy source.Hydrogen production from electrolytic water splitting has attracted much attention as a green energy conversion technology.Therefore,it is very important to find low-price,efficient and stable electrocatalysts for hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?in the renewable energy conversion system of hydrogen production from electrolytic water splitting.Recent studies have shown that the rich mineral nanostructures on the earth provide a new way to obtain new and advanced energy materials,especially pyrite nanomaterials,which arouse great interest.Pyrite is widely used in the fields of optoelectronics,energy storage and electrocatalysis because of its diversity,availability,versatility and adjustability.In addition,pyrite can also improve its properties by grafting with promoters,resulting in good interface,structure and electronic tuning,Based on ternary pyrite-type transition metal phosphorus sulfides,this paper studies the size control,doping control,morphology control and other aspects,which provides a reference for the wide application of transition metal phosphorus sulfides and the recognition of active sources.The main research of this paper includes the following three parts.?1?Using MOF and cheaper conductive carbon black?XC-72?as precursors,a novel electrocatalyst with three-doped porous carbon encapsulated super-small CoPS nanoparticles was prepared by one-step phosphosulphiding.The uniformly distributed metals in the precursor Co-MOF were sulfided into uniformly distributed and ultra-small CoPS nanoparticles?about 5 nm?by phosphosulphiding.N-containing organic ligands and conductive carbon black formed cross-linked N,P and S tri-doped porous carbon during phosphosulphiding,which wrapped CoPS nanoparticles,prevented the active components from falling off,promoted the penetration of electrolyte,and improved the efficiency of mass transfer and electron transfer.The overpotential of the material was93 mV when the current density reached 10 mA cm^-2 in the process of HER in acidic electrolyte.In alkaline electrolyte,the overpotential of the material when the current density reached 10 mA cm^-2in the process of HER and OER were 191 mV and 320 mV respectively.At the same time,it was found that the overall water splitting of catalyst started before 1.4 V by testing.Because of the special structure of CoPS nanoparticles encapsulated with tri-doped carbon,the catalyst exhibits good stability and can maintain for more than 30 hours.?2?Quaternary transition metal phosphorus sulfide electrocatalysts grown on a conductive carbon cloth?CC?with heteroatom Fe-doped CoPS nanowire arrays were constructed.The successful doping of Fe with larger ion radius was proved by XRD and TEM.The effect of different Fe doping amount on HER activity was investigated.The experimental results showed that the heteroatom Fe doping could optimize the electronic structure of the catalyst,so the HER performance of the catalyst could be effectively improved.The overpotential of the catalyst is only63 mV when the current density reaches 10 mA cm^-2 in the HER,which is basically the same as that of commercial Pt/C.The catalyst maintains long-term stability at high and low current density?over30 hours?.Based on the model of Fe_0.25Co_0.75PS NWs/CC with the highest activity,the hydrogen adsorption energies at 16 different sites?6 Top sites,4 Center sites and 6 Bridge sites?after relaxation were obtained by theoretical calculation,and the main sources of the high activity of the catalyst were identified.This work has certain guiding significance for the development and recognition of quaternary transition metal phosphosulphides in the future.?3?The precursors of cobalt-based hydroxide?Co-LMH?nanosheets and low-cost conductive carbon black?CCB?were prepared by a simple,mild and environmentally friendly method.Ultra-thin CoPS nanosheets were prepared by one-step phosphosulphiding.The existence of CCB can not only effectively prevent the agglomeration during the preparation of precursor and phosphosulphiding,but also make better use of the advantages of two-dimensional materials and expose more active sites.Moreover,CCB fuses with CoPS nanosheets during phosphosulphiding,improving the intrinsic conductivity of CoPS with semiconductor properties.The preparation method is feasible for large-scale preparation of high-quality transition metal phosphosulphides nanosheets.At the same time,the most active electrocatalysts were selected through carrier selection and annealing temperature adjustment.The catalyst exhibits well HER activity in acidic and alkaline electrolytes.When the current density reaches 10 mA cm^-2,the overpotential of the catalyst is 64mV and 115 mV,respectively.Because of the protection of CCB,the catalyst has good stability at high and low current density.This work provides a possibility for the practical industrial application of transition metal phosphorus sulfides.