Study On Transition Metal Boride Catalysts For Water Splitting Based On A Self-assembly Strategy

With the depletion of traditional fossil energy,such as oil and coal,and the increasingly serious environmental pollution,it is urgent to find and develop a clean and renewable energy.Hydrogen energy is considered as an effective substitute for traditional energy because of its portability,high energy efficiency,no carbon emission and no pollution.Among many technologies,hydrogen production by water electrolysis driven by renewable energy such as solar energy,wind energy or tidal energy has attracted a lot of attention.However,in the two-and-a-half reactions of water splitting,hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,precious metals such as platinum group metals and iridium-based compounds are usually used to reduce overpotential and obtain high performance,or non-precious metals whose performance or stability is not as good as precious metals are selected to reduce costs.Therefore,in order to meet the requirements of the practical application and development of large-scale water electrolysis,the construction and development of efficient,stable and low-cost water electrolysis electrocatalysts is an important subject to accelerate the development of hydrogen energy economy.In this paper,based on the self-assembly interaction between boric acid and transition metal ions,highly conductive porous nitrogen-carbon materials and nickel foam were used to form uniformly loaded transition metal boride to construct water electrolysis electrocatalysts with excellent catalytic activity.Th e specific works are as follows:（1）Using nitrogen-doped porous carbon polyhedron derived from zeolitic imidazolate framework compound ZIF-8 as precursor,boron-nitrogen doped porous carbon polyhedron supported amorphous ruthenium boride and ruthenium nanoparticles composite catalysts（Ru B_x-Ru@BNPCH）were prepared by simple two-solvent adsorption self-assembly process and one-step thermal reduction method.The micro-morphology and structural composition of the catalyst were analyzed by SEM,TEM,EELS,BET,XRD,XPS.The electrocatalytic hydrogen evolution performance of Ru B_x-Ru@BNPCH was studied by CV,LSV and other electrochemical testing methods,and the overall water splitting performance of Ru B_x-Ru@BNPCH/GC//Ru O₂/GC double electrode was studied.Thanks to the high specific surface area caused by the porous structure of porous carbon polyhedron doped by B/N,a large number of exposed active sites caused by amorphous Ru B _x,and the synergism among Ru nanoparticles,Ru B_x nanoparticles and BNPCH,the prepared Ru B_x-Ru@BNPCH catalysts showed excellent HER activity in alkaline and acidic media.For the current density of 10 m A cm^-2 driven by HER,Ru B_x-Ru@BNPCH only needs the overpotential of 5 m V and 33 m V,respectively.In addition,for industrial-scale water electrolysis,Ru B_x-Ru@BNPCH can provide high current density of 300 m A cm^-2 for HER in alkaline solution at extremely low overpotential of 114 m V.This study provides a simple way to integrate ruthenium nanoparticles and amorphous ruthenium boride into porou s carbon matrix to develop efficient,stable and reasonably priced HER electrocatalysts to replace the most advanced platinum catalysts.At the same time,it also provides a suitable strategy for the design of high efficiency electrocatalysts and opens up a new prospect.（2）Based on the strategy of rapid electrodeposition and electrostatic self-assembly,polymer film and transition metal borate nanostructures were uniformly deposited on nickel foam,and a general preparation method of bifunctional electrocatalysts for HER and OER（represented as PAB-M/NF,PAB for aminophenylboric acid polymer film and M for Ru,Ni,Co and Fe）was constructed.Due to the high conductivity of nickel foam,the unique composite structure of polymer film combined with nanostructure of the catalyst,rapid electron and mass transfer rates,and the Lewis acid behavior of borate ions can promote the adsorption of oxygen-containing intermediates similar to Lewis base with lone-pair electrons,the prepared PAB-M/NF catalysts showed excellent HER and OER activity in alkaline medium.In the electrolyte of 1 M KOH,for driving the current density of10 m A cm^-2 for HER and OER,PAB-Ni/NF,PAB-Co/NF,PAB-Fe/NF and PAB-Ru/NF only needs the overpotential of 161,209,98,24 and 302(20 m A cm^-2),274,244,204 m V,respectively.Among them,the PAB-Ru/NF catalyst exhibited the optimal HER and OER catalytic activities.In addition,for industrial-scale water electrolysis,PAB-Ru/NF at a very low cell pressure of 1.519 V can provide the current density of 10 m A cm^-2 for total hydrolysis in alkaline solution.