Preparation Of Boron Doped Vertically Aligned Graphene Arrays With Plated Iron Group Metal Borides As Electrocatalysts For Overall Water Splitting

With the increasing global energy demand and the gradual depletion of fossil resources,human beings are now facing a serious energy crisis.It is urgent to find a new sustainable energy.Hydrogen energy is known as the most promising renewable green energy in the 21st century.Among many hydrogen production methods,electrolytic water splitting is a simple,clean and efficient sustainable hydrogen production method,including two half reactions of hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.In order to reduce the high overpotential generated in the process of electrolytic water splitting and save energy consumption,platinum group metals and iridium/rubidium-based compounds are used in the industry to accelerate the reaction rate of HER and OER.However,their scarcity and high cost greatly hinder the large-scale development of hydrogen production from electrolytic water.Therefore,it is of great significance to research and development a high efficiency,low-cost and stable non-precious-metal bifunctional electrocatalyst for electrolytic water splitting in a wide pH range for promoting the large-scale development of low-energy electrolytic water hydrogen production industry.In this paper,a novel electrocatalyst material is prepared by using boron doped vertically aligned graphene arrays?B-VG?and iron group metal borides?IMBs?,which is applied in the field of overall water splitting for hydrogen production in a wide pH range.This paper includes two parts:1)The B-VG with stable structure,ordered orientation and uniform pore size is prepared by controlling the process conditions of directional freezing,and the controllable preparation method of B-VG is established.A series of composite catalyst materials are synthesized by electroless plating iron group metal borides on B-VG substrate?IMBs@B-VG?.FESEM,FETEM,XRD and XPS are used to study the morphology,elemental composition and electronic states of the catalyst materials.The results show the successful formation of vertical array structure of B-VG and the uniform loading of amorphous FeCoNiB nanoparticles.CV,LSV,EIS and CP are used to test the electrochemical properties of IMBs@B-VG.As a result,FeCoNiB@B-VG shows the largest electrochemically active surface area,the fastest charge transfer rate and the highest electrocatalytic activity among the series of IMBs@B-VG,with an overpotential of 31 m V and a Tafel slope of 30m V dec^-1in 1.0 M KOH solution,an overpotential of 148 m V and a Tafel slope of87 m V dec^-1in 0.5 M H₂SO₄for HER.FeCoNiB@B-VG also shows an overpotential of 387 m V and a Tafel slope of 60 m V dec^-1in 1.0 M KOH,as well as an overpotential of 635 m V and a Tafel slope of 264 m V dec^-1in 0.5 M H₂SO₄for OER.Besides,FeCoNiB@B-VG shows a good stability for 10 h in a wide pH range.Compared with various earth abundant non-precious-metal based electrocatalysts for water electrolysis,FeCoNiB@B-VG exhibits a higher electrocatalytic activity,which shows an attractive practical value in the field of overall water splitting for hydrogen production.2)The change of the relative content of Co and Niin IMBs has a significant effect on the catalytic activity of the materials.Therefore,a series of FeCo_xNi_yB@B-VG electrocatalysts?x=Co/?Co+Ni?%,y=Ni/?Co+Ni?%,16.7%?83.3%?are prepared by controlling the molar concentration of cobalt and nickel salts in the chemical deposition formula.On the basis of maintaining the relative content of Fe,the relative contents of Co and Niin FeCoNiB@B-VG are changed.LSV,CV,EIS are used to test he electrochemical properties of FeCo_xNi_yB@B-VG electrocatalysts.As a result of experiment,the FeCo_66.7Ni_33.3B@B-VG electrocatalyst exhibits the highest electrocatalytic activity in a wide pH range,with a low overpotential of 28 m V and a Tafel slope of 30 m V dec^-1in 1.0 M KOH solution,an overpotential of 143 m V and a Tafel slope of 49 m V dec^-1in 0.5M H₂SO₄solution for HER.FeCo_66.7Ni_33.3B@B-VG also exhibits an overpotential of 200 m V and a Tafel slope of 34 m V dec^-1in 1.0 M KOH solution,as well as an overpotential of 569 m V and a Tafel slope of 225 m V dec^-1solution in 0.5 M H₂SO₄for OER.In addition,FeCo_66.7Ni_33.3B@B-VG displays a good long-term stability for 10 h in a wide pH range.Compared with FeCoNiB@B-VG and most of earth abundant non-precious-metal electrocatalysts,FeCo_66.7Ni_33.3B@B-VG shows a better electrocatalytic performance,exhibiting a broad practical application prospect in the field of electrocatalysis,which contributes to the large-scale development and application of low-energy electrolytic water hydrogen production industry.