Regulation Of Dendrite Look-like Graphene Structure And Catalytic Performance

Fuel cells,as the new energy resource in the 21st century,can convert chemical energy directly into electrical energy with high efficiency and less pollution.Catalyst is one of the key factors to determine the cost and performance of the battery.Graphene has been widely investigated as an ecofriendly replacement of noble metals for electrocatalytic applications due to large specific surface area,good electrical conductivity and high mechanical strength.However,graphene exhibits low electrocatalytic activity towards reduction reaction of oxygen due to stable valence structure.Doped graphene has been proved to be a good catalyst towards reduction reaction of oxygen since doping cause considerably atomic disordering in the graphene.In this work,we will show that graphene grow on three-dimensional NiCu dendrites has high activity towards ORR without any doping.Firstly,porous NiCu dendrites were prepared by hydrogen bubble dynamic template electrodeposition.The effects of CuSO₄ concentration,?NH₄?₂SO₄ concentration and H₂SO₄ concentration on the morphology and chemical compositions of deposits were investigated.As the concentration of CuSO₄ increased,the pore size and wall thickness increased significantly,and the dendrites became denser,the copper content of deposits also showed an increasing trend.As the concentration of?NH₄?₂SO₄increased,the pore size of the coating became larger,the pore walls became denser,and the dendrites became slender.However,it had little effect on the composition of deposits.The addition of H₂SO₄ made the pore size significantly smaller,and the dendrites became compact.The nickel content of deposits was reduced due to the addition of H₂SO₄.Therefore,by adjusting the composition and concentration of the plating solution,porous NiCu dendrites with copper content?atomic percentage?of 5%,20%,50%were prepared for depositing graphene,which have similar dendritic structure.Secondly,dendrite look-like graphene were prepared by Chemical vapor deposition at 900°C using porous NiCu dendrites as template.It was found that with the increase of copper content of the porous NiCu dendrites,coarsening of dendrite look-like nano structure became more serious,the defects increased,the thinckness of the graphene became smaller.Linear sweep voltammetry and electron transfer number show that defects in graphene can improve the ORR activity.When using porous NiCu dendrites with 50%copper content as the template,the deposited graphene showed the higher activity.The onset potential,half-wave potential were-0.191 V vs.Ag/AgCl,-0.358 V vs.Ag/AgCl,the electron transfer number was 3.6at-1.0 V.In addition,the graphene with curvature structure had higher catalytic activity than graphene prepared on the flat Cu foil.Finally,dendritic look-like graphene was also prepared by plasma enhanced chemical vapor deposition at 750°C.The results show that the graphene prepared by plasma enhanced chemical vapor deposition can maintain the curvature structure.The defects still increased with the increase of copper content of the porous NiCu dendrites,and the thickness of the graphene decreased with the increase of copper content of the porous NiCu dendrites.Graphene prepared by using porous NiCu dendrites with 50%copper content had the most positive onset potential-0.149 V vs.Ag/AgCl,the most positive half-wave potential-0.356 V vs.Ag/AgCl and the biggest electron transfer number 3.9 at-1.0 V.Compared with the dendritic graphene prepared by chemical vapor deposition,the graphene prepared by plasma enhanced chemical vapor deposition had higher catalytic activity because of more curvature structure and more defects.