Transition Metal-doped Manganese Oxide:Synthesis by Warm Plasma and Electrocatalytic Performance for Oxygen Evolution Reaction
By using renewable electricity proton exchange membrane(PEM),water electrolysis can produce"green hydrogen"of which the rate-determining step is oxygen evolution reaction.Considering the problems of stability,activity and cost,manganese oxides(MnOx)doped with transition metals as a kind of electrocatalysts(Fe-MnOx,Co-MnOx,and Ni-MnO()were directly synthesized in one-step by gliding arc warm plasma.Complementary characterizations of the crystal structure,morphology,element composition,and surface valence state on this kind of synthetic catalysts were conducted.The results show that MnOx mostly consists of crystalline Mn2O3 and amorphous Mn3O4.Although the transition metal doped catalysts possess the very approximate crystalline compositions to MnOx,they showed a remarkable decrease in particle size and an increase in specific surface area are achieved.Introducing Co to form Co-MnOx can increase surface density of electrons as compared to pure MnOx.We further reveal a unique current step of MnOx-based catalysts in acidic medium which appears in three consecutive potential regions(low Ⅰ:1.4-1.8 V,low Ⅱ:1.8-2.4 V,and high Ⅲ:2.4-2.7 V)under cyclic voltammetry(CV)measurements.This current step process is quite consistent with the electrode dynamics curve(as reference)which is reduced by a simplified version of Bulter-Volmer equation,during which the electrocatalytic behavior involves manganese at multi-valence states.At low potential regions Fe-MnOx achieves the highest activity among all catalysts,while at high potential region only Co-MnOx achieves.Furthermore,Co-MnOx onset potential is 160 mV lower than that of pure MnOx,and three times of the ending current density of pure MnOx during bulk electrolysis under potentiostat.Consistent with the trend in activity,at low potential regions Fe-MnOx is the most stable,while at high potential region Co-MnOx is.Consequently,the significant increase in oxygen evolution reaction activity and stability of manganese oxides doped with transition metals is attributed to transition metal doping,which obviously optimizes the particle size,specific surface area,and electronic structure of MnOx.
MnOxtransition metal dopingcurrent stepoxygen evolution reactiongliding arc warm plasma
万方数据
维普
