Preparation Of Self-supported Transition Metal Based Nanocatalysts For Alkine Oxygen Evolution Reaction

Hydrogen is a promising alternative for traditional fossil fuels because of its ultra high energy density and zero-pollutant emission feature.Water electrolysis is a safe,facile and environmental method for hydrogen production,which includes two half reactions of hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.However,the slow kinetics of OER greatly limits the efficiency of overall water splitting.IrO₂and Ru O₂are the best OER electrocatalysts,but their scarcity and high price impede their large-scale application.Transition metal based catalysts is an ideal alternative to traditional noble metal catalysts because of their abundant reserves,low cost and active d-orbital electrons.Compared with the powder catalysts,self-supporting catalysts have many advantages such as high loading,uniform morphology and size,good conductivity and high stability.We designed and prepared three self-supporting transition metal based nanocatalysts and investigated their alkaline OER performance.The main work of this thesis is as follows:（1）We solvothermally grew Ni-MOF nanosheet array on nickel foam（Ni-MOF/NF）by using 4,4’-biphenyl dicarboxylic acid as organic ligand.Compared with Ni-MOF powder/NF,Ni-MOF/NF showed higher OER electrocatalytic activity.Meanwhile,the ultrathin two-dimensional nanosheet structure of Ni-MOF/NF can ensure sufficient infiltration of electrolyte and improve mass transfer efficiency during OER process.In addition,the effect of Fe doping on the OER performance of Ni-MOF/NF was investigated.The OER activity of Ni Fe-MOF/NF is much higher than that of Ni-MOF/NF.Ni Fe-MOF/NF demands a low overpotential of 280 m V to attain the current density of 100 m A cm^-2.In contrast,a much larger overpotential of440 m V is needed for Ni-MOF/NF to drive 100 m A cm^-2.（2）Firstly,Co（OH）F nanowire array was grown on titanium mesh（TM）through hydrothermal reaction,and then an amorphous Fe-P shell was electrodeposited on the surface of Co（OH）F nanowire.This Fe-P@Co（OH）F/TM electrode only needs a low overpotential of 267 m V to drive the current density of 10m A cm^-2.It is should be noted that an oxide layer will form on the surface of Fe-P shell during OER process.In this special structure,Co（OH）F nanoarray provides ultra-high specific surface area,and Fe-P acts as a highly conductive medium can efficiently conduct electrons to the oxide layer,thus showing excellent OER electrocatalytic activity.In addition,the influence of deposition time on the structure and OER performance of Fe-P@Co（OH）F/TM electrode was also investigated.It was concluded that the optimal electrondeposition time of Fe-P@Co（OH）F/TM electrode is 20 min.（3）CuO_xnanowire was prepared by thermal oxidation,and then a highly conductive indium-doped tin oxide（ITO）film was coated on the surface of CuO_xnanowire by magnetron sputtering.Compared with CuO_x,the OER electrocatalytic performance of ITO-CuO_xwas slightly improved.Corresponding analysis showed that the charge transfer impedance of ITO-CuO_xis less than that of CuO_x,indicating that ITO film can improve the conductivity and further promotes the OER performance.