Design And Synthesis Of Transition Metal-based Nanoarray For Electrocatalytic Hydrogen Evolution

Among the many energy carriers,hydrogen energy shows great potential and advantage in sustainable energy application.Electrocatalytic decomposition of water is an environmentally friendly and sustainable method for hydrogen production.In order to realize large-scale preparation of hydrogen and solve the energy crisis,it is necessary to develop efficient,durable and inexpensive electrocatalysts.Transition metal compounds have been extensively studied for electrocatalytic decomposition of water for hydrogen production due to their fast electronic conductivity,long stability,good catalytic performance and reasonable blending between electrons.However,most transition metals compounds exhibit lower conductivity,which limits their high electrocatalytic activity.Therefore,the electrocatalysts are usually grown directly on the surface of conductive substrates to achieve efficient electrocatalytic activity for hydrogen evolution of the composite catalysts.In this paper,three methods,including element doping,metal oxide composite and bimetallic alloy modified transition metal oxide,are used to optimize hydrogen evolution electrocatalysts to achieve sustainable energy conversion.The main contents of this paper are as follows:1.N-doped Ni3S2 nanowires(NWs)was synthesized on nickel foamed substrates by a simple annealing method and used for efficient electrocatalytic hydrogen evolution in acidic and alkaline environments.Compare with Ni3S2 nanorods prepared by conventional hydrothermal method,the one-dimensional nanowires Ni3S2 prepared by one-step tube furnace calcination can provide a large specific surface area and expose more active sites.The addition of N significantly affected the electron density of Ni3S2 and improved the electrocatalytic activity.The N-doped Ni3S2 nanowires showed good electrocatalytic activity for hydrogen evolution in 1 M KOH electrolyte and 0.5 M H2SO4 electrolyte.The N doped Ni3S2 nanowires have a low overpotential,and the overpotential is 196 mV and 105 mV at a current density of 10 mA cm-2,in the electrolyte of 0.5 M H2SO4 and 1 M KOH,respectively.N was introduced into one-dimensional nanowires to expose more active sites,and the electronic structure was optimized.And the close contact between the foamed nickel substrate and the catalyst speeds up the electron transport rate.These structural characteristics make N-doped Ni3S2 nanowires show better electrochemical activity and stability than Ni3S2 nanorods prepared by hydrothermal method.2.NiO nanoparticles were precipitated on the surface of NiMoSx by high reductive hydration to construct the NiMoS,@NiO composite nanomaterials,and 316L stainless steel with alkali resistance and good HER activity was selected as the conductive substrate to achieve high hydrogen evolution activity in alkaline environment.In the 1 M KOH electrolyte,the optimized composite structure catalyst NiMoSx@NiO exhibits excellent hydrogen evolution activity and electrochemical stability.The onset potential is as low as 40 mV,and the overpotential is 92 mV at a current density of 10 mA cm-2,and the Tafel slope(43 mV dec-1),which are comparable to commercial Pt/C.The results show that due to the addition and regulation of hydrazine hydrate,the precipitated NiO is dotted in NiMoSx nano-flower spheres.The synergistic optimization of the two materials enables efficient HER in alkaline environment.3.CoMoOx cubic nanorod metal oxide precursor was synthesized by hydrothermal method,and then calcined in reduction atmosphere to prepare CoMo/CoMoOx composite structure catalyst.By optimizing the mass ratio of reactants,reaction temperature and reaction time,the optimal CoMo/CoMoOx catalyst showed high hydrogen evolution activity.In alkaline environment,the onset overpotential of the optimal CoMo/CoMoOx catalyst is about zero,and the Tafel slope is only 28 mV dec-1,which is equal to the height of Pt/C catalyst(onset overpotential is 0 mV,Tafel slope is 32 mV dec-1).In addition,when the cathodic current density is 20 mA cm-2 and 200 mA cm-2,the overpotential of 35 mV and 280 mV is required.The results show that by calcining the precursor of CoMoOx nanorods in reduction atmosphere,the precipitated CoMo alloy exhibits high active center,and the precursor of nanorods provides high specific surface area,the kinetics of hydrogen evolution in the rapid Tafec step can be obtained by the optimization of the two methods.