Preparation And Electrocatalytic Properties Of Transition Metal (Co,Ni) Compound Quasi-Three-Dimensional Electrode

With the shortage of fossil fuels and the continuous deterioration of the environmental,it is extremely urgent to develop a clean,efficient and sustainable new energy.Among various methods,hydrogen production by water electrolysis is a prospect for obtaining renewable energy.The water electrolysis consists of two half-reactions:oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).However,due to the slow reaction kinetics of OER,the overpotential for water electrolysis is large,so it is necessary to develop a highly efficient electrocatalyst to reduce the overpotential of water spilling.As far as we know,transition metal compounds will produce actual catalyst metal oxide/hydroxide during the electrolytic water process,which is beneficial to increase the efficiency of water spilling.Therefore,in order to reduce the overpotential of water spilling,Co and Ni-based electrocatalysts were obtained by different preparation methods and their electrocatalytic properties were testing.The main works are as follows:(1)Co3O4 particles were prepared via a coordination-compound method(CCM)with[Co(3,5-pdc)(2,2-bpy)(H2O)2]2H2O as a complex precursor.For comparison,the Co3O4 sample was also prepared via a coprecipitation method(CPM).The morphology of Co3O4-CCM is a regular tetrakaidecahedron,which is completely different from that of Co3O4-CPM.Electrochemical properties of Co3O4 were investigated using cyclic voltammetry and galvanostatic charge-discharge measurements.And the specific capacitance of Co3O4-CCM is 243.8 F g-1,which is 1.77 times greater than that of Co3O4-CPM.In addition,it has been found that the electrocatalytic electrode prepared by the drop casting method has a large interface resistance and is easy to fall off,which leads to the poor performance of water spilling.(2)Herein,a unique line-sphere layered superstructure Ag/CoO is prepared via a facile alternating electrodeposition method.Compared to electrocatalysts with CoO as the innermost layer,the Ag/CoO catalysts with Ag nanowires(NWs)as the initial layer take more advantages of the low conductance for water splitting.Electrochemical tests reveal that the layered superstructure material with n+1 layers of Ag NWs and n layers of CoO(An+1Cn)exhibits excellent catalytic activities and stabilities for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).Based on the kinetics and thermodynamic measurements of the catalytic processes,a reasonable catalytic mechanism of overall water splitting has been proposed for different electrocatalysts.The results show that the diffusion of hydrogen-containing species may be the rate-determining step.(3)A novel Ag/Ni3S2 superstructure layered material was synthesized by alternating electrodeposition on carbon cloth.By using the influence of the substrate on the morphology and properties of the material,two different morphologies of Ni3S2 were prepared in the same material,and they were connected by the Ag layer,which greatly improved the OER activity of the material after their interaction.The result shows that A catalyst(N2A1)with two layers of Ni3S2 and one layer of Ag may be a promising catalyst for the electrolysis of water for oxygen evolution.It has been found that the main catalytic activity in the OER process is the NiOOH formed during the process.At the same time,the temperature-dependent experiment proves that the adsorption and desorption of the active substance on the electrode surface determine the rate of the whole reaction:the catalytic activity of Ni3S2 mainly utilizes its more active sites and smaller redox reaction activation energy.