Synthesis And Electrocatalytic Performance Of Ni And Mo-based Nanostructures

In the past half century,the exploitation and utilization of renewable energy and new energy conversion technologies have received increasing attention due to the huge shortage of energy supply caused by population growth and industrial development.Electrocatalytic water splitting is considered to be an important part of modern clean energy.It consists of hydrogen evolution reaction?HER?and oxygen evolution?OER?reaction.Nickel and molybdenum transition metal-based nanomaterials have been widely used to catalyze various electrochemical reactions due to their low cost and high catalytic activity.In this thesis,a series of Ni?Mo based nanocomposites were designed and the influences of their morphology and electronic structure on electrocatalytic performance were investigated.The main research content is the following three parts:Combining the advantages of N,P codoped carbon and transition metal carbides,MoC based HER electrocatalysts were prepared by oxidative polymerization and carbonization treatments.With the strong coupling between carbon nanotubes?CNTs?and the MoC nanoparticles generated in situ,as well as the Mott-Schottky effect between metal MoC and N,P codoped carbon,MoC/NPC@CNTs800 achieved excellent HER performance.The electrochemical experiments showed that it only required an overpotential of 175 mV for HER to provide a current density of 10 mA/cm2 and exhibited excellent stability with continuous hydrogen evolution for 12 h.The UOR electrocatalysts with Ni/NiO Schottky interface were prepared using the interface electron transfer as guiding ideology.Ni/NiO@NC₃₀₀,Ni/NiO@NC₄₀₀ and Ni/NiO@NC500 nanocomposites were obtained at different carbonization temperatures.The results showed that the existence of Ni/NiO heterogeneous interface can promote the fracture of C-N bond in urea;the carbon "armor" layers can weaken the corrosion of the active sites in the strongly alkaline environment and improve the long-term durability of the catalysts.Thanks to that,Ni/NiO@NC₄₀₀ could drive the current density of 50 mA/cm2 at 1.40 V in urea oxidation reaction?UOR?.In addition,it showed excellent stability of urea oxidation.The final potential had only increased by 2 mV after long-term stability test of 12 hours.In order to use the same catalyst to promote water splitting,the synthetic strategy of mild etching was adopted to the large-scale preparation of bifunctional electrocatalysts,which the amorphous NiMoO4 grown on the nickel foam?NF?.Owing to the amorphous structure with a large number of defects and three-dimensional self-supporting conductive substrates,NF/NiMoOxPy showed excellent HER and UOR activities.To reach the current density of 10 mA/cm2,the overpotentials of HER and UOR were only 116 mV and 1.359 V,respectively.When it is simultaneously used as a cathode and anode for urea-assisted water splitting,only a voltage of 1.48 V is required to provide the current density of 10 mA/cm2,which is much lower than 1.66 V required for full water splitting.In addition,owing to the close combination of surface network nanostructures and NF,NF/NiMoOxPy exhibited excellent long-term stability of urea electrolysis.