The Synthesis Of Co,Ni-based Nanomaterials For Electrochemical Performance

With the continuous development of the economy and society,the energy crisis has become a major problem for humanity in the future.With the gradual reduction of fossil energy and the continuous deterioration of the environment,the development of efficient,clean,sustainable energy and new technologies for energy conversion and storage are imminent.In many innovative strategies,electrochemical hydrolysis to produce high purity hydrogen is considered a high promising approach.The electrolysis of water consists of two reactions:hydrogen evolution at the cathode and oxygen evolution at the anode.However,the barrier required to directly electrolyze water is high.Therefore,it is necessary to develop an appropriate electrocatalyst to reduce the energy barrier of the electrolysis water and reduce the cost.At this stage,precious metals and related oxides are considered to be the most efficient catalysts,but the high prices and limited reserves of these catalysts have caused them to be extremely limited in practical applications.Considering the earth's elemental reserves,preparation costs,environmental protection,catalytic activity,and long-term stability,inexpensive transition metal-based catalysts,especially Ni-and Co-based catalysts,are potential alternatives to precious metal catalysts.The main content of this thesis is to design and synthesize cobalt or nickel-based nanocomposite electrocatalysts,and to study the catalytic electrolyzed water performance of these electrochemical catalysts with specific morphology and structure.The main work of this paper is as follows:(1)We demonstrate the successful synthesis of Mo-Ni2P nanowires on a conductive Ni foam substrate from NiMoO4 nanowire arrays via a topotactic phosphidation conversion reaction.The Mo-Ni2P nanowires electrocatalyst has excellent electrocatalytic activity under different pH environments(acidity,neutrality,and basicity)and reaches a current of 10 mA/cm2 in an electrolyte solution with pH of 0,7 and 14.The required overpotentials for density are 64,84,and 78 mV,respectively.This indicates that the catalyst system has high electrocatalytic activity in a wide pH environment range;in addition,the catalyst system also has high electrochemical stability over the entire pH range.The successful preparation of the Mo-Ni2P nanowire array electrocatalyst will provide a new approach for the design and application of novel,highly efficient,stable,and inexpensive non-precious metal hydrogen evolution electrocatalysts.(2)Mn doped CoN nanostructured materials on conductive carbon fiber cloth(CFC)were successfully prepared from a Mn-Co2(OH)2CO3/CFC nanowire array precursor via a topotactic nitridation conversion reaction.The Mn-CoN nanowire array not only has excellent electrocatalytic activity in different alkaline environments,but also has excellent oxygen evolution activity and stability in a neutral solution having a pH of 7.The synergistic effect of Mn and CoN enhances the conductivity and electron transport ability of pure CoN,thereby enhancing its electrocatalytic performance.(3)In view of the excellent catalytic activity brought about by the above-mentioned single metal doping,we report the synthesis of dual-cation(Fe,Co)incorporated NiSe2 nanosheets on carbon cloth(Fe,Co-NiSe2/CFC)as an efficient bifunctional electrocatalysts for hydrogen and oxygen generation reactions.The Fe,Co-NiSe2 three-dimensional nanosheet array exhibits excellent hydrogen evolutionand oxygen evolution capability in an alkaline environment.When used as bi-functional electrodes for overall water splitting,the current density of 10 mA cm-2 is achieved at a low cell voltage of 1.52 V.We demonstrate that the dual-cation incorporation significantly distorts the lattice,leading to increased active site exposure and strong electronic interaction near the surface.In addition,we systematically explored the effects of different amounts of bimetallic doping on the electrocatalytic activity of NiSe2.(4)Hybrid Ni/Ni2P nanoparticles with graphitic carbon coating supported by 3D N,S dual modified binder-free macroporous carbon framework(Ni/Ni2P@3DNSC)were successfully prepared via sequential carbonization reduction process of melamine foam and phosphidation conversion reaction.The catalyst exhibits excellent hydrogen evolution,oxygen evolution,and full water resolvability in an alkaline environment.We systematically studied the effect of annealing temperature and phosphating degree on its catalytic performance.A general summary about this thesis and the prospects for further work are presented.