Structural Design,Synthesis And Oxygen Reduction Performance Of Nickel-Based Carbon Nanomaterial Electrocatalysts

The increasing consumption of non-renewable fossil fuels from the first industrial revolution to the present makes it imperative to develop efficient and sustainable green energy conversion technologies.As one of the green energy conversion technologies that can convert chemical energy into electrical energy,the rate of the cathode oxygen reduction reaction（ORR）,a key component,directly determines the efficiency of a proton exchange membrane fuel cell.However,the current electrocatalyst materials used in ORR mainly contain precious metals such as platinum,which have the disadvantages of scarce reserves,high prices,poor stability and resistance to toxicity,limiting the development of fuel cell technology,hence the need to develop low or non-platinum catalysts to replace commercial ORR electrocatalysts.In this paper,the influence of the composition,structure and morphology of nickel-based electrocatalysts on the performance of electrocatalysts was investigated through the study of material preparation methods,and two ORR electrocatalysts with high and stable catalytic performance were obtained,and the specific research work is summarized as follows:1.PtNi alloy nanoparticles were first prepared by hydrothermal synthesis,then Pt Ni alloy nanoparticles were loaded onto the structure of nickel-doped zinc metal-organic framework material（MOF-Zn）by organic ligands,followed by the successful synthesis of electrocatalyst materials（Pt Ni@Ni-N-C）loaded with Pt Ni alloy nanoparticles on top of nickel and nitrogen co-doped defective graphitic carbon by high temperature pyrolysis and acid washing.Finally,the ORR catalytic performance of the electrocatalyst material was systematically investigated.The electrochemical results show that the catalyst has an ORR onset potential of 1.03 V（vs.RHE）,a half-wave potential of 0.90 V（vs.RHE）,an electron transfer number of 3.97 and good long-term electrochemical catalytic stability under alkaline solution conditions.The ORR catalytic activity of Pt Ni@Ni-N-C materials was significantly improved compared to single Pt Ni alloy nanoparticle materials,N-C nanomaterials formed by direct pyrolysis of MOF-Zn and Ni-N-C nanomaterials formed by direct pyrolysis with Ni-doped MOF-Zn without Pt Ni alloy nanoparticles loading.It was further shown that the synergistic catalytic effect of Pt Ni alloy and Ni-N-C increased the number of ORR active sites and effectively enhanced the electron transport capacity of the material,thus enhancing the ORR catalytic activity of the material.2.The melamine-Ni²⁺/Co²⁺complex precursors were first synthesised by adding melamine to an ethanolic solution containing nickel and cobalt ions by a simple coordination method,and then the melamine-Ni²⁺/Co²⁺complex precursor powders were directly calcined by a one-step calcination method to successfully prepare composites（Co Ni@N-GCNTs）of Co Ni alloy nanoparticles and"nanoclusters-like"Co or Ni co-wrapped in bamboo-like nitrogen-doped carbon nanotubes.Finally,the ORR catalytic performance of the Co Ni@N-GCNTs material was systematically investigated.The electrochemical test results showed that the ORR onset potential and half-wave potential of the electrocatalyst material under alkaline conditions were0.97 and 0.86 V（vs.RHE）respectively,which were similar to the performance of commercial10 wt%Pt/C catalysts,but the long-term stability and methanol tolerance were better than the commercial 10 wt%Pt/C catalysts.It was found that the Co Ni alloy particles distributed throughout the N-GCNTs,as well as the graphitized N-doped carbon nanotubes and Ni/Co-N-C together contributed more catalytic active sites,while the encapsulated Co Ni alloy particles also prevented the nanoparticles from agglomerating into spheres due to spatial site resistance,resulting in a high ORR catalytic activity and stability of the electrocatalyst.