Construction Of Fe/Co Modified Three-Dimensional Carbon Nanoelectrocatalysts For Oxygen Reduction Reaction

Rational construction of highly active and robust non-noble metal carbon-based oxygen reduction electrocatalysts is a vital factor in facilitating commercialization applications of fuel cells and Zn-air batteries.In this thesis,three-dimensional hybrid carbon-based electrocatalysts with excellent oxygen reduction catalytic performance were successfully developed from the aspects of carbon carriers and three-dimensional structure by means of spray lyophilization,high-temperature calcination process,and metal ion-induced structure evolution.By controlling several variable parameters,including the atomic ratio of precursors,thermal crosslinking temperature,reaction time,and the temperature,heating rate,and atmosphere during the heat treatment process,the influence of the hybrid structure and composition of materials fabricated under different conditions on its electrocatalytic activity was explored.The main investigated contents of this paper are as follows:（1）Herein,two-dimensional material Ti₃C₂T_x MXene is used as the carbon carrier,boric acid,urea,and cobalt acetate are used as the boron,nitrogen,and cobalt sources,respectively.Trace level Co modified 3D hybrid titanium carbonitride MXene and boron-carbon-nitrogen nanotubes catalyst（Ti CN-BCN-Co）is fabricated by spray-lyophilization and high-temperature pyrolysis.This strategy not only avoids the oxidation of Ti₃C₂T_x MXene,but also introduces nitrogen atoms into the titanium carbide lattice during high temperature calcination,forming a more electrocatalytically active Ti CN crystal phase.Additionally,the excellent conductivity of the Ti CN MXene material compensates for the low electrical conductivity of the BCN material.The obtained Ti CN-BCN-Co exhibits superior ORR catalytic activity with a positive half-wave potential of 0.83 V vs.RHE and outperforms commercial Pt/C in terms of stability and methanol tolerance.Impressively,the Zn-air battery with Ti CN-BCN-Co cathode achieves a superior specific capacity of 791 m Ah g^-1 and long-term stability of 200 h.（2）Herein,the melamine-formaldehyde resin is used as a novel nitrogen-rich carbon precursor,a three-dimensional hybrid architecture electrocatalyst of carbon-based microspheres and N-doped bamboo-like CNTs loaded with Co₃Fe₇/Fe₃C heterojunction nanoparticles is prepared by facile one-step coordination polymer strategy.Specifically,melamine-formaldehyde resin,as carbon and nitrogen sources,is employed to furnish coordination sites for metal ions to realize a high dispersion.And heterojunction nanoparticles are successfully synthesized through regulating the quantity of coordination positions.Thanks to the abundant active sites exposed by the three-dimensional hybrid porous structure with a larger SSA,coupled with the dynamic synergy of multi-level structure containing carbon microspheres,CNTs,and heterojunction interface engineering.The optimized CST-Fe Co displays superb oxygen reduction catalytic activity with a positive half-wave potential of0.855 V vs.RHE.Furthermore,the CST-Fe Co air electrode of liquid zinc-air battery reveals a large specific capacity of 805.6 m Ah g _Zn^-1,a remarkable peak power density of 162.7 m W cm^-2,and a long charge/discharge cycle stability of 220 h,surpassing the commercial Pt/C catalyst.