Structural Design Of Carbon-based Nanomaterials For Electrocatalytic Applications

With the development of new electrochemical energy conversion devices,the development of low-cost and highly active electrocatalyst materials has attracted widespread attention in academia and industry.Carbon-based nanomaterials have the advantages of wide sources,low cost,high electrical conductivity,good chemical stability,and controllability of structures and functions,and therefore have great application prospects in the practical development of energy conversion technologies.From the perspective of structural design of carbon-based nanomaterials,this paper studies a series of scientific issues related to carbon-based nanomaterials by constructing suitable model systems and using a combination of experiments and theoretical simulations.For example,the effects of mass transfer and dual-doping on the electrocatalytic activity,the importance of the synergistic engineering of the graphitized structure,pore structure,and chemical structure of the material in the electrocatalytic reaction,and the effect of structural design on the electrosynthesis of hydrogen peroxide.The main research results are as follows:One-dimensional N,P co-doped hollow carbon nanofibers with hierarchical porous structure,one-dimensional electrolyte/reactant transport channels,and abundant catalytic active sites were designed and prepared via coaxial electrospinning technology,followed by high-temperature pyrolysis treatment.The as-prepared carbon nanomaterial exhibits an excellent trifunctional electrocatalytic activity for oxygen reduction reaction,oxygen evolution reaction,and hydrogen evolution reaction.Impressively,the as-obtained material shows particularly excellent catalytic performance for oxygen electrocatalytic reactions as characterized by a low potential deviation(?E)of 0.73 V between the half-wave potential of oxygen reduction reaction and the potential reaching 10 mA cm-2 for oxygen evolution reaction.Subsequently,using this type of material as a model system,the effect of mass transfer on the performance of oxygen reduction reaction was studied.Considering flexibility of coaxial electrospinning technology,a series of dual-doped carbon submicrotubes were designed and prepared by adjusting the composition of the core solution during the coaxial electrospinning process.The effect of dual-doping on the catalytic activity of carbon-based nanomaterials for oxygen reduction reaction was studied by using this type of material as a model system.It was found that N,P co-doping shows the best catalytic activity and catalytic kinetics of oxygen reduction reaction over N,S and N,B co-doping.Density functional theory calculations revealed that N,P co-doping could synergistically modulate catalytic reaction pathways and the electronic structure of carbon network,thus generating the active edge C site situated around the oxidized P site nearby a graphitic N atom.Bimetallic zeolitic imidazolate frameworks with different metal ratios were prepared by a simple one-step solution reaction,and then carbonized to obtain Co-N-C materials.Subsequently,the effect of the synergistic engineering of graphitized structure,hierarchical porous structure,and active species distribution on the performance of oxygen electrocatalytic reactions in Co-N-C materials were studied.Density functional theory calculations revealed that the interaction between N-doped graphene and Co could modulate the charge distribution of N-doped graphene,thus generating the active C sites near pyridinic N.A N,o co-doped carbon xerogel was obtained by the pyrolysis treatment of a polyacrylonitrile-based polymer xerogel as the precursor.Subsequently,the importance of structural design for the electrosynthesis of hydrogen peroxide was investigated.It was found that the N,o co-doped carbon xerogel shows an excellent performance for the electrosynthesis of hydrogen peroxide as revealed by the hydrogen peroxide selectivity of more than 90%at the potential range of 0.15-0.6 V.Then,density functional theory calculations were used to study the catalytic active site of N,O co-doped carbon networks for the two-electron pathway oxygen reduction reaction.