Tuning Of Tubular Mesoporous Carbon-based Catalysts And Its Electroreduction Performance

The excessive burning of fossil fuels not only causes serious environmental pollution and climate change,but also the potential exhaustion of non-renewable resources is forcing countries around the world to accelerate the pace of switching to renewable energy.Under the background of green,clean and sustainable development,electrocatalytic conversion technology has become a research hotspot.Electrocatalytic carbon dioxide reduction（CO₂RR）and oxygen reduction（ORR）are the electrocatalytic reactions involved in key energy conversion technologies,which involve multi-electron proton coupling transfer.Therefore,it is urgent to develop new and efficient catalytic systems to jointly solve the problems of diffusion and mass transfer,high reaction energy barrier and low selectivity.In recent years,carbon-based catalytic materials have attracted wide attention as non-noble metal catalysts because of their chemically adjustable surface,good electrical conductivity and adjustable porosity.Aiming at the scientific problem of low density of accessible active center.In this paper,a tubular ordered mesoporous carbon-based catalyst was designed and prepared by regulating the pore structure and active center of carbon materials,and the structure-activity relationship between ordered mesoporous channel configuration and active center and CO₂RR and ORR activities was revealed.The research contents are as follows:（1）In electrocatalytic reduction reaction systems,the exploration of efficient electrocatalysts is one of the key tasks,and most researches focused on designing new active centers;however,the mass transport that determines reactant supply and electrolyte ionic and electronic conductance is often overlooked.Therefore,we achieve on spatially locating active centers into parallelly bimodal mesopores by precisely engineering mesopore geometries,through which the contribution of the paralleled transport channels to the activity of gas-consuming reactions was quantitatively determined.Under the same conditions,the partial current density for CO₂-to-CO conversion of bimodal ordered mesoporous carbon-based electrocatalysts is 2.9 times higher than that of unimodal ordered mesoporous catalysts in the kinetic region of-1.1 V vs.RHE.Likewise,the strong correlation between the activity enhancement of the supported molecular catalyst and the ORR reaction and the bimodal mesoporous geometry was further verified.In addition,the bimodal ordered mesoporous carbon-based catalyst is favorable for the deep reduction of O₂ to H₂O compared to the unimodal ordered mesoporous.（2）In order to further regulate the ORR reaction pathway,on the basis of previous research,the active center was regulated,and ordered mesoporous carbon-based catalysts doped with different transition metals were designed and synthesized.Among them,Fe-O-C,a bimodal ordered mesoporous carbon catalyst with Fe-O_x doped,exhibited a significant two-electron reaction pathway in the ORR reaction,with H₂O₂ selectivity o up to 94%and H₂O₂ yield as high as 750 mmol g^-1_cat h^-1.The active coordination structure of Fe-O_x was confirmed by experiments and characterization,and it is the C atom adjacent to the Fe single atom that really plays a catalytic role.By further regulating the coordination environment of Fe,the ORR reaction pathway and product selectivity can be effectively regulated.For example,when the coordination environment is adjusted to Fe-N_x coordination,Fe-N-C catalysts undergo an almost complete four-electron transfer pathway to reduce O₂ to H₂O.