Synthesis And Electrochemical Properties Of Carbon-based Nanocatalysts

Carbon-based nanomaterials are widely investigated in the field of electrocatalysis due to the specialties of low cost and adjustable structure.On one hand,carbon materials can provide reactive sites and be used as electrocatalysts directly.On the other hand,it can be used as a carrier to reduce the amount of precious metals and improve the utilization of precious metals.Among them,the composition regulation,charge structure,morphology design and structure-effective relationship of carbon materials have become the hot topics of great significance in the field of carbon-based catalysts.In this paper,carbon based nanomaterials are optimized for their electronic and morphological structures with the aim of improving the efficiency of multiple electrocatalytic reactions(oxygen reduction reaction,ORR;Oxygen evolution reaction,OER,et al.).In order to improve the intrinsic activity of catalytic active centers,the charge structures of materials were designed from two aspects:intramolecular charge transfer(heteroatomic doping,M-Nx structure)and intermolecular charge transfer(metal-carbon matrix composites).In addition,the morphology and pore structure of carbon based catalysts can also be tuned by optimizing the synthetic route,thus increasing the number of exposed active centers.The specific research contents of this thessis are as follows:(1)The nitrogen doped carbon nanocages(N-CCs)with porous self-supporting structure and high specific surface area were synthesized by the hard template method.By investigating the specific surface area of materials at different carbonization temperatures,the variation of nitrogen species and the effect of catalytic performance,it was clear that the doping of nitrogen provides ORR/OER catalytic active sites.The porous cage structure is conducive to the diffusion of electrolytes/reactants,and improve the effective utilization of active sites.It provided that a new view and analytic method for the synthesis and structural relationship of heteroatomic doped carbonbased catalysts.(2)On the basis of N-CCs,Fe source was introduced to prepare Fe/N co-doped carbon nanocage(Fe-NCCs)with monodisperse Fe-Nx species.By controlling the species variables and the toxicity experiment of Fe-Nx,it was concluded that Fe-Nx species and N-species had a synergistic effect and jointly induced the charge distribution transfer on Fe-NCCs surface.The catalytic performance of ORR is comparable to that of commercial Pt/C in alkaline medium.(3)N/F co-doped hollow carbon nanospheres(NF-Cs)were synthesized by in situ template pyrolysis using PVDF as fluorine source and template,the dopamine as carbon and nitrogen source.The experimental and theoretical calculations results showed that N doping promotes the adsorption of O2 molecules on the catalyst surface and improves the catalytic activity.The F atom promotes the desorption of*OOH intermediates,which were benefit to the selectivity of the catalysts and dominate 2e-reaction path for the ORR.In addition,due to its abundant porous structure and large surface area,N,FCs exhibits excellent electrochemical synthesis performance of H2O2 in acidic/alkaline media.(4)The carbon nanobowls(CBs)was used as the carrier to load Pd nanoparticles(Pd/CBs).Because of its high surface area and abundant oxygen-containing surface groups,CBs are conducive to the uniform dispersion and anchoring of Pd nanocrystals,and reduce the particle size of Pd.The special morphology and surface structure are beneficial to increase the electrode/electrolyte interface area of Pd/CBs nanocomposites,and improve the mass transfer between reactants and gas products,thus showing excellent FAOR catalytic activity.(5)On the basis of work(4),the ultrafine Rh nanocrystalline(Rh/N-CBs)loaded on N-doped carbon nanobowls(N-CBs)were further synthesized.Experimental and theoretical calculations showed that a near-zero hydrogen adsorption free energy produced by the chemical bonding of Rh with the pyrrole-N doped in N-CBs is responsible for the excellent HER activity of Rh/N-CBs electrocatalysts.At the same time,Rh/N-CBs has excellent catalytic performance on HzOR,it is a promising electrochemical hydrogen bifunctional electrochemical catalyst.(6)The Co9S8@porous graphene layers/N,S-doped carbon nanotubes(Co/S/N800)were fabricated by one-step thermal treatment.In this electrocatalyst,the co-doped of and S could promote the ORR activity,and the Co9S8 nanoparticles make a major contribution to the excellent OER activity.Moreover,the graphene layers coated on the surface of Co9S8 enhance the electrochemical stability of Co9S8.Noteworthily,a rechargeable Zn-air battery with the nanohybrid as the oxygen cathode showed better performance than that with a mixture of Pt/C and Ir/C.