Preparation Of Non-noble Electrocatalysis Toward Oxygen Oxygen Reduction Reaction And The Study On Their Catalytic Performance

Fuel cell is an electrochemical energy conversion device which is considered as the primary choice among the clean,efficient power generation technologies in the 21st century,exhibiting a promising application in the protable electronic equipment,transportation and stationary electric power generator.Among them,polymer electrolyte membrane fuel cells?PEMFCs?and aqueous metal-air batteries with low working temperature and high energy densities are the most promising ones closed to commercialization.Oxygen reduction reaction?ORR?is the cathodic reaction of the fuel cells.Currently,Pt is used as the most effective and stable electrocatalyst for the ORR.However,the the resources of Pt are rare and the price is high,greatly hampering the development and application of fuel cells.Therefore,it is imperative to develop non-plantiumn or non-noble metal electrocatalysts for ORR.This thesis aims at developing low cost,high active,Pt alternative carbon based electrocatalysts towards ORR.Focused on the issues of low density in active sites and poor mass transportation in the carbon based electrocatalysts,we propose to construct novel catalysts with three dimentional porous structure and abundant active sites to achieve high activity and stability.Electrochemical methods and spectro-microscopy techniques were employed to study the essence of the catalytic behavior of the electrocatalysts for ORR.The main results are as following:1.To solve the issue of low density in active sites for the carbon-based electrocatalysts,aniline?ANI?with abundant C and N element,phytic acid?PA?containing P and ferric chloride hexahydrate?FeCl₃·6H₂O?were adoped as precursors,which allows the polymerization of ANI and P doping achieved in one step.A carbon aerogel co-doped by N and P?PANI-Fe/PA-N1050?was obtained followed by a high temperature pyrolysis.The electrocatalyst exhibits a half-wave potential(E_1/2)of 0.844 V vs.RHE in the alkaline media.Compared to its counterparts PANI-N1050,PANI-Fe-N1050 and PANI-PA-N1050,and the ORR catalytic activity and stability of PANI-Fe/PA-N1050 are significantly improved.Combined with X-ray photoelectron spectroscopy?XPS?analysis,it is concluded that PANI-Fe/PA-N1050 catalyst is rich in Fe-Nx,graphitized N,and P-C active sites,which thereby promotes the ORR.2.With the aim at overcoming the poor mass transport in caon-based electrocatalysts,melamine foam?MF?with porous structure was employed as the template,together with citric acid as the Fe³⁺complexing agent,and FeCl₃,a citric acid-iron/melamine foam derived catalyst?CA-Fe/MF-N900?was prepared.The electrocatalyst show a ORR half-wave potential of 0.83 V vs.RHE in the alkaline electrolyte.Compared to its counterparts MF-N900?0.74 V vs.RHE?,MF/Fe-N900?0.80 V vs.RHE?,ORR catalytic activity and stability are significantly improved.The ORR activity enhancement could be ascribed to the porous structure that allows the active sites exposing and the mass transportation is reinforced.3.Taking account of both improved active sites density and optimized mass transport,melamine foam?MF?was used as the template to construct large pores,and polyaniline nanosheets were grown on 3D melamine foam by in-situ polymerization to construct small pores after experienced pyrolysis process.The obtained electrocatalyst exhibits a comparable onset potential?1.01 V vs.RHE?and half-wave potential?0.86 V vs.RHE?with commercial 20%Pt/C,but superior long-term stability.The outstanding catalytic performance is attributed to the populated active sites taking advantage of the large surface area,the superior electro-conductivity and the facilitated mass transportation by virtue of the unique hierarchically interconnected porous carbon structure.