Templated Synthesis And Electrocatalytic Oxygen Reduction Performance Of Nitrogen-Doped Carbon-Based Materials

Oxygen reduction reaction?ORR?of cathode is the decisive step of fuel cell reaction.Therefore,the development of high performance ORR electrocatalysts has very important theoretical research and application value.Commercial oxygen reduction catalysts are mainly platinum-based noble metal catalysts.However,the low reserves and high prices of platinum and other noble metals seriously hinder the commercialization of fuel cells.Therefore,the development of low-cost and highly active non-noble metal oxygen reduction catalysts to replace Pt-based catalysts is the key to achieve large-scale application of fuel cells.At present,the main research directions of non-noble metal oxygen reduction catalysts are to explore the active sites of oxygen reduction catalysis,to increase the density of active sites of oxygen reduction catalysis,and to construct excellent three-dimensional electron/proton transport pathways.In view of this,nitrogen-doped carbon-based materials with unique micro-nano morphology were prepared by in-situ polymerization,chemical vapor deposition,pyrolysis and carbonization using Layered double hydroxide?LDH?and manganese dioxide nanowires as growth templates,which are cheap and easily available for raw materials.The catalytic activity and mechanism of oxygen reduction were discussed in detail.The research work of this paper is mainly carried out in the following two aspects:1.Co_x/Mg₂/Al-LDH layered dihydroxides?Cox/Mg₂/Al-LDH?were synthesized by urea co-precipitation method as growth templates.The coordination between the abundant hydroxyl groups on the surface of dopamine and the metal on the surface of Co_x/Mg₂/Al-LDH was utilized to realize the uniform growth of polydopamine on the surface of LDH lamellae.Subsequently,with melamine as both carbon and nitrogen sources,cobalt ions in LDH were reduced to cobalt nanoparticles during high temperature carbonization,which effectively catalyzed the in-situ catalytic growth of carbon nanotubes on the surface of LDH lamellae.At the same time,nitrogen-doped carbon shells were formed in the polydopamine layer during high temperature carbonization.Due to the unique spatial confinement of nitrogen-doped carbon shells,carbon nanotubes?CNTs@NCS?pillared carbon composites were obtained after removal of soluble alumina oxides by acid pickling.The prepared p-CNTs@NCS catalyst exhibits excellent catalytic activity for oxygen reduction in alkaline electrolyte.The initial potential?0.99 V vs.RHE?and half-wave potential?0.88 V vs.RHE?are superior to those of commercial platinum-carbon catalysts and can be used as air electrodes to assemble primary Zn-air batteries.2.Using manganese dioxide nanowires with high aspect ratio as growth templates,the nitrogen-doped hollow carbon nanotubes were obtained by in-situ polymerization and high-temperature pyrolysis,carbonization and pickling.In the process of in-situ polymerization of dopamine,pyridine-2-formaldehyde,a copolymer containing pyridine nitrogen structure,was introduced into the precursor to effectively increase the pyridine nitrogen content in nitrogen-doped hollow carbon tubes.Nitrogen-doped hollow carbon nanotubes have excellent electron/electron transport properties due to their hollow tube structure,which significantly improves their catalytic activity for oxygen reduction.The prepared nitrogen-doped hollow carbon tube catalyst has high methanol toxicity resistance and cyclic stability in alkaline electrolyte.The initial potential?0.92 V vs.RHE?and half-wave potential?0.84 V vs.RHE?are comparable to those of commercial platinum-carbon catalysts.