The Synthesis Of Carbon Supported Transition Metal Composites And Their Electrocatalytic Properties

With the consumption of traditional fossil fuel and the aggravation of environmental pollution,clean energy storage and conversion technologies such as metal air batteries and fuel cells are attracting more and more attention.However,the slow dynamics of the electrode surface seriously limits the efficiency of the energy storage and conversion technologies.Normally,noble metal catalysts are used to promote the reaction process.However,the high price and bad stability of noble metal catalysts greatly increases the cost of electrochemical energy systems,which limits their commercial application.Therefore,the development of non-noble metal catalysts is critical to reduce the cost of these energy conversion devices.So far,the catalytic activity of non-noble metal is still cannot meet the commercial demands.Therefore,it is very significant to develop non-noble metal catalysts with high performance and low cost.Based on this,this paper focuses on the synthesis of transition metal and nitrogen co-doped carbon material,and exploring the correlation between the property of materials and catalytical activity.The main findings are summarized below:1.To avert the aggregation and improve the dispersity of cobalt during pyrolysis,several strategies have been employed,such as surfactant-assisted method,silica-protection approach,hard template replication.In this study,we demonstrate an efficient method to obtain electrocatalyst（Co@NC）with small size,crystalline and homogeneously embedded Co nanoparticles in nitrogen-doped carbon using benzimidazole as stabilizer.Addition of benzimidazole have improved cobalt dispersity due to coordination of N ligands.Contrariwise,the g-C₃N₄ intermediate was completely transmuted to nitrogen-doped carbon nanotubes（Co@NCNTs）without benzimidazole addition.This is because that the smaller Co particles in Co@NC promote to shut-down carbon nanotubes growth in favor of encapsulating the Co nanoparticles.A half wave potential of 0.88 V has been attained for oxygen electroreduction in alkaline solution on the optimized sample Co@NC,which is 34 mV higher than commercial Pt/C.Moreover,the Co@NC-based Zn–air battery has shown admirable discharge performance,power density and ultrahigh stability compared to Pt/C air electrode.2.Both oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are crucial for metal-air batteries.Transition metal and nitrogen co-doped carbon catalysts（M-N-C,M=Fe,Co）possess good ORR performance.On the other hand,Ni-Febi-metal alloys and their derivatives exhibit excellent OER activity Here,a promising bifunctional catalyst comprising of Feand FeNi₃ nanoparticles embedded in nitrogen-doped carbon nanotubes（Fe/FeNi₃@NC）is fabricated.In 0.1 MKOH solution,the prepared Fe/FeNi₃@NC catalyst demonstrates excellent ORR performance with a half-wave potential of 0.83 V,which can comparable to Pt/C.Likewise it offers outstanding catalytic activity toward OER by delivering a current density of 10 mA cm^-2 at 1.58 V.