Preparation And Electrocatalytic Performance Of Transition Metal/Carbon Composite Cathode Materials

With the development of the economy,the two problems of global energy crisis and environmental degradation have become increasingly serious and have received widespread attention from society.Fuel cells have the advantages of high conversion efficiency,high power density,quiet operation and no pollution,which could solve energy shortages better.Catalytic Wet Air Oxidation（CWAO）is one of the most economical and environmentally friendly advanced oxidation processes.Carbon materials are ideal for the preparation of catalysts with wide availability,environmental acceptability,corrosion resistance and unique surface properties.However,due to the poor electrochemical performance of carbon materials and the high cost of precious metals,it has become a research hotspot to increase the electrochemical activity of materials by loading transition metals on carbon materials in recent years.In this work,cobalt and nitrogen co-doped reduced graphene oxide（Co-N-rGO）composites are prepared by a facile low-temperature hydrothermal method.Structure characterization reveals that cobalt and nitrogen are co-ordinately attached to the rGO sheets with the formation of covalent C-N and Co-O-C linkages.Cyclic voltammetry and linear sweep voltammetry show that the Co-N-rGO composite possesses higher electrocatalytic activity and four-electron selectivity for oxygen reduction reaction（ORR）as compared to the rGO,Co-rGO and N-rGO.In addition,the Co-N-rGO composite presents excellent stability and durability in alkaline medium comparable to commercial Pt/C.The strong covalent linkages between the cobalt/nitrogen and rGO not only enable potent synergy of cobalt,nitrogen and rGO in catalysis,but also ensure structure stability of the composite.Due to the superior ORR activity of Co-N-rGO,high-temperature heat treatment is not able to improve its activity any more.The low-temperature hydrothermal method is anticipated to be used as a low-cost and facile preparation approach for ORR catalysts,and the superb ORR performance of Co-N-rGO endow it with great application potential in fuel cells,metal-air batteries and other ORR-related electrochemical industries.Oxygen in air is an eco-friendly and economical oxidant,and catalytic wet air oxidation technology have a great potential to sustain effective wastewater treatment.A new Ni@NiO/GF composite cathode material is prepared by loading Ni@NiO on porous graphite felt for catalytic wet air oxidation system by the impregnation method.Such a process demonstrates effectiveness in degrading dyes over a wide pH range at low energy consumption.The average total organic carbon（TOC）removal rate of0.375 mg TOC h^-1 and specific energy consumption of 0.0763 kW h（kg-TOC）^-1 are obtained when the process is applied to treat the 100 mg L^-1 rhodamine B（RhB）.The high RhB degradation efficiency is attributed to the huge adsorption capacity of Ni@Ni/GF composite towards RhB as well as the superior catalytic activity of Ni@NiO towards the oxidation of RhB by oxygen（O₂）.The RhB is degraded at the Ni@Ni/GF composite cathode through a non-radical pathway,such a pathway enables effective pollutant degradation at low energy input,which endows the cathodic air oxidation process with economical advantage as compared to EF or EF-like processes following free radical pathway.