Preparation Of Cobalt-based Composites Catalyst And Their Electrochemical Behaviors

The growing demand for energy has stimulated great interest in novel renewable energy conversion and storage systems.Oxygen reduction reaction（ORR）on the cathode plays a decisive role in the fuel cell,while oxygen evolution reaction（OER）on the anode is an important reaction for water splitting and fuel synthesis.However,both reactions are complex multi-electron transfers,which result in slow kinetics.Therefore,bifunctional catalysts with high activity for ORR and OER are required in renewable energy technologies such as metal-air batteries,fuel cells,and water splitting devices,and the exploitation of new electrocatalysts is pivotal to future development in these fields.At present,the high efficient electrocatalysts for ORR and OER are precious metals such as Pt,Ir and Ru.However,the scarcity of these materials hinders their large-scale applications.Moreover,the stability of noble-metal based catalysts is poor.Thus,it is urgent to find high-effective and stable bifunctional catalysts based on non-precious metals.Various non-noble metal materials,such as oxides,sulfides,and selenides,exhibit good catalytic activity towards ORR and OER.In this paper,cobalt-based composite catalysts were prepared.Then the electrochemical tests were carried out to evaluate the oxygen-involving bifunctional performance of the catalysts.The main contents are as follows:Firstly,the precursor is obtained by hydrothermal method,and then the precursor and sulfur powder are calcined with a certain proportion at low temperature to obtain the CoS/CoO heterostructure catalyst of porous nanosheet.CoS/CoO is characterized by SEM,TEM and BET,the results of which disclose the porous characteristics of CoS/CoO with large specific surface area.By using XPS,it can be obtained that the valence state of Coin CoS/CoO was Co（Ⅱ）.Besides,the strong interaction between CoS and CoO can be observed.Electrochemical test results show that the ORR and OER activity of CoS/CoO are higher than that of individual CoS and CoO.Moreover,CoS/CoO shows good stability.The bifunctional potential difference is calculated to be0.73 V,which is lower than that of CoS and CoO.The main reasons for the enhanced electrocatalytic activity of CoS/CoO are as follows:1.Large specific surface area can expose more active sites;2.The synergistic effect between CoS and CoO.Secondly,precursor and polymer with glucose are synthesized under hydrothermal conditions sequentially.Then the polymer is calcined at high temperature to obtain the intermediate product,which is the cobalt nanoparticles coated by carbon film with 3D structure（Co@GC）.Then the intermediate product and sulfur powder are placed together in the tube furnace to calcinie,the product of which is the sandwich-like carbon film coated CoS₂ nanoparticles,denoted as CoS₂@GC.Experimental results show that the catalytic performance of OER and ORR of CoS₂@GC is significantly higher than that of unvulcanized Co@GC.Under alkaline conditions,CoS₂@GC exhibits the higher half-wave potential than Pt/C（～10 m V）,the limiting diffusion current density is-5.54m A cm^-2 with a 4 e^-ORR pathway.As for OER tests,the overpotential is small（～330m V）at current density of 10 m A cm^-2.The bifunctional potential difference of CoS₂@GC is 0.65 V.Therefore,the Co-based composite obtained by simple method with high activity and stability can be used as alternative to precious metals.