Preparation And Catalytic Performance Of Cobalt-based Catalysts Toward Hydrogen Production At High Current Density

Hydrogen production from electrolytic water is a potential green hydrogen production technology.In order to further reduce the cost and improve the efficiency of hydrogen production,it is necessary to develop electrocatalysts that can realize high current density cathode hydrogen evolution reaction（HER）and anode oxygen evolution reaction（OER）under low overpotential.The results show that Co based catalysts have high catalytic properties of HER and OER,low cost,simple preparation and easy to regulate the active structure.Therefore,it is expected to replace precious metal electrocatalysts.However,it is difficult for a single co active species to achieve high current density HER and OER at low overpotential.Therefore,effective strategies are urgently needed to improve its active structure and enhance its catalytic performance.In this paper,the original active structure of Co based catalyst was regulated by alloying,compounding and forming bimetallic compounds,and HER and OER with high current density under low overpotential were successfully realized.The main research content of this paper includes the following three aspects.（1）Co/Ni alloy@CNT was obtained by alloying CO with Ni and combining Co/Ni alloy with carbon nanotube（CNT）and Melamin（ME）,which was used as HER and OER bifunctional catalyst.It is found that CO/Ni alloying exposes more active sites and improves the electrochemical active area;At the same time,the existence of CNT greatly improves the charge transfer efficiency.The overpotential required to achieve her current densities of 10 and 1000 m A cm^-2 in 1 M KOH with the promotion of optimized sample Co/Ni（1:1）@CNT(η_10-HER andη_1000-HER)are 96 and393 m V respectively;Over potential required to achieve OER current densities of 10 and 500 m A cm^-2(η_10-OER andη_500-OER)are 345 and 498m V,respectively.（2）A series of ZIF-67（1:X）Fe（1:Y）electrocatalysts were obtained by calcining ZIF-67 after Fe ion exchange in air atmosphere.It is found that they are composite oxides composed of Co₃O₄ and various Fe oxides（Fe₂O₃,Fe₃O₄or Co Fe₂O₄）.Among them,the optimized sample is ZIF-67（1:4）Fe（1:1）.Under its promotion,in 1 M KOH,η_10-HERis 76 m V,η_1000-HER is 381 m V;η_10-oer is 295 m V,η_500-oer is 375 m V.The high efficiency and bifunctional catalytic performance of the sample is attributed to its maximum electrochemical active area and minimum charge transfer resistance.（3）Cobalt manganese bimetallic oxide was obtained by citric acid method and modified with urea and calcined in air.Although the Co/Mn ratio was adjusted,the products were（CO,Mn）（CO,Mn）₂O₄ with tetragonal spinel structure.Although the crystal structure is similar,the different ratio of CO/Mn optimizes the surface active components suitable for HER or OER reaction.Among these catalysts,The HER catalytic performance of urea-Co Mn（2:1）500 is the most outstanding,while urea-Co Mn（1:1）500 has the best OER catalytic performance.In the former,η_10-HER is 177 m V,η_1000-HER is 414 m V.What the latter hasη_10-OER is 308 m V,η_500-OER is 471 m V.