Bimetallic Cobalt-Copper MOF Material for Bifunctional Oxygen Electrocatalysis

Abstract

Recently, metal organic frameworks (MOFs) have garnered wide attention for their ability to efficiently and effectively catalyze reactions such a water oxidation, which includes oxygen evolution reactions (OER) and hydrogen evolution reactions (HER), and oxygen reduction reactions (ORR). Still MOFs often suffer from low conductivity, small pore size and organic linkers can often block the active metal centers. However, MOFs can be tailored to overcome these deficiencies by modifying their active metal centers and organic linkers that that can allow MOFs to have: 1. highly porous structure for enhanced diffusion, 2. high surface area 3. improved adsorption of reactants, 4. chemical stability, 5. thermal stability and 6. high conductivity.1,2,3 These attributes aid in enhancing electrocatalytic performance of this material. In addition, the facile synthesis, robust nature and use of abundant materials that are inexpensive, such as transitional metals and organic ligands, help make MOFs a promising material to use for electrocatalysis of water oxidation and oxygen reduction reactions. In this study a bimetallic MOF was synthesized via a solvothermal method using cobalt chloride, copper chloride and 2-aminobenzene-1,4-dicarboxylic acid. Cobalt and copper were chosen as metal ion centers because of their low cost in comparison to conventional noble metals, their known catalytic activity towards ORR and OER in both alkaline and acidic media, and the complexes they form with 2-aminobenzene-1,4-dicarboxylic acid that lead to octahedral structures, heterogeneity in the MOF and unsaturated coordination in active metal sites.2,3 The resulting bimetallic MOF material formed a petal like morphology that showed catalytic activity both towards ORR and OER in an alkaline environment, with a half way potential 0.76 V versus RHE for ORR in 0.1 M KOH and an overpotential of 0.31 V at 10 mA/cm2 versus RHE for OER in 1 M KOH. Making this Cu-Co MOF material a potential bifunctional electrocatalyst electrode material for applications in regenerative fuel cells and metal-air batteries.