Bimetallic metal-organic framework glass as a highly efficient bifunctional electrocatalyst for overall water splitting: the roles of metal sites

Metal-organic framework (MOF) glasses can be used as references to investigate the atomic structure-activity correlation of bimetallic electrocatalysts, considering their stable framework structure as well as well-defined active sites. In this work, a bimetallic MOF glass, a cobalt-based zeolitic imidazole framework with guest nickel ions (ZIF-62(Co)-Ni), is fabricated to study its bimetallic functions in oxygen and hydrogen evolution, using a simple dipping-melting-quenching approach based on the ZIF-62(Co) glassy behavior. We elucidate the specific roles of the host cobalt and guest nickel sites in these two electrocatalytic processes through in situ Raman analysis and density functional theory calculations. When generating oxygen, nickel sites facilitate the process by utilizing the hydroxyl spillover from the cobalt sites. However, when producing hydrogen, nickel sites dominate. This distinct bimetallic functionality enables the superior electrocatalytic performance of ZIF-62(Co)-Ni. The cell voltage for overall water splitting is as low as 1.74 V at a current density of 100 mA cm-2 and remains stable for over 200 h, outperforming most state-of-the-art bifunctional non-precious electrocatalysts. A bimetallic MOF glass, ZIF-62(Co)-Ni, is used to study its bimetallic functions in oxygen and hydrogen evolution. The cobalt and nickel sites provide unique functionality, resulting in superior water splitting performance.