Metal-Organic Frameworks with Assembled Bifunctional Microreactor for Charge Modulation and Strain Generation toward...

Two-dimensional metal-organic frameworks (MOFs) have served as favorable prototypes for electrocatalytic oxygen evolution reaction (OER). Despite promising catalytic activity, their OER reaction kinetics are still limited by the sluggish four-electron transfer process. Herein, we develop a ferrocene carboxylic acid (FcCA) partially substituted cobalt-terephthalic acid (CoBDC) catalyst with a bifunctional microreactor composed of two species of Co active sites and ligand FcCA (CoBDC FcCA). Benefiting from the ultrathin nanosheet structure, CoBDC FcCA catalyst exhibits an excellent OER performance with a low overpotential of 280 mV to reach 10 mA cm^-2 and a small Tafel slope of 53 mV dec^-1. Structure characterization together with theoretical calculations directly unravel the coordination for two species of Co active moieties with FcCA forming a microreactor of tensile strain, leading to a conversion of the Co spin from a high spin state (t_2g⁵e_g²) to an intermediate spin state (t_2g⁶e_g¹) to regulate antibonding states of Co 3d and O 2p orbital. In situ spectroscopic measurements for mechanistic understanding reveal that this CoBDC FcCA catalyst possesses an optimal OH* adsorption energy for propitious formation of O-O bonds in the OOH* intermediate, thus effectively decreasing the thermodynamic Gibbs free energy of the rate-determining step (O* → OOH*) to accelerate reaction kinetics for the whole OER process. When loaded on an integrated BiVO₄ photoanode as a cocatalyst, CoBDC FcCA enables highly active solar-driven oxygen production from water splitting.