Spin State Modulation on Metal-Organic Frameworks for Electrocatalytic Oxygen Evolution.

Electrochemical oxygen evolution reaction (OER) kinetics are heavily correlated with hybridization of the transition metal d-orbital and oxygen intermediate p-orbital, which dictates the barriers of intermediate adsorption/desorption on the active sites of catalysts. Herein, w e develop a strategy involving strain engineering and coordination regulation to enhance the hybridization of Ni 3d and O 2p orbitals, and the as-synthesized Ni-2,6-naphthalenedicarboxylic acid metal-organic framework (DD-Ni-NDA) nanosheets delivered a low OER overpotential of 260 mV to reach 10 mA cm -2 . By integrating an alkaline anion exchange membrane electrolyzer and Pt/C electrode, 200 and 500 mA cm -2 current densities w ere reached with cell voltages of 1.6 and 2.1 V, respectively. When loaded on BiVO 4 photoanode, the nanosheet enables highly active solar-driven water oxygen. Structural characterizations together with theoretical calculations reveal that the spin state of centre Ni atoms is regulated by tensile strain and unsaturated coordination defects in DD-Ni-NDA, and such spin regulation facilitates spin-dependent charge transfer of the OER. Molecular orbital hybridization analysis reveals the mechanism of OH* and OOH* adsorption energy regulation by changes in DD-Ni-NDA spin state, which provides a deeper understanding of the electronic structure design of catalysts for the OER. This article is protected by copyright. All rights reserved.