Lattice Strain Induced by Linker Scission in Metal–Organic Framework Nanosheets for Oxygen Evolution Reaction

Abstract

For electrochemical energy conversion, highly efficient and inexpensive electrocatalysts are required, which are principally designed and synthesized by virtue of structural regulations. Herein, we propose a rational linker scission approach to induce lattice strain in metal–organic framework (MOF) catalysts by partially replacing multicoordinating linkers with nonbridging ligands. Strained NiFe-MOFs with 6% lattice expansion exhibit a superior catalytic performance for the oxygen evolution reaction (OER) under alkaline conditions; the overpotential is reduced to 230 mV (86.6 mV dec–1) from 320 mV (164.9 mV dec–1) for the unstrained NiFe-MOFs at a current density of 10 mA cm–2. Operando studies by using synchrotron radiation X-ray absorption and infrared spectroscopy identified the emergence of a key *OOH intermediate on Ni3+/4+ sites during OER, providing strong evidence that the Ni3+/4+ sites are the active sites and the formation of *OOH is the rate-limiting step. The first-principles calculations were performed to reveal the strain-induced electronic structure changes of the NiFe-MOFs and the Gibbs free energy profile during OER. It is found that the optimized Ni 3d eg-orbital facilitates the formation of *OOH, thus enhancing the OER performance of the strained MOFs.