Enhancing the electrocatalytic activity of metal–organic frameworks in the oxygen evolution reaction by introducing high-valent metal centers

Abstract

Metal–organic frameworks (MOFs) have tremendous potential as electrocatalysts for the oxygen evolution reaction (OER), but their performance is often limited by low intrinsic activity. In this study, we demonstrate a facile and effective strategy to promote the electrocatalytic activity of MOFs in the OER by introducing high-valent metal centers. We utilize microwave heating to synthesize a Ni-based conductive MOF (Ni–HHTP) with abundant Ni³⁺ centers, where HHTP refers to 2,3,6,7,10,11-hexahydroxytriphenylene. The resultant Ni³⁺–HHTP requires a small overpotential (136 mV) to produce a current density of 10 mA cm⁻², the performance exceeding that of Ni²⁺–HHTP and commercially available RuO₂ and IrO₂. Our study shows that Ni³⁺–HHTP has a larger electrochemical surface area and higher intrinsic activity in the OER compared to Ni²⁺–HHTP. Density functional theory calculations show that the high intrinsic activity of Ni³⁺–HHTP can be attributed to the modification of the rate-limiting step and the lower energy barrier. We also show that this strategy can be applied to Co–HHTP and Fe–HHTP, resulting in a higher content of high-valent metal centers and improved OER performance.