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

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.