Highly conjugated 2D COF/MOF composites for bifunctional electrocatalytic alkaline HER and OER with enhanced activity and stability

Abstract

Electrocatalytic water splitting, consisting of anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER), represents a promising renewable energy technology for producing ultra-high purity hydrogen through efficient energy conversion and storage. However, the practical implementation of this technology in alkaline environments is hindered by the sluggish kinetics of both HER and OER, which significantly limit water splitting efficiency.The development of highly active and stable alkaline HER/OER electrocatalysts is urgently needed yet remains challenging.In this work, we synthesized a novel two-dimensional (2D) highly conjugated COF/MOF composite (COF-C₄N/THQ-M) through a post-synthesis method. This method enables controlled growth of part of COF-C₄N at the edges of THQ-M MOF to prevent structural disintegration of THQ-M, consequently to enhance surface charge transfer efficiency and further to improve catalytic activity and stability. By regulating metal sites, COF-C₄N/THQ-Co and COF-C₄N/THQ-Co₂Fe₁ are proposed to be optimal alkaline HER electrocatalysts with an overpotential of 58 mV at -10 mA cm ^-2 and alkaline OER electrocatalyst with 314 mV at 10 mA cm ^-2 , respectively, superior to most of the reported non-precious metals electrocatalysts. The charge transfer characteristics and the pathways of alkaline HER and OER were calculated based on DFT calculations to reveal the synergistic mechanism of COF-C₄N and THQ-M. This work provides a novel idea for developing highperformance bifunctional electrocatalysts for alkaline water splitting applications based on hybrid highly conjugated COF/MOF systems.