Benzenehexathiol-Based Conductive Two-Dimensional Metal–Organic Frameworks as HER Cocatalysts for Photocatalytic Overall Water Splitting: Influence of the Metal Center

Abstract While overall water splitting (OWS) based on particulate photocatalysts is a promising method for green hydrogen production, conventional hydrogen evolution reaction (HER) cocatalysts have the drawback of inducing unwanted side reactions related to oxygen, such as the oxygen reduction reaction (ORR), which reduces the OWS efficiency. In the present study, a series of conductive two-dimensional metal–organic frameworks based on benzenehexathiol (MBHT, M = Co, Ni, Cu) was applied as an HER cocatalyst to Al-doped SrTiO3 (SrTiO3:Al) photocatalyst, and the effect of the central metal on the cocatalyst activity was evaluated. After single-phase synthesis and subsequent loading of miniaturized MBHT on SrTiO3:Al, CoBHT afforded the highest OWS activity, achieving an apparent quantum efficiency of 7.2% at 365 nm. Furthermore, CoBHT on SrTiO3:Al boasted of stability after 20 h of operation. Electrochemical measurements and DFT calculations revealed that CoBHT exhibited good HER electrocatalytic activity while possessing reaction selectivity suitable for HER cocatalysts or inherent inertness to ORR. This series of features enabled CoBHT to drive stable OWS operation over SrTiO3:Al without an oxygen barrier layer that is essential for conventional HER cocatalysts.