Energy bands matched photocatalysis enhancement based on viologen derivatives electron-transfer-mediator

Abstract

The photocatalytic H₂ evolution reaction (HER) is an important strategy for solar energy storage. Photogenerated electron transfer is the rate-limiting step in the whole photodriven H₂ evolution process. Viologen derivatives could act as electron transfer mediators (ETMs) to enhance the electron transfer rate from photosensitizer to proton reduction sites. Viologen derivatives with non-conjugated substituent groups sharply promoted photocatalytic HER performance under covalent triazine framework (CTF) model photosensitizer catalysis. Whereas viologen derivatives with conjugated substituent groups decreased the photocatalytic HER kinetics. Viologen derivatives with non-conjugated substituent groups had stronger electron capturing ability and could be easily reduced to a diradical state for proton reduction. o-CTF coupled with 1 wt% Pt co-catalyst and 2 wt% 1,1′-bis(4-carboxybenzyl)-[4,4′-bipyridine]-1,1′-diium bromide (CBV) ETM yielded a 246.8 μmol h⁻¹ H₂ evolution rate, which is 17.76 times higher than that of pure o-CTF and 2.19 times higher than that of an o-CTF + 1%Pt system.