Polymeric viologen-based electron transfer mediator for improving the photoelectrochemical water splitting on Sb₂Se₃...

The photogenerated charge carrier separation and transportation of inside photocathodes can greatly influence the performance of photoelectrochemical (PEC) H₂ production devices. Coupling TiO₂ with p-type semiconductors to construct heterojunction structures is one of the most widely used strategies to facilitate charge separation and transportation. However, the band position of TiO₂ could not perfectly match with all p-type semiconductors. Here, taking antimony selenide (Sb₂Se₃) as an example, a rational strategy was developed by introducing a viologen electron transfer mediator (ETM) containing polymeric film (poly-1,1'-dially-[4,4'-bipyridine]-1,1'-diium, denoted as PV²⁺) at the interface between Sb₂Se₃ and TiO₂ to regulate the energy band alignment, which could inhibit the recombination of photogenerated charge carriers of interfaces. With Pt as a catalyst, the constructed Sb₂Se₃/PV²⁺/TiO₂/Pt photocathode showed a superior PEC hydrogen generation activity with a photocurrent density of -18.6 mA cm^-2 vs. a reversible hydrogen electrode (RHE) and a half-cell solar-to-hydrogen efficiency (HC-STH) of 1.54% at 0.17 V vs. RHE, which was much better than that of the related Sb₂Se₃/TiO₂/Pt photocathode without PV²⁺ (-9.8 mA cm^-2, 0.51% at 0.10 V vs. RHE).