Designing vanadium-modified photocatalysts for HER and OER using visible and UV light

Abstract

Photocatalytic water splitting is a promising way to produce hydrogen, which could serve as an eco-friendly fuel produced from renewable energy sources like the sun. TiO2 is one of themost widely used photocatalysts, but it can only utilize UV light, which constitutes only a very small part of the whole spectrum of natural sunlight. To produce photocatalysts that utilize the solar spectrum more efficiently, it is necessary to modify TiO2 and make it visible light active. In this project, vanadium-modified TiO2 photocatalysts with 1 at%-, 5 at%- and 25 at%V were produced to investigate the role of V-species as a visible light absorber as well as their possible role as a co-catalyst. For V-concentrations of 5 at%- and 25 at%, the resulting catalystsconsisted of composites between TiO2 and V2O5 while no individual VOx compounds could be detected for the low-concentration 1 at%-samples. All of the samples showed an improved visible light absorption.The catalysts were tested for their photocatalytic activity towards OER and HER under UV light in order to investigate the ability of the V-species to act as a co-catalyst. Their role as a light absorber was analysed with HER experiments under visible light with the addition of Pt. All experiments were performed using a sacrificial agent for the respective complementary reduction and oxidation reaction. While none of the synthesized catalysts was active under UV light, the sample with 5 at% was able to produce hydrogen under visible light illumination, contrary to unmodified anatase. Due to the formation of a heterojunction between the two oxides, the V2O5 in the composite structure was able to act as a light absorber, transferring excited electrons into TiO2 where they could then react with protons to form H2.