Thermally Assisted Photoelectrochemical Water Splitting with Rh-Doped SrTiO ₃ Nanoparticle Photocatalysts

Solar-based water splitting using suspensions of photocatalyst nanoparticles could be an attractive means for the production of hydrogen but requires ∼10% solar-to-hydrogen efficiency for economic viability. Here we investigate the effects of increasing temperature on the rate of photoelectrochemical (PEC) hydrogen evolution reaction (HER) for photocathodes based on visible light absorbing SrTiO3 nanoparticles doped with Rh (SrTiO3:Rh) and a p-Si/SiO2/Cr/Pt Schottky metal-insulator semiconductor (Si-MIS) diode. We construct our PEC cells using Aquivion, a perfluorosulfonic acid ionomer, which facilitates temperature control. Under visible light illumination, we observe that the HER rate for Si-MIS decreases by approximately 6× when temperature is increased from 25 °C to ∼40 °C, while the rate for SrTiO3:Rh increases by a factor of 2× over the same temperature range. We also observe that under UV (365 nm) illumination the PEC rates for the SrTiO3:Rh nanoparticle photocathodes increase by ∼10×. The increase in PEC efficiency is consistent with our previous report of improved photocarrier transport in SrTiO3:Rh nanoparticles with increasing temperature, and points to the significance of using heat both as a tool for gaining mechanistic insights into the water splitting process and to improve its efficiency.