Probing Photoelectrochemical Hydrogen and Oxygen Evolution at Individual Al:SrTiO₃/Rh_2-yCr_yO₃ Photocatalyst Particles

Particle-based photocatalysts for overall water splitting convert solar energy into hydrogen fuel without the use of any photovoltaic devices. As such they have the potential to revolutionize renewable energy production on Earth. While proven efficiencies have reached 1.1%, further improvements of photocatalyst technology depend on a better understanding of energy loss mechanisms on the individual particle level. Here, we conduct the first in operando photoelectrochemical measurements on individual micrometer-sized Al-doped SrTiO₃/Rh_2-yCr_yO₃ photocatalyst particles. We find that the photocatalyst particles behave mainly as water oxidation photoanodes reaching up to 0.5 mA cm^-2 at 0.8 V versus RHE and a photovoltage of ∼1.00 V under 4.7 mW cm^-2 ultraviolet illumination. This proves that charge separation in the unbiased Al:SrTiO₃/Rh_2-yCr_yO₃ catalyst is driven by a junction at the n-semiconductor-liquid contact. While O₂ is detected symmetrically around photocatalyst particles, uneven H₂ evolution profiles reflect an irregular Rh_2-yCr_yO₃ cocatalyst distribution. Additionally, the H₂ evolution activity varies significantly between different photocatalyst particles. This suggests that performance gains are possible by better controlling catalyst composition on the microscale.