Insights Into Overall Photocatalytic Water Splitting Through Simultaneous In Situ H₂ and O₂ Measurements

Photocatalytic overall water splitting is a promising pathway to produce green hydrogen but also presents unique research challenges due to the need to detect both gaseous products (H₂ and O₂). While gas chromatography (GC) is the most commonly employed method in this context, it faces multiple shortcomings: low time resolution as well as the need to alter the reaction conditions (vacuum or carrier gas flushing) to feed the products into the GC, which limits the extent to which obtained insights can be translated into scalable photoreactors (where H₂ and O₂ accumulate). Against this backdrop, we report a novel, sensor-based experimental method which allows for simultaneous in situ detection of H₂ and O₂ in both the liquid and gas phase. It is based on a standardized modular photoreactor platform and integrates optical O₂ and electrochemical H₂ sensors for real-time measurements during water splitting. Using this method, we investigate photocatalytic overall water splitting using Rh_2-yCr_yO₃/Al:SrTiO₃, determining the irradiance dependence, thermal activation barrier, optimal cocatalyst loading, and H/D kinetic isotope effect. This highlights the versatility of the described method as well as the depth of information that can be obtained through the in situ H₂/O₂ detection approach.