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

## TL;DR

A new sensor-based method enables real-time tracking of hydrogen and oxygen during water splitting, improving understanding of the process for green hydrogen production.

## Contribution

A modular photoreactor platform with in situ H2 and O2 sensors for simultaneous real-time measurements during water splitting is introduced.

## Key findings

- The method allows for real-time detection of H2 and O2 in both liquid and gas phases.
- The study determines the irradiance dependence and thermal activation barrier for Rh2−yCryO3/Al:SrTiO3.
- Optimal cocatalyst loading and H/D kinetic isotope effect were identified using the new method.

## Abstract

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 Rh2−y
Cr
y
O3/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.

A photoreactor setup allowing for simultaneous in situ detection of H2 and O2 in the liquid as well as gas phase is described. Using this system, overall water splitting with Rh2−y
Cr
y
O3/Al:SrTiO3 is investigated, determining irradiance dependence, thermal activation barrier, optimal cocatalyst loading, and H/D kinetic isotope effect.© 2026 WILEY‐VCH GmbH