Multi-phase real-time monitoring of oxygen evolution enables in operando water oxidation catalysis studies

Understanding the reactivity of water oxidation catalysts (WOCs) is critical for designing advanced materials for sustainable energy technologies. Here, we show how optical oxygen sensors based on fluorescence quenching enable the simultaneous real-time in operando monitoring of O 2 evolution in solution and in the gas phase, thereby opening new avenues for advanced mechanistic studies under true operating conditions. The advantages of the system are demonstrated by rationalizing and overcoming reactivity limitations of two prototype molecular WOCs.