High-speed analysis of oxygen evolution kinetics using microamperometry: application to a SrTiO3 photocatalyst sheet

• Microamperometry speeds up the kinetic analysis of photocatalytic oxygen evolution. • A half-day experiment to measure the evolution rate under seven light intensities. • Future application to assessment of minimal oxygen production. Photocatalytic water splitting for hydrogen production is a cornerstone of clean energy technology. However, rapidly and accurately evaluating the rate of oxygen evolution remains a bottleneck in material development. This study proposes a combination of microamperometry and light pulse trains to enable high-speed analysis of the oxygen evolution kinetics. A half-day experiment was sufficient to determine the dependence of the evolution rate on a SrTiO 3 photocatalyst sheet with seven light power densities ranging from 0.57 to 75 W m −2 . A 1/2-order rate law for oxygen evolution was observed at light power densities greater than 14 W m −2 . The random movement and recombination of excited electrons and holes limited the water splitting yield, resulting in the 1/2-order rate law. With smaller power densities, the kinetic order shifted to unity. This shift may affect the water-oxidation yield under natural sunlight, as the power density of UV light on the ground falls in the order of 10 W m −2 . The rate of oxygen evolution was further quantified in solutions with varying oxygen content in a range of 0.02–0.22 mmol l −1 . The presence of oxygen at 0.05 mmol l −1 negatively affected oxygen evolution. The backward reaction of water splitting likely caused the negative effects observed in the O 2 -rich solutions. The key concept demonstrated here, reducing the physical distance between the reaction and detection sites in liquid, will be useful to quickly observe the kinetics of many other reactions at liquid–solid interfaces.