Development of a Deposition Method of IrO _x Cocatalysts on SrTaO₂N Photocatalysts for Higher Oxygen Evolution Activities under Visible-Light Irradiation

The conversion of solar energy to chemical energy for storage is key to achieving a zero-emission society. To this end, hydrogen production from particulate photocatalysts, such as SrTaO2N (STON), through sunlight-induced water splitting is a promising solution. In this study, we report an effective method for loading Ir-based cocatalysts onto STON photocatalysts. The IrOx-modified STON particles exhibit an oxygen evolution activity with an apparent quantum efficiency of over 10% in an AgNO3 solution, which has previously not been achieved. In addition, it was determined that a high temperature of 1173 K for cocatalyst loading effectively improves the oxygen evolution rate. Furthermore, IrOx modification of STON particles by the adsorption method accompanied by high-temperature annealing under an ammonia flow affords a higher photocatalytic activity and improved reproducibility compared with those of STON particles synthesized via the conventional impregnation method owing to homogeneous loading. Our results should be useful for increasing the photocatalytic activity by developing fine cocatalyst/photocatalyst structures