Photo‐induced Intercalation of Cobalt(II) Tellurium Oxide as an Oxygen Evolution (Photo)electrocatalyst

Abstract Herein, we report on (a) the application of cobalt(II) tellurium oxide (Co 3 TeO 6 ) as a photo‐electrocatalyst, to enhance the photo‐electrocatalytic (PEC) oxygen evolution reaction (OER) in alkaline media, compared to the electrocatalytic (EC) OER (in the absence of light), and (b) to store charge upon illumination and release charge upon the termination of illumination under OER potential bias conditions. These nanomaterials were synthesized employing the sol‐gel method and calcined at temperatures ranging from 400 to 1100 °C. They were physically characterized and tested for their capacity to (i) act as a catalyst towards the OER, under EC and PEC conditions, and (ii) to convert and store light‐energy as chemical‐energy. Under PEC conditions CTO‐900, which predominantly consisted of Co 3 TeO 6 , exhibited a five‐fold increase in activity compared to EC conditions as current density increased from 0.58 mA cm −2 (EC) to 3.10 mA cm −2 (PEC) at 1.8 V ( vs . RHE). Additionally, CTO‐900 displayed the ability to not only store charge (upon illumination), but to also release this stored charge (after the termination of illumination), realising a current density of 2.07 mA cm −2 in the dark (under OER potential bias conditions). Photo‐induced charge storage is due to the intercalation of potassium ions into Co 3 TeO 6 .