Role of CoO_x cocatalyst on Ta₃N₅ photocatalysts studied by transient visible to mid-infrared absorption spectroscopy

Tantalum nitride (Ta₃N₅) photocatalysts attract considerable attention owing to their visible light absorption below 600 nm and suitable band structures for reduction and oxidation of water to generate hydrogen and oxygen gas. Herein, we investigated the effects of CoO_x on the dynamics of photogenerated charge carriers in Ta₃N₅ powder photocatalysts by using microsecond to millisecond transient visible to mid-IR absorption spectroscopy. Transient absorption measurements revealed that most of the electrons in Ta₃N₅ are deeply trapped at the defects, most likely originating from oxygen vacancies and reduced Ta species. Two important roles of CoO_x were elucidated: effective capture of holes to prolong electron lifetime and reduction of defects as recombination centers, which further elongates the lifetime of both electrons and holes.