A Mechanistic Approach on Oxygen Vacancy-Engineered CeO2 Nanosheets Concocts over an Oyster Shell Manifesting Robust Photocatalytic Activity toward Water Oxidation

Lethargic kinetics is the foremost bottleneck of the photocatalytic water oxidation reaction. Hence, in this respect, the CeO₂ coral reef made up of nanosheets is studied focusing on the oxygen vacancy that affects the water oxidation reaction. First, CeO₂ was prepared in an oyster shell/crucible with the presence/absence of urea by a simple calcination technique to tune the oxygen vacancy. More oxygen vacancy was detected in CeO₂ prepared from urea and oyster shell, which is evidenced from Raman and PL analyses. Further, the oyster shell-treated sample was found to be of nanosheet type with numerous pores as observed via TEM analysis. The theoretical approach was adopted to expose the role of oxygen vacancies and the fate of scavenging agents in the water oxidation mechanism. It was observed that an oxygen vacancy plays a vital role in minimizing the activation energy hump and opposes the reverse reaction. The apparent conversion efficiency of 7.1% is calculated for the oxygen evolution reaction. Oxygen vacancy, quantum confinement effect, and charge separation efficiency are mainly responsible for the better photocatalyzed water oxidation reaction and hydroxyl radical production. This investigation will help in providing valuable information toward designing cost-effective oxygen vacancy-oriented nanosheet systems and the importance of vacancy in the water-splitting reaction.