Spatially charge-separated 2D homojunction for photocatalytic hydrogen production

Suppression of photogenerated charge recombination is crucial for efficient photocatalytic hydrogen production. Homojunctions have garnered more attention than heterojunctions due to their superior crystal binding and band structure matching. However, most homojunctions suffer from redox interference caused by continuous oxidizing and reducing phases that impede the ability to improve photocatalytic activity. Consequently, the preparation of homojunction photocatalysts with completely spatial separation of both in charge and redox phases remains challenging. Here, the preparation of a two-dimensional (2D) homojunction CeO₂ with a back-to-back geometry and fully separated oxidizing and reducing phases is reported. The prepared CeO₂ is composed of nanosheets with two contrasting smooth and rough surfaces. Experimental and theoretical results indicate that the rough surface contains more highly reducing CeO₂{220} and strongly visible-light-absorbing CeO₂{200} facets than the smooth surface. The 2D homojunction CeO₂ produces three-times more hydrogen than normal CeO₂ nanosheets, and even more than that of CeO₂ nanosheets loaded with gold nanoparticles. This work presents a new homojunction photocatalyst model with completely spatial separation of both in charge and redox phases that is expected to inspire further research into homojunction photocatalysts.