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 CeO 2 with a back‐to‐back geometry and fully separated oxidizing and reducing phases is reported. The prepared CeO 2 is composed of nanosheets with two contrasting smooth and rough surfaces. Experimental and theoretical results indicate that the rough surface contains more highly reducing CeO 2 {220} and strongly visible‐light‐absorbing CeO 2 {200} facets than the smooth surface. The 2D homojunction CeO 2 produces three‐times more hydrogen than normal CeO 2 nanosheets, and even more than that of CeO 2 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.