Metal carbide‐based cocatalysts for photocatalytic solar‐to‐fuel conversion

Semiconductor-based photocatalytic solar-to-fuel conversion has proven an appealing strategy for achieving carbon-neutral and green-hydrogen production. However, almost all semiconductors exhibit unsatisfactory photocatalytic performance due to insufficient surface-active sites, weak selectivity, and fast charge-carrier recombination. For these reasons, cocatalyst loading has become an encouraging strategy for improving photocatalytic activity and selectivity. Owing to the scarcity, and cost of noble metal-based cocatalysts, utilization of low-cost noble-metal-free cocatalysts, such as metal carbide-based cocatalysts, has aroused tremendous attention. This review highlights some recent crucial advances in active metal carbide-based cocatalysts for photocatalytic solar-to-fuel conversion. First, the fundamentals of metal carbide-based cocatalysts are presented, including the photocatalytic mechanism, advantages, drawbacks, and design rules. Second, three synthesis approaches of high-active metal carbide-based cocatalysts, namely constructing metal carbide nanostructures, epitaxial synthesis of metal carbides on nanostructured carbon, and crystal imperfection construction on metal carbides, are thoroughly addressed. Subsequently, applications of metal carbide-based cocatalysts in photocatalytic hydrogen production, CO2 reduction, and nitrogen reduction are further discussed. Finally, the crucial challenges and important directions of metal carbide-based cocatalysts for photocatalytic solar-to-fuel conversion are proposed. This review demonstrates some new options for rationally designing and developing novel and efficient metal carbide-based cocatalysts for highly active and selective photocatalytic solar-to-fuel conversion.