Carbon, nitrogen and phosphorus containing metal-free photocatalysts for hydrogen production: progress and challenges

Photocatalytic hydrogen production from water is a green and renewable path for solar fuel production. Hydrogen can be advantageously stored directly and burned without emission of deleterious CO and NOx gases. Photocatalysis therefore shows significant promise as a part solution to a sustainable and affordable energy supply in an era post-fossil fuels. Influenced by the Fujishima-Honda effect, significant advances in photocatalytic hydrogen production have occurred at the laboratory-scale. For wide adoption however, the photocatalysts will need to be made from earth-abundant materials, be stable and scalable from laboratory-to-large-scale, and have high conversion efficiency. In this regard, metal-free photocatalysts show practical promise in meeting these requirements. To foster research in materials design, here we critically review recent significant developments in metal-free photocatalysts consisting of carbon, nitrogen and phosphorus, and discuss how future large-scale hydrogen production via overall water-splitting could be accomplished economically.