Defects enriched carbon nitride sponge with high surface area for enhanced photocatalytic hydrogen evolution

The limited efficiency of traditional photocatalysts necessitates innovative solutions for sustainable hydrogen production. In this study, a three-dimensional (3D) sponge-like porous carbon nitride (SCN-x) was successfully synthesized using a novel method involving the removal of unstable organic frameworks. The resulting SCN-x exhibits a highly interconnected network structure and significantly higher surface area (116.5 m²/g), compared to normal pure carbon nitride (PCN). Furthermore, this method introduces significant defects into SCN-x, such as additional foreign oxygen atoms, which not only modulate its band structure but also provide more active sites at the defects. These features increase the number of photo-induced electron-hole pairs due to enhanced light absorption, and suppresses their recombination by enabling them to efficiently participate in the reaction with increased number of active sites. As a result, compared to PCN, the optimal SCN-0.5 sample exhibits 86.6 times higher photocatalytic hydrogen production rate under visible light irradiation, along with excellent stability and a high apparent quantum yield (AQY) of 5.8 % under 420 nm illumination. Furthermore, with additional calcination under air, the 2SCN-0.5 sample delivers a record-high hydrogen evolution rate of 1663.5 μmol∙h^-1∙g^-1 under natural sunlight irradiation. This work presents a novel method for preparing a metal-free photocatalyst by introducing significant defects and a high surface area, enabling efficient large-scale hydrogen production under natural sunlight.