Alkali metal cation adsorption–induced surface polarization in polymeric carbon nitride for enhanced photocatalytic hydrogen peroxide production

Photocatalytic hydrogen peroxide (H 2 O 2 ) generation on the catalyst surface from oxygen is an electron-demanding process, making the construction of an electron-rich surface highly advantageous. In this study, a localized electric field was observed on the surface of polymeric carbon nitride (g-C 3 N 4 ) when alkali metal cations were adsorbed onto it. These fields effectively inhibited surface carrier recombination and extended their lifespan, thereby enhancing H 2 O 2 production. As a result, g-C 3 N 4 achieved a superior H 2 O 2 yield of 2.25 mM after 1 h in a 0.25 M K + solution, which was 2.06 times greater than that (1.09 mM) achieved in a pure solvent. Notably, the increase in photocatalytic efficiency showed a remarkable dependence on ion species. At low concentrations, H 2 O 2 generation efficiency was in the order of Li +  < Na +  < K +  < Rb +  < Cs + . However, after optimizing the ion concentration, the highest H 2 O 2 production was achieved in a solution containing K + instead of Cs + . Molecular dynamics simulations and temperature-dependent photocatalysis experiments revealed that the synergistic interaction between adsorption energy and adsorption distance was crucial in governing the extent to which alkali metal cation adsorption enhanced g-C 3 N 4 photocatalytic H 2 O 2 production. This study provides theoretical insights for the design of materials for electron-demanding photocatalysis and aids in understanding variations in photocatalytic behavior in natural waters.