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

Photocatalytic hydrogen peroxide (HO) 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-CN) when alkali metal cations were adsorbed onto it. These fields effectively inhibited surface carrier recombination and extended their lifespan, thereby enhancing HO production. As a result, g-CN achieved a superior HO 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, HO generation efficiency was in the order of Li < Na < K < Rb < Cs. However, after optimizing the ion concentration, the highest HO 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-CN photocatalytic HO 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.