Potassium ions and cyano group modified g-C₃N₄ for effective generation of H₂O₂ through two-electron oxygen reduction

Potassium ions (K⁺) doped graphitic carbon nitride (g-C₃N₄) was prepared by a thermal etching method using potassium hydroxide (KOH) as an ion source. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that the generation of the cyano group was detected while introducing K⁺. Under simulated sunlight irradiation, the sample with a K⁺ doping amount of 10% showed the highest hydrogen peroxide (H₂O₂) generation rate of 2,140.2 µmol h⁻¹ g⁻¹. The apparent quantum yield (AQY) at 400 nm and the solar-to-chemical conversion (SCC) are 4.35% and 1.23%, respectively. K⁺ acted as a bridge between g-C₃N₄ layers, which enhanced charge transfer efficiency. Meanwhile, the cyano group enhanced the adsorption capacity of protons (H⁺) and promoted the yield of H₂O₂. The catalyst exhibited excellent photocatalytic stability based on four-cycle experiments. In addition, a mechanism study showed that superoxide radicals (·O₂⁻) were the most important active species in the reaction system. Photocatalytic production of H₂O₂ was achieved through consecutive single-electron steps. This study deepens the understanding of the oxygen reduction reaction process and opens up a new venue for improving H₂O₂ generation.