Polymer carbon nitride (PCN) is widely used in photocatalysis. However, pristine PCN has disadvantages such as insufficient visible light absorption and low photogenerated carrier separation efficiency that greatly limited the photocatalytic efficiency. As a non-toxic metal, gallium has the potential to solve the defects of PCN. Gallium ions coordinated with nitrogen in carbon nitride to form Ga-N active sites and improved the photocatalytic activity. The doped potassium ions form a transmission channel for charge redistribution and transfer between adjacent layers, which is beneficial for better separation of photoexcited carriers. In this study, a series of PCN co-doped with gallium and potassium (Ga-K-PCN) were prepared. The experimental results indicated photocatalytic generation of hydrogen peroxide proceeds through the 2e⁻ oxygen reduction reaction pathway. Notably, Nyquist plots and photocurrent results further proved that the presence of Ga-N sites and potassium ion doping could significantly improve the separation/transfer of intra-planar and interlayer charge carriers and thus enhance photocatalytic efficiency. The Ga10-K3-PCN photocatalysts promoted yield of H₂O₂, with reactivity at 28.2 μmol/(g·h) and solar-to-chemical conversion efficiency at 0.64%, surpassed that of a typical photo-catalyst based on PCN (0.18%).