Photocatalytic Production of over 2 wt % Hydrogen Peroxide Solution via Potassium-Ion Regulation of Nitrogen-Rich Carbon Nitride.

Photocatalytic hydrogen peroxide (H2O2) generation represents a green pathway to produce H2O2, but currently its application is significantly limited by the low accumulated H2O2 concentration. Due to the metastable nature of H2O2, an ideal photocatalyst should possess excellent optoelectronic properties for fast H2O2 generation and a suitable surface to prevent H2O2 decomposition by photogenerated charge carriers. In this work, we have developed an efficient photocatalyst based on nitrogen-rich carbon nitride (C3N5). Potassium ion (K+) was applied to modify the electronic structure and surface properties of C3N5 to improve its H2O2 accumulation concentration. It shows that K+ can lower exciton binding energy and extend the lifetime of photogenerated charge carriers. A more stable *OOH intermediate is formed on KC3N5, with the O2 adsorption configuration changed from the Yeager type to the Pauling type on KC3N5. As a result, KC3N5 shows a selectivity of 97.2% for H2O2 generation pathway, achieving a H2O2 production rate of 44.2 mmol h-1 g-1 with an apparent quantum yield (AQY) of 89.3% at 420 nm. More impressively, after 16 h of continuous reaction, the H2O2 concentration reaches 656.8 mM (2.2 wt %), a concentration close to medical-use requirements. The findings provide a strategy for practical photocatalytic H2O2 production by regulating both excitonic properties and O2 adsorption behavior in photocatalysts.