Boosted scavenger-free photocatalytic H2O2 production over alkali-doped poly(heptazine imide) under controlled solution conditions

Abstract

Photocatalysis renders appealing mechanisms for synthesizing hydrogen peroxide (H2O2) under ambient conditions; however, it still suffers from low efficiency due to the high kinetic barriers, low reaction selectivity, and severe recombination of photo-generated charge carriers. This study contributes to establishing a fundamental understanding of the influence of the solution environment, specifically the solution pH, on the photocatalytic performance of H2O2 production. By adjusting the solution environment from neutral to alkaline, the photocatalytic system, consisting of a prototype photocatalyst of alkali-doped poly(heptazine imide), exhibited a 9-fold increase in the production of H2O2, with an unprecedented rate of 6.78 gcat−1h−1. Mechanistic studies demonstrate that alkaline conditions can trigger the rarely occurring two-electron water oxidization, thus enabling H2O2 formation through both the oxygen reduction reaction and water oxidization pathways simultaneously. Moreover, the high pH condition also plays an important role in shifting the band edge of the photocatalyst and alleviating the photocatalytic decomposition of H2O2. These fundamental insights may provide guidelines for the development of superior photocatalytic systems.