Decoration of dual cocatalysts on ultra-thin carbon nitride for efficient H2O2 photosynthesis

Abstract

Photocatalytic O2 reduction using solar-driven photocatalysts has emerged as a more energy-efficient and environmentally benign approach for H2O2 synthesis compared to the traditional anthraquinone oxidation method. However, when water is used as the electron donor, the photocatalytic activity remains low, primarily due to the sluggish kinetics of the water oxidation reaction. Therefore, the addition of hole scavengers is typically required to facilitate the reduction of O2 to H2O2. In this work, we developed a dual-catalytic-site photocatalyst to improve water oxidation kinetics and enhance the overall efficiency of H2O2 production. The photocatalyst was constructed by co-depositing reduced graphene oxide (rGO) and cobalt oxide (CoOx) onto ultrathin graphitic carbon nitride (g-C3N4) nanosheets (~1.4 nm thick), which were prepared via a facile two-step thermal exfoliation method. The obtained rGO/g-C3N4/CoOx photocatalyst exhibited a dramatically H2O2 production rate in the absence of a sacrificial agent, 6.4, 2.1 and 1.8 times higher than that of pristine g-C3N4 and samples modified solely with either rGO or CoOx, respectively. Using only water and O2 as reactants, the rGO/g-C3N4/CoOx achieved efficient H2O2 generation with an apparent quantum yield (AQY) of 12.2% at 420 nm and a solar-to-chemical conversion (SCC) efficiency of 0.63%. Photoluminescence studies revealed that the enhanced photocatalytic activity originated from facilitated charge separation and transfer in the g-C3N4. The rGO accelerated electron transport and the subsequent oxygen reduction reaction, while CoOx enhanced hole transfer, effectively promoting water oxidation. This study highlights the effectiveness of dual-catalytic-site engineering as a promising approach for developing highly active photocatalysts for solar-driven H2O2 synthesis from only water and O2.