Carbon quantum dots aqueous solution as electrolyte for H2O2 production based on photoelectrochemical water splitting

Abstract

Modulation of electrolyte to tailor the activity and selectivity for photoelectrochemical (PEC) water splitting has been long neglected. Herein, we boosted H₂O₂ accumulation on a BiVO₄ photoanode via PEC water oxidation in a series of carbon quantum dots (CQDs) aqueous solutions with aliphatic amino acids as precursors. Mott–Schottky measurements demonstrated CQDs solution can tune catalytic voltage location of the BiVO₄ substrate. Open circuit voltage decay (OCVD) demonstrated that the system can achieve efficient charge separation owing to the fabricated dynamic heterojunction between CQDs particles and BiVO₄ substrate. Owing to the energy gradient, water oxidation may occur on the more hydrophilic CQDs surface, which regulated H₂O₂ generation mediated by the formation of hydroxyl radicals (OH˙) from water, as evidenced by electron paramagnetic resonance (EPR). Assisted by a Clark electrode and linear sweep voltammetry, we evidenced that CQDs can efficiently retard H₂O₂ decomposition. Overall, H₂O₂ production was performed with a rate averaging 0.33 μmol min⁻¹ cm⁻² at 1.23 V with a Faraday efficiency (FE) of 93.5%, in which O₂ evolution was nearly completely suppressed. By contrast, the commonly used HCO₃⁻ electrolyte only afforded an H₂O₂ evolution rate of 0.032 μmol min⁻¹ cm⁻², corresponding to FE of 18.2%. Here, we executed PEC water oxidative H₂O₂ accumulation in CQDs solution directly, and the innovation can hopefully draw more attention to catalytic media for improving PEC performance.