Highly durable photoelectrochemical H2O2 production via dual photoanode and cathode processes under solar simulating and external bias-free conditions

Abstract

This study demonstrated efficient solar-to-H₂O₂ conversion through a photoelectrochemical (PEC) cell that maximizes the utilization of solar energy by having double side generation of H₂O₂ on both the photoanode and cathode. This work was accomplished by preparing (i) efficient BiVO₄ (BVO) photoanodes modified with various metal dopants (Mo, W, or Cr), (ii) surface-treatment with phosphate on the as-synthesized photoanodes, and (iii) single-walled carbon nanotube (CNT) electrodes with anchored anthraquinone (AQ-CNT), a reversible H₂O₂-evolving catalyst that has been widely used in the H₂O₂ production industry. The introduction of Mo into BVO and surface phosphate treatment on BVO (P-Mo-BVO) enhanced the faradaic efficiency (FE) of H₂O₂ production from water oxidation and slowed the H₂O₂ decomposition kinetics with achieving highly durable PEC reactions over 100 h (90% photocurrent remained), while bare Mo-BVO experienced the rapid decline of the photocurrent during irradiation with the dissolution of BiVO₄. The utilization of AQ on the cathode made the H₂O₂ production by oxygen reduction highly selective and suppressed competing H₂ production completely. Consequently, the optimized configuration of a BVO photoanode modified with Mo (10 atom%) and phosphate and an AQ-CNT cathode enabled H₂O₂ production on both electrodes, yielding H₂O₂ production with FE values of 40–50% and ∼100%, respectively, across a broad range of potentials (0.75 to 2 V_RHE) and a net H₂O₂ production rate of 0.66 μmol min⁻¹ cm⁻² at 1.0 V_RHE. This dual electrode system also successfully demonstrated H₂O₂ production under an external bias-free condition with a net H₂O₂ production rate of 0.16 μmol min⁻¹ cm⁻² and FE value of ∼43% and ∼100% for photoanodic and cathodic production, respectively. To the best of our knowledge, this is the most durable PEC system for H₂O₂ production obtained using a BiVO₄-based photoanode that enabled the simultaneous photoanodic and cathodic production of H₂O₂.