Tandem Photoelectrochemical Cells for Hydrogen Peroxide With Glyceric Acid Production

While photoelectrochemical (PEC) oxygen reduction for hydrogen peroxide (H₂O₂) production offers a sustainable alternative to the energy-intensive and detrimental anthraquinone process for industrial production, continuous and stable long-term operation remains challenging due to sluggish charge transfer kinetics and poor corrosion resistance of the photoelectrode. Herein, we synthesized a heterojunction photocathode comprising CuO and W-doped CuBi₂O₄ decorated with Pd nanoparticles (Pd:CuO/W-CBO) for efficient and stable PEC H₂O₂ generation. The optimized photocathode achieves an average Faradaic efficiency exceeding 90% with a low onset potential of 1.08 V_RHE, enabling a stable operation for over 50 h at 0.7 V_RHE. The CuO overlayer effectively suppresses dissolution of Cu and Bi species, improving the stability of CuBi₂O₄-based photoelectrodes. More importantly, a bias-free PEC system utilizing the Pd:CuO/W-CBO photocathode and a Pt/TiO_x anode was constructed for simultaneous solar-driven H₂O₂ production and electrochemical glycerol oxidation to high-value chemicals. This unassisted system delivers a current density of 3.75 mA cm^-2 under one sun illumination. Further employing a large-scale photocathode (10 cm²) enables H₂O₂ and C₃ chemical production rates of 250.4 and 127.6 µmol h^-1, respectively. Regulating H₂O₂ permeation using an anion exchange membrane considerably enhances the selectivity to 56% for oxidation of glycerol to glyceric acid, markedly outperforming systems using proton/cation exchange membranes (∼20%). Additionally, the cathodically generated H₂O₂ enables rapid water disinfection, achieving >99.9% bacterial inactivation within 180 min. This work demonstrates a scalable PEC platform for stable concurrent solar-driven H₂O₂ generation and glycerol valorization while enabling energy conversion.