A g-C3N4 based photoelectrochemical cell using O2/H2O redox couples

Abstract

Utilization of solar energy for electric power production provides a practical approach for partially solving the energy crisis and at the same time reducing environmental pollution. Here, we demonstrate a photoelectrochemical cell based on a g-C₃N₄ photocatalyst using O₂/H₂O redox couples, fabricated with iron(III) phthalocyaninate [Fe^III(Pc)Cl] mixed with g-C₃N₄ sprayed on carbon paper as the cathode and a nickel mesh (Ni mesh) coated with g-C₃N₄ as the anode. Under irradiation, g-C₃N₄ in the anode harvests photons and produces excited electrons and holes. The produced electrons transfer to the cathode by an external circuit and reduce O₂ near the cathode to H₂O₂, electrochemically catalyzed by g-C₃N₄ through two-electron, two-proton processes, while the produced H₂O₂ is further reduced by [Fe^III(Pc)Cl] to H₂O. The generated holes in the anode oxidize H₂O to H₂O₂ by two-electron, two-proton processes. The formed H₂O₂ can further be oxidized by the Ni mesh with O₂ generation. This photoelectrochemical cell achieves an open-circuit voltage of 0.91 V under AM 1.5G solar light (1 sun, 100 mW cm⁻²) in 0.1 M HCl under air atmosphere. The total solar to electric power efficiency of this cell is 0.146%. Additionally this cell can generate and store H₂O₂ (chemical energy) with the electrodes disconnected under light, where water oxidation photocatalyzed by g-C₃N₄ will occur on both the electrodes. By connecting the electrodes, the cell can be operated as a fuel cell using H₂O₂ as the fuel in the absence of sunlight with an area-specific capacity of 350 mC cm⁻² and a mass-specific capacity of 237 C g⁻¹.