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

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 O-2/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 O-2 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 O-2 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).