(22a) Photoelectrochemical Water Splitting by p-Type Copper Oxide Photocathodes Made Via Scalable Processes

A scalable method for hydrogen generation by splitting water via a photoelectrochemical cell was studied. Flame spray pyrolysis and spin coating processing methods were used for preparing copper oxide nanoparticles and copper oxide photocathodes. Copper oxide p-type semiconductor nanoparticles made by flame spray pyrolysis were spin coated on conducting ITO substrate and served as photocathodes for photoelectrochemical splitting of water. The film thickness was controlled by the concentration of the CuO suspension solution and numbers of layer deposited on the substrate. As sintering temperature set to 600 ^oC, crystalline diameter increased from 28 nm (before sintering) to 110 nm and the bandgaps decreased from 1.68 eV to 1.44 eV. A 387 nm thickness CuO film with bandgap 1.44 eV was demonstrated to have 1.48% total conversion efficiency and 0.91% photon-to-hydrogen generation efficiency. The photocurrent density was measured to be 1.20 mA/cm² at applied voltage of -0.55 V vs. Ag/AgCl in 1 M KOH electrolyte. Based on the Mott-Schottky plot, the carrier density was estimated to be 6.2×10²¹ cm^-3 and the flatband potential to be 0.23 V vs. Ag/AgCl. Furthermore, the valence band edge and conduction band level was found to lie at -5.00 eV and -3.66 eV respect to the vacuum respectively.