Studies on Promotional Effect of Electrode Surface Modifications in Photoelectrochemical Water Splitting

Abstract

Solar light-assisted photoelectrochemical (PEC) water splitting is a promising way to generate renewable hydrogen, which is a valuable fuel and ideal substitute for fast-depleting conventional fossil fuels on earth. In the design and fabrication of PEC cell, semiconductor working electrode (WE) is the most critical key component that facilitates light absorption and drives photoelectrochemical redox reactions for water splitting. Aiming to achieve low-cost, durable and efficient WE, in recent years different material modification strategies, especially the surface modifications, have been investigated by researchers that have yielded promising outcome. Use of bilayered nano-hetero-structured (BNH) thin films of metal oxide semiconductors as photoelectrode is one such modifications. Present study is a systematic investigation on few BNH thin film photoanodes, synthesized by appropriately combining three low-cost and earth-abundant metal oxides (WO3, CuO and BiVO4), along with impurity incorporation in the overlayer. Bilayered thin films, grown over ITO/FTO glass substrate by spray-pyrolysis and ultrasonic spray pyrolysis techniques, were thoroughly characterized for structural, topographical, morphological and compositional characteristics by using X-ray diffractometry, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and UV-visible spectrometry. Prepared BNH films were tested as WE for PEC water splitting in 3-electrode electrochemical cell, in conjunction with platinum counter electrode and saturated calomel reference electrode, under 150 W Xenon arc light source illumination, to record open circuit potential (Voc), short circuit current (Isc), photocurrent density (Iph), and applied bias photon-to-current efficiency (ABPE). Flat band potential (Vfb), charge carrier density (Nd) and charge transfer kinetics were also evaluated through electrochemical impedance measurements. A major increment in PEC cell performance has been recorded on using prepared films, against monolayered pristine films. The study has thrown a deeper insight on the role and significance of such surface-modified BNH film photoanodes in PEC solar-water-splitting. newline