The study of role of susbtrates for the photoelectrochemical performance of bismuth vanadate

The substantive and continuous release of greenhouse gases into the atmosphere severely impacts Earth’s biosphere. This contributes to the rising frequency of natural disasters, which cause significant damage to life and property. To control and reduce greenhouse gas emissions, a shift from conventional to renewable energy is essential. Energy storage systems are crucial for managing renewable energy, which is affected by both diurnal and seasonal fluctuations. Among various storage methods, chemical energy storage is often preferred due to the existing infrastructure for handling chemicals. Hydrogen, being clean, energy-dense, and renewable, serves as a promising chemical energy carrier and an alternative fuel for power generation, transportation, and industry applications. Photoelectrochemical (PEC) water splitting is potentially a cost-effective and efficient approach to produce green hydrogen directly from water. Within such systems, photoelectrodes play a central role, and their selection depends on criteria such as elemental abundance, light absorption, electrical properties, band edge alignment, photostability, and catalytic activity. Bismuth vanadate (BiVO4) emerges as a promising photoanode meeting several of these requirements, though its performance is limited by severe charge recombination, limited photovoltage and sluggish water oxidation kinetics. To address recombination, nanostructures can be employed to shorten the diffusion distance of photogenerated carriers, while porous substrates can help to reduce the ion transport distance in tandem devices and to negate the effect of short hole diffusion length. An initial search focused on transparent conducting oxides (TCOs) that can be deposited at room temperature. Using a glancing angle deposition system, three-dimensional nanostructure arrays were fabricated through shadowing effect combined with substrate rotation. By introducing a slit aperture between target and substrate holder of ion beam sputtering chamber, well-separated nanorods were achieved across a large-area 6” substrate. Post-deposition annealing conditions were optimized to obtain transparent and conductive oxide layers. Argon-annealed ITO nanorods, showing good transmittance and relatively low sheet resistance, were identified as promising nanostructured substrates for BiVO4. Subsequently, BiVO4 was deposited on ITO nanorods using the SILAR technique; however, the ITO substrate was not stable under the deposition conditions. To overcome this, WO3 nanorods were employed as the nanostructured template for BiVO4, deposited via both SILAR and electrochemical methods. BiVO4 films prepared by electrochemical deposition on WO3 nanorods exhibits twice the photocurrent compared to BiVO4 deposited on a flat WO3 layer. Finally, BiVO4 was deposited on porous substrates using electrochemical deposition. Pulsed electrochemical deposition was chosen over continuous deposition methods to mitigate mass transfer limitation within porous framework. This section further highlights the importance of the local conductivity of porous substrates in enabling efficient electrochemical deposition.