Energy-Inexpensive Galvanic Deposition of BiOI on Electrodes and Its Conversion to 3D Porous BiVO₄-Based Photoanode

The present work focuses on energy-neutral, bias-free, scalable galvanic synthesis of highly crystalline thin films of BiOI on a fluorine-doped tin oxide (FTO) electrode (BiOI/FTO). Electrodes as developed were subjected to extensive characterization techniques viz. field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, atomic force microscopy, X-ray diffractometer, ultraviolet–visible spectroscopy, and other electrochemical techniques to observe physio(electro)chemical correlation between galvanic deposition and electrodeposition. In the next step, these BiOI/FTO electrodes were utilized to develop 3D porous BiVO₄/FTO electrodes (termed as g-BiVO₄) via a mild thermochemical process. The g-BiVO₄/FTO electrode prepared this way exhibited exceptional photoelectrochemical performance for sulfite oxidation, achieving 1.2 mA cm–² at a bias potential of 1.23 V versus reversible hydrogen electrode (RHE) with the early photocurrent onset (0.21 V vs RHE), as comparable to electrodeposited BiVO₄ on a FTO electrode (e-BiVO₄/FTO). We also fabricated Schottky barrier diode to shed light on the charge-transport mechanism of the g-BiVO₄/FTO electrode. In order to improve water oxidation kinetics, we further photodeposited cobalt acetate (CoAc) on the g-BiVO₄/FTO electrode. The CoAc-g-BiVO₄/FTO electrode, on optimization, showed a photocurrent of 0.73 mA cm–² at 1.23 V under the illumination of 20 mW cm–² blue light-emitting diode with 36 h of sustained water catalytic performance. This demonstrates the importance of galvanic deposition process as an alternative to the high energy-demanding synthesis techniques such as electrodeposition, hydrothermal, and so forth.