SILAR deposition of bismuth vanadate photoanodes for photoelectrochemical water splitting

Abstract

Wet chemical syntheses of nanomaterials and especially of thin-film coatings with controllable morphology, structure and composition are very promising for industrial applications due to their inherent simplicity and low cost, provided that the performance of the synthesized nanomaterials can match those achieved with vacuum-based depositions. Here we show the fabrication of bismuth vanadate (BiVO₄) thin films using a simple and scalable method called SILAR (Successive Ionic Layer Adsorption and Reaction), which is based on a series of immersion cycles in different precursor solutions. We present a comprehensive study on the growth of BiVO₄ layers, assessing the role of the deposition parameters on the structural, morphological, optical and electronic properties of the deposited films. We demonstrate the fabrication of phase pure BiVO₄ coatings showing excellent crystallinity and tuneable absorption properties, with band gap ranging between 2.8 and 2.4 eV. We then assessed these films as photoanodes for photoelectrochemical water oxidation, demonstrating the interplay of the synthesis parameters (precursor concentration, number of immersion cycles, annealing temperature) in affecting the water splitting performance. Champion samples were combined with a conventional co-catalyst for the oxygen evolution reaction and tested under simulated sunlight, recording photocurrents of 4.4 mA cm⁻² (at 1.23 V vs. RHE, the reversible hydrogen electrode) in borate buffer with the presence of a hole scavenger, with only a small reduction to 3.9 mA cm⁻² when tested without the hole scavenger. Our BiVO₄ are amongst the best performing photoanodes, and this study further promotes ongoing work focused on optimizing BiVO₄ to enhance its performance for water splitting applications.