Comparative assessment of FTO and ITO substrates for BiVO4 photoanodes: superior surface quality enabling faster water oxidation in ITO

Abstract

We fabricated bismuth vanadate (BiVO₄) photoanodes using the metal–organic decomposition (MOD) method on fluorine-doped tin oxide (FTO) and indium tin oxide (ITO) substrates to compare their photoelectrochemical (PEC) performance. The current density of FTO/BiVO₄ (F/B, 0.671 mA cm⁻² at 1.23 V_RHE) was higher than that of ITO/BiVO₄ (I/B, 0.210 mA cm⁻² at 1.23 V_RHE). Although the surface quality of BiVO₄ appeared to be better when grown on ITO, the poor junction between ITO and BiVO₄ was identified as the primary cause of the low current density, as evidenced by the lower charge separation efficiency and higher resistance observed in the I/B (F/B: 112.1 Ω, I/B: 249.3 Ω). Pattern-illumination time-resolved phase microscopy (PI–PM) further revealed that more electrons remained on the I/B surface due to inefficient electron transfer to the ITO substrate. In addition, rapid trap-mediated recombination in the I/B, as confirmed by near-field heterodyne transient grating (NF-HD-TG) analysis, further supports these findings and likely contributes to the low current density. However, it was observed that water oxidation occurred more rapidly on I/B (τ = 0.281 s) compared to F/B (τ = 0.553 s), which appears to be due to the superior surface quality. This suggests that if substrate damage from heat can be minimized, ITO may be more suitable than FTO for photoelectrodes for water oxidation.