Comment on “Boosting the solar water oxidation performance of a BiVO4 photoanode by crystallographic orientation control” by H. S. Han, S. Shin, D. H. Kim, I. J. Park, J. S. Kim, P. Huang, J. Lee, I. S. Cho and X. Zheng, Energy Environ. Sci., 2018, 11, 1299

Abstract

Han et al. claimed that a predominantly (001)-oriented BiVO₄ photoanode was successfully fabricated on fluorine-doped SnO₂ (FTO) polycrystals through microscale epitaxy by employing laser ablation deposition, leading to a staggering sixteen-fold increase in the efficiency of the BiVO₄ photoanode for solar water oxidation compared to a spin-coated BiVO₄ photoanode with random orientation. However, the assessment of crystallographic texture was inaccurately conducted through electron backscatter diffraction observations, and was then erroneously confirmed by the θ–2θ scan and pole figures of X-ray diffraction. Contrary to their assertions, our reanalysis of the presented data uncovers that the BiVO₄ photoanode likely contains merely ∼6.2% of (001)-oriented grains, with the (011/101)-oriented grains constituting ∼2.9% and the (024/204)-oriented grains comprising ∼3.9% of the overall composition. The remaining grains exhibit a nearly random orientation. The existence of a mere ∼6.2% (001) texture does not seem to conclusively correspond with the sixteen-fold increase in the efficiency of the BiVO₄ photoanode in solar water oxidation. The impact of various other microstructural variations (such as porosity and grain integrity) resulting from the diverse deposition techniques on the efficacy of solar water splitting necessitates thoughtful consideration. Moreover, the apparent scarcity of (101)-oriented grains in the underlying FTO layer raises doubts on its capability to facilitate (001)-textured growth of BiVO₄ through the alleged microscale epitaxy, as substantial evidence substantiating this assertion is lacking.