A selectively exposed crystal facet-engineered TiO2 thin film photoanode for the higher performance of the photoelectrochemical water splitting reaction

Abstract

In the present study, a selectively exposed (101)-crystal facet engineered TiO₂ photoanode is investigated for the higher efficiency of the hydrogen evolution reaction. To date, even though the photoelectrochemical performance (PEC) dependent on exposed crystal facets has been calculated and demonstrated in semiconducting microcrystals, selectively exposed crystal facets of photocatalyst thin films have not been reported yet. Herein, we demonstrate a TiO₂ thin film photoanode with 100%-exclusively exposed crystal facets and suggest a methodology to obtain metal oxide thin film photoanodes with selectively exposed crystal facets. A selectively exposed crystal facet-manipulated metal oxide thin film photoanode is fabricated over pre-synthesized microcrystals through a three-step strategy: (1) hydrothermal synthesis of microcrystals, (2) positioning of microcrystals via polymer-induced manual assembly, and (3) fabrication of selectively exposed crystal facets of a TiO₂ thin film through a secondary growth hydrothermal reaction. Based on the synthesis of representative TiO₂ microcrystals with dominantly exposed (101), (100) and (001) crystal facets, the selectively exposed crystal faceted TiO₂ thin film photoanode is comparatively investigated for practical PEC performance. The photocurrent density of the selectively exposed (101) crystal faceted TiO₂ thin film photoanode is determined as 0.13 mA cm⁻² and has an 18% conversion efficiency of incident photon-to-current at a 0.65 V Ag/AgCl potential under AM 1.5G illumination. Its photoelectrochemical hydrogen production reached 0.07 mmol cm⁻² for 12 h, which is higher than those of (100) and (001) faceted photoelectrodes.