Highly transparent Bi4Ti3O12 thin-film electrodes for ferroelectric-enhanced photoelectrochemical processes

In a photo-electrochemical (PEC) cell, rapid spatial separation of the photo-generated carriers and their transport kinetics within the photo-electrode materials are fundamental to achieving high-performance devices and avoiding charge recombination. Recently the use of ferroelectric potential in ferroelectric photo-active semiconductors has shown to be an effective strategy to modulate the charge transfer properties both in the bulk phase and at the surface of semiconductors. In this perspective, the Aurivillius perovskite Bi4Ti3O12 (BiTO) is of great interest owing to its excellent photocatalytic activity and strong spontaneous ferroelectric polarization. The use of BiTO powder for the photocatalytic reduction of CO2 has recently been reported, but its utilization as a photo-electrode for the photo-electrochemical (PEC) reduction of carbon dioxide has never been exploited, especially assisted by a ferroelectric potential. In this work, highly transparent BiTO-based thin film photo-cathodes were fabricated via a sol-gel/spin coating coupled process and optimized, for the first time in the literature, for CO2 PEC reduction. The influence of the number of depositions on the photo-electrochemical properties was initially accurately investigated and an optimized photo-electrode was thus obtained, which registered a maximum current density of -4.1 mA cm^2 under illumination conditions. In addition, the effect of the ferroelectric potential on the photo-electrochemical performances was accurately studied in this optimized system producing a current density increment of about 50% and an enhanced charge transfer ability, thus demonstrating the possibility of effectively adopting ferroelectric polarization in BiTO photo-electrodes to boost the photo-electrochemical reduction of CO2.