Preparation and optimization of TiO2 photoanodes fabricated by pulsed laser deposition for photoelectrochemical water splitting

Quasi-1D TiO2 nanostructures prepared by pulsed laser deposition (PLD) are tested as photoanodes for photoelectrochemical water splitting application and compared with TiO2 nanotube arrays prepared by anodic oxidation. PLD TiO2 films with controlled structure and morphology ranging from compact to vertically oriented or hierarchical porous nanostructures are deposited by ablating a TiO2 target with nanosecond UV laser pulses in the presence of an O2 background atmosphere at different pressures. Thermal treatments at different temperatures are used to transform the so-obtained amorphous systems into nanocrystalline structures (mainly anatase). The effect of film density and thickness is also considered by depositing different amounts of material per unit surface. The morphology and the phase composition of the samples are characterized by SEM and Raman spectroscopy, while the photoelectrochemical water splitting performances are investigated by monitoring the photocurrent generated under illumination in a three-electrode cell. Voltammetric scans and electrochemical impedance spectroscopy analysis were also used to correlate the morphology of PLD samples with their electrochemical properties and their working mechanism in the absence and presence of a light radiation. A clear correlation between structural/morphological properties and photoelectrochemical behavior is found and ideal values of the synthesis parameters are identified, which allow the identification of the optimal quasi-1D nanoporous morphology for water splitting applications. The use of sacrificial organic reagents as hole scavengers was also considered to improve the photoelectrochemical performance of the samples.