Atomic Layer Deposition of Ti _<i>x</i> Fe _{2– <i>x</i>} O ₃ Photoanodes and Photocurrent Response Optimization Using the Response Surface Methodology

Hematite (Fe₂O₃) is a promising visible-light-active semiconductor material for photoelectrocatalytic applications; however, it has yet to achieve its theoretical maximum efficiency. Researchers globally are making significant efforts to enhance its performance and surpass the current efficiency limitations. Here, we report the photoelectrocatalytic performance of Ti _<i>x</i> Fe_2-<i>x</i> O₃ films deposited by atomic layer deposition (ALD) using FeCp₂ and Ti(OMe)₄ as precursors. The response surface methodology (RSM) with a face-centered central composite design (FC-CCD) was used to model and optimize the photocurrent response of Ti _<i>x</i> Fe_2-<i>x</i> O₃ thin film photoanodes. Deposition parameters, including the cycle ratio of TiO₂ to Fe₂O₃, total number of ALD cycles, and deposition temperature, were selected as independent variables, while the photocurrent density (PCD) at 1.23 and 1.70 V vs RHE was used as the response variable. Thin film depositions were carried out according to the FC-CCD design matrix, followed by postannealing at 500 °C for 1 h in air. The films were then evaluated for their photocurrent response using a photoelectrochemical cell under standard AM 1.5G illumination, 100 mW/cm². The experimental photocurrent responses were fitted to a second-order polynomial equation, resulting in the development of a mathematical model that establishes a relationship between the deposition parameters and PCD of Ti _<i>x</i> Fe_2-<i>x</i> O₃ photoanode. Analysis of model parameters revealed that film thickness and dopant concentration are the most significant factors influencing the PCD of Ti _<i>x</i> Fe_2-<i>x</i> O₃ photoanode. This study confirms that RSM-based FC-CCD can be efficiently applied for the modeling and optimization of photocurrent response of Ti _<i>x</i> Fe_2-<i>x</i> O₃ photoanodes.