Enhanced PEC Activity of Hematite Photoanodes Driven by Improved Charge-Transfer Dynamics Investigated Using IMPS/IMVS

Solar energy is one of the most effective and promising options among the renewable energy sources and has nearly unlimited availability; however, it is challenging to harvest it in a sustainable manner. The generation of hydrogen and oxygen using solar light to split water is a prominent way to harvest solar energy and use hydrogen as the fuel, subjected to the development of cost-effective and efficient hydrogen evolution and oxygen evolution catalysts. Catalysts composed of noble metals are efficient for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), but their use is economically not viable for commercial applications. The material should therefore be from earth-abundant sources; iron oxide scores the best as a promising photoelectrochemical (PEC) catalyst with the highest earth abundance index. The evaluation of the PEC catalytic performance involves measurements of several kinetic and efficiency parameters. The present manuscript focuses on the investigation of such kinetic parameters using two important spectroscopic tools: intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. Iron oxide photoanodes with different thicknesses generated using an electrochemical deposition route are used as the photoanode material. These two spectroelectrochemical tools are used to explain the enhanced catalytic performance at 1 μm thickness of the hematite film through the measurement of the charge transfer and recombination kinetics to explain the thickness-dependent PEC catalytic performances.