Integrated experimental and DFT-based study on pH-dependent photoelectrochemical performance of Ca2Fe2O5

Abstract

In this study, photoelectrochemical (PEC) performance of Ca2Fe2O5 nanoflakes were explored to understand corrosion and degradation tendency. Ca2Fe2O5 nanoflakes were synthesized via a modified two step thermochemical method consisting of hydrothermal reaction and chemical conversion. Detailed characterization using SEM, XRD, and TEM confirmed the highly crystalline and (200) faceted Ca2Fe2O5 nanoflake morphologies. PEC measurements, conducted in six distinct electrolyte conditions, revealed significant photocurrent variations with respect to pH change, highlighting pH 11 as the optimal environment. Electrochemical impedance spectroscopy (EIS) was applied to elucidate charge transfer rate depending on the hydrogen evolution reaction (HER) mechanisms. Furthermore, DFT calculations provided insights into the surface interactions of Ca2Fe2O5 with hydrogen and hydroxide absorbates, elucidating the electronic and structural change during PEC reactions. The simulation demonstrated that, while hydrogen adsorption induced Fe-O bond dissociation, hydroxide adsorption showed minimal effect on surface bonds. HER overpotentials were calculated for both Tafel and Volmer step, elucidating the facile and stable HER in OH terminated surface environments. These findings underscore the importance of alkaline electrolyte environment in optimizing the PEC stability and efficiency of Ca2Fe2O5 photocathodes.