Understanding electrode-intermediate interaction of a highly active and cyclable Fe_xCo_1-xS_y aerogel for Oxygen Evolution Reaction and pseudocapacitive applications

Facilitating the nucleophilic attack of metal centers by OH⁻ for conducive adsorption of reaction intermediates and charge carriers along with easily accessible active sites is a determining factor for efficient Oxygen Evolution Reaction (OER) and pseudocapacitive charge storage. Herein, we report a bimetallic sulfide aerogel with hierarchical porosity prompting fast charge and mass transportation, while sulfurization and secondary metal incorporation instigate the increase of moderately binding active sites leading to favorable electrode-intermediate interaction. The electrode exhibits an overpotential of 335 mV at 500 mA cm⁻² and a specific capacitance of 3983.2 Fg^-1 at 1 Ag^-1, with robust performance for 50 h and a 46% increase in capacity retention. From X-ray Photoelectron Spectroscopy (XPS) and Ammonia Temperature Programmed Desorption (NH₃-TPD) analysis, lower M^δ+/M^2/3+ results in higher OER performance, with Fe³⁺ in FeOOH providing moderately binding sites, while higher M^δ+/M^2/3+ enhances cyclability for pseudocapacitive charge storage by inhibiting overoxidation and active site leaching. This work demonstrates the effect of simultaneous refinement of electronic structure and accessibility towards electrochemical performance by pairing the unique structural advantages of aerogels with the distinct chemical features of sulfides.