Quantifying Chemical Capacitance and Diffusion Coefficients in Hydrogenated La 0.6 Sr 0.4 FeO 3– δ via Operando Spectro-Electrochemical Characterizations

spectro-electrochemical signal, calibrated by coulometric titration, maps absorbance changes to proton concentration, enabling direct determination of its potential dependence. Impedance spectroscopy separates ionic and electronic contributions, yielding potential-dependent chemical capacitance and ionic conductivity. Defect-chemistry analysis further supports the reliability of the observed potential-dependent trends. We believe this approach is readily transferable to other redox-active oxides.