Simplified FTacV model to quantify the electrochemically active site density in PGM-free ORR catalysts

The development of platinum group metal-free catalysts is considered the most prominent path for reducing the cost of low-temperature fuel cells (LTFC). Despite the great advancement in the field, its further progress is currently limited by the ability to understand and mitigate the catalysts' degradation mechanisms, which up to recent years was limited by the lack of activity descriptors. Recent work showed that this could be solved using Fourier-transformed alternating current voltammetry that enables to deconvolute Faradaic currents arising from the redox reaction of the active sites from the capacitive currents, and by that accurately measure the electrochemically active site density of these catalysts in situ fuel cells. However, the analysis of the results can be complex, requiring simulation software for accurate parameter extraction. Herein, a simplified analysis of Fourier-transformed alternating current voltammetry is presented. This was done by mapping the influence of various variables, such as resistivity, capacitance, and thermodynamic and kinetic dispersion, on the accuracy of electrochemically active site density measurements. Under specific, yet realistic, operating conditions, a single equation with the peak current of the 5th harmonic as the only variable can be used to quantify electrochemically active site density with high accuracy. This approach was demonstrated using molecular catalysts, iron phthalocyanine, as a model molecule, and a commercial, heat-treated catalyst. Free analysis software is also provided to facilitate the easy use of this method.