Distribution of relaxation times analysis of rotating disk electrode impedance spectra
Roswitha Zeis, Friedrich-Alexander-University Erlangen-Nürnberg, Germany
The rotating disc electrode (RDE) is the standard method for screening oxygen reduction reaction (ORR) catalysts [1]. The Koutecký-Levich equation, the mathematical description of the RDE, allows the determination of key parameters such as the kinetic current and the number of electrons transferred. However, under non-ideal conditions, the current plateau corresponding to the limiting current is not flat, and the polarization curves do not correlate with the rotation speed, limiting the applicability of this equation.
We, therefore, propose an alternative technique to analyze the RDE. Electrochemical impedance spectroscopy (EIS), combined with the distribution of relaxation times (DRT) analysis, allows the assignment of impedance polarization losses to individual physicochemical processes [2].
The technique is demonstrated on a polycrystalline platinum RDE in KOH and HClO4 electrolytes. DRT analysis distinguishes between mass transport and charge transfer resistance of the ORR. This method allows the analysis of RDE data under conditions where conventional processing techniques are likely to fail.
References
[1] Kocha, S. S. et al. Best Practices and Testing Protocols for Benchmarking ORR Activities of Fuel Cell Electrocatalysts Using Rotating Disk Electrode. Electrocatalysis 8, 366–374 (2017).
[2] Weiß, A., Schindler, S., Galbiati, S., Danzer, M. A., Zeis, R. Distribution of Relaxation Times Analysis of High-Temperature PEM Fuel Cell Impedance Spectra. Electrochim Acta 230, 391–398 (2017).