An Algorithm for the Extraction of Tafel Slopes

The Tafel equation, which serves as a linearized representation of the Butler-Volmer expression, permits the extraction of fundamental parameters of electrochemical systems, such as exchange current densities and Tafel slopes. However, the application of these linear fitting procedures become problematic in the cases of experimental data featuring nonlinearities in the Tafel (log(J) - V) response. This is especially troubling in low-overpotential regimes, where charge transfer kinetics generally dominate electrode behavior (as opposed to diffusion-limited currents at higher overpotentials) and linearization is expected to be most applicable. As a response to this complication and the ad-hoc forms of fitting that may arise from it, this report outlines a systematic method for the determination of Tafel slopes through a rigorous, quantitative framework. The algorithm's performance is benchmarked using electrochemical measurements of well-characterized reactions for water splitting, hydrogen evolution, and dioxygen reduction at iridium and platinum electrodes. As a final validation test, we show that the exchange currents extracted through this automated fitting procedure, used in conjunction with the Butler-Volmer model, are capable of reproducing the original electrochemical data in kinetically controlled regimes.