Taffit: An Excel Tool for Fitting Tafel Data

Tafel analysis is widely used to characterize electrode kinetics. The technique has found use in electrochemistry, catalysis, materials, and corrosion research. Accurate Tafel analysis is especially critical in comparison of electrocatalysts. However, classical Tafel analysis (CTA) relies on the user's subjective selection of a linear range in the Tafel plot; dependent on linear regression of the user-selected range, kinetic parameters can vary by orders of magnitude. As use of CTA in the literature grows, a need is identified for more reliable, user-independent Tafel analysis. Here, Taffit, an algorithm constructed in the widely available Microsoft Excel, is presented. Taffit generates a Tafel plot from linear sweep voltammetric data and determines the exchange current density j ₀, charge transfer coefficient α, and Tafel slopes by closest statistical fit. Comparisons between Taffit and CTA are made for the hydrogen evolution reaction (HER, 2H⁺ + 2e ⇌ H₂) on glassy carbon (GC) and platinum electrodes. Taffit finds log j ₀ values of -7.2 and -3.9 for GC and Pt under H₂ at pH 0, as measured without resistive compensation. This is the first report of j ₀ for HER on GC. Because algorithmic fitting in the low overpotential region uses both cathodic and anodic branches of the Tafel plot, Taffit has greater precision than CTA. Agreement is also shown between literature values reported by CTA and those obtained by Taffit for HER on metal phosphide and selenide electrocatalysts. The Taffit algorithm substantially reduces subjectivity to improve the accuracy and precision of Tafel analysis.