Having established that our model and approach for fitting Tafel parameters is capable of simultaneously fitting the parameters for CO and H2 formation for different sets of data taken from the literature with quantified uncertainty (see Section S11 of the SI for plots of all H2 and CO polarization curves and the corresponding fitted Tafel parameter values), we sought to determine whether the fitted Tafel slopes and transfer coefficients converged to a set of cardinal values or to a set of values consistent with the transfer coefficients determined from DFT calculations. Bockris and co-workers derived what they refer to as cardinal values for the transfer coefficient of 𝛼 $ = 0.5, 1.0, 1.5, etc. This can be done starting with Equation S48 and assuming integer values for s and q, a 𝜈 of 1, and a symmetry factor of the rate determining step, 𝛽 = 0.5.