The steady-state velocities of an electrodic redox reaction have been determined on noble metals and some of their alloys. They are expressed in terms of the exchange current densities i0. Correspondingly, measurements of i0's as a function of temperature are recorded. The heats of activation at the reversible potential are independent of the properties of the substrate. However, log (reaction rate at the reversible potential) is linear with the work function of the substrate. Reactions in Cl− containing solutions have velocities greater than those in SO4– – solutions, and the ratio υCl– / υSO4– – depends upon the substrate in the order Pd > Au > Pt. The lack of dependence of the heat of activation upon the substrate is consistent with an electron transfer and not an atom-transfer model for the electrodic redox reactions. It is consistent with a weak interaction model. The dependence of the exchange current densities upon the substrate can be shown quantitatively to depend on the change of electrokinetic potential with the change of substrate-solution PD (potential difference) which occurs by carrying out the same reaction at a series of interfaces at which the metal-solution PD's are different, while the reversible potentials are the same. The anion effects cannot be due to blocking or bridging. They may be due to change in the φ2–b potential arising from a differing contact adsorption of the anions.