Dynamics of potential oscillations in the electrochemical oxidation of formic acid on Pt

A mechanistic model for the galvanostatic potential oscillation in the electrochemical oxidation of formic acid on Pt (H. Okamoto, N. Tanaka and M. Naito, Chem. Phys. Lett., 1996, 248, 289) is analyzed here from the viewpoints of nonlinear dynamics and bifurcation. The model assumes the potential-dependent adsorption, desorption, and reaction of water and carbon monoxide. It is shown that the adiabatic elimination of the potential is warranted in the dynamics and so the essential variables for the dynamics are only chemical ones. The potential oscillation occurs in a certain range of the applied current due to a Hopf instability. The potential dependence of the adsorption and desorption of water to and from the electrode plays an essential role in the Hopf bifurcation. The current dependence of the stability of the system is also a result of the potential dependence of the amount of adsorbed water.