Probing anodic reaction kinetics and interfacial mass transport of a direct formic acid fuel cell using a nanostructured palladium–gold alloy microelectrode

The anodic reaction kinetics and interfacial mass transport of a direct polymer electrolyte membrane formic acid fuel cell have been investigated in an all solid-state electrochemical cell using a highly active nanostructured palladium–gold alloy microelectrode as an in situ probe. Well-defined “S-shaped” steady-state cyclic voltammograms exhibiting current-rising region at lower overpotentials and limiting current region at higher overpotentials have been first obtained for the electrochemical oxidation of formic acid at varying temperature. The “S-shaped” steady state polarization curves and chronoamperometric curves enable convenient measurements of the anodic reaction kinetics and interfacial mass transport of formic acid under real polymer electrolyte membrane conditions. It is encouragingly found that formic acid can be directly oxidized to CO2 with the first electron transfer being the likely rate-determining step and the formation of surface poison can be neglected. The exchange current density for the electrooxidation of formic acid is on the order of magnitude of 10−7 A cm−2 in the temperature range of 20–60 °C. The permeability and diffusion coefficient of formic acid through a Nafion® 117 membrane are of the order of magnitude of 10−9 mol cm−1 s−1 and 10−6 cm2 s−1, respectively. The combination of a nanostructured microelectrode and an all solid-state electrochemical cell offers a versatile approach to evaluate potential electrocatalysts for fuel cells and electrochemical sensors employing polymer electrolyte membranes.