Kinetic evaluation of the formic acid electrooxidation on steady state on palladium using a flow cell

Abstract

The HCOOH electrooxidation reaction (FAO) is studied on palladium in a 0.5 M HCOOH +0.5 M H2SO4 solution. The steady state current - potential curve is measured in the potential region 0.1 < E (vs. RHE) / V < 0.6 by chronoamperometry. Open circuit potential transient is also recorded as well as potentiodynamic sweeps at 0.01 V s−1. The absence of adsorbed CO is confirmed by voltammetric stripping, in agreement with published spectroscopic measurements. On this basis, a kinetic mechanism is proposed, involving adsorbed hydrogen and formate as reaction intermediates, which can also describe the spontaneous HCOOH dehydrogenation reaction at open circuit. The mechanism involves two reaction pathways. One where current is generated entirely by the oxidation of Had, which explains the electrocatalytic activity of palladium at low potentials. The other pathway, which prevails at high potentials, includes the electrooxidation of both, Had and HCOOad, reaction intermediates. The corresponding theoretical expression for the current density - potential dependence on steady state is derived, which accurately correlates the experimental results.