Complex Electrooxidation of Formic Acid on Palladium

Andressa Mota-Lima,Ernesto R Gonzalez,Markus Eiswirth

doi:10.5935/0103-5053.20140098

Abstract

Herein, oscillatory formic acid (FA) electrooxidation on polycrystalline palladium is investigated and compared with the one on polycrystalline platinum; major differences between both are attributed to differences on the kinetics of sub-set chemical network as well as to preferential routes admitted on palladium surface. To presume the kinetic rate of poison accumulation on palladium, FA oxidation was accomplished in presence of occluded hydrogen and hydrogen-free electrodes. The preferential routes were presumed from the temporal pattern. Markedly, oscillations during FA electrooxidation have minimum potential at 0.2 V, which is linked to the fast rate of direct dehydrogenation; moreover, it has one of the largest induction period (ca. 60 min) and oscillatory period (20 min) observed in electrochemistry, since subsurface hydrogen slows down the rate of CO accumulation on the surface.

Highlights

Complex electrooxidation involves a variety of multistable states within which autonomous oscillations are the focus of much attention
Bistability, rather than oscillations, was registered in this set of experiments. It is a typical behaviour around the Sandde-Node bifurcation point that is characterised by an abrupt change between two surface states
Bistability appears at relatively high values of current for an electrochemical cell controlled by a galvanostat device

Summary

Introduction

Complex electrooxidation involves a variety of multistable states within which autonomous oscillations are the focus of much attention. Among the interesting properties of oscillatory state, the enhanced thermodynamic efficiency[1,2,3,4] seems to be the one that would most attract the fuel-cell-technologist’s attention. Complex kinetics on palladium has been scarcely investigated. The present contribution is dedicated to analyze the complex formic acid (FA) electrooxidation on flat polycrystalline palladium and the effect of subsurface hydrogen on the oscillatory dynamic. Concerning electrochemical properties, palladium’s ability to promote electroreaction is attested by the hydrogen oxidation reaction (HOR) in which the exchange current (io) is as high as the one observed on platinum.[5] Other aspects about electrochemistry on palladium is found in reference 6

Results

Discussion

Conclusion