Abstract
The electrocatalytic oxidation of formic acid and formaldehyde on Pd and on amorphous Pd(Si) was studied by cyclic voltammetry and the results compared with the literature for similar systems. The oxidation of HCOOH on Pd occurs through direct catalytic dehydrogenation via (:C(OH)2)ads while on Pd(Si) this intermediate does not appear to be formed. This is a consequence of the presence of inert Si on the surface that diminishes the probability of adjacent free sites. At high HCOOH concentrations, that intermediate undergoes dehydration on the Pd surface and COads oxidation peak is observed. For HCHO, the oxidation mechanism on both electrode materials appears similar to that previously proposed for Pt. However, the oxides formed on the amorphous Pd(Si) alloy are more reactive than those on Pd thus affecting the overall kinetics of the process for both organic molecules, a fact revealed by the increase in anodic currents observed in the voltammograms.
Highlights
The electrochemical oxidation of small organic molecules has been widely studied due to their potential utilization as fuels in energy conversion systems1,2
The purpose of this work is to study the electrocatalytic oxidation of formic acid and formaldehyde on polycrystalline Pd and amorphous Pd(Si) alloy by steady-state cyclic voltammetry
The anodic currents observed between 0.9 and 0.2 V in the cathodic sweep are related to the oxidation processes [1,2,3]. These processes are initially superimposed to the reduction of the PdO layer that is formed at potentials more anodic than 0.9 V where the initial oxidation of formic acid practically ceases
Summary
The electrochemical oxidation of small organic molecules has been widely studied due to their potential utilization as fuels in energy conversion systems. The reasons for that are related to their low toxicity, facility of storage and handling and mainly their high energy density Due to their simple molecular structure they should undergo a more straightforward reaction mechanism than other possible organic fuels. They present some limitations that hinder their use and justify the large number of studies periodically published on the subject. Such limitations are: (a) the low exchange current density on several transition metals makes it necessary to use noble metals, e.g., Pt, Pd or its alloys, as electrocatalysts and (b) the oxidation pathways generate some intermediate species that strongly adsorb on the surface blocking the active sites and inhibiting the reaction. The authors showed that on Pd the oxidation undergoes a special route because the total dehydrogenation of the molecule by the catalyst sur-
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