A Multielectrode Electrochemical and Scanning Differential Electrochemical Mass Spectrometry Study of Methanol Oxidation on Electrodeposited Pt<i>_x</i>Ru<i>_y</i>

Abstract

Methanol electro-oxidation was studied on a series of electrodeposited Pt x Ru y catalysts constructed as multielement band electrodes. A combination of electrochemical and scanning differential electrochemical mass spectrometry measurements were performed to evaluate the composition-dependence of methanol oxidation, methanol decomposition, CO 2 current efficiency, and the product distribution at 25 and 50 °C. At 25 °C, cyclic voltammetry revealed that the presence of Ru led to enhanced methanol oxidation rates over that of pure Pt. Methanol decomposition showed a similar composition-dependence. Mass spectrometry measurements revealed the evolution of HCOOH and CO 2 during methanol oxidation and allowed indirect determination of H 2 CO produced. Notably, these products were not observed during methanol decomposition. The most active electrode compositions and the highest instantaneous current efficiencies for the formation of CO 2 were found to depend on several factors. At 25 °C, the maximum activity was ∼10% Ru, while at 50 °C the most active composition increased to ∼25% Ru. Pure Pt had the highest instantaneous current efficiency for CO 2 at both temperatures. The product distribution reflected high CO 2 evolution for Pt, with an increasing fraction of the product emerging as H 2 CO at higher Ru content. Increasing the temperature improved the CO 2 current efficiency for all electrode compositions. These results confirm that methanol oxidation occurs though a parallel reaction pathway on Pt x Ru y electrodes. In addition, the balance between the different reaction pathways depends on several factors, including Ru composition and temperature.