Trends in C1-C4 Alcohol Oxidation Activity Enhancement for Tunable Silicon Oxide Encapsulated Platinum Electrocatalysts

Abstract

Electrooxidation of carbon monoxide (CO) and small oxygenate molecules is of great interest for direct alcohol fuel cell (DAFC) and electroorganic synthesis. Herein, we demonstrate that carbon-modified silicon oxide (SiOxCy) overlayers with nanoscopic thickness can greatly enhance the activity of Pt electrodes towards the oxidation of CO and five different oxygenate molecules. Trends in activity are reported with respect to the composition and structure of the SiOxCy overlayers, revealing that low-density, carbon-rich overlayers enhance peak current densities towards the oxidation of formic acid, methanol, ethanol, 1-propanol, and 1-butanol by 370%, 290%, 190%, 130%, and 30%, respectively, compared to bare Pt controls. Unlike conventional alloy electrocatalysts, the alcohol oxidation activity of SiOxCy|Pt electrodes did not strongly correlate with their ability to oxidize CO intermediates, suggesting that that C-H bond scission and/or oxidation of aldehyde or carboxylic acid intermediates, rather than CO intermediates, are the rate limiting steps during the oxidation of C1 and C2 alcohols. For larger alcohols like propanol and butanol, oxidation activity on encapsulated electrodes diminishes relative to bare Pt, which is attributed to mass transport limitations introduced by the overlayer. Overall, the structure-property-performance relationships uncovered in this study provide new insights into how overlayers can alter reaction mechanisms and can be used to guide design of encapsulated catalysts for alcohol oxidation and electroorganic synthesis reactions.