Faradaic efficiency of ethanol oxidation to CO2 at metallic nanoparticle/short-side-chain PFSA solid-state electrolyte interfaces investigated by on-line DEMS

Abstract

Ethanol has attracted attention as a renewable fuel for application in electrochemical reformers, for the production of hydrogen, and in fuel cells. The electro-oxidation of ethanol, however, faces a central drawback related to the difficulty for the CC bond cleavage, which is required for its complete electro-oxidation to CO2. Thus, the efficiency has to be increased and this is the main challenge for the use of ethanol as a fuel in such devices. In this study, the ethanol electro-oxidation was studied at metallic nanoparticle/Aquivion® solid-state interfaces. The nanostructured electrocatalysts were formed by Pt/C, Rh/C, Sn/Pt/C, and Sn/(PtRh)/C nanoparticles, and the electrocatalysis was tested at temperatures ranging from 25 to 140 °C. Potentiostatic and potentiodynamic measurements showed a marked effect of the temperature on the electrocatalytic activity and, principally, on the stability, due to lower poisoning by adsorbed reaction intermediates above 100 °C. By using a new setup for coupling the solid-state electrolyte cell with a DEMS (Differential Electrochemical Mass Spectrometry) equipment, with a proper calibration, it was possible to determinate the faradaic efficiency of ethanol electrochemical oxidation to CO2 at each studied condition. The results showed that the CO2 current efficiencies (CCE) increased from approximately zero, at 25 °C, to 54.0, 44.1, 22.7, and 13.1% for Rh/C, Pt/C, Sn/(PtRh)/C (1:3), and Sn/Pt/C (1:3), respectively, at 120 °C, under potentiostatic conditions. The impact of the temperature was more prominent for Rh/C, and this was associated to its ability for ethanol dehydrogenation in the methyl group, resulting in the formation of adsorbed oxametallacycle species, that facilitates the direct cleavage of the CC bond, this step being more rapid at 120 °C than at ambient temperature.