Influence of H- and OH-adsorbates on the ethanol oxidation reaction – a DEMS study

Abstract

The ethanol oxidation reaction (EOR) was investigated by potentiodynamic techniques on Pt/C, Rh/C, Pt–Rh/C, Pt–SnO₂/C and Pt–Rh–SnO₂/C by differential electrochemical mass spectrometry (DEMS) in a flow cell system. Prior to the cyclic voltammetries, adsorption of H- and OH-species was carried out by chronoamperometry at E_ad = 0.05 and 1 V vs. RHE, respectively, in order to examine their influence on the EOR on the different electrocatalysts. For the sake of comparison, another adsorption potential was chosen at E_ad = 0.3 V vs. RHE, in the double layer region (i.e. in the absence of such adsorbates). For this study, 20 wt% electrocatalysts were synthesized using a modified polyol method and were physically characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and transmission electron microscopy (TEM). When comparing the first and second cycles of the cyclic voltammograms (CVs) on Pt/C and Pt–SnO₂/C, the presence of H_ad on the electrocatalyst surface seems to hinder the initiation of the ethanol electrooxidation, whereas the reaction onset potential is shifted negatively with the presence of OH-adsorbates. In contrast to them, the EOR on Rh/C is enhanced when the electrocatalyst surface is covered with H_ad and is inhibited after adsorption at E_ad = 0.3 and 1 V vs. RHE. Finally, on Pt–Rh/C and Pt–Rh–SnO₂/C, neither the H- nor OH-adsorbates do impact the EOR initiation. The lowest EOR onset was recorded on Pt–SnO₂/C and Pt–Rh–SnO₂/C electrocatalysts. The CO₂ currency efficiency (CCE) was also determined for each electrocatalyst and demonstrated higher values on Pt–Rh–SnO₂/C.