Electrocatalytic oxidation of ethanol on Pt, Pt-Ru and Pt-Sn nanoparticles in polymer electrolyte membrane fuel cell-Role of oxygen permeation

We have recently shown that in low temperature, polymer-electrolyte membrane direct ethanol fuel cells oxygen permeating from cathode is able to chemically oxidize ethanol at the anode surface [A. Jablonski, P.J. Kulesza, A. Lewera, Journal of Power Sources 196 (2011) 4714-4718]. Such process is responsible for significant amounts of acetaldehyde and acetic acid present at anode outlet, which are not related to the flow of electric current in external circuit. Here, for the first time, we report unbiased distribution of products of ethanol electrooxidation on Pt, Pt-Ru and Pt-Sn as a function of fuel cell voltage (under load) and temperature. We show here that for Pt anode and for cell voltage above 300 mV oxidation of ethanol to acetic acid does not occur as a result of electric current flow, but it is caused exclusively by chemical reaction between ethanol and oxygen permeating from cathode. This explains the obvious contradiction, which can be found in scientific literature regarding ethanol electrooxidation on Pt. Namely acetic acid is not observed in spectroelectrochemical, ex situ experiments in conditions comparable to working direct ethanol fuel cell, where it is detected in case of in situ, fuel cell experiments. Relation between unbiased distribution of products and anode catalyst's type, cell voltage, cell discharge current and temperature is also discussed. Oxygen permeation via Nation 117 at 80 degrees C expressed in unit of electric current has been estimated to be at least 2.5-3.5 mA/cm(2). (C) 2011 Elsevier B.V. All rights reserved.