Electroreduction of Gaseous Ethylene on a Platinized Nafion Membrane

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Abstract
The electroreduction kinetics of gaseous ethylene (1 atm, 20 or 100 mole percent, ) on a platinized Nafion 117 membrane has been examined using polarization and product composition measurements. The platinum electrodes were prepared on roughened Nafion 117 by a chemical‐reduction method and characterized electrochemically by cyclic voltammetry of hydrogen adsorption and visually by SEM and TEM. Two distinctly different electrode morphologies resulted when using low (0.02N) or high (0.05N) concentration of platinic acid (all other plating variables remained constant) and, based upon visual micrographic examination, are descriptively called a mossy or film morphology electrode, respectively. The platinum deposit of the film morphology electrode was thinner and less porous and, at a given loading, resulted in higher electroactive surface area per unit weight of platinum. The ethylene reaction kinetics were found to be similar to those reported in the literature for reduction of ethylene dissolved in aqueous solutions; ethane and hydrogen were the only products detected. The film and mossy electrode morphology in the Tafel region gave similar results upon comparing the current density normalized by the platinum loading. This indicates that the platinum embedded within the Nafion, formed early in the deposition reaction and the assumed site for the electrochemistry, is similar for the two morphologies. The implications of this work for electrodes for use in solid polymer electrolyte cells for gaseous reactants are discussed.

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