Ethyne oxidation and hydrogenation on porous Pt electrode in acidic solution

Electrocatalytic ethyne oxidation and reduction on Pt was studied by on-line mass spectrometry (DEMS). It was shown that the initial step in both processes involves a rapid reactant adsorption on the metal surface. The adsorbate consists of molecular ethyne, partially dehydrogenated hydrocarbon residues C2Hx and C2-oxygen-containing species in a ratio dependent on the electrode potential. The maximum electrode coverage is achieved in the potential range 0.2–0.4 V, whereas the major part of the adsorbate is ethyne itself. Ethane was identified as the main volatile product of the cathodic hydrogenation of the surface species. A trace amount of 1-butene was formed in a slow side reaction. Evolution of a mixture of ethane and ethene was observed in the presence of bulk reactant. Measurements at various sweep rates revealed that electrooxidation of the preadsorbed ethyne to CO2 at E>0.8 V is much faster than its electroreduction in the hydrogen potential region. The optimal conditions for monitoring and/or utilization of ethyne in an electrochemical cell working in a programmed step potential mode are specified.