Product distributions and efficiencies for ethanol oxidation at PtNi octahedra

An octahedral PtNi catalyst has been evaluated for direct ethanol fuel cells (DEFC) by measuring its performance and product distribution in a proton exchange membrane electrolysis cell. This avoids errors due to the chemical reaction between ethanol and oxygen that occurs in a DEFC. The performance of the PtNi/C catalyst at low potentials was similar to that of a commercial Pt/C catalyst, while its selectivity for complete oxidation of ethanol to carbon dioxide was significantly higher. For example, at 0.2 V vs. a hydrogen-producing cathode the faradaic yield of CO2 was 73% at PtNi/C at an average current of 5.6 mA, but only 55% at Pt/C, at 5.1 mA. Consequently, the PtNi/C catalyst would provide higher DEFC efficiencies than Pt/C, or commercial PtRu/C. The voltammetric behaviors of PtNi/C and Pt/C have also been compared in a liquid electrolyte at ambient temperature, where it was found that the activity of the PtNi/C for ethanol oxidation was improved greatly by heating in acetic acid. This removes surface Ni and capping agents and greatly improved CO tolerance. However, the superior CO tolerance of the cleaned PtNi/C relative to Pt/C was not reflected in polarization curves measured at 80 °C in PEM cells.