Ethanol electro-oxidation on Pt/C and PtSn/C catalysts in alkaline and acid solutions

Carbon supported Pt and PtSn were prepared by a modified polyol method. The electrocatalytic activities and stabilities of the Pt/C and PtSn/C catalysts towards ethanol electro-oxidation reactions (EORs) were investigated by potentiodynamic and potentiostatic methods in a 0.1 M NaOH solution (or 0.5 M H2SO4) containing 0.01 M ethanol. On both catalysts, the EOR currents in the alkaline solutions were much higher than those in the acid solutions, and the onset potentials of the EOR in alkaline solutions were less positive than those in acid solutions, indicating that the kinetics of the EOR improve in alkaline solutions. Even though a significant improvement was observed in acid media on PtSn/C, compared with Pt/C, only negligible improvement was observed in alkaline media. The apparent activation energies of the EOR on the PtSn/C catalyst varies from 21 to 33 kJ mol−1, depending on the potentials, which are slightly lower than the corresponding values on the Pt/C catalyst (25∼42 kJ mol−1) under the same conditions. The Tafel slopes are divided into two parts–at low overpotentials, Tafel slopes on both catalysts are close to 120 mV dec−1, which is in agreement with the proposed mechanism–Temkin-type adsorption for both OHad and ethoxi at low overpotentials; in contrast, at high overpotentials, Tafel slopes on both catalysts are over 300 mV dec−1 due to the oxide formation on the surface.