Significantly improved and synergistic effect of Pt–ZnO–Bi2O3 ternary hetero-junctions toward anode-catalytic oxidation of methanol in alkali

Abstract

Pt-nanoparticle decorated nano-sized ZnO–Bi2O3 hetero-junctions of various compositions are synthesized along with binary Pt–ZnO and Pt–Bi2O3, characterized and used as anode-catalysts for methanol oxidation reaction in alkali. The peak current density of most of the Pt–ZnO–Bi2O3 catalysts in cyclic voltammetry is higher than these of Pt– Bi2O3 and Pt– ZnO indicating beneficiary and synergistic effect of the ternary composites. The best Pt–ZnO–Bi2O3 electrode containing ZnO:Bi2O3 = 5:1, exhibits significantly high current density, 932.1 mA mg−1 Pt which is 9.7, 5.5 and 12.1 times higher than that of Pt–Bi2O3 (95.4), Pt–ZnO (167.8) and synthesized Pt (76.5) catalysts. The mass normalized equilibrium exchange current density (4.46 × 10−4 mA mg−1 Pt) towards methanol oxidation reaction on the best electrode is approximately 3.6 × 104 and 9.5 times higher than these on Pt–Bi2O3 and Pt–ZnO electrodes. The chronoamperometry conforms to the results of CV study. The charge transfer resistance of the catalyst obtained from Nyquist plot is 12.6 and 8.2 times less than these offered by Pt–Bi2O3 and Pt–ZnO catalysts. Multi-scan CV experiments with the best ternary composite shows excellent stability in catalytic activity towards methanol oxidation reaction. The HPLC study helps understanding the selectivity of the catalysts among various products, which facilitates prediction of mechanistic pathways.