Morphology-Controlled Promoting Activity of Nanostructured MnO2 for Methanol and Ethanol Electrooxidation on Pt/C

Abstract

Herein, an evident microstructure effect of MnO2 in the electrooxidation of methanol and ethanol on Pt/MnO2/C electrocatalyst composite is reported. In this context, urchin-like MnO2 composed of identical nanorods and microcubes of MnO2 were selectively synthesized via reduction of KMnO4 by HCl and forced hydrolysis of MnCl2 by urea, respectively. The physicochemical studies showed smaller crystallite size (11 nm) and higher BET surface area (61 m2 g–1) of MnO2-nanorods as compared to the MnO2-microcubes with crystallite size of 15 nm and BET surface area of 26 m2 g–1. The HRTEM analysis was performed to evaluate the inherent morphology effect of MnO2 on the size and dispersion of Pt crystallites in Pt/MnO2/C composite, and the results showed miniaturization and higher dispersion of Pt crystallites in the presence of MnO2-nanorods. The cyclic voltammetry studies revealed higher current response and lower overpotential by the MnO2-nanorod-modified Pt/C as compared to the MnO2-microcube-modified Pt/C and bare Pt/C during alcohol electrooxidation reaction. The chronopotentiometry and chronoamperometry analyses showed lower alcohol oxidation overpotential and longer polarization time/stability for MnO2-nanorod-modified Pt/C as compared to the MnO2-microcube-modified Pt/C and bare Pt/C. Further, in CO stripping voltammetry study, the MnO2-nanorod-modified Pt/C showed higher current response and stronger negative shift in the CO electrooxidation potential. The MnO2-nanorods provide more triple-phase interfaces for better adsorption of oxidizing species which facilitate the oxidation of poisoning species via synergic effect during alcohol electrooxidation reaction. All these results together corroborate enhanced antipoisoning and promoting activity of MnO2-nanorod as compared to MnO2-microcube for methanol and ethanol electrooxidation reactions on Pt/C. The end results in this report hold adequate significance in future development of electrocatalysts based on suitably structured transition metal oxides for fuel cell applications.