Cornered silver and silver[sbnd]platinum nanodisks: Preparation and promising activity for alkaline oxygen reduction catalysis

Abstract

A simple method for the efficient synthesis of cornered Ag and AgPt nanodisks by using triangular Ag nanoplates as reactants has been developed. The triangular Ag nanoplates are heated and reshaped to spherical nanodisks; in turn, through the introduction of PtCl42− ions, the spherical nanodisks undergo sculpturing and a subsequent displacement reaction to form cornered Ag nanodisks and AgPt nanodisks with pores. The selected-area electron diffraction pattern shows that the cornered Ag nanodisks are composed of two basal Ag (111) planes, thus indicating the occurrence of selective etching on the spherical nanodisks by this method. The analyses provided by X-ray diffraction spectroscopy and line-scanned energy-dispersive spectroscopy confirm the compositions of these cornered nanodisks and the mixed alloy in the Ag–Pt nanodisks. For the investigation of the practical feasibility of the application of the proposed method, these cornered Ag and AgPt nanodisks were then used as methanol-tolerant electrocatalysts in the alkaline oxygen reduction reaction (ORR). Electrochemical measurements were performed using an ultrathin-film rotating ring-disk electrode. The two types of nanodisks are found to have high stabilities and improved activities in 1M NaOH electrolyte. In the electrolyte with free methanol, the mass activities at −0.1V (vs. Ag/AgCl; within kinetic control region) in terms of the currents normalized to Ag mass for the Ag nanodisks and AgPt nanodisks are 6.98×10−4 and 2.01×10−3mAμg−1, respectively, which are greater than the value of 2.09×10−4mAμg−1 for Ag nanoparticles. The order in terms of the ORR activity is found to be as follows: cornered AgPt nanodisks>cornered Ag nanodisks>Ag nanoparticles. Additionally, in the presence of methanol, all the cornered nanodisk catalysts experience cathodic currents, indicating that the ORR occurs despite the use of a methanol solution.