Multiple cyclic voltammetry of noble-metal-based alloy electrocatalyst for methanol oxidation: Revealing a universal criterion of auxiliary metal selection and a new mechanism of activity enhancement

Abstract

Methanol oxidation catalysts are mainly based on Pt/Pd-based alloys, and various complex strategies are often employed to improve their activity. It is a common practice to clean the contaminants adsorbed on the surface of noble-metal-based catalysts by multiple cyclic voltammetry (MCV) prior to activity test. In this study, we find that this common practice can enhance the activity of noble-metal-based alloy catalysts for methanol oxidation by up to nearly three times. For the first time, a universal criterion is proposed for screening auxiliary metal elements that can significantly improve the activity by this simple practice: oxidable but insoluble in the potential range of CV. Also for the first time, a new activity enhancement mechanism by this common MCV is revealed: noble metal migration, valence state change and oxygen vacancy. As a proof-of-concept, Pt-Sn and Pd-CoSn exhibit high catalytic activity and durability after MCV, making the performance of flexible methanol fuel cells more prominent as well. This work puts forward a universal criterion of auxiliary metal selection and a new mechanism for the remarkably improved activity obtained by MCV, which provides a facile method for obtaining a series of highly active catalysts in the ethaline electrocatalysis field.