Insights into the Electronic Effects in Methanol Electro-Oxidation by Ternary In_1–xSn_xPd₂ Intermetallic Compounds

The gradual substitution of one element by another from a different group in isostructural intermetallic compounds allows for a systematic variation of the total number of electrons per unit cell with only minor variation in geometric parameters. Thus, electronic (ligand) influences can be evaluated with only negligible geometric (ensemble) influences. Herein, the correlation between electronic and electrocatalytic properties in the methanol oxidation reaction (MOR) is investigated by increasing the valence electron count per formula unit through the substitution of indium (three valence electrons) in the isostructural series In1–xSnxPd2 by tin (four valence electrons). The MOR peak current densities show a distinct change in slope with varying substitution degrees. Within the reaction network for the oxidation of small organic molecules, it is suggested that the MOR mainly proceeds via CO (indirect path) when 0 ≤ x < 0.8 and via formate (direct pathway) when 0.8 ≤ x ≤ 1. The use of intermetallic compounds as platform materials opens perspectives into a fundamental understanding of electrocatalysis, which is a key issue for the effective development of catalysts for low-temperature methanol fuel cells and other relevant catalytic reactions.