Deciphering the Electrochemical Activity and Selectivity of Earth-Abundant Transition Metal-Based Catalysts for the Alcohol Electrooxidation—Current Status

Abstract

Since alternative anode reactions such as the electrochemical alcohol oxidation reaction (AOR) are becoming increasingly important for water electrolysis in the course of a sustainable defossilization and electrification of the energy and chemical industry, this paper reviews the progress in understanding the electrocatalytic activity and selectivity of non-noble metal-based (non-NMB) catalysts regarding AOR and especially, the glycerol oxidation reaction (GOR). Starting from Ni-based catalysts, the review aims to consolidate the current state of knowledge for improving electrocatalytic activity based on mechanistic models and to transfer it to Co- and Cu-based materials. Several main influences on the catalytic activity can be identified via the involvement of metal ions (metal redox reactions) or oxygen species (oxygen redox reactions), which lead to the importance of M─O motifs for the electrocatalytically active ensemble on the surface of an electrically conductive non-NMB catalyst. In addition to the electrocatalytic activity, this work delves into possibilities for influencing the selectivity during AOR, which include the catalyst itself, electrode potential, or the pH value of the electrolyte. Furthermore, the chemical structure of the alcohol proves to be crucial, especially when oxidizing vicinal alcohols, because differentiating products from oxidative (pseudo)glycol cleavage and hydrogen atom transfer can complicate understanding selectivity influences.