Electrocatalytic Oxygen Reduction and Oxygen Evolution in Mg‐Free and Mg–Containing Ionic Liquid 1‐Butyl‐1‐Methylpyrrolidinium Bis (Trifluoromethanesulfonyl) Imide

Abstract

Abstract Aiming at a better understanding of the air electrode processes in Mg‐air batteries, we have investigated the activity of different electrode materials, viz., Pt, Au, glassy carbon (GC) and manganese (III)‐ and (IV)‐oxides (Mn 2 O 3 and MnO 2 ) for the electrocatalytic oxygen reduction (ORR) and oxygen evolution (OER) reactions in the ionic liquid 1‐butyl‐1‐methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (BMP‐TFSI) and the influence of Mg 2+ thereon. Employing planar model electrodes in a rotating ring disk electrode (RRDE) setup, we used cyclic voltammetry at different rotation rates to test the reversibility of these reactions and quantify the number of electrons transferred during the ORR. Reversible ORR and OER are observed for all electrodes in neat BMP‐TFSI electrolyte, while in the Mg 2+ containing electrolyte (Mg‐TFSI 2 ) the OER is strongly hindered for all electrode materials. This goes along with the rapid build‐up of a passivation layer during cycling, which increasingly inhibits also the ORR. The morphology and chemical composition of the passivation layer were characterized by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS), indicating that MgO 2 is the main product formed by the ORR.