Oxygen reduction reaction in room temperature protic ionic liquids

The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbon electrodes using cyclic voltammetry and potential-step chronoamperometry in 11 room temperature protic ionic liquids (PILs). The diffusion coefficient and solubility of oxygen in seven PILs were determined by nonlinear curve fitting of potential-step chronoamperometry at a platinum microelectrode. The diffusion coefficient of oxygen in the PILs was consistently on the order of 10-6 cm2 s-1. The ORR in the PILs was found to largely follow an electrochemical-chemical-electrochemical- chemical (ECEC) mechanism, as demonstrated by digital simulation of cyclic voltammograms at platinum, gold, and glassy carbon electrodes. The influence of electrode material on peak potential, heterogeneous rate constant, and transfer coefficient was studied. The influence of temperature on kinetics and thermodynamic properties like activation energy of ORR, activation energy of diffusion, and enthalpy of dissolution of oxygen in ethylammonium nitrate, bis(methoxyethyl)ammonium benzoate, and bis-(methoxyethyl)ammonium sulfamate was also investigated. © 2013 American Chemical Society.