Rotating Ring-Disc Electrode Investigation of the Aprotic Superoxide Radical Electrochemistry on Multi-Crystalline Surfaces and Correlation with Density Functional Theory Modeling: Implications for Lithium-Air Cells

Abstract

The realization of a practical Lithium-air cell depends on understanding the oxygen reduction reaction (ORR), identifying a stable electrolyte and finding a suitable cathode. This study investigates the superoxide radical, its side reactions and correlates density functional theory (DFT) predictions of the surface activity to the experimental kinetics. The ORR on glassy carbon (GC), multi-crystalline Pt and multi-crystalline Au substrates in oxygen saturated 0.1 M Tetraethylammonium Perchlorate (TEAClO4) in Dimethyl Sulfoxide (DMSO) was studied using cyclic voltammetery and the rotating ring-disk electrode (RRDE) technique. The RRDE data was analyzed using kinetic models to understand the electrochemistry of the superoxide radical and calculate the surface reaction rate constants. The percentage of the superoxide radicals detected at the ring from GC, Pt and Au surfaces correlated linearly to the modeled activities of the substrates. Further, the modeled activity trend was found to correlate strongly with the ORR onset potential. This study validates the DFT catalyst screening approach. It also shows that side reactions involving the superoxide radical occurs in fresh, anhydrous DMSO based electrolytes.