(544bi) Theoretical Investigation of the Effects of Metal Cations on Oxygen Reduction Reaction in Non-Aqueous Metal-Air Batteries

Theoretical investigation of the effects of metal cations on oxygen reduction reaction in non-aqueous metal-air batteries

Saurin H. Rawal, William C. McKee, and Ye Xu

Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA

Non-aqueous metal-air batteries with high theoretical gravimetric energy density represent one of the future technologies to potentially replace Li-ion secondary batteries.^1,2 This has led to renewed interest in the fundamental aspects of the oxygen reduction reaction (ORR) and oxygen evolution reaction in non-aqueous electrolytes. Herein we present a DFT-based theoretical study of ORR by different cations (including Li, Na, and K) on Au surfaces to investigate the reaction mechanism. We show that the stability of the adsorbed molecular superoxide anion and the corresponding metal superoxide species are affected by the presence of explicit solvent molecules and interfacial electric field.³ The formation and solvation of O₂^- open up thermochemical ORR pathways in the solution phase, which leads to the formation of solid products at smaller overpotentials than on Au surfaces.^4,5 We propose, based on additional theoretical calculations, reaction pathways for the formation of alkali superoxide vs. peroxide in solvents that explain the observed product selectivity due to different alkali species. The insulating nature of the discharge products e.g. Li₂O₂ leads to low energy efficiency and associated technological problems in Li-airbatteries. Thus we have furthermore explored the consequences of incorporation of dopant cations in terms of the crystalline and electronic structures of Li₂O₂.

References

(1) P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.M. Tarascon, Nat. Mater. 2012, 11, 19.

(2) A.C. Luntz, B.D. McCloskey, Chem. Rev. 2014, 114, 11721.

(3) S.H. Rawal, W.C. McKee, Y. Xu, Phys. Chem. Chem. Phys. 2017, 19, 32626.

(4) Y. Zhang, X. Zhang, J. Wang, W.C. McKee, Y. Xu, Z. Peng, J. Phys. Chem. C 2016, 120, 3690.

(5) S. Ma et al., Phys. Chem. Chem. Phys. 2017, 19, 12375.