Cation Size Effect on Oxygen Reduction Reaction in Aprotic Electrolytes

Abstract

The most important cathodic process in alkali metal-air (M-O2) batteries is the electrocatalytic oxygen reduction reaction (ORR) typically forming superoxide (MO2), and peroxide (M2O2).1 Cation size in aqueous solvents have been demonstrated to affect the ORR activity due to the cation hydration energy.2 However, within aprotic electrolytes, the reaction mechanisms and the activity of ORR with respect to cation size remains undetermined.Traditionally, electrochemistry has been involved in the analysis of the reaction mechanisms of ORR. Nonetheless, this technique by itself is not suitable to identify intermediaries and products of the redox reactions taking place at the electrochemical interface. The combination of cyclic voltammetry with in situ Raman spectroscopy provide the opportunity to study and develop a fundamental understanding of the ORR under potential control, accessing reaction pathways and relating them directly to surface structure.3 In this sense, the breakthrough of Shell-Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS)4,5 is noteworthy. SHINERS is a non-destructive, powerful technique for surface analysis that has been demonstrated to provide SERS effect even in the absence of intrinsic roughness and without requiring Au, Ag or Cu to be used as working electrodes.3,5 In this work, electrochemical measurements and SHINERS are utilised to study the effect of cation upon electrified interfaces during ORR. Zhang, J., Zhang, X.-G., Dong, J.-C., Radjenovic, P. M., Young, D. J., Yao, J.-L., Yuan, Y.-X., Tian, Z.-Q. & Li, J.-F. Real-Time Monitoring of Surface Effects on the Oxygen Reduction Reaction Mechanism for Aprotic Na–O2 Batteries. J. Am. Chem. Soc. 143, 20049–20054 (2021).Kumeda, T., Tajiri, H., Sakata, O., Hoshi, N. & Nakamura, M. Effect of hydrophobic cations on the oxygen reduction reaction on single‒crystal platinum electrodes. Nat. Commun. 9, 1–7 (2018).Guan, S., Attard, G. A. & Wain, A. J. Observation of Substituent Effects in the Electrochemical Adsorption and Hydrogenation of Alkynes on Pt{hkl} Using SHINERS. ACS Catal. 10, 10999–11010 (2020).Li, J. F., Huang, Y. F., Ding, Y., Yang, Z. L., Li, S. B., Zhou, X. S., Fan, F. R., Zhang, W., Zhou, Z. Y., Wu, D. Y., Ren, B., Wang, Z. L. & Tian, Z. Q. Shell-isolated nanoparticle-enhanced Raman spectroscopy. Nature 464, 392–395 (2010).Galloway, T. A., Dong, J.-C., Li, J.-F., Attard, G. & Hardwick, L. J. Oxygen reactions on Pt{hkl} in a non-aqueous Na+ electrolyte: site selective stabilisation of a sodium peroxy species. Chem. Sci. 10, 2956–2964 (2019).