Mixed Lithium and Sodium Ion Aprotic DMSO Electrolytes for Oxygen Reduction on Au and Pt Studied by DEMS and RRDE

Abstract

In order to advance the development of metal-air batteries and solve possible problems, it is necessary to gain a fundamental understanding of the underlying reaction mechanisms. In this study we investigate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER, from species formed during ORR) in Na+ containing dimethyl sulfoxide (DMSO) on poly and single crystalline Pt and Au electrodes. Using a rotating ring disk electrode (RRDE) generator collector setup and additional differential electrochemical mass spectrometry (DEMS), we investigate the ORR mechanism and product distribution. We found that the formation of adsorbed Na2O2, which inhibits further oxygen reduction, is kinetically favored on Pt overadsorption on Au. Peroxide formation occurs to a smaller extent on the single crystal electrodes of Pt than on the polycrystalline surface. Utilizing two different approaches, we were able to calculate the heterogeneous rate constants of the O2/O2− redox couple on Pt and Au and found a higher rate for Pt electrodes compared to Au. We will show that on both electrodes the first electron transfer (formation of superoxide) is the rate-determining step in the reaction mechanism. Small amounts of added Li+ in the electrolyte reduce the reversibility of the O2/O2− redox couples due to faster and more efficient blocking of the electrode by peroxide. Another effect is the positive potential shift of the peroxide formation on both electrodes. The reaction rate of the peroxide formation on the Au electrode increases when increasing the Li+ content in the electrolyte, whereas it remains unaffected on the Pt electrode. However, we can show that the mixed electrolytes promote the activity of peroxide oxidation on the Pt electrode compared to a pure Li+ electrolyte. Overall, we found that the addition of Li+ leads to a Li+-dominated mechanism (ORR onset and product distribution) as soon as the Li+ concentration exceeds the oxygen concentration. Graphical abstract

Mass transfer analysis of boron-doped carbon nanotube cathodes for dual-electrolyte lithium–air batteries

“…Lithium-ion batteries (LIBs) have brought great convenience and contributions to the lives of human beings, but LIBs have reached their energy density limit. [1][2][3][4] Lithium-air batteries (LABs) have attracted much attention because of their extremely high theoretical energy density, but there are still many problems. For example, the large overpotential, and the generated insoluble products that plug the electrode and lead to battery failure.…”

Towards a Generalized ORR Mechanism in M2+‐Containing DMSO: Oxygen Reduction and Evolution in Ca2+‐Containing DMSO on Atomically Smooth and Rough Pt

“…However, especially regarding alkaline earth metal-air systems the performance is insufficient, and a fundamental understanding of the underlying mechanisms is required. As Na-O 2 [1][2][3][4][5] and K-O 2 [6][7][8] systems drew attraction as alkaline metal alternatives to Li-O 2 [9][10][11][12][13][14][15][16][17] systems, the Mg-O 2 [18][19][20] and Ca-O 2 [21][22][23][24][25][26] systems also experienced a raising interest. Na, K, Mg and Ca are very cheap and easily available materials, as their abundance in the earth crust is magnitudes larger compared to lithium.…”