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), multicrystalline Pt and multi-crystalline Au substrates in oxygen saturated 0.1 M Tetraethylammonium Perchlorate (TEAClO 4 ) 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. The Lithium-air cell is an attractive technology for beyond Li-ion applications due to its high theoretical specific energy of 3505 Wh Kg −1 which is significantly higher than current lithium-ion cells. To achieve practical application as a replacement for Li-ion cells, current Li-air cells must overcome problems of (i) poor cycle life; (ii) high charge and discharge overpotentials resulting in low columbic efficiency and low power density; 1 (iii) eventual ambient air operation. The poor cycle life reported in many articles can be traced to the oxidative instability of the electrolyte 2-4 in conjunction with electrode passivation due to irreversible product deposits and high overpotentials for decomposing Li 2 O 2 . 5,6 The issue of electrolyte instability has been extensively reported since the early attempts to fabricate a secondary lithium-air cell adopting typical lithium-ion cell electrolytes. Alkyl carbonate based electrolytes were found to undergo nucleophilic attack, form passivating films and consume the electrolyte.2 Extensive studies on a wide variety of electrolytes such as acetonitrile, 7 ethers, 3 dimethylformamide, 4 dimethylsulfoxide (DMSO), 8 and various ionic liquids 9,10 have been carried out and relatively stable electrolytes were identified.11 Further, the donor number of the electrolyte solvent was found to be critical to the mechanism of the oxygen reduction reaction (ORR).12 Thus 1,2 dimethoxyethane (DME) and dimethylsulfoxide (DMSO) were extensively adopted for further study due to their high donor numbers and relative stability. Ionic liquids were also studied due to similarly favorable properties and their inherently good conductivity. 9,10,13,14 Nevertheless, oxidative stability continues to be of concern. Recently, the stability of DMSO has been called into question. 17 While the ev...

Tuning anion solvation energetics enhances potassium–oxygen battery performance

“…− electrolytes are comparable but lower than that observed ClO 4 − electrolytes. Since the DN of TFSI − electrolytes is higher than that of PF 6 − by only ∼10 kJ•mol −1 , very similar behavior to PF 6 − was expected. The FTIR spectra indicated a lack of K + -TFSI − coordination, allowing for the formation of independent K + -(DMSO) n species in solution that can go on to associate with O 2 /O 2 − .…”

“…Thus, the oxygen reduction reaction (ORR) is the key to the rapid growth of battery specific energy density required for long-range electric transportation, ever-more energy-intensive electronic devices, and long-duration (10 to 100 h per cycle) energy storage (1)(2)(3). Since the demonstration of the secondary Li-O 2 cell by Abraham and Jiang (4), the ORR in nonaqueous electrolytes has been the subject of sustained interest (5)(6)(7). Unfortunately, Li-O 2 batteries suffer due to the high-energy barrier to the oxygen evolution reaction (OER) (1,8), parasitic side reactions (9), Li dendrite growth (10), and unstable electrolytes (11)(12)(13)(14).…”

Sequential catalysis controls selectivity in electrochemical CO2 reduction on Cu

“…52 We emphasize that long range transport of active species from one electrode to another is not unprecedented in electrochemistry and is the operating principle of a rotating ring disk electrode. [52][53][54][55] We also note that interdigitated electrodes relying on liquid phase diffusion of species from one electrode to another have been successfully employed for electroanalysis purposes. 56,57 However, in these cases, one electrode is used to reduce a species and the second is used to oxidize the intermediate.…”

Understanding the Oxygen Reduction Reaction Activity and Oxidative Stability of Pt Supported on Nb‐Doped TiO2

“…The setup has been rated to have a collection efficiency of 25 %, which was verified to be 26.8 % by experiments with the ferrocyanide/ferricyanide couple (see the Supporting Information, Section S1). The RRDE is an ideal system to unravel complex reaction pathways, with the ability to identify intermediates produced over the course of a reaction by holding the ring at potentials at which the reduction products are oxidized (or vice versa) . The hydrodynamics of the RRDE ensure that desorbed intermediates or products from the disk are swept towards the ring.…”