Cyclic voltammetry and differential electrochemical mass spectrometry (DEMS) have been combined to study the cycling performance of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at a gold electrode in non-aqueous dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) based LiClO 4 and N(Bu) 4 ClO 4 containing electrolytes. An Au-sputtered Teflon membrane (with a thickness of Au of only 50 nm resulting in an extremely short pore length on the electrolyte side) has been used as a model for a gas diffusion electrode (GDE) in this study: The oxygen molecules diffuse through a membrane from the gas side and are reduced at Au on the electrolyte side. The redox couple O 2 −• /O 2 is the predominant reaction during ORR in N(Bu) 4 ClO 4 based electrolytes whereas the calculated number of electron transferred is one. In presence of Li-ions, the average number of electrons transferred is 2 during oxygen reduction, which indicates the formation and oxidation of peroxide during ORR and OER respectively. The mass spectrometric cyclic voltammograms (MSCVs) data show that the maximum true coulombic efficiency of OER/ORR in DMSO and NMP is about 60% and 25%, respectively, with the evolution of CO 2 in NMP at 0.1 V (vs. Ag + /Ag) due to the decomposition of the electrolyte. One of today's challenges is the development of an energy storage system that can provide both high capacity and good cycling performance. Secondary lithium-air batteries are promising candidates as they provide a high theoretical capacity. However in practice, cycling performance is bad. The key step in discharging these batteries is the reduction of oxygen present in air. So far the oxygen reduction reaction has been investigated thoroughly in aqueous media, but only little fundamental research has been done in non-aqueous solvents.The first non-aqueous lithium-air battery was introduced in 1996 by Abraham and Jiang 1 as an alternative energy storage system for future applications. The specific energy of a Li-air battery amounts to 5.21 kWh/kg (including the weight of O 2 ), based on the assumption that Li fully reacts with O 2 to form Li 2 O.1 However, in practice the route to Li 2 O has proven irreversible. Hence, a more reasonable specific energy of 3.5 kWh/kg is obtained assuming lithium peroxide (Li 2 O 2 ) 2 as the sole discharge product. In practice Li-air batteries suffer from rapid capacity fading due to several obstacles such as poisoning the lithium electrode with CO 2 , 3 moisture and the instability of organic electrolyte used today against superoxide ion radical (O 2 -• ). 4 One main challenge to overcome in the attempt to develop a reversible Li-O 2 batteries with high capacity is the selection of an appropriate non-aqueous electrolyte which is characterized by high stability in the presence of lithium oxide species and a wide potential window. There are further requirements for the electrolyte in battery applications, such as low flammability, low vapor pressure and a large temperature range in which it is p...

The electrochemical behavior of Mg deposition and stripping at Au-electrode in magnesium aluminum chloride complex (MACC) tetraglyme electrolyte has been studied using differential electrochemical mass spectrometry (DEMS) and scanning tunneling microscopy (STM). During Mg deposition no dendrites are formed. MACC electrolyte supports reversible Mg deposition with high coulombic efficiency. Despite of the high coulombic efficiencies that has been observed in MACC, appreciable ethylene formation due to the decomposition of tetraglyme has been detected solely during Mg stripping. The mechanism of organic solvent decomposition will be discussed. This ethylene formation is quantitatively responsible for the missing charge balance of Mg-deposition and dissolution. Possible origins will be discussed.

Secondary lithium-air batteries are promising candidates for a future energy storage system as they provide in theory high capacity; however, in practice they show bad cyclebility. The key step in discharging these batteries is the reduction of oxygen present in air. So far the oxygen reduction reaction (ORR) has been investigated thoroughly in aqueous media, but little research has been done in non-aqueous solvents. Organic carbonates are unsuitable for the use in lithium-air batteries because they decompose upon charging [1]. Recently Scrosati [2] showed by XRD that tetraethylene glycol dimethyl ether (tetraglyme) is an appropriate electrolyte for Li-air battery whereas Bruce [3] using XRD and FTIR techniques demonstrated that, tetraglyme is not the best electrolyte because it decomposes in the first few cycles. On the other hand, Li2O2 has been reported as the major discharge product using dimethyl sulfoxide (DMSO) as an electrolyte [4]. Since spectroscopic techniques are superior to diffraction methods in detecting charge/discharge products, mass spectrometry in combination with electrochemistry (DEMS) has been used in this study to determine the electrolyte stability, water content, the amount of O2 reduced and evolved in a variety of aprotic electrolytes such as ethers (tetraglyme) and sulfoxide (DMSO). O2 solubility in aqueous and different non-aqueous electrolyte and its dependence on the flow rate of the electrolyte has been studied. Crucial is a knowledge of the O2 solubility in these electrolytes. We will present a new method for its determination using differential electrochemical mass spectrometry (DEMS) based on the convection and diffusion behaviour characteristices of the dual thin layer cell used for DEMS. [5] References: [1] F. Mizuno, et al., Electrochemitry, 2010, 78, 403. [2] H Jung et al., Nat. Chem., 2012, 4, 579. [3] S. Freunberger, et al., Angew. Chem. Int. Ed., 2011, 50, 8609. [4] Z. Peng, et al., Science, 2012, 337, 563. [5] Fuhrmann, J.; Linke, A.; Langmach, H.; Baltruschat, H., Numerical calculation of the limiting current for a cylindrical thin layer flow cell Electrochimica Acta 2009, 55, 430-438.