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Aiming at a better molecular scale understanding of electrolyte degradation processes at electrode|electrolyte interfaces typical for modern batteries, in particular for lithium ion batteries (LIBs), we have developed a novel Differential Electrochemical Mass Spectrometry (DEMS) approach, and applied this for analyzing the evolution of volatile decomposition products at a high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode. Using a standard LP30 lithium ion battery electrolyte as well as 1.0 M LiPF 6 in either ethylene carbonate (EC) or dimethyl carbonate (DMC), respectively, the gas evolution rates during potentiodynamic cycling and in potential step experiments were monitored online, with high time resolution, in half-cell measurements. Following the potential and time dependent appearance of the reaction products and their fragments, the major gases evolved were identified as H 2 , CO 2 and CO. Their formation at the LNMO electrode at high potentials is explained by Ni4+ catalyzed dehydrogenation of organic carbonates, as evidenced in the potential step experiments from the correlation of the charge passed and the continuous gas formation even after decay of current down to zero. Differences in the potential dependent and in the time dependent product formation rates in the three electrolytes point to a non-additive behavior of the solvents EC and DMC in LP30. The results clearly illustrate the potential of this set-up for detailed studies of electrolyte degradation processes in modern battery systems. [ABSTRACT FROM AUTHOR]

Abstract: Using a combined spectro-electrochemical DEMS/ATR-FTIRS set-up, we have investigated the adsorption/oxidation of glycerol on a Pt thin film electrode by potentiodynamic, potentiostatic, and adsorbate-stripping experiments. The potential and time dependent development of the glycerol adlayer was followed by highly surface sensitive in situ ATR-FTIR spectroscopy, while the volatile products formed during the glycerol adsorption/oxidation process were simultaneously monitored by online differential electrochemical mass spectrometry (DEMS). For the assignment of the detected glycerol adsorbates, comparative experiments were carried out, investigating the adsorption/oxidation of glyceraldehyde and glyceric acid. The data show that (i) during the adsorption/oxidation of glycerol, COad is formed in the potential range between 0.1 and 0.7 V RHE, which can be oxidized further to CO2 at potentials above 0.5V, that (ii) beside COad, adsorbed glycerol (at 0.3 and 0.4V) and glycerate (between 0.6 and 0.9V) are formed, that (iii) glyceric acid is a dead end in the electrochemical oxidation of glycerol, and that (iv) glyceraldehyde is an intermediate to COad formation. [Copyright &y& Elsevier]

Disentangling the potential dependent surface(electro)chemical processes can be an arduous task, in particular for ill-defined electrode surfaces or when several reactions either coincide or occur without electron transfer. Employing ultrahigh vacuum surface preparation, electrochemical measurements and in situ spectroscopic / structural characterisation we have investigated the potential dependent surface processes proceeding on a Ru(0001) single crystal electrode in the absence and presence of specifically adsorbing anions in acid electrolyte. Online differential electrochemical mass spectrometry (DEMS) measurements clearly identify anodic H 2 formation in both cases, a recently reported phenomenon (Scott et al. Catal. Sci. Technol. 10 (2020) 6870), suggesting that this can be induced not only by OH adsorption, but also by other strongly adsorbing anions such as bisulfate. Furthermore, operando surface X-ray diffraction (SXRD) measurements demonstrate that the composition of the adlayer depends significantly on the potential history of the electrode, where strongly adsorbed hydroxyl species lead to pronounced hysteresis effects. Such complex processes are proposed to be characteristic for strongly interacting electrodes in general, not only for Ru. [ABSTRACT FROM AUTHOR]