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• Borohydride oxidation over realistic carbon-supported Pt, Au and AuPt catalysts. • Well-defined mass transport in rotating disk and thin-layer flow cell measurements. • Sensitive online hydrogen evolution DEMS measurements using a liquid N 2 trap. • Number of electrons transferred in BOR from Koutecky-Levich and DEMS data. • Synergistic effects in BOR activity and selectivity in a bimetallic catalyst. We report results of a systematic study of the borohydride oxidation reaction (BOR) in borohydride containing 0.5 M NaOH electrolyte over Pt/C, Au/C and AuPt/C thin-film catalyst electrodes, performed under enforced mass transport conditions. Employing rotating disk electrode (RDE) and thin-layer flow cell differential electrochemical mass spectrometry (DEMS) measurements, we identify kinetic limitations over a wide range of transport conditions. Together with the highly sensitive detection of evolved hydrogen as a function of potential, due to the use of a cold trap at the mass spectrometer inlet, this allows us to separate changes in the reaction selectivity, from complete to incomplete borohydride oxidation, from other kinetic limitations. Evaluation of the (apparent) number of electrons transferred per borohydride ion, both from the RDE measurements via the Koutecky-Levich formalism and from the DEMS measurements via the H 2 formation current, further supports the identification of complete borohydride oxidation (8 electron transfer) and incomplete oxidation (< 8 electrons transfer) reaction conditions. Using data on isotope labeled BD 4 - oxidation that we had published earlier, we identify weak secondary kinetic isotope effects for all catalysts, which indicate that B-H bond breaking does not represent the rate limiting step. [Display omitted] [ABSTRACT FROM AUTHOR]

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]

Borohydride electrooxidation in alkaline solution on Pt/C, AuPt/C and Au/C catalysts was studied systematically, employing online mass spectrometry analysis and isotope labeling. The potential-dependent oxidative and reductive partial reactions and their contribution to the overall reaction, as well as under open-circuit conditions, are determined and discussed. The open-circuit potential formed is shown to be a classical example for a mixed potential, resulting from the ongoing partial reactions. [ABSTRACT FROM AUTHOR]

The extensive investigation via classical Molecular Dynamics (MD) simulations of the halide-free "water-in-salt" electrolyte (WiSE) consisting of sodium acetate (8 m) and potassium acetate (32 m), unveils the interactions between cations, anions and water molecules. The WiSE's application as electrolyte in symmetric aqueous sodium-ion batteries, featuring NASICON-type Na 2 VTi(PO 4) 3 /C (NVTP/C) as active material at both the positive and the negative electrode, is also reported. In situ X-ray diffraction (XRD) measurements resolve the structural evolution of NVTP/C during the highly reversible sodium de/intercalation. Differential Electrochemical Mass Spectrometry (DEMS) confirms the remarkable stability of the highly concentrated electrolyte. Symmetric cells employing two NVTP/C electrodes and a green 32K8N electrolyte show an average discharge voltage of 1.13 V with stable cycling performance and a coulombic efficiency above 99.1% at 1C and 99.9% at 10C over 500 cycles. Compared to the fluorinated 9.2 m NaOTF, the 32K8N electrolyte has substantially lower cost, environmental impact and superior coulombic efficiency in symmetric cells. Image 1 • Halide-free Water-in-Salt electrolyte (WiSE). • Low-cost and green electrolyte. • Environmentally friendly aqueous Na-ion batteries. • Na 2 VTi(PO 4) 3 for positive and negative electrodes in symmetric Na-ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: The influence of ammonium ions on the activity and selectivity of the electrocatalytic oxygen reduction reaction (ORR) on polycrystalline Pt was investigated in model studies under continuous mass transport, both in sulfuric and perchloric acid solutions. Ammonium was found to increase the yield of hydrogen peroxide, particularly in sulfuric acid, but also in perchloric acid solutions, and also at higher potentials (0.80–0.90VRHE) typical for fuel cell cathode operation, which may severely impair the long-term stability of membranes and electrodes in fuel cells exposed to fuel gases and/or air containing ammonia. Adsorbed species, assigned to ammonia and nitric oxide, were identified on a Pt film electrode using in situ FTIR spectroscopy. Adsorbed nitric oxide could only be observed in perchloric acid solutions. The higher coverage of adsorbed ammonia in sulfuric acid solution is attributed to a stabilization by coadsorbed (bi-)sulfate species; the higher total coverage in this electrolyte can explain the larger effect of ammonium ions on the ORR activity and selectivity in sulfuric compared to perchloric acid solution. [Copyright &y& Elsevier]

The practical utilization of ether electrolytes has long been restricted due to the concern on its electrochemical oxidation stability. Recently, it has been demonstrated that ethers are compatible with a series of polyanionic cathodes for sodium batteries. However, the specific cathode-electrolyte interface is still poorly understood. In this work, via the use of highly complementary surface and interfacial characterization techniques, we identify that the use of an 1 M NaPF 6 -diglyme solution allows the formation of a unique polymer-inorganic cathode-electrolyte-interphase (CEI) on high-voltage Na 3 V 2 (PO 4) 2 F 3 polyanionic cathodes, contributing to excellent cyclability (capacity retention of 96.2% after 300 cycles at 0.5C, 1C = 128 mAh g−1) and outstanding rate capability (124, 120 and 112 mAh g−1, at 5C, 10C and 20C, respectively). The peculiar interfacial chemistry disclosed here may open up new opportunities for building high performance sodium batteries. The use of an 1 M NaPF 6 -diglyme solution allows the formation of a unique polymer-inorganic cathode-electrolyte-interphase (CEI) on high-voltage Na 3 V 2 (PO 4) 2 F 3 polyanionic cathodes, enabling excellent cyclability and outstanding rate capability for Na 3 V 2 (PO 4) 2 F 3 -based sodium metal batteries. The peculiar interfacial chemistry disclosed opens up new opportunities for building high performance sodium batteries. [Display omitted] • An 1 M NaPF 6 -diglyme electrolyte allows stable cycling of Na//Na 3 V 2 (PO 4) 2 F 3 cells. • A polymer-inorganic cathode-electrolyte-interphase forms in this electrolyte. • The unique surface/interfacial chemistry is comprehensively studied. • The use of ether electrolyte enables low heat dissipation in cells. [ABSTRACT FROM AUTHOR]

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]

Herein we address the key challenge towards the practical use of high-voltage lithium-ion cathode materials, i.e., the insufficient stability of the electrolyte towards oxidation. The transition metals in such materials, especially nickel, catalyze the decomposition reaction of the electrolyte, ultimately leading to poor cycling stability and rapid fading of the battery. To tackle this challenge, a new combination of electrolyte additives is introduced, targeting stabilized electrode/electrolyte interfaces and interphases for both the anode and cathode. The results show that the synergistic effect of tris(trimethylsilyl) phosphite (TTSPi) and bis(2,2,2-trifluoroethyl) carbonate (TFEC) can significantly improve the performance of cathode half-cells and also of lithium-ion full-cells with a cell voltage higher than 4.5 V. Cells using both TTSPi and TFEC as additives show greatly enhanced cycling stability, increased capacity, and improved coulombic efficiency, which can be even further improved when adding also lithium bis(oxalato)borate. Image 1 • Design of an electrolyte composition for high-voltage cathodes. • Enhanced performance for 5 V cathodes and graphite anodes. • In-depth analysis of the SEI and CEI in half-cells and full-cells. • Synergistic effect of TTSPi and TFEC for high-voltage cathodes and graphite anodes. • Further improvement by adding also LiBOB. [ABSTRACT FROM AUTHOR]