Thermogravimetric Analysis Coupled With Mass Spectrometry Research Articles

Exploring the reactivity of Na3V2(PO4)3/C and hard carbon electrodes in sodium-ion batteries at various charge states

The interest in post-lithium batteries as an alternative to lithium-ion batteries boosted recently due to their substantial abundance, low cost, inherent safety, and sustainability. In recent years, the crucial need for the improvement of battery safety has been emphasized and safety remains a critical barrier for post-lithium technology. Therefore, the thermal stability and reaction enthalpies of electrochemically de-sodiated sodium vanadium phosphate (Na3V2(PO4)3/C) positive electrode and commercial coconut-shell derived hard carbon (HC) at various states of charge (SOCs) were systematically investigated. This study employed the 3D Tian-Calvet calorimeter (C80) and thermogravimetric analysis coupled with mass spectrometry (TGA-MS), to gain comprehensive insights into the thermodynamic aspects of these materials. Thermal stability of electrode materials at distinct sodiation / de-sodiation states draws great attention in cell design and is one of the reasons for the strong state of charge (SOC) dependence of the thermal runaway phenomenon, which represents the most critical safety issue for batteries. This combined experimental approach provides a comprehensive understanding of thermal stability and associated reactions in both, sodium vanadium phosphate (NVP) and hard carbon (HC) electrodes. NVP/C reacts with the electrolyte between 150 and 300 °C, releasing ∼400 J/g heat, although it thermally decomposed beyond 150 °C. The sodiated HC initiates decomposition at 100 °C, releasing ∼750 J/g heat in two steps in a reaction to the electrolyte. These data can facilitate optimizing the design of thermal management systems according to the cell's thermal performance.

H2[Pt(C2O4)2] as a Tailor‐made Halide‐free Precursor for the Preparation of Diesel Oxidation Catalysts: Nanoparticles Formation, Thermal Stability and Catalytic Performance

AbstractThe aim of this study was to investigate a tailor‐made metal precursor and its chemical properties to tune the properties of supported metal nanoparticles (NPs) and their catalytic performance when used as Diesel Oxidation Catalyst (DOC). The formation of extremely small Pt NPs from a new halide‐free Pt complex was investigated, namely bis(oxalato)platinate, H2[Pt(C2O4)2]. The size evolution of the supported NPs, from the formation upon the Pt precursor decomposition on γ‐alumina to the sintering of the NPs at high temperatures, was followed by thermogravimetric analysis coupled with mass spectrometry (TG‐MS) and differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. A correlation between the NPs’ size of the catalyst and the performance for the CO, C3H6, C3H8 and NO oxidation reactions pointed out a retained activity during test cycles, showing low sensitivity to the test conditions applied (i. e., temperature and gas composition). The overall catalytic performance was better in the fresh catalysts compared to the reference catalyst prepared from platinum nitrate, Pt(NO3)4. In particular, the different dispersion of the Pt NPs over the support obtained from the two precursors was identified as the reason for the different catalytic performance, retaining small NPs size after the tests cycles.

Synthesis, characterization, and thermal decomposition performance of 1,2,3-triazolyl-substituted 1,3,5-triazines with carbonyl, ester, and azide functional groups

Based on the organocatalytic reaction of enamine azide addition of 2,4,6-triazido-1,3,5-triazine to acetylacetone acetoacetic ester, we synthesized a series of previously unknown mono-, di-, and tri(1,2,3-triazolyl)-substituted-1,3,5-triazines that additionally carried carbonyl, ester, and azide groups. The structure of the obtained compounds was proved by NMR (1H, 13C) and IR spectroscopy, and the composition was confirmed by elemental analysis. With the aid of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) coupled to mass spectrometry (TG-MS), we obtained data on the thermal behavior and decomposition mechanism for these compounds. We demonstrated that di(1,2,3-triazolyl)-substituted 1,3,5-triazines have an increased thermal stability and have higher values of decomposition onset temperature (220–250 °C) in comparison with tri(1,2,3-triazolyl)-substituted 1,3,5-triazines (180 °C and 160 °C, respectively).

Co-gasification of biomass and oil shale under CO2 atmosphere: Comparative analysis of fixed-bed reactor, gas chromatography and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS)

Co-gasification of biomass with oil shale offers potential for integrating renewable and fossil energy sources, reducing reliance on fossil fuels. Biomass (pine and birch wood and bark) and oil shale blends (10–30 wt%) were gasified under CO2 conditions using thermogravimetric analysis coupled with mass spectrometry (TGA-MS), fixed-bed reactor, and gas chromatography. Results revealed an interaction between oil shale and biomass, enhancing CO and CH4 concentrations in the producer gas. Bark samples demonstrated higher CO concentrations compared to wood samples, particularly in pine, with 16.1 vol% and 5.4 vol%, respectively. While birch wood showed increased H2 evaporation in TGA-MS experiments, oil shale's impact on H2 concentration was inhibitive, as shown by quantitative analysis. Pine bark, with a threefold catalytic index compared to other biomass samples, demonstrated the highest total gas concentrations (19.2 vol%). Interestingly, pine bark char blends exhibited the lowest surface areas (up to 434 m2/g) among the tested samples.

Reinvestigating the concurring reactions in early-stage cellulose pyrolysis by solution state NMR spectroscopy

Low temperature pre-treatments increase the char yield during cellulose carbonization. Although this effect is mostly understood on a kinetic basis, the formed chemical structures leave room for scrutiny. In ongoing ambitions to enhance the char yield of bioderived precursors, the thereby occurring chemistry was reinvestigated. A set of isothermal heating protocols ranging from 150° to 250°C was applied to man-made Ioncell® cellulose fibers and to Avicel® PH-101 microcrystalline cellulose. The prepared cellulosic samples were examined by solution state NMR using a tetra-n-butyl phosphonium acetate ([P4444][OAc]): DMSO-d6 (1:4 wt%) electrolyte as dissolving medium. Complementary, IR spectroscopy, size-exclusion chromatography (SEC) and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) measurements were performed. The NMR spectra evidenced the formation of levoglucosan end capped moieties as being the first and major occurring reaction during low temperature pre-treatments. In contrast to other mechanistic proposals, no signs for carbonyl or alkene functionalities were discernible in the cellulosic material soluble in the NMR electrolyte, even after treatment at 250 °C for several hours. Thermal cross-linking was observed in SEC already at temperatures not known to significantly influence the overall char yield. In the solution state analytics only partial solubility was observed, owing to the formation of a reluctant fraction previously described as “thermostable condensed phase”. This resulted in analytical blind spots and led to discrepancies between NMR results and FTIR spectra in which carbonyl and alkene vibrations were clearly discernible. Those discrepancies might also imply the co-existence of different fractions in the early stages of cellulose pyrolysis.

1,2,3-Triazole mediated, non-halogenated phosphorus containing protective coatings from castor oil: Flame retardant and anti-corrosion applications

Halogenated flame retardants are under regulatory scrutiny despite their outstanding flame retardancy. The present study focuses on the development of non-halogenated flame retardant and corrosion-resistant polyurethane coatings from castor oil. Towards this attempt, a non-halogenated, hydroxy functionalized, triazole and phosphorus-containing reactive flame retardant (HTP-FR) with anti-corrosive properties was designed and synthesized by azide-alkyne cycloaddition of 2-azidoethanol, and Diphenyl prop-2-yn-1-yl phosphate. By adding HTP-FR to castor oil in 50 and 100 weight percentages, CO-HTP-PUs (CO-HTP-50, CO-HTP-100, where HTP-FR was loaded as 50 and 100 wt%, respectively) were made and their flame-retardant and corrosion resistance properties were tested. The parent castor oil and MDI-based polyurethane (CO-PU) was concurrently synthesized and investigated as control for comparative appraisal. The FR behaviour of the PUs was examined using bomb-calorimetric testing and lab-scale flame tests. From the lab-scale flame test, it was found that the intumescent char length of the CO-HTP-100 after burning is longer than that of the CO-HTP-50 due to its high HTP-FR content. A substantial decrease in gross heat of 8.23, and 13.17 % was observed for the CO-HTP-50, and CO-HTP-100, respectively compared to the control CO-PU. The intumescent FR mechanism of CO-HTP-PUs was studied using Thermogravimetric Analysis coupled with Mass Spectroscopy (TGA-MS) analysis and Energy-dispersive X-ray spectroscopy (EDX) elemental analysis with mapping. The increase in P content of the post-burn sample in comparison to their unburn counterparts, and the expulsion of nitrogen gas from the triazole moiety from CO-HTP-PUs corroborated the intumescent FR mechanism. High char yields at 700 °C of CO-HTP-100 (20.3 wt%) and CO-HTP-50 (15.5 wt%) when compared to control CO-PU (3.6 wt%) also substantiated the FR behaviour of CO-HTP-PUs. The performance of these protective coatings against corrosion was investigated by the electrochemical methods. The significantly low corrosion current (Icorr) values (2.60 × 10−9 A/cm2), high polarization resistance (42.7 × 104 Ω cm2), bulk resistance values (10.4 × 106 Ω cm2) and low corrosion rate (3.0 × 10−5 mm/year) of CO-HTP-100 demonstrate the excellent corrosion resistance property of HTP-FR.

Structural and morphological properties of in-situ biosynthesis of biocompatible bacterial cellulose/Laponite nanocomposites

Bacterial cellulose (BC) membranes were produced in culture media containing Komagataeibacter xylinus microorganism and four different concentrations of Laponite (Lap) XLG up to 1.0% (m/v) to evaluate the availability of in-situ method for production of BC/Lap nanocomposites. The effect of Lap on the structure and some properties of the biosynthesised polymer was evaluated by thermogravimetric analysis coupled to mass spectrometry (TGA-MS), Fourier Transform infrared (FT-IR) and Raman (FT-Raman) vibrational spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). TGA-MS and vibrational spectroscopy indicated that Lap particles were not incorporated into the BC membranes using 0.10 or 0.25% of the inorganic phase whereas all obtained results showed that its presence had a strong influence on the BC properties. This result can be an effect of the interaction of hydrophilic Lap particles with elementary fibrils of cellulose, expelled from the bacteria, fostering the disruption of chains organization. However, the 3D hierarchical organization of BC at the microscale was not collapsed according to SEM and AFM images. As the amount of Lap increased in the culture medium and in the produced membrane, the ribbons became less defined, suggesting the predominance of thinner ribbons. The transparency of the membranes was enhanced when the nanoclay loading was raised. The presence of high clay loadings in the BC/Lap nanocomposite did not negatively impact the cell viability against keratinocytes in comparison to pristine BC membranes, opening new opportunities to explore such nanocomposites for biomedical, pharmaceutical and cosmetics uses.

The Saga of Water and Halide Perovskites: Evidence of Water in Methylammonium Lead Tri‐Iodide

AbstractThe environment humidity effects on performance of halide perovskites (HaPs), especially MAPbI3, are known. Nevertheless, it is hard to find direct experimental evidence of H2O in the bulk materials at the levels lower than that of Monohydrate (MAPbI3.H2O). Here, for the first time, direct experimental evidence of water being released from bulk (µm‐s deep) of MAPbI3 single crystal is reported. The thermogravimetric analysis coupled with mass spectrometry (TGA‐MS) of evolved gases is used to detect the MS signal of H2O from the penetrable depth and correlate it with the TGA mass loss due to H2O leaving the material. These measurements yield an estimate of the average H2O content of 1 H2O molecule per three MAPbI3 formula units (MAPbI3.0.33H2O). Under the relatively low temperature conditions no other evolved gases that can correspond to MAPbI3 decomposition products, are observed in the MS. In addition to being direct evidence that there is H2O inside MAPbI3, the data show that H2O diffuses into it. With this article, a solid basis is proved for further studies on the mechanisms through which water modifies the properties of MAPbI3 and all the other halide perovskites.

K4Nb6O17 layered hexaniobate: revisiting the proton-exchanged reaction

The layered hexaniobate of K4Nb6O17 composition and its derivatives comprise nanostructured materials that exhibit suitable properties for application in catalysis, electrochemistry, and energy, for instance. The exchange of K+ cations to obtain the acidic or protonic niobate form is the main route to originate appropriate precursors to promote the hexaniobate exfoliation, yielding a dispersion of thin layers (2D particles) that can be scrolled under exclusive conditions. Hexaniobate presents two regions�(I and II), being the former considered more accessible than region II. In this work, the proton exchange efficiency of the K4Nb6O17 was investigated by thermogravimetric analysis coupled to mass spectrometry (TGA-MS) and metal analysis by inductively coupled plasma spectroscopy (ICP). The products of thermal decomposition profile of the HxK(4-x)Nb6O17 phase were isolated at defined temperature values and characterized by X-ray diffractometry and Raman spectroscopy. The cation exchange percentages obtained by TGA-MS (68.0%) and by quantification of deintercalated K+ by ICP (64.0%) are similar and endorse that region II can also be modified and, consequently, contribute to the exfoliation process.

Development of Pore Morphology During Nitrate Group Removal by Calcination of Mesoporous CexZr1-x-y-zYyLazO2-δ Powders.

Here, we present a study of the development of the micro- and mesoporosity of a CexZr1-x-y-zYyLazO2-δ oxygen storage material upon treatment at temperatures up to 1050 °C. The investigated powder, obtained from nitrate-based metal oxide precursors in a specially developed hydrothermal synthesis, is highly crystalline, features a high surface area and does not show phase segregation at high temperatures. By employing an advanced methodology, consisting of state-of-the-art argon physisorption, thermogravimetric analysis coupled with mass spectrometry (TG-MS) and X-ray powder diffraction (XRD) along with Raman spectroscopy, we correlate the stability of the mesopore system to the presence of surface-bound nitrate groups introduced during synthesis, which prevent sintering up to a temperature of 600 °C. In addition, the connectivity of mesopores was further studied by hysteresis scanning within the argon physisorption measurements. These advanced physisorption experiments suggest a three-dimensionally interconnected pore system and, in turn, a 3D network of the material itself on the nanometer scale which appears to be beneficial to endow the mesopore space with enhanced stability against sintering and mesopore collapse once the removal of nitrate groups is completed.

Tailoring the yttrium content in Ni-Ce-Y/SBA-15 mesoporous silicas for CO2 methanation

A series of nickel-cerium-promoted mesoporous silica (SBA-15) catalysts modified with different loadings of yttrium were synthesized by cetyltrimethylammonium bromide (CTAB)-assisted impregnation. The catalysts were tested in CO2 methanation reaction and characterized by N2 sorption, X-ray fluorescence (XRF), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (XRD), H2 chemisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), CO2 temperature-programmed desorption (CO2-TPD), and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The best catalytic performance in CO2 methanation was found for Y-modified NiCe/SBA-15 catalysts compared to the unpromoted sample. The modification with 10 wt% of yttrium gave the highest CO2 conversion of 61% ± 2% at 350 °C. We attribute this increase to an improved dispersion of Ni, increased reducibility of Ni species, higher ratio of Ce3+/(Ce3+ + Ce4+), and increased moderate basicity found for 15Ni10Ce10Y/SBA-15. This paper shows that 10 wt% of Y loading not only improves the catalytic activity in CO2 methanation, but also gives stable performance. The tested 15Ni10Ce10Y/SBA-15 catalyst did not exhibit activity loss during 26 h of time-on-stream (TOS) experiment at 350 °C. Moreover, carbon deposits and sintered nickel particles could hardly be found in 15Ni10Ce10Y/SBA-15 catalyst used for 7 h.

Insights into the Stability and Activity of MIL-53(Fe) in Solar Photocatalytic Oxidation Processes in Water

MIL-53(Fe) is a metal organic framework that has been recently considered a heterogeneous photocatalyst candidate for the degradation of water pollutants under visible or solar radiation, though stability studies are rather scarce in the literature. In this work, MIL-53(Fe) was successfully synthesized by a solvothermal method and fully characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), N2 adsorption–desorption isotherm, Thermogravimetric analysis coupled with mass spectrometry (TGA-MS), UV-visible diffuse reflectance spectroscopy (DRS), elemental analysis and wavelength dispersive X-ray fluorescence (WDXRF). The effects of pH, temperature, solar radiation and the presence of oxidants (i.e., electron acceptors) such as ozone, persulfate and hydrogen peroxide on the stability of MIL-53(Fe) in water were investigated. The as-synthetized MIL-53(Fe) exhibited relatively good stability in water at pH 4 but suffered fast hydrolysis at alkaline conditions. At pH 4–5, temperature, radiation (solar and visible radiation) and oxidants exerted negative effect on the stability of the metal–organic framework (MOF) in water, resulting in non-negligible amounts of metal (iron) and linker (terephthalic acid, H2BDC) leached out from MIL-53(Fe). The photocatalytic activity of MIL-53(Fe) under simulated solar radiation was studied using phenol and metoprolol as target pollutants. MIL-53(Fe) on its own removed less than 10% of the pollutants after 3 h of irradiation, while in the presence of ozone, persulfate or hydrogen peroxide, complete elimination of pollutants was achieved within 2 h of exposure to radiation. However, the presence of oxidants and the formation of some reaction intermediates (e.g., short-chain carboxylic acids) accelerated MIL-53(Fe) decarboxylation. The findings of this work suggest that MIL-53(Fe) should not be recommended as a heterogeneous photocatalyst for water treatment before carrying out a careful evaluation of its stability under actual reaction conditions.

Further insights on the thermal degradation of aluminum metaphosphate prepared from aluminum dihydrogen phosphate solution

A study of the high temperature (up to 1200 °C) degradation of aluminum metaphosphate Al(PO3)3 has been carried out to evaluate the stability of this compound used for many purposes. For the preparation of Al(PO3)3, an aluminum dihydrogen-phosphate Al(H2PO4)3 solution has been heated at 700 °C. Thermal degradation of Al(PO3)3 has been followed through the measurement of weight loss on isothermal mode at 1000 and 1200 °C and by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS). Structural data have been obtained by 27Al, 31P and 1H MAS NMR spectroscopy. NMR analyses have shown that [A] and [B] allotropic forms of Al(PO3)3 are formed after the preparation procedure. In addition, NMR revealed that hydroxyls groups are also present in the sample, and they form POH groups. TGA-MS showed that they are decomposed at a temperature of 875 °C, while the decomposition of Al(PO3)3 into AlPO4 and P2O5 begins at 1000 °C.

Comprehensive Characterization of APTES Surface Modifications of Hydrous Boehmite Nanoparticles.

Hydrous boehmite (γ-AlOOH) nanoparticles (BNP) show great potential as nanoscale filler for the fabrication of fiber reinforced nanocomposite materials. Notably, the particle-matrix interaction has been demonstrated to be decisive for improving the matrix-dominant mechanical properties in the past years. Tailoring the surface properties of the nanofiller enables to selectively design the interaction and thus to exploit the benefits of the nanocomposite in an optimal way. Here, an extensive study is presented on the binding of (3-aminopropyl)triethoxysilane (APTES), a common silane surface modifier, on BNP in correlation to different process parameters (concentration, time, temperature, and pH). Furthermore, a comprehensive characterization of the modified BNP was performed by using elemental analysis (EA), thermogravimetric analysis (TGA) coupled with mass spectrometry (TGA-MS), and Kaiser's test (KT). The results show an increasing monolayer formation up to a complete surface coverage with rising APTES concentration, time, and temperature, resulting in a maximal grafting density of 1.3 molecules/nm2. Unspecific multilayer formation was solely observed under acidic conditions. Comparison of TGA-MS results with data recorded from EA, TGA, and KT verified that TGA-MS is a convenient and highly suitable method to elucidate the ligand binding in detail.

The Effect of Slurry Wet Mixing Time, Thermal Treatment, and Method of Electrode Preparation on Membrane Capacitive Deionisation Performance

Capacitive deionisation (CDI) electrodes with identical composition were prepared using three deposition methods: (1) slurry infiltration by calendering (SIC), (2) ink infiltration dropwise (IID), and (3) ink deposition by spray coating (IDSC). The SIC method clearly showed favourable establishment of an electrode with superior desalination capacity. Desalination results showed that electrodes produced from slurries mixed longer than 30 min displayed a significant reduction in the maximum salt adsorption capacity, due to the agglomeration of carbon black. The electrodes were then thermally treated at 130, 250, and 350 °C. Polyvinylidene difluoride (PVDF) decomposition was observed when the electrodes were treated at temperatures higher than 180 °C. The electrodes treated at 350 °C showed contact angles of θ = 0°. The optimised electrodes showed a salt adsorption capacity value of 24.8 mg/g (130 °C). All CDI electrodes were analysed using specific surface area by N2 adsorption, contact angle measurements, conductivity by the four-point probe method and salt adsorption/desorption experiments. Selected reagents and CDI electrodes were characterised using thermogravimetric analysis coupled with mass spectrometry (TGA-MS) and differential scanning calorimetry (DSC), as well as scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). Electrode structure and the development of the critical balance between ion- and electron- conductive pathways were found to be a function of the electrode slurry mixing procedure, slurry deposition technique and thermal treatment of the electrodes.

Structural and Electrochemical Properties of "Disordered, Spinel-like" Structures Derived from NCM111 Materials By Chemical Delithiation

Li-ion batteries (LIBs) are being widely used in various consumer electronics applications and battery electric vehicles. In current and next-generation LIBs, particularly Ni-rich NCMs (e.g. Li1+x[Ni0.6Co0.2Mn0.2]1-xO2) are considered as a promising class of cathode active materials (CAMs) due to their high specific capacities, their high power and energy densities, and their good structural stability.[1] In order to meet cycle-life requirements and to maintain a safe state of operation, LIBs are only cycled within a specific potential range, significantly limiting the usage of the specific capacity achievable with these materials. A major problem for NCMs are over-charge and/or harsh cycling conditions, which lead to highly aggravated capacity fading and ultimately to cell-failure. One fundamental degradation mechanism for NCM materials is the deleterious oxygen evolution from the NCM surface at high degrees of delithiation (>80% state of charge, SOC),[1,2] which results in the formation of an oxygen-depleted spinel and/or rock salt phase on the NCM particle surface as well as in a concomitant oxidation of the electrolyte.[3,4] A thorough understanding of the exact structures of the O-depleted phases produced by lattice oxygen release from the NCM materials and of their effects on the cycling performance of LIBs are still missing, which hampers the development of countermeasures. In the literature, oxygen release from partially delithiated NCMs has been frequently studied by thermal treatment, showing that with increasing Ni content the temperature at which oxygen is released decreases while the amount of released oxygen increases.[3,5–7] A detailed study of chemically delithiated NCM111 (Li1+x[Ni1/3Co1/3Mn1/3]1-xO2) using electrochemical testing methods, thermogravimetric analysis coupled with mass spectrometry (TGA-MS), X-ray diffraction (XRD), scanning electron microscopy, and gas physisorption measurements is the main objective in this work. Chemical delithiation to various degrees was executed with the oxidation agent NO2BF4 in anhydrous acetonitrile. Electrochemical testing suggests minor modification of the NCM material upon chemical delithiation resulting in less specific reversible capacity and that an electrochemically inactive phase is formed after oxygen depletion, which increases polarization and significantly decreases the reversible specific capacity of the NCM material. TGA-MS analysis is used to characterize the oxygen release behavior of the chemically delithiated samples, while XRD analysis by Rietveld refinement leads to the observation and allows the quantification of a spinel phase after thermal treatment of the chemically delithiated materials. Disintegration of the secondary structure of the NCM material was observed during chemical and electrochemical delithiation, resulting in a surface area increase by a factor of »10 and »5, respectively. The obtained results help for a better understanding of the processes happening during the oxygen release of NCM materials at high SOC, while providing reference data of phases found electrochemically in over-charge and/or under harsh cycling conditions.

Carbothermic reduction of carbon aerogel-supported Fe during the catalytic decomposition of toluene

Iron-catalyzed tar decomposition is studied by inspecting changes in catalytic activity and its correlation to the metal oxidation numbers. A carbon-aerogel-supported iron (Fe/CAG) catalyst was used herein to decompose toluene (model tar) at between 500 °C and 700 °C. The catalytic decomposition was studied in a conventional reaction system, and the catalyst was characterized prior to and after the reaction to understand the effect of the structural changes in the catalytic activity. The results demonstrated that the iron oxidation state and coke deposition strongly depend on the reaction temperature. The X-ray diffraction patterns confirmed that at T < 700 °C, several Fei+ are present, while at 700 °C, Fe° prevails, suggesting a reconstruction of the metal clusters on the surface. The Fe/C ratio determined by elemental mapping (EDS), as well as thermogravimetric analysis coupled to mass spectrometry (TGA-MS) of the spent catalysts, confirmed that this surface reconstruction is related to carbothermic reduction of the metal oxides and assisted by carbon deposition.

Washing of Ni-Rich Cathode Active Materials for Lithium-Ion-Batteries: Mechanistic Understanding

Ni-rich cathode active materials (CAMs) for lithium-ion batteries, like NCM851005 (Li1+δ(Ni0.85Co0.10Mn0.05)1-δO2), are promising candidates for achieving the energy density target needed for battery electric vehicles [1]. However, these materials are susceptible to the formation of surface impurities and, for this reason, an additional washing step is needed to remove these surface contaminants [2,3]. It was shown that this washing step results in a H+/Li+ exchange in the near-surface region of the CAM and a metal oxohydroxide-like structure is formed [4]. In the subsequent drying/heating step, thermogravimetric analysis coupled with mass spectrometry (TGA-MS) showed the initial release of water, indicating the formation of a surface spinel-like shell; upon further heating to 250 °C, oxygen release detected by TGA-MS suggests the formation of a rocksalt-like surface layer [5].In this work, we investigate the mechanism behind the formation of surface groups on Ni-rich CAMs during washing, using TGA-MS, on-line mass spectrometry (O-MS), and near-edge X-ray fluorescence spectroscopy (NEXAFS). In addition, we synthesized and characterized the model materials, LiNiO2 (LNO), HNiO2, and LixH1-xNiO2 to deconvolute the different effects playing a role during the drying/heating step after washing.At first, we washed the pristine material with an excess of water (CAM:H2O mass-ratio of 1:5), to examine the effect of washing. The model material HNiO2 (Nickel oxohydroxide) was also synthesized from a simple water-based synthesis. Afterwards, TGA-MS analysis was performed in order to deconvolute the release of physisorbed water from the evolution of water and O2 produced by the thermal decomposition of the surface protonated species of the washed material. The TGA-MS protocol contains a temperature hold phase at 25 °C, then a heat ramp (10 K/min) to 120 °C with a hold at this temperature for 30 minutes, followed by a second temperature ramp to 450 °C, and a final hold at this temperature (see upper panel, Figure 1). In Figure 1 (upper panel), the weight loss of the measured samples is shown. After the initial release of physisorbed water from the washed LNO at ≈ 180 °C (m/z = 18 trace, see middle panel). At higher temperatures (>250 °C), a release of oxygen (m/z=32 trace, see bottom panel) is initiating, and the overall weight loss amounts to ≈ 0.75 wt.% once a temperature of 450 °C is reached. In contrast, when the pristine unwashed LNO sample is heated to 450 °C, the overall weight loss is only minor (<0.1 wt%) and no O2 is evolved (black lines).Surprisingly, the model HNiO2 material does not show the thermal separation of water and oxygen evolution, and both gases are starting to evolve simultaneously at ≈ 180 °C (see red lines). By chemical partial lithiation of HNiO2 to produce LixH1-xNiO2, the oxygen evolution is shifted to higher temperatures, so that water and oxygen are not being evolved anymore at the same temperature, as was the case for washed LNO. We will discuss the likely mechanism for this behavior, supporting our arguments with a surface and bulk by means of NEXAFS on pristine and washed-and-heated materials. Furthermore, the reactivity of the differently washed/heated CAMs and the model compounds with the electrolyte will be examined by O-MS. Acknowledgement This work is financially supported by the BASF SE Network on Electrochemistry and Battery Research.

Study of the Reactions between Ni-Rich Positive Electrode Materials and Aqueous Solutions and their Relation to the Failure of Li-Ion Cells

The handling of positive electrode active materials must be done carefully due to their propensity to degrade when exposed to ambient atmosphere. The growth of impurities on Ni-rich layered lithium transition metal oxides (LTMOs) is particularly concerning as these materials readily react with H2O and CO2 in atmosphere. The resulting surface impurity species have detrimental effects on the performance of the Li-ion cell and are commonly removed by washing the positive electrode active materials. However, little is understood about the reaction between these materials and aqueous solutions. In this study, LTMOs samples were exposed to acidic and neutral aqueous solutions for various periods of time. The resulting material samples were analysed by X-ray powder diffraction (XRD), thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and by scanning electron microscopy (SEM). The solutions collected after washing were analysed by pH titration and inductively coupled plasma optical emission spectrometry (ICP-OES). From this, we propose two pH-dependent regimes that define the reaction between the positive electrode material and the aqueous solution used for washing. Possible consequences of these reactions on cell performance and lifetime are discussed.

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid.

In this study, in situ infrared spectroscopy techniques and thermogravimetric analysis coupled with mass spectrometry (TGA-MS) are employed to characterize the reactivity of the ionic liquid, 1-butyl-3-methylimidazolium dicyanoborohydride (BMIM+DCBH-), in comparison to the well-characterized 1-butyl-3-methylimidazolium dicyanamide (BMIM+DCA-) ionic liquid. TGA measurements determined the enthalpy of vaporization (ΔHvap) to be 112.7 ± 12.3 kJ/mol at 298 K. A rapid scan Fourier transform infrared spectrometer was used to obtain vibrational information useful in tracking the appearance and disappearance of species in the hypergolic reactions of BMIM+DCBH- and BMIM+DCA- with white fuming nitric acid (WFNA) and in the thermal decomposition of these energetic ionic liquids. Attenuated total reflectance measurements recorded the infrared spectra of the reactant sample (BMIM+DCBH-) and the liquid reaction products after reacting with WFNA. Computational chemistry efforts, aided by the experimental results, were used to propose key reaction pathways leading to the hypergolic ignition of BMIM+DCBH- + WFNA. Experimental results indicate that the hypergolic reaction of BMIM+DCBH- with WFNA generates both common and unique intermediates as compared to previous BMIM+DCA- + WFNA investigations: nitrous oxide was generated during both hypergolic reactions indicating that it may play a crucial role in the hypergolic ignition process, NO2 was generated in significantly higher concentrations for BMIM+DCBH- than for BMIM+DCA-, CO2 was only generated for BMIM+DCA-, and HCN was only generated during thermal decomposition and hypergolic ignition of BMIM+DCBH-.