Electrochemical process for benzanthrones and planar polycyclic aromatic oxo compounds

The title compds., useful in the prodn. of dye intermediates, are prepd. in acid media in an electrolysis cell whose electrodes are sepd. by a membrane. At the cathode, anthraquinones are reductively cyclized with glycerol [56-81-5] to give the corresponding benzanthrones. In the anode chamber the oxidn. state of a transition metal ion is electrochem. increased by 1 and the resulting ion serves as a chem. oxidant for a planar polycyclic arom. compd. Thus, to the cathode chamber contg. 46.8 g anthraquinone [84-65-1] in 1300 g H2SO4, 31.05 g glycerol was added dropwise while the current was running. On the anodic side 10 g MnSO4.H2O was suspended in 130 g 88% H2SO4. benzanthrone [82-05-3] (85%) Was isolated from the cathodic portion, while the anolyte was used to cyclooxidize 10 g 4,4'-bibenzanthrone [116-90-5] to dioxoviolanthrone [64346-54-9] which was reduced with NaHSO3 to dihydroxyviolanthrone (I) [26545-62-0] in 76.4% yield. I was used as an intermediate in the synthesis of vat dyes. [on SciFinder (R)]

Towards reproducible lithium-ion battery cycling using liquid-phase transmission electron microscopy

Jing Hou

Electric vehicles (EVs) have gained widespread attention in recent years as the dominant strategy for curbing CO2 emissions through transport electrification. Lithium-ion batteries (LIBs) are currently the most suitable and almost exclusively employed energy storage device for powering EVs. Nickel-rich layered oxides of the general formula LiNixCoyMnzO2 (NCM) are widely used as the cathode in LIBs due to their high capacity and low cost. However, the increasing nickel content reduces the stability for the higher energy density that is particularly required for meeting the mileage demand. Hence, understanding the degradation mechanisms of Ni-rich NCM is of great importance for optimizing the performance of battery systems. This thesis aims to develop methodologies for reproducible and reliable testing of battery systems using transmission electron microscopy (TEM) in the liquid phase in order to probe, at the nanoscale, the evolution of the cathode materials as they respond to the electrochemical charge/discharge cycling. In detail, this thesis first establishes lithium-ion battery electrochemical processes in a microcell, such as electroplating and charge/discharge analysis. The setup is optimized through the electrode configuration and preparation, while the cycling conditions are adapted for achieving similar electrochemical performance as compared to the conventional bulk cell. With the optimized cell, primary NCM particles are probed using in situ electrochemical cells coupled with a scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDS). The electrochemically induced evolution of NCM that is analyzed using liquid cell TEM uncovers the various degradation mechanisms for the same material under different cycling conditions and for specimens with different Ni content that are cycled under the same conditions. The results offer insights for controlling the electrochemical parameters in the liquid cell for battery studies. Ultimately, the structural and chemical information on the degradation of NCM cathodes can guide our way for designing more advanced NCM cathodes with desirable capacity and enhanced stability simultaneously.

EPFL2021

Alternative anode materials for methane oxidation in solid oxide fuel cells

Joseph Sfeir

Fuel Cells are electrochemical devices that are able to directly convert chemical energy to electrical energy, without any Carnot limitation. Hence, their energy efficiencies are relatively high. Among the various types of fuel cells, solid oxide fuel cells (SOFC) are operated at high temperatures and in principle can run on various fuels such as natural gas and hydrogen. As natural gas is sought to become one of the main fuels of the next decades, its direct feed to a SOFC is desirable as the reaction free energy is high CH4 + 2O2 = CO2 + 2H2O, ΔrG°800°C = -800.8kJ/mol At present, conventional SOFC are operated with pure hydrogen or partially to fully reformed natural gas implying an efficiency penalty. SOFC anodes are generally made of electrocatalytically active Ni-YSZ cermet. Pure CH4 is not fed directly to the anode, because of problems associated with the anode deactivation and coking as CH4 leads to the detachment of Ni particles from the YSZ support and their encapsulation by carbon. To overcome this problem, partially oxidized or reformed CH4 is used. For SOFCs running on direct CH4 feed, alternative anode materials to Ni-YSZ, or new anode formulations are necessary. However, in this case, several parameters influence the anode performance and stability. The anodes should withstand reduction at a low PO2 of around 10-24 atm, be compatible with the SOFC electrolyte, possess an acceptable conductivity and thermal expansion coefficient, and appropriate catalytic and electrocatalytic properties along with low coking activity. LaCrO3 and CeO2-based materials as well as some metal catalysts were studied here for their potential application as anodes in direct oxidation of CH4. This choice of materials was made as lanthanum chromite and ceria-based materials are mixed conductors known to resist quite well to the very reducing conditions in SOFC as they are commonly used for interconnect and electrolyte materials respectively. Moreover, these compounds possess some catalytic activity for CH4 activation and combustion. LaCrO3 and CeO2-based materials show rather low electrical conductivity (on the order of 1 S/cm in reducing conditions), necessitating the application of an extra material for proper current collection. Nevertheless, these oxides possess many of the stringent characteristics cited above. For SOFC anode purposes, LaCrO3-based compounds, substituted with Ca, Sr, Mg, Mn, Fe, Co and Ni, were synthesized by a modified citrate route from nitrate precursors. An optimal calcination temperature of 1100°C was found to be necessary to obtain XRD-pure yet sinteractive compounds. Conductivity measurements in air and in reducing atmospheres of 10-21 atm showed that the La A-site substituents (Ca and Sr) influenced the conductivity more than the Cr B-site substituents (Mg, Mn, Fe, Co and Ni). In humidifed H2, the total conductivity was maximally of 6.5 S/cm. Surface reaction with YSZ electrolyte was evidenced by SEM, XPS and SIMS, in reducing conditions, especially under current load, when these powders were applied as anodes. A current induced demixing effect was noted for heavily substituted LaCrO3. Ceria-based compounds, doped with Y, Nb, Pr and Gd, were synthesized through 3 different techniques: the solid-state method, coprecipitation and the NbCl5 route. The coprecipitation route was found to be most appropriate for Y, Pr and Gd, whereas for Nb a modified precipitation and the NbCl5 technique were the most efficient. Co-doping of Nb and Gd or Pr was studied in order to increase the electronic as well as the ionic conductivity in CeO2. Among all dopants, Nb was found to promote most the adhesion to YSZ electrolyte sheets. Adding Nb to Gd-doped ceria improved the electrode adhesion on YSZ sheets, but deteriorated its conductivity in oxidizing conditions. No interfacial reaction with YSZ was observed by HRTEM when Nb-doped ceria anodes were sintered on YSZ at 1200°C/4h. Catalytic measurements were undertaken with these materials in CH4 rich atmospheres. Different reaction mixtures were chosen to simulate the various SOFC operating conditions: partial oxidation, CO2 reforming by recycling and H2O reforming. Among the different elements, Sr and Ni were found to be the most active substituents for LaCrO3, as they promote all three types of reactions. The combination of both elements is favorable not only for catalytic use, but also for electrode application as they tend to increase the electronic conductivity of the material. Temperature programmed oxidation (TPO) and TEM made on the catalysts after runs in CH4, showed a very low carbon coverage over these oxides, except in the case of Fe substitution, over which carbon deposition was promoted. XPS analysis showed also that all B-site substituted compounds did not segregate after the catalytic runs whereas Ca and Sr (A-site substituents) tended to segregate in H2 and H2O rich atmospheres. Thermodynamic calculations, made using correlations developed in literature, show that Ca and Sr are expected to segregate in H2 and H2O rich atmospheres as they tend to form volatile hydroxyl species. Also, the thermodynamic stability of the LaCrO3 was observed to depend much on the substitution. For CeO2-based oxides, the activity for steam reforming increased from Nb

EPFL2002

Electrochemical model of solid oxide fuel cell for simulation at the stack scale. Part II: Implementation of degradation processes

Stefan Diethelm, Daniel Favrat, Arata Nakajo, Pietro Tanasini, Jan Van Herle

The degradation of the electrochemical performance of solid oxide fuel cell (SOFC) devices is a major hurdle to overcome before commercialisation. The interplay between the phenomena and the long testing times complicate the research, which highlights the relevance of modelling to propose mitigation approaches. This study comprises two parts. This Part II proposes approaches for the simulation of the degradation induced by: (i) interconnect corrosion, (ii) loss of ionic conductivity of the ion-conducting materials, (iii) nickel particle growth in the anode, (iv) chromium contamination and (v) formation of insulating phases in the cathode. The literature survey highlights the lack of data for a completely consistent calibration of the models, despite the simplifications. The support for the implementation is the electrochemical model validated in Part I and a two-dimensional model of the cell and interconnection system. The cathode largely contributes to the degradation. The local overpotential predominantly governs chromium contamination, which can promote the formation of insulating phases, as operation proceeds. The local electronic current density has comparatively a weak direct influence on the degradation. Qualitative agreement with experimental data from the literature could be achieved, without dedicated adjustments of the parameters. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3596435] All rights reserved.