Anne C. Co

A Kinetic Study of the Oxygen Reduction Reaction at LaSrMnO3 - YSZ Composite Electrodes

The primary focus of this paper is on the establishment of reliable methods for the determination of the mechanism and kinetics of the oxygen reduction reaction (ORR) at solid oxide fuel cell cathodes consisting of lanthanum strontium manganite [(La 0 . 8 Sr 0 . 2 ) 0 . 9 8 MnO 3 , LSM] in a 50 vol % mixture with yttria-stabilized zirconia electrolyte (LSM-YSZ composite). Techniques used include half-cell cyclic voltammetry and electrochemical impedance spectroscopy (EIS) methods in a variable po 2 atmosphere at temperatures ranging from 600 to 900°C. The exchange current densities for the ORR, determined both from the low and high field cyclic voltammetry data and from the charge-transfer resistance from EIS data, are shown to agree closely, yielding an apparent activation energy of ca. 120 kJ/mol for the ORR at these composite cathodes. No evidence for diffusion-controlled reactions is seen under the conditions of our work. In this paper we also show the theoretically predicted impact of temperature on the Tafel slope, as well as on the potential range over which the low- and high-field approximations, are valid.

In Situ Quantification and Visualization of Lithium Transport with Neutrons

A real-time quantification of Li transport using a nondestructive neutron method to measure the Li distribution upon charge and discharge in a Li-ion cell is reported. By using in situ neutron depth profiling (NDP), we probed the onset of lithiation in a high-capacity Sn anode and visualized the enrichment of Li atoms on the surface followed by their propagation into the bulk. The delithiation process shows the removal of Li near the surface, which leads to a decreased coulombic efficiency, likely because of trapped Li within the intermetallic material. The developed in situ NDP provides exceptional sensitivity in the temporal and spatial measurement of Li transport within the battery material. This diagnostic tool opens up possibilities to understand rates of Li transport and their distribution to guide materials development for efficient storage mechanisms. Our observations provide important mechanistic insights for the design of advanced battery materials.

Revealing Chemical Processes Involved in Electrochemical (De)Lithiation of Al with in Situ Neutron Depth Profiling and X-ray Diffraction.

Herein we report a direct measurement of Li transport in real-time during charge and discharge process within an Al matrix using neutron depth profiling (NDP). In situ NDP was used to reveal and quantify parasitic losses during the first 25 mAhr/g of lithiation, followed by the formation of LiAl protrusions from the surface of pristine Al. Evidence of Li entrapment is also reported during delithiation. Subsequent lithiation and delithiation showed electrochemical charge passed to be equivalent to the amount of lithium incorporated into the Al matrix with negligible difference, suggesting that the parasitic losses including the formation of the solid electrolyte layer may be confined to the first lithiation. Parallel in situ XRD measurements also confirm the transformation of β-LiAl from a solid solution of α-LiAl, revealing solid solution-mediated crystallization of β-LiAl.

Characterization and performance of anodic mixed culture biofilms in submersed microbial fuel cells

Microbial fuel cells (MFCs) were designed for laboratory scale experiments to study electroactive biofilms in anodic chambers. Anodic biofilms and current generation during biofilm growth were examined using single chambered MFCs submersed in algal catholyte. A culture of the marine green alga Nanochloropsis salina was used as a biocatholyte, and a rumen fluid microbiota was the anodic chamber inoculum. Electrical impedance spectroscopy was performed under varying external resistance once a week to identify mass transport limitations at the biofilm-electrolyte interface during the four-week experiment. The power generation increased from 249 to 461mWm-2 during the time course. Confocal laser scanning microscopy imaging showed that the depth of the bacterial biofilm on the anode was about 65μm. There were more viable bacteria on the biofilm surface and near the biofilm-electrolyte interface as compared to those close to the anode surface. The results suggest that biofilm growth on the anode creates a conductive layer, which can help overcome mass transport limitations in MFCs.

The Potential of Using Li-Ion Batteries for Radiation Detection

This work describes the measurement of the change in current of two types of Li-ion batteries, both commercial off-the-shelf and in-house-assembled coin cells, under radiation exposure. The discharging batteries were irradiated with a neutron beam with a 30-mm diameter (adjustable to 10 mm and 5 mm) using the Ohio State University Research Reactor and was measured for the change of electric current with a Keithley SourceMeter. We have observed an increase in current when the batteries were exposed to gamma rays and a decrease in current when only thermal neutrons were applied. We discussed the mechanisms that are responsible for inducing such changes, including the electrode polarization caused by irradiation. The immediate application of a single coin cell in a current mode can be a small neutron or gamma-beam monitor or a near-core flux monitor in a high-flux environment.

Modification of 4-(2-pyridylazo)-resorcinol postcolumn reagent selectivity through competitive equilibria with chelating ligands

Abstract Aminopolycar☐ylate ligands were added to the 4-(2-pyridylazo)-resorcinol (PAR) postcolumn reagent to alter the reagent selectivity towards transition metals. Addition of ethylenediaminetetraacetic acid (EDTA) completely suppressed the reaction between PAR and the metal ions. Addition of 0.1 mM nitrilotriacetic acid (NTA) to 1 mM PAR lowered the response to specific transition metal ions, but completely suppressed the PAR response to the lanthanides. Increasing the NTA concentration to 8 mM resulted in complete suppression of the PAR response to all metal ions except Cu2+ and Co2+ for which the detection limits were 3 and 1 ng, respectively. The observed selectivity results from the slow rate of conversion of metal ions from the M(NTA)24− form to M(PAR)2.

Enhancing the real-time detection of phase changes in lithium–graphite intercalated compounds through derivative operando (dOp) NMR cyclic voltammetry

Robust and reliable diagnostic tools that can be employed under operating conditions are crucial to understanding performance and failure mechanisms in battery processes. The operando spectrum of a battery often consists of a strongly overlapping mixture of time dependent and independent resonances due to the compositional complexity. Here we report a new method called derivative operando (dOp) that improves the resolution of operando nuclear magnetic resonance (NMR) spectra by removing time independent signals and further distinguishes between time dependent signals associated with the formation and removal of species. This approach not only provides better resolution but also more clearly reveals correlations between resonances and the chemical transformations occurring at a specific potential. With the dOp-NMR method we detect the formation of lithium graphite intercalation compounds (GICs), including the signatures of LiC72 and its precursors, which have been previously undetected. We also observe a clear correlation of the dOp 7Li NMR spectra of lithium metal dendrites on the counter electrode with the chemistry of the working electrode.

Investigation of Chloride Poisoning Resistance for Nitrogen-Doped Carbon Nanostructures as Oxygen Depolarized Cathode Catalysts in Acidic Media

HCl electrolysis used to manufacture Cl2, a compound of high industrial value, suffers from its high energy requirements. Significant energy savings can be attained by an alternative oxygen depolarized cathode (ODC)-based process where oxygen is reduced at the cathode instead of protons. Though the ODC process is extremely attractive, the state of the art catalysts for oxygen reduction reaction (ORR) suffer from chloride ion poisoning and/or involve toxic chemicals such as hydrogen sulfide (H2S). In the present work, we demonstrate that non-metal containing CNx catalysts do not get deactivated upon exposure to chloride ion environment unlike Pt/C or RhxSy/C where significant chloride ion poisoning was observed. The synthesis of these CNx materials is also extremely facile and scalable. In addition, the performance of the synthesized CNx catalysts was found to be very stable in HCl environment. Thus, the results presented here demonstrate the promise of CNx materials as alternative catalysts for ODC-based HCl electrolysis process to manufacture Cl2 in a sustainable and safer way.Graphical Abstract