Electrochemical studies of capacitance in cerium oxide thin films and its relationship to anionic and electronic defect densities

Small polaron carrier density in epitaxial, doped CeO_2 thin films under low oxygen partial pressure was determined from electrochemically-measured capacitance after accounting for interfacial effects and shown to agree well with bulk values

Modulating metal-oxygen bonding in lithiated metal oxides with point defects

The strength of the metal-oxygen (M-O) bond in oxides principally determines the band structure and the stability of oxygen relative to O2 gas. Accordingly, such bonding is central to energy storage (for determining the redox potential) and electrocatalysis (for determining adsorbate bonding strength at the electrochemical interface). Traditionally, the M-O bond strength is tuned by changing the metal. We have recently discovered another important knob in LiXMO2: metal vacancies and antisite defects. In these materials, which are ubiquitous as positive electrodes in lithium-ion batteries, metal vacancies can form by moving a metal into the Li van der Waals gap. X-ray and neutron scattering measurements confirmed that introducing metal vacancies can substantially contract neighboring M-O bond length, transforming single bonds to double bonds (i.e., terminal metal oxo ligand). In select local configurations, even the peroxo species (O-O)2- can form. These variations of oxygen bonding leads to dramatic variation in the energetics of the bonding and antibonding states as well as the stability of oxygen relative O2 gas. In this talk, I will discuss the connection between local defect configurations and the M-O and O-O bonding in LiXMO2, where M spans 3d, 4d and 5d transition metals

Ionic and Electronic Conductivity of Nanostructured, Samaria-Doped Ceria

The ionic and electronic conductivities of samaria doped ceria electrolytes, Ce_(0.85)Sm_(0.15)O_(1.925−δ), with nanometric grain size have been evaluated. Nanostructured bulk specimens were obtained using a combination of high specific-surface-area starting materials and suitable sintering profiles under conventional, pressureless conditions. Bulk specimens with relatively high density (≥92% of theoretical density) and low medium grain size (as small as 33 nm) were achieved. Electrical A.C. impedance spectra were recorded over wide temperature (150 to 650°C) and oxygen partial pressure ranges (0.21 to 10^(−31) atm). Under all measurement conditions the total conductivity decreased monotonically with decreasing grain size. In both the electrolytic and mixed conducting regimes this behavior is attributed to the high number density of high resistance grain boundaries. The results suggest a possible variation in effective grain boundary width with grain size, as well as a possible variation in specific grain boundary resistance with decreasing oxygen partial pressure. No evidence appears for either enhanced reducibility or enhanced electronic conductivity upon nanostructuring

High electrochemical activity of the oxide phase in model ceria–Pt and ceria–Ni composite anodes

Fuel cells, and in particular solid-oxide fuel cells (SOFCs), enable high-efficiency conversion of chemical fuels into useful electrical energy and, as such, are expected to play a major role in a sustainable-energy future. A key step in the fuel-cell energy-conversion process is the electro-oxidation of the fuel at the anode. There has been increasing evidence in recent years that the presence of CeO_2-based oxides (ceria) in the anodes of SOFCs with oxygen-ion-conducting electrolytes significantly lowers the activation overpotential for hydrogen oxidation. Most of these studies, however, employ porous, composite electrode structures with ill-defined geometry and uncontrolled interfacial properties. Accordingly, the means by which electrocatalysis is enhanced has remained unclear. Here we demonstrate unambiguously, through the use of ceria–metal structures with well-defined geometries and interfaces, that the near-equilibrium H_2 oxidation reaction pathway is dominated by electrocatalysis at the oxide/gas interface with minimal contributions from the oxide/metal/gas triple-phase boundaries, even for structures with reaction-site densities approaching those of commercial SOFCs. This insight points towards ceria nanostructuring as a route to enhanced activity, rather than the traditional paradigm of metal-catalyst nanostructuring

Ceria as a Thermochemical Reaction Medium for Selectively Generating Syngas or Methane from H_2O and CO_2

Doped CeO_2 with a low specific surface area is thermochemically cycled between MO_2 and MO_(2-δ) using H_2O and CO_2 as oxidants. The system rapidly and selectively produces syngas in the absence of a metal catalyst, and CH_4 in the presence of Ni. The Ni catalyst, which permits intermediate C to form on its surface, is proposed to shift the product from syngas to CH_4

Inverse opal ceria–zirconia: architectural engineering for heterogeneous catalysis

The application of inverse opal structured materials is extended to the ceria–zirconia (Ce_(0.5)Zr_(0.5)O_2) system and the significance of material architecture on heterogeneous catalysis, specifically, chemical oxidation, is examined

Ifitm3 Limits the Severity of Acute Influenza in Mice

Interferon-induced transmembrane (IFITM) proteins are a family of viral restriction factors that inhibit the entry processes of several pathogenic viruses, including influenza A virus (IAV), in vitro. Here we report that IAV-infected knockout mice lacking the Ifitm locus on chromosome 7 exhibited accelerated disease progression, greater mortality, and higher pulmonary and systemic viral burdens as compared to wild type controls. We further observed that the phenotype of Ifitm3-specific knockout mice was indistinguishable from that of mice lacking the entire Ifitm locus. Ifitm3 was expressed by IAV target cells including alveolar type II pneumocytes and tracheal/bronchial respiratory epithelial cells. Robust Ifitm3 expression was also observed in several tissues in the absence of infection. Among murine Ifitm promoters, only that of Ifitm3 could be induced by type I and II interferons. Ifitm3 could also be upregulated by the gp130 cytokines IL-6 and oncostatin M on cells expressing appropriate receptors, suggesting that multiple cytokine signals could contribute to Ifitm3 expression in a cell or tissue-specific manner. Collectively, these findings establish a central role for Ifitm3 in limiting acute influenza in vivo, and provide further insight into Ifitm3 expression and regulation

Electrochemical kinetics of SEI growth on carbon black, II: Modeling

Mathematical models of capacity fade can reduce the time and cost of lithium-ion battery development and deployment, and growth of the solid-electrolyte interphase (SEI) is a major source of capacity fade. Experiments in Part I reveal nonlinear voltage dependence and strong charge-discharge asymmetry in SEI growth on carbon black negative electrodes, which is not captured by previous models. Here, we present a theoretical model for the electrochemical kinetics of SEI growth coupled to lithium intercalation, which accurately predicts experimental results with few adjustable parameters. The key hypothesis is that the initial SEI is a mixed ion-electron conductor, and its electronic conductivity varies approximately with the square of the local lithium concentration, consistent with hopping conduction of electrons along percolating networks. By including a lithium-ion concentration dependence for the electronic conductivity in the SEI, the bulk SEI thus modulates the overpotential and exchange current of the electrolyte reduction reaction. As a result, SEI growth is promoted during lithiation but suppressed during delithiation. This new insight establishes the fundamental electrochemistry of SEI growth kinetics. Our model improves upon existing models by introducing the effects of electrochemical SEI growth and its dependence on potential, current magnitude, and current direction in predicting capacity fade.Comment: 1 manuscript, 7 main text figures, 2 supplementary information figure