Characterization of 3D Interconnected Microstructural Network in Mixed Ionic and Electronic Conducting Ceramic Composites

The microstructure and connectivity of the ionic and electronic conductive phases in composite ceramic membranes are directly related to device performance. Transmission electron microscopy (TEM) including chemical mapping combined with X-ray nanotomography (XNT) have been used to characterize the composition and 3-D microstructure of a MIEC composite model system consisting of a Ce0.8Gd0.2O2 (GDC) oxygen ion conductive phase and a CoFe2O4 (CFO) electronic conductive phase. The microstructural data is discussed, including the composition and distribution of an emergent phase which takes the form of isolated and distinct regions. Performance implications are considered with regards to the design of new material systems which evolve under non-equilibrium operating conditions

Three-Dimensional Microstructural Imaging and Charge Transport Modeling Tools for Fuel Cell Materials

Fuel cells and other electrochemical energy storage and conversion technologies are increasingly being used as clean energy alternatives for mobile and stationary power generation. The viability of fuel cells as a marketable energy source continues to benefit from improvements in performance, longevity, and cost. Each of these factors is intimately linked to the performance of materials which constitute these systems, leading to significant research dedicated to optimization of underlying fuel cell components and materials. A commonality among fuel cell types is their reliance on effective transport of ions, electrons, and gases through three-dimensional transport networks that have complex underlying structures, often on the micro- and nano-scales. The present work is dedicated to aiding in fuel cell materials design by developing methods which elucidate the role of three-dimensional microstructure in transport. Digital representations of fuel cell material microstructure are first obtained by either a) artificially generating ideal structures that mimic the behavior of the real system or b) imaging real microstructure samples by a three-dimensional imaging technique, synchrotron-based x-ray nanotomography. An existing charge transport model, called Electrochemical Fin Theory, based on extended surface fin analysis is then adapted for the study of three-dimensional structures relevant to solid oxide and electrospun polymer electrolyte membrane fuel cells. The application and validation of this electrochemical fin modeling approach showcases the benefits of using this technique, which include sensitivity to local inhomogeneities, and significantly reduced computational requirements when compared to traditional mesh-based numerical simulations

Three-dimensional microstructural mapping of poisoning phases in the Neodymium Nickelate solid oxide fuel cell cathode

Nd-Nickelate (NNO), Nd1.95NiO4+delta, an alternative solid oxide fuel cell cathode material, has been imaged and mapped in 3D using synchrotron-based x-ray nanotomography. The NNO cathode material, which suffered from silicon contamination during fabrication, was found to contain the desired NNO, plus two distinct poisoning phases. The likely composition and description of the poisoning phases are presented, as well as a detailed description of the microstructural mapping and material characterization. The insulating poisoning phases are likely to have deleterious implications for the cell, as they have a tendency to form a coating layer on the NNO surface, significantly decreasing its active area. Additional losses may be expected due to the poisoning phases inhibiting ionic and electronic transport pathways, increasing cathode polarization resistance. (C) 2013 Elsevier B.V. All rights reserved