Gary D. Maupin

Bio: Gary D. Maupin is an academic researcher from Pacific Northwest National Laboratory. The author has contributed to research in topics: Diesel particulate filter & Combustion. The author has an hindex of 17, co-authored 32 publications receiving 2191 citations.

Diffusion Limitations in the Porous Anodes of SOFCs

Abstract: Concentration polarization is important because it determines the maximum power output of a solid oxide fuel cell (SOFC) at high fuel utilization. Anodic concentration polarization occurs when the demand for reactants exceeds the capacity of the porous ceramic anode to supply them by gas diffusion mechanisms. Many models simulate this behavior by assuming an anomolous high value for the tortuosity (eg, t=17), a measure of the bulk diffusional resistance for a porous ceramic. However, recent experiments at several laboratories, including results reported herein, have provided strong evidence that typical sintered powder ceramics (30-50% porosity) have much lower tortuosities (t=2.5-3), indicating that the bulk diffusional resistance is too small to be responsible for concentration polarization. We find evidence that concentration polarization originates in the immediate vicinity of the reactive sites near the anode/electrolyte interface, at the triple phase boundaries (TPBs) between the Ni catalyst particles, the gas, and the oxygen conducting YSZ ceramic. A model is proposed to describe how concentration polarization is controlled by two localized phenomena: competitive adsorption of reactants in areas adjacent to the reactive TPB sites, followed by relatively slow surface diffusion to the reactive sites. The model parameters (adsorption activation energy and surface diffusion coefficients) were more » determined by fitting to well-characterized SOFC voltage-current performance data, and are in good agreement with data from the literature. Results suggest that future SOFC design improvements should focus on optimization of the reactive area, adsorption, and surface diffusion at the anode/electrolyte interface, rather than on anode thicknesses or bulk porosities. « less

Conductive protection layers on oxidation resistant alloys for SOFC interconnect applications

Abstract: Conductive oxide coatings are used as protection layers on metallic interconnects in SOFCs to improve their surface stability and electrical performance, as well as to mitigate or prevent chromium poisoning to cells. This paper discusses materials requirements for this particular application and summarizes our systematic study on varied conductive oxides as potential candidate materials for protection layers on stainless steel substrates. Overall, it appeared that chromites such as (La,Sr)CrO 3 improved surface stability, but might not be good candidates for protection layer applications due to chromium vaporization, albeit at a lower rate than Cr 2 O 3 , from these oxides at high temperatures in air or moist air. The application of non-chromite perovskite (La,Sr)FeO 3 (LSF) protection layers resulted in improved oxidation resistance and electrical performance. It is doubtful, however, that LSF can be an effective barrier to prevent chromium release during long term SOFC stack operation due to chromium diffusion through the LSF coatings. With a high oxygen ion conductivity, the coatings of Sn-doped In 2 O 3 failed to provide protection to the metal substrate and are thus not suitable for the protection layer applications. The best performance was achieved using thermally-grown (Mn,Co) 3 O 4 spinel protection layers that substantially improved the surface stability of the metal substrates, and prevented chromium outward migration.

Solution Combustion Synthesis of Nanoscale Materials

Abstract: Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Radiation effects in crystalline ceramics for the immobilization of high-level nuclear waste and plutonium

Abstract: This review provides a comprehensive evaluation of the state-of-knowledge of radiation effects in crystalline ceramics that may be used for the immobilization of high-level nuclear waste and plutonium. The current understanding of radiation damage processes, defect generation, microstructure development, theoretical methods, and experimental methods are reviewed. Fundamental scientific and technological issues that offer opportunities for research are identified. The most important issue is the need for an understanding of the radiation-induced structural changes at the atomic, microscopic, and macroscopic levels, and the effect of these changes on the release rates of radionuclides during corrosion.

Direct hydrocarbon solid oxide fuel cells.

Abstract: Solid Oxide Fuel Cells (SOFCs) are one of the most promising technologies for future efficient conversion of the chemical energy stored in fuels to electrical energy. One of the primary advantages of SOFCs is the potential to operate with a wide variety of fuels. While H2 is the fuel of choice for most fuel cells, operation with fossil-derived and bio-derived hydrocarbon fuels would bypass the costly requirement of a new H2 infrastructure, and accelerate adoption of fuel cell technology. This is feasible as SOFCs transport oxygen anions from the air electrode (cathode) to the fuel electrode (anode). The primary barrier to the realization of fuel flexible SOFCs is the anode material set. Traditional SOFC anodes are based on Ni composites. While these are very efficient for H2 and CO fuels, Ni catalyzes graphite formation from dry hydrocarbons, leading to rapid degradation of cell performance and possible mechanical failure. This motivates the development of new anode materials and composites. The principle requirements of an anode are oxygen anion conductivity, electronic conductivity, and electrocatalytic activity toward the desired reaction. This entry reviews the primary issues in direct hydrocarbon anode development and discusses the new materials and composites that have been developed to meet this challenge.

Invited review “sol-gel” preparation of high temperature superconducting oxides

Abstract: This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as “chelate gel” or “amorphous chelate” route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.