ICMCTF2010 Session TS2: Coatings for Fuel Cells and Batteries

Monday, April 26, 2010 1:30 PM in Room Royal Palm 4-6
Monday Afternoon

Time Period MoA2 Sessions | Abstract Timeline | Topic TS2 Sessions | Time Periods | Topics | ICMCTF2010 Schedule

Start Invited? Item
1:30 PM TS2-3 Recent Progress in Development of Protective Coatings for SOFC Interconnect at PNNL
Gordon Xia, Josh Templeton, Zimin Nie, Gary Yang, Jeff Stevenson, Xiaohong (Shari) Li (Pacific Northwest National Laboratory)
Due to their good oxidation resistance and excellent thermal expansion match to the other stack components, ferritic stainless steels are among the most promising candidate materials for interconnect applications in intermediate-temperature planar SOFC stacks. In particular, newly developed compositions demonstrate improved properties relevant to the interconnect applications over traditional ones. However, to help accelerate commercialization of SOFC technology, it is desirable to find more cost-effective alternatives for the applications. Thus, efforts have been initiated to identify and develop ferritic stainless steels that demonstrate comparable performance to the newly developed alloys, but are more cost-effective. This paper will present details of recent progress on this work, including evaluation of the effectiveness of protective coatings on the inexpensive candidate steels.
1:50 PM TS2-4 Effect of Substrate Alloy Composition on Oxidation and Electrical Conductivity Behavior of Co-plated Interconnect Steels
Jiahong Zhu, Zhonghe Bi (Tennessee Technological University)

In the planar design of a solid oxide fuel cell (SOFC) stack, the interconnect acts not only as electrical connection between the various cells but also as the mechanical support for the thin electroactive ceramic parts and as gas-proof separation of air and fuel gas. With the reduction of the SOFC operating temperatures to 600-800°C, chromia-forming ferritic steels are widely used as interconnect materials in the planar-type SOFC stacks currently under development. One of the most serious problems for these ferritic steels such as Crofer 22 APU is the Cr volatility and associated “poisoning” of the cathode under the operating environments of SOFC. Co plating is widely used for protecting these interconnect alloys, with the Co layer subsequently thermally converted into a Co-containing spinel coating at the SOFC operating temperatures; however, the effect of the substrate alloy composition on the microstructure, composition and the electrical conductivity of the converted spinel coating has not been systematically evaluated. In this presentation, six Fe-Cr alloy substrates with different compositions including three relatively simple model alloys and three commercial alloys were electrodeposited with a 5-mm Co layer, followed by thermal oxidization at 800°C in air for 100 h. The surface morphology and scale microstructure of the oxide layer formed on different substrates were studied with X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. It was demonstrated that the addition of La and Mn into the alloys appeared to alter scale growth behavior of the plated Co layer, with La leading to a more adherent scale/metal interface and Mn leading to a thinner Cr2O3 layer. In addition, diffusion of Co into the substrates was observed except for the SS430 substrate. Outward diffusion of Mn was restricted to the Cr-rich scale layer, leading to formation of a Co3O4 spinel outer layer essentially free of Mn. For the three commercial alloy substrates (Crofer 22 APU, SS430, and ZMG 232), the thickness of the Cr-rich oxide scale was much thinner and their area-specific resistance (ASR) was lower than that of three home-made alloys. The scale ASR of the different alloys could be correlated with the thickness of the Cr-rich oxide scale formed on them.

2:10 PM TS2-6 Constitution, Microstructure, and Battery Performance of Magnetron Sputtered Li-Co-O Thin Film Cathodes for Lithium-Ion Batteries as a Function of the Working Gas Pressure
Carlos Ziebert, Bernt Ketterer, Monika Rinke, Christel Adelhelm, Sven Ulrich, Karl-Heinz Zum Gahr, Sylvio Indris, Thomas Schimmel (Karlsruhe Institute of Technology, Germany)

Despite of their widely use in mobile communication and portable electronic equipment there is a strong need for further development and optimization of the components for lithium-ion batteries, especially for the positive electrode (cathode). Nanocrystalline thin film cathode materials are of increasing interest due to their potential to provide both high power and high energy density.

Li-Co-O thin film cathodes have been deposited onto Si and stainless steel substrates by RF magnetron sputtering from a ceramic LiCoO2 target at various working gas pressures ranging from 0.15 to 25 Pa. The composition, crystal structure and thin film morphology were examined using inductive coupled plasma optical emission spectroscopy (ICP-OES), carrier gas hot extraction (CGHE), X-ray diffraction (XRD), Raman spectroscopy (RS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thin film properties such as intrinsic stress, conductivity and film density were determined. As deposited films at 0.15 Pa as well as in the range between 5 Pa and 10 Pa working gas pressure showed a nanocrystalline metastable rocksalt structure with an unordered cation arrangement and were nearly stoichiometric.

With increasing annealing temperature a cation ordering process was observed by XRD. Heat treatment of the films deposited at 10 Pa Argon gas pressure at 600 °C leads to the formation of the hexagonal high temperature phase HT-LiCoO2 with a layered structure. The Raman spectrum of the films deposited at 0.15 Pa and annealed at 400°C indicates the formation of the low temperature phase LT-LiCoO2 with a cubic spinel-related structure, which is assumed to be stabilized due to high compressive stress in the film.

The battery performance of the as grown and the annealed thin film cathodes was studied and it was revealed that the discharge capacity strongly depends on the crystal structure of the films. Thin Li-Co-O films with a perfect layered HT-LiCoO2 structure showed the highest discharge capacities.
2:30 PM Invited TS2-7 Anode Coatings for a Direct Glucose Fuel Cell Application
Tanja Vidakovic (Otto-von-Guericke-Unversity, Germany); Ivan Ivanov (Max-Planck-Insittue, Germany); Kai Sundmacher (Otto-von-Guericke-Unversity & Max-Planck-Institute, Germany)

In this presentation some of our efforts to date on different anode coatings for application in a direct glucose fuel cell will be reviewed. Our initial research in this area focused on gold and gold surfaces coated by self-assembled monolayer (SAM) [1]. We have shown that the activity of gold for glucose oxidation is strongly influenced by temperature and an applied potential window. The rough gold undergoes structural changes at elevated temperature, which leads to loss of activity for glucose oxidation and lower affinity for the self-assembly. The transformation of "active" into "inactive" surface can be prevented by SAM formation. The SAM modified gold exhibits high activity for glucose oxidation.

The SAM modified gold surface was further used for enzyme (glucose-oxidase (GOx)) immobilization. For this purpose the pyrroloquinoline quinine (PQQ) mediator was covalently attached, followed by an attachment of a modified enzyme cofactor flavin adenine dinucleotide (FAD) and a reconstitution of an apo-GOx. Our results showed that the activity for glucose oxidation decreases with an increase of number of layers and the activity of enzyme modified gold electrode can not be assigned to enzyme itself.

Our recent approach concentrates on use of conductive organic salts (charge transfer complexes (CTC)) as an active surface for enzyme immobilization [2]. This enzymatic electrode exhibits high stability and activity for glucose oxidation and significant oxygen tolerance. The influence of different parameters, including CTC loading and morphology, GOx loading, membrane thickness, etc. on the activity of the bioanode has been investigated.

[1] Ivanov, I.; Vidaković, T.; Sundmacher, K. The influence of a self-assembled monolayer on the activity of rough gold for glucose oxidation, Electrochemistry Communications 2008, 10, 1307

[2] Ivanov, I.; Vidaković, T.; Sundmacher, K. Glucose Electrooxidation for Biofuel Cell Applications. Chemical and Biochemical Engineering Quarterly 2009, 23, 77.

3:10 PM TS2-9 Pseudocapacitive Performance of Hybrid Manganese Oxide Films with Multiwalled-CNTs Additions
Chung-Kwei Lin, Chien-Yie Tsay, C.-H. Wu, Chin-Yi Chen (Feng Chia University, Taiwan); Sheng-Chang Wang (Southern Taiwan University, Taiwan)
In the present study, hybrid manganese oxide films with additions of multiwalled carbon nanotubes (MWCNTs) were prepared by sol-gel process. Manganese acetate was used as the precursors and MWCNTs were added during the process. The effects of MWCNTs addition and post heat treatment on the material characteristics and pseudocapacitive performance of the hybrid MWCNTs/MnOx films were investigated. These films were characterized by X-ray diffraction and scanning electron microscopy. Pseudocapacitive performance of the films was evaluated by cyclic voltammetry (CV). In addition, synchrotron X-ray absorption spectroscopy was used to reveal the difference before and after CV test. Experimental results showed that manganese oxide composed of Mn3O4 and Mn2O3 phase. MWCNTs served as the template for the growth of manganese oxide films. With the addition of MWCNTs, not only the specific capacitance increased but also the reliability improved. Among the hybrid films prepared in the present study, manganese oxide films with 0.05 wt.% MWCNTs addition heat treated at 350 oC exhibited the best electrochemical performance.
3:30 PM TS2-10 Conductive Coatings for Stainless Steel Bipolar Plates for PEM Fuel Cells
Gayatri Dadheech, Mahmoud Abd Elhamid (General Motors)
Stainless steel is a candidate for use as a metallic bipolar plate material in proton exchange membrane fuel cells (PEMFCs). It offers many advantages over conventional graphite plates, yet stainless steel has a passive resistive oxide which reduces the overall power output of the PEMFC. It is therefore necessary to reduce the contact resistance across the interface between metallic bipolar plate and porous gas diffusion medium (GDM) to improve the fuel cell performance. An electrochemically stable and electrically conducting coating has been developed to reduce the interfacial contact resistance at the GDM and stainless steel bipolar plates for its use in PEM fuel cells. The approach relies on coating the bipolar plates with a nano-thin layer of gold using a physical vapor deposition technique or by other similar methods. The results show that the interfacial contact resistance is decreased by as much as a factor of four when these coatings are applied on stainless steel bipolar plates. Data from ex-situ and in-situ fuel cell testing demonstrate the impact on overall fuel cell performance of the nano-thin gold coatings.

3:50 PM TS2-12 Deposition of Hydrothermally Synthesized Pt on Carbon Nanofibers for Use as Direct Methanol Fuel Cell Electrodes
Chieh-Yun Huang, Chih-Ming Chung, Jyh-Ming Ting (National Cheng Kung University, Taiwan)

Deposition of Pt particles on carboneous materials using wet impregnation, physicalevaporation, electrodeposition, microwave-assisted polyol strategy, supercritical fluid method, and microemulsion have been reported. These methods, however, are often complex and not environmentally friendly, and often require expensive equipments. In this paper, we report the dposition of Pt particles on carbon nanofibers (CNFs) using a convenient hydrothermal method. The sizes and the distribution of the resulting Pt particles can be effectively controlled using this method. The obtained Pt modified CNFs were characterized using transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy. Electrodes were also fabricated using selected Pt modified CNFs for using in direct methanol fuel cells. The electrodes were examined for the methanol electro-oxidation using cyclic voltammetry.

Time Period MoA2 Sessions | Abstract Timeline | Topic TS2 Sessions | Time Periods | Topics | ICMCTF2010 Schedule