Nalini P. Subramanian

Highly Active Carbon Composite Electrocatalysts for PEM Fuel Cells

Highly active carbon composite catalysts were developed using a carbon based metal-free catalyst developed at USC as a support through catalyzed pyrolysis followed by chemical post-treatments. Materials characterization studies indicated that the nature of nitrogen functional groups on the carbon surface and the carbon nanostructures play a critical role in the activity and stability. The catalytic activity as high as 2.0 A cm at 0.2 V was obtained for the carbon composite catalyst in the fuel cell, and no irreversible activity loss was observed during stability test.

Analysis of Molten Carbonate Fuel Cell Performance Using a Three-Phase Homogeneous Model

In this study a three-phase homogeneous model was developed to simulate the performance of the molten carbonate fuel cell ~MCFC! cathode. The homogeneous model is based on volume averaging of different variables in the three phases over a small volume element. This approach can be used to model porous electrodes as it represents the real system much better than the conventional agglomerate model. Using the homogeneous model the polarization characteristics of the MCFC cathode was studied under different operating conditions.

Full Cell Mathematical Model of a MCFC

Fuel cells convert chemical energy into electrical energy and have the advantage of continuous operation due to continuous supply of reactant gases. The high temperature molten carbonate fuel cell ~MCFC! like any other fuel cell offers clean and efficient energy and is currently used in stationary power applications. The state-ofthe-art MCFC includes NiO cathode, Ni-Cr anode, stainless steel ~SS! current collectors and 32-68 mol % of Li2CO3 /K2CO3 electrolyte held in LiAlO2 matrix. Current research efforts are aimed at increasing the performance and the lifetime of the MCFC through development of better cell components. Researchers interested in improving MCFC performance need to focus on cell components that have scope for yielding the maximum decrease in cell polarization. A full cell model would prove useful in analyzing the performance of MCFC in detail and in determining voltage losses in different regions of the cell. Previous modeling work in MCFC was focused on studying the performance of individual electrodes under different gas compositions and temperature. Yuh and Selman 1 modeled the performance of the MCFC cathode

OPTIMIZATION OF THE CATHODE LONG-TERM STABILITY IN MOLTEN CARBONATE FUEL CELLS: EXPERIMENTAL STUDY AND MATHEMATICAL MODELING

This project focused on addressing the two main problems associated with state of art Molten Carbonate Fuel Cells, namely loss of cathode active material and stainless steel current collector deterioration due to corrosion. We followed a dual approach where in the first case we developed novel materials to replace the cathode and current collector currently used in molten carbonate fuel cells. In the second case we improved the performance of conventional cathode and current collectors through surface modification. States of art NiO cathode in MCFC undergo dissolution in the cathode melt thereby limiting the lifetime of the cell. To prevent this we deposited cobalt using an electroless deposition process. We also coated perovskite (La{sub 0.8}Sr{sub 0.2}CoO{sub 3}) in NiO thorough a sol-gel process. The electrochemical oxidation behavior of Co and perovskites coated electrodes is similar to that of the bare NiO cathode. Co and perovskite coatings on the surface decrease the dissolution of Ni into the melt and thereby stabilize the cathode. Both, cobalt and provskites coated nickel oxide, show a higher polarization compared to that of nickel oxide, which could be due to the reduced surface area. Cobalt substituted lithium nickel oxide (LiNi{sub 0.8}Co{sub 0.2}O{sub 2}) and lithium cobalt oxide were also studied. LiNi{sub x}Co{sub 1-x}O{sub 2} was synthesized by solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor. LiNi{sub x}Co{sub 1-x}O{sub 2} showed smaller dissolution of nickel than state of art nickel oxide cathode. The performance was comparable to that of nickel oxide. The corrosion of the current collector in the cathode side was also studied. The corrosion characteristics of both SS304 and SS304 coated with Co-Ni alloy were studied. This study confirms that surface modification of SS304 leads to the formation of complex scales with better barrier properties and better electronic conductivity at 650 C. A three phase homogeneous model was developed to simulate the performance of the molten carbonate fuel cell cathode and the complete fuel cell. The homogeneous model is based on volume averaging of different variables in the three phases over a small volume element. This approach can be used to model porous electrodes as it represents the real system much better than the conventional agglomerate model. Using the homogeneous model the polarization characteristics of the MCFC cathode and fuel cell were studied under different operating conditions. Both the cathode and the full cell model give good fits to the experimental data.