Fuel cell performance

The majority of fuel cells including SOFC are limited largely by ion transport rate through membranes, i.e., ohmic polarization. Studies on the SOFC with the SDC (Ceo.8Smo.2OL9) electrolyte at 500 °C showed that decreasing the thickness of the electrolyte from 0.35 mm to 0.15 mm led to the increase in the current density from 0.2 W/cm to 0.4 Therefore, it is highly desirable to use a 

Ca-stabilized Zr02 and stainless steel have been used as an external support. The key factors for the preparation of the externally supported electrode and electrolyte layers are the compatibility of thermal expansion coefficients of the substrate support and electrodes and their potential interactions. The uncontrolled interactions between electrodes and support substrates could lead to deterioration of the electrodes. 

Self-supported SOFC can be classified into anode-supported and cathode-supported fuel cells. The SOFC assembly for laboratory testing has a shape of button with 1 - 2 cm in diameter and less than 500 im in thickness. The majority of these button cells are anode-supported cells due to the easy of their fabrication as compared with that of the cathode-supported cell. These self-supported fuel cell usually possess thin (5-20 p,m) electrolyte and can operate at reduced temperatures ( 800 °C). The low temperature operation is the key to decrease 

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Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

The single cell thus fabricated was placed in a single chamber station as illustrated in Fig. 2. A humidified mixture of methane and oxygen was supplied to the station so that both electrode compartments were exposed to the same composition of methane and oxygen. For the measurement of the cell temperature, a thermocouple (TC) was placed approximately 4 mm away from the cathode site. For the evaluation of the fuel-cell performance, Ft wires and Inconel gauzes were used as the output terminals and electrical collectors, respectively. 

Zhou WJ, Song SQ, Li WZ, Zhou ZH, Srm GQ, Xin Q, Douvartzides S, Tsiakaras P. 2005. Direct ethanol fuel cells based on PtSn anodes The effect of Sn content on the fuel cell performance. J Power Sources 140 50-58. 

Gasteiger HA, Panels JE, Yan SG. 2004. Dependence of PEM fuel cell performance on catalyst loading. J Power Sources 127 162-171. 

Some PEM fuel cell performance data were obtained using an electrical resistor to provide a variable load. Two digital multimeters and a shunt resistor were used to measure the voltage and current, so we could calculate the power produced. 

Drew, K., Girishkumar, G., Vinodgopal, K., and Kamat, P.V. (2005) Boosting fuel cell performance with a semiconductor photocatalyst Ti02/Pt-Ru hybrid catalyst for methanol oxidation. Journal of Physical Chemistry B, 109 (24), 11851-11857. 

Huebner W, Reed DM, and Anderson HU. Solid oxide fuel cell performance studies anode development. In Singhal SC, Dokiya M, editors. Proceedings of the Sixth International Symposium on Solid Oxide Fuel cells (SOFC-VI), Pennington, NJ The Electrochemical Society, 1999 99(19) 503-512. 

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

The introduction of such a layer can dramatically improve the fuel cell performance. For example, in the SOFC with bilayered anode shown in Figure 6.4, the area-specific polarization resistance for a full cell was reduced to 0.48 Hem2 at 800°C from a value of 1.07 Qcm2 with no anode functional layer [24], Use of an immiscible metal oxide phase (Sn()2) as a sacrificial pore former phase has also been demonstrated as a method to introduce different amounts of porosity in a bilayered anode support, and high electrochemical performance was reported for a cell produced from that anode support (0.54 W/cm2 at 650°C) [25], Use of a separate CFL and current collector layer to improve cathode performance has also been frequently reported (see for example reference [23]). 

Thomas, X., Ren, S., and Gottesfeld, J., Influence of ionomer content in catalyst layers on direct methanol fuel cell performance, Electrochem. Soc., 146, 4354, 1999. 

In a proton exchange membrane (PEM) fuel cell, protons travel through a film 18 microns thick which is the proton exchange membrane. Electrons are blocked by the film and take another path which provides the electric current flow. Over time and usage tiny holes can form on the film which reduces fuel cell performance. If the film is made thicker and stronger, then performance suffers. 

Figure 14.16 the shows fuel cell stack performance of a 1 kWe atmospheric PEMFC stack using PtRu anodes, operating on various gas compositions. As can be clearly seen, already small concentrations of CO lead to a large decrease of fuel cell performance. An air-bleed of 1.5% air in hydrogen is able to mitigate this ef-... 

A. B. Anderson, E. Grantscharova, andS. Seong, Systematic theoretical study of alloys of platinum for enhanced methanol fuel cell performance, J. Electrochem. Soc. 143, 2075-2082 (1996). 

From the above experimental results, it can be seen that the both PtSn catalysts have a similar particle size leading to the same physical surface area. However, the ESAs of these catalysts are significantly different, as indicated by the CV curves. The large difference between ESA values for the two catalysts could only be explained by differences in detailed nanostructure as a consequence of differences in the preparation of the respective catalyst. On the basis of the preparation process and the CV measurement results, a model has been developed for the structures of these PtSn catalysts as shown in Fig. 15.10. The PtSn-1 catalyst is believed to have a Sn core/Pt shell nanostructure while PtSn-2 is believed to have a Pt core/Sn shell structure. Both electrochemical results and fuel cell performance indicate that PtSn-1 catalyst significantly enhances ethanol electrooxidation. Our previous research found that an important difference between PtRu and PtSn catalysts is that the addition of Ru reduces the lattice parameter of Pt, while Sn dilates the lattice parameter. The reduced Pt lattice parameter resulting from Ru addition seems to be unfavorable for ethanol adsorption and degrades the DEFC performance. In this new work on PtSn catalysts with more... 

ASME PTC50, Fuel Cell Performance Code... 

Key Parameter Typical Requirements Expected fuel cell performance... 

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