Fuel Cell Analysis

The following is a tabulation of conversion factors common to fuel cell analysis. 

XAS has been successfully employed in the characterization of a number of catalysts used in low temperature fuel cells. Analysis of the XANES region has enabled determination of the oxidation state of metal atoms in the catalyst or, in the case of Pt, the d band vacancy per atom, while analysis of the EXAFS has proved to be a valuable structural tool. However, the principal advantage of XAS is that it can be used in situ, in a flooded half-cell or true fuel cell environment. While the number of publications has been limited thus far, the increased availability of synchrotron radiation sources, improvements in beam lines brought about by the development of third generation sources, and the development of more readily used analysis software should increase the accessibility of the method. It is hoped that this review will enable the nonexpert to understand both the power and limitations of XAS in characterizing fuel cell electrocatalysts. 

Sundmacher K, Scott K (1999) Direct methanol polymer electrolyte fuel cell analysis of charge and mass transfer in the vapour-liquid-solid system. Chem Eng Sci 54 2927-2936... 

Operations of most fuel cell power systems involve a mixture of gases. Therefore, we need to perform thermodynamic analysis and transport phenomena analysis with a mixture of gases. The gas mixture may be a mixture of ideal gases or a mixture of real gases. In this book, the presentation of fuel cell analysis is restricted to the mixture of ideal gases only. 

Zero-Order Fuel Cell Analysis Model... 

Provides case studies on fuel cell analysis... 

The degree of enzyme purity will ultimately affect fuel cell performance, particularly when enzyme preparations are used to form immobilized films on electrode surfaces in DET reactions. Contaminating proteins that do not provide electron transfer effectively foul the electrode. When enzyme immobilization techniques are specific to the enzyme, then enzyme purity may not be as much as an issue, but rarely the immobilization technique is absolutely specific to the cathodic or anodic enzyme. For example, an attractive immobilization strategy is to link a particular enzyme to an electrode via its cofactor (e.g., flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD), etc.) [59]. The cofactor is linked to the electrode material first and then the apoenzyme is allowed to naturally bind to the cofactor all other proteins in the enzyme preparation that cannot bind the cofactor remain unbound and can be removed. Enzymes used in fuel cells are not so unique, and proteins in the immobilizing preparation may use the same cofactor but not the same fuel during fuel cell analysis or operation. 

At the catalyst-electrolyte surface we have gas-phase diffusion, and there can also be additional surface diffusion. In surface diffusion, gas molecules physically or chemically absorb onto a solid surface. If it is physical absorption, the species are highly mobUe. If it is chemisorption and the molecule is more strongly bonded to the specific site, species are not directly mobile but can move via a hopping mechanism. Surface diffusion rates can be measured by direct measurement of the flux of a nonreacting gas across the material surface. The difference between the measured diffusion and predicted Knudsen diffusion is calculated to be the surface diffusion component. Values of the surface diffusion coefficient (Ds) are 10 cm /s in solids and liquids, but these vary widely since surface interaction is involved. Also, Ds is a strong function of temperature and surface concentration. Surface diffusion adds to the overall diffusion but is typically less than one-half of the Knudsen component and so has been mostly neglected in fuel cell analysis. 

W. Gopel, and H.-D. Wiemhofer, Electrode kinetics and interface analysis of solid electrolytes for fuel cells and sensors, Ber. Buns. Phys. Chem. 94, 981-987 (1990). 

In order to describe the geometrical and structural properties of several anode electrodes of the molten carbonate fuel cell (MCFC), a fractal analysis has been applied. Four kinds of the anode electrodes, such as Ni, Ni-Cr (lOwt.%), Ni-NiaAl (7wt.%), Ni-Cr (5wt.%)-NijAl(5wt.%) were prepared [1,2] and their fractal dimensions were evaluated by nitrogen adsorption (fractal FHH equation) and mercury porosimetry. These methods of fractal analysis and the resulting values are discussed and compared with other characteristic methods and the performances as anode of MCFC. 

According to the procedure of sol deposition described in Section 2.3, more than 10% Au can be deposited on XC72R, thus allowing the use of the catalysts in fuel cells and other electrochemical applications [36]. In all the experiments the common mother gold solution 1 (Section 2.3) was used containing a low PVA amount (PVA Au = 0.05) in order to facilitate the adsorption step. Table 8 shows the results. According to ICP analysis, an almost total gold adsorption was obtained. 

Wang Y, Li L, Hu L, Zhuang L, Lu J, Xu B. 2003. A feasibility analysis for alkaline membrane direct methanol fuel cell Thermodynamic disadvantages versus kinetic advantages. Electrochem Commun 5 662. 

Aqueous, alkaline fuel cells, as used by NASA for supplemental power in spacecraft, are intolerant to C02 in the oxidant. The strongly alkaline electrolyte acts as an efficient scrubber for any C02, even down to the ppm level, but the resultant carbonate alters the performance unacceptably. This behavior was recognized as early as the mid 1960 s as a way to control space cabin C02 levels and recover and recycle the chemically bound oxygen. While these devices had been built and operated at bench scale before 1970, the first comprehensive analysis of their electrochemistry was put forth in a series of papers in 1974 [27]. The system comprises a bipolar array of fuel cells through whose cathode chamber COz-containing air is passed. The electrolyte, aqueous Cs2C03, is immobilized in a thin (0.25 0.75 mm) membrane. The electrodes are nickel-based fuel cell electrodes, designed to be hydrophobic with PTFE. 

Lehrhofer, J. et al., Integrated analysis of the "sponge iron reactor" and fuel cell system, Proc. 1996 Fuel Cell Seminar, Orlando, FL, 710,1996. 

Worldwide over 150 demonstration plants have been installed. These represent around 40 to 50 MW of electrical generating capacity. Nearly 75% is installed in Japan, over 15% in North America, and 9% in Europe. The U.S.-based International Fuel Cells (IFC) and its partner Toshiba are responsible for producing over 70%, Fuji over 25%, and Mitsubishi about 2% (WFCC analysis). These phosphoric acid systems are operating in real world commercial situations and have clearly demonstrated their suitability for on-site cogeneration. 

IEA Implementing Agreement on Advanced Fuel Cells, Annex V Fuel Cell System Analysis, Final Report, May 1995. 

Choi YM, Compson C, Lin MC, and Liu M. Ab initio analysis of sulfur tolerance of Ni, Cu, and Ni-Cu alloys for solid oxide fuel cells. J Alloys Compd 2007 427 25-29. 

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