Films Fuel Cells

In more recent reports, a thin-film fuel cell sandwiched between two silicon wafers that had been anisotropically etched to form feed holes and channels for the reactants (H2 and O2) demonstrated a stable voltage of 0.75 V over 300 h at a current... 

Miniature Thin-Film Fuel Cells. In 1990. C.K. Dyer (Bell Communications Research, Morristown. New Jersey ) reported the successful construction of a tiny electrochemical device (unconventional fuel celli... 

Fig. 41. Cross-section of thin film fuel cell batteries with plate type porous ceramic support. From ref. [110].

Shao, Z., Kwak, C., and Haile, S. M. Anode-Supported Thin-film Fuel Cells Operated in a Single Chamber Configuration, Solid State Ionics, 175, 39 (2004). 

Morse, J.D. Jankowski, A.F. Graff, R.T. Hayes, J.P. Novel proton exchange membrane thin-film fuel cell for microscale energy conversion. Proceedings of the 46th National Symposium of the American Vacuum Society, 25 October-29 October 1999 J. Vac. Sci. Technol. A Vacuum, Surfaces Films 2000, 18, 2003-2005. 

Another power source for cell phones was being developed by a scientist at Motorola, Christopher Dyer. Dyer s thin-film fuel cell would generate power from a gas mixture containing both hydrogen and oxygen (whereas the usual systems need separate gas supplies)—something which Dyer said in a 1999 article9 should result in a simpler and cheaper system. Dyer, who first reported on his work in 1990 when he was still at Bell Communications Research,10 described an extremely thin (less than a millionth of a meter) gas-permeable electrolyte sandwiched between two thin layers of platinum. 

Bell Researcher Develops Thin-Film Fuel Cell, Hydrogen Letter, February 1990. 

Kruigkanand A,LiuZ,DuttaI,WagnerFT (2011) Electrochemical and microstructural evaluation of aged nanostructured thin film fuel cell electrocatalyst. J Electrochem Soc 158(11) B1286-B1291... 

Geneva presented a thin film fuel cell concept in a 1962 patent [12]. Also in 1962, Sandstede from the Battelle Institute in Frankfurt gave the first report on the use of hydrocarbons as fuel in solid oxide cells [13]. At about the same time, fuel cell work was started in France by Kleitz [14], and in Britain, a patent was filed in 1963 [15] to form fuel cells by depositing layers on a porous metallic carrier. In Japan, Takahashi published in 1964 his first results obtained on fuel cells with solid oxide electrolytes [16]. 

Gancs L, Kobayashi T, Debe MK, Atanasoski R, Wieckowski A (2008) Crystallographic characteristics of nanostructured thin-film fuel cell electrocatalysts a HRTEM study. Chem Mater 20(7) 2444-2454... 

FIGURE 42.5 Concept drawing of a thin-film fuel cell (from Ref 1). 

Joseph Bostaph et al., Thin Film Fuel Cells for Low Power, Portable Applications, Proc. of the 39th Power Sources Conf, p. 152, June 2000. 

Modified Leverett Function Appropriate for Fuel Cell Media The standard Leverett function has been found to be appropriate for qualitative matching of the flow characteristics through the media however, actual measurements of PEFC diffusion media show different quantitative behavior. Kumbur et al. [47] presented a modified Leverett function appropriate for thin-film fuel cell DM to estimate the capillary pressure as a function of liquid saturation and hydrophobic additive content This empirical fit was derived from the direct measurement of capillary pressure-saturation for different types of DMs (cloth and paper) with PTFE content ranging from 0 to 20% of weight and a nnicrop-orous layer. Figure 5.35 depicts the measured capillary pressure (Pc) versus nonwetting liquid saturation for carbon paper DM tailored with 20% PTFE content. The nature of the capillary pressure-saturation curves exhibits a continuous S shape, rather than J shape, and yields four inflection points. For saturation leads under 0.5, the capillary pressure in the DM was fit to a modified Leverett function, appropriate for the hydrophobic pores ... 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

There are five classes of fuel cells. Like batteries, they differ in the electrolyte, which can be either liquid (alkaline or acidic), polymer film, molten salt, or ceramic. As Table 1 shows, each type has specific advantages and disadvantages that make it suitable for different applications. Ultimately, however, the fuel cells that win the commercialization race will be those that are the most economical. 

The tape-casting method makes possible the fabrication of films in the region of several hundred micrometers thick. The mechanical strength allows the use of such a solid electrolyte as the structural element for devices such as the high-temperature solid oxide fuel cell in which zirconia-based solid electrolytes are employed both as electrolyte and as mechanical separator of the electrodes. 

The deposition of thin conductive oxide films on flat zirconia components has also received considerable attention both for fuel cell applications20 and also for SEP21 and NEMCA studies.22,23 The interested reader is referred to the original references for experimental details. 

II. Ease of electrical connection Here the main problem is that of efficient electrical current collection, ideally with only two electrical leads entering the reactor and without an excessive number of interconnects, as in fuel cells. This is because the competitor of an electrochemically promoted chemical reactor is not a fuel cell but a classical chemical reactor. The main breakthrough here is the recent discovery of bipolar or wireless NEMCA,8 11 i.e. electrochemical promotion induced on catalyst films deposited on a solid electrolyte but not directly connected to an electronic conductor (wire). 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

Two new technologies have reduced the cost of alkali fuel cells to the point where a European company markets taxis that use them. One is the use of CO2 scrubbers to purify the air supply, making it possible to use atmospheric O2 rather than purified oxygen. The other is the development of ultrathin films of platinum so that a tiny mass of this expensive metal can provide the catalytic surface area needed for efficient fuel-cell operation. 

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