Electrodes fabrication

Very substantial advances have been made in terms of improvements in electrode stmctures and increases in the Pt utili2ation as illustrated in Figure 1. It appears that Pt loadings of less than 0.2 mg Pt/cm are adequate to obtain acceptable performance in PEFCs using pure H2 as the fuel (see Thin films). Whereas early electrodes contained 4 mg Pt/cm, the most recent developments in electrode fabrication have permitted Pt loadings to be reduced to 0.13 mg Pt/cm in a thin-film stmcture, while maintaining high performance. 

All AB, alloys are very brittle and are pulverized to fine particles in the hydrid-ing-dehydriding process (see Sec. 7.2.1). Thus electrodes must be designed to accommodate fine powders as the active material. There are several methods of electrode fabrication Sakai et al [35] pulverize the alloy by subjecting it to several hydrogen absorption-desorption cycles, before coating the resulting particles with Ni by chemical plating. The powder is mixed with a Teflon dispersion to obtain a paste which is finally roller-pressed to a sheet and then hot-pressed to an expanded nickel mesh. The fabrication of a simple paste electrode suitable for laboratory studies is reported by Petrov et al. [37],... 

Figure 9. SET transistor, based on self-assembling of gold nanoclusters on electrodes fabricated by electron-beam epitaxy. (Reprinted with permission from Ref [26], 1997, American Institute of Physics.)...

A similar route has been followed most recently by Weiss et al. who have fabricated a multi-island SE device from self-assembled ID gold nanocrystal chains [28]. They assembled thiol-stabilized 50 nm Au particles in a chainlike structure and used subsequently electron-beam lithography for electrode fabrication. Here it has to be... 

Fig. 8 (a) The I-V curve measured for a junction consisting of an LB monolayer of margaric acid formed on an Al bottom electrode and a top Au electrode fabricated via the PALO technique, (b) Semilogarithmic plot of current density vs the chain-length of fatty-acid monolayers. The fit to a straight line gives a slope of fl = 0.86 A-1. (Reprinted with permission from [78])... 

Xu X, Jiang Z, Fan X, and Xia C. LSM-SDC electrodes fabricated with an ion-impregnating process for SOFCs with doped ceria electrolytes. Solid State Ionics 2006 177 2113-2117. 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

Rajalakshmi, N., and Dhathathreyan, K. S, Gatalyst layer in PEMFG electrodes— Fabrication, characterization and analysis. Chemical Engineering Journal 2007 129 31. ... 

The most efficient system devised by Monsanto uses electrodes fabricated from carbon steel plate, electro-coated on one face with cadmium. These are stacked in parallel so that the electrolyte can be pumped through the gap between successive plates. Overall tire system forms a series of electrochemical cells with a cadmium cathode and a carbon steel anode. Each plate of metal forms the cathode of one cell and the anode of the next in the stack. Electric current is passed across the stack. The electrolyte contains phosphate and borate salts as corrosion inhibitors, EDTA to chelate any cadmium and iron ions generated by corrosion together with hex-amethylenebis(ethyldibutylammonium) phosphate to provide the necessary telraal-kylammonium ions. This electrolyte circulates through the cell from a reservoir and there is provision for the introduction of acjylonitrile and water as feedstock. The overall cell reaction is ... 

Cgo single molecules between electrodes fabricated by electromigration [103] to create single Cgo molecule transistors were measured at a temperature of 40 mK. The results showed the coexistence and competition of the effects of Coulomb repulsion, Kondo correlations and superconductivity [104]. The Kondo effect had been previously observed in similar devices [105]. Recently a SAM of a tricarboxylic acid fullerene derivative was used to fabricate a transistor. The SAM was created by allowing the fullerene compound to self assemble on top of an AI2O3 layer just above the aluminum drain electrode the source lead was created by... 

Fig. 5a-d AFM images of DNA assembled in various devices, a Mixed-sequence DNA between platinum electrodes spaced by 40 nm. Scale bar 50 nm. b Height image of poly(dG)-poly(dC) DNA bundles on platinum electrodes. The distance between electrodes is 200 nm, and the scale bar is 1 um. c High magnification image of the device shown in b. Several DNA bundles clearly extend over the two electrodes. Scale bar 200 nm. d Poly(dG)-poly(dC) DNA bundles on platinum electrodes fabricated on a mica substrate. Scale bar 500 nm. For all these devices, no conduction was observed (from [59], with permission Copyright 2001 by the American Institute of Physics)... 

Bayer AG has addressed this problem by patenting [152] electrodes fabricated from nickel or coated with nickel [153] having a columnar structure. Since these electrodes are said not to corrode, they allow long-term, continuous fluorination and require lower voltages, making the process more economical. 

As the technology of electrode fabrication has advanced, the use of microelectrodes in electrochemistiy has allowed new kinds of experiments to be done. Explain why the use of microelectrodes in C.V allows fast scan experiments (up to 1,000,000 V per second) to be done. (Gosser)... 

FIG. 21. Cross section through a commercial Prototech electrode fabricated from a carbon fabric impregnated with PTFE- bonded, Pt-catalyzed soot particles. The layer of light color below the electrode is the SiC matrix, determined to keep the electrolyte between the electrodes. 

Practical aspects of electrode fabrication are discussed in D. T. Sawyer,... 

V. CARBON FILM ELECTRODES A. Carbon Film Electrode Fabrication... 

Similar data were obtained with an electrode fabricated from tannic acid-dispersed Air-Spun graphite 200-10 vs. a silver-silver chloride electrode in cell DC-1 (Figure 9). 

In another series of experiments electrodes fabricated from several carbon materials were tannic acid-dispersed and performance-tested in DC-1 against silver-silver chloride. Generally it was necessary to soak the electrode (after drying) in a concentrated sodium chloride solution to coagulate the carbon more completely before mounting in the cell. In this series, a feed solution of 0.03V sodium chloride, identical applied voltages (0.30... 

Y. Sekine and E.A.H. Hall, A lactulose sensor based on coupled enzyme reactions with a ring electrode fabricated from tetrathiafulvalen-tetra-cyanoquinodimetane, Biosens. Bioelectron., 13(9) (1998) 995-1005. 

S. Hashioka, M. Saito, E. Tamiya and H. Matsumura, Deoxyribonucleic acid sensing device with 40-nm-gap-electrodes fabricated by low-cost conventional techniques, Appl. Phy. Lett., 85 (2004) 687-688. 

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