Alkaline fuel cells nickel catalysts

A significant cost advantage of alkaline fuel cells is that both anode and cathode reactions can be effectively catalyzed with nonprecious, relatively inexpensive metals. To date, most low cost catalyst development work has been directed towards Raney nickel powders for anodes and silver-based powders for cathodes. The essential characteristics of the catalyst structure are high electronic conductivity and stability (mechanical, chemical, and electrochemical). 

Alkaline fuel cells (AFC) — The first practical -+fuel cell (FC) was introduced by -> Bacon [i]. This was an alkaline fuel cell using a nickel anode, a nickel oxide cathode, and an alkaline aqueous electrolyte solution. The alkaline fuel cell (AFC) is classified among the low-temperature FCs. As such, it is advantageous over the protonic fuel cells, namely the -> polymer-electrolyte-membrane fuel cells (PEM) and the - phosphoric acid fuel cells, which require a large amount of platinum, making them too expensive. The fast oxygen reduction kinetics and the non-platinum cathode catalyst make the alkaline cell attractive. 

Alkaline Fuel Cell The electrolyte for NASA s space shuttle orbiter fuel cell is 35 percent potassium hydroxide. The cell operates between 353 and 363 K (176 and 194°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinum-palladium and platinum-gold alloy powder catalysts bonded with polytetrafluoro-ethylene (PTFE) latex and supported on gold-plated nickel screens for current collection and gas distribution. A variety of materials, including asbestos and potassium titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are usually nickel, plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 27-62. 

Hydrogen was the only really useful non-exotic fuel, but using it with relatively inexpensive nickel catalysts in an alkaline fuel cell required high temperatures and pressures, costly pressure vessels, and ancillary equipment. 

The alkaline fuel cell (AFC) with its liqnid alkaline electrolyte KOH uses gas diffusion electrodes with a hydrophobic porous part, which is not flooded by the alkaline electrolyte, and a hydrophilic part containing electrolyte and thus leading to a three-dimensional three-phase boundary layer. As the electrode potentials in alkaline electrolyte are shifted towards more negative values, corrosion is less problematic. Raney Nickel and silver are the state-of-the-art catalysts. The practical use... 

Multicomponent alloys of nickel and aluminum activated by Ti, Mo are most widespread and wide by used materials for hydrogen electrodes of low temperature alkaline fuel cells. To make hydrogen electrodes skeletal nickel prepared by alkali-soluble of alloy with composition 50 %Ni -i- 47 % A1 -i-3 % Ti is used. Raney catalyst is processed by 20 % suspense of Fluoroplast F-4 D with following drying in vacuum at 50 °C that permits pyrophoric catalyst to protect against self combustion and serves hydrophobic binder to form electrodes [5]. 

A considerable contribution to the development of alkaline fuel cells was made toward the end of the 1950s by the German physicists Eduard Justi and his coworkers. They made electrodes with nonplatinum catalysts, the so-called Raney-type skeleton metals nickel for the hydrogen side and silver for the oxygen side (Justi et al. 1954). The catalysts were included into a matrix of carbonyl nickel. These electrodes were named Doppel-Skelett (DSK) = double skeleton electrodes (Justi and Winsel, 1962). 

In 1966, the Institut Francaise de Petrole (IFP) designed and built a methanol fuel processor of much smaller size for an alkaline fuel cell [12], which is shown in Figure 9.2. The methanol steam reformer was operated at 250 °C and contained a fixed bed of copper/chromium catalyst. The alkaline fuel cell required the removal of carbon dioxide from the reformate and thus a small diethanol-amine gas scrubber was built. Residual carbon oxides were removed by a methanation reactor, which contained a nickel/chromium fixed catalyst bed. 

AUcaline fuel cells (AFCs, hydrogen-fuelled cells with an alkaline liquid electrolyte such as KOH(aq)) are the best performing of all known conventional hydrogen-oxygen fuel cells operable at temperatures below 200 C. This is due to the facile kinetics at the cathode and at the anode cheaper non-noble metal catalysts can be used (such as nickel and silver [3,4]), reducing cost. McLean et al. gave comprehensive review of alkaline fuel cell technology [5]. The associated fuel cell reactions both for a traditional AFC and also for an AMFC are ... 

Alkaline fuel cells (AFCs) were used to provide electrical power for many manned spacecrafts. The electrolyte is KOH and the catalysts include silver, nickel, and different metal oxides. AFC catalysts are relatively inexpensive compared to catalysts used for other types of fuel cells. The fuel and oxidant used in an AFC must be completely free of CO2 since even a small amount reacts strongly with the electrolyte, producing forms of carbonates that poison the ionic conductivity of the electrolyte. Therefore, pure hydrogen and oxygen must be used, limiting the use of the AFC to special applications, like spacecrafts and submarines, where cost of the fuel and oxidant is not a major issue. 

Transition metal alloys, notably Raney nickel, have also been investigated extensively as catalysts because of their interesting electronic and chemical properties [94]. Raney nickel is a solid catalyst, composed of fine grains of a nickel-aluminum alloy, and has been used in many industrial processes. Its application in the fuel cell field has been focused on alkaline fuel cells (AFC) rather than PEM fuel cells, due to potential corrosion in PEM operation media. Raney nickel s unique catalytic activity for the HOR as a non-noble catalyst makes it worth inclusion in this chapter. 

Linnekoski JA, Juha A, Krause, AO, Keskinen J, Lamminen J, Anttila T. Processing of Raney-nickel catalysts for alkaline fuel cell apphcations. J Fuel Cell Sci Technol 2007 4(l) 45-8. 

The alkaline fuel cell (AFC) uses an alkaline electrolyte such as potassium hydroxide (usually in a solution of water) in order to operate. AFC systems are classified as low-temperature fuel cells and usually operate between 60°C and 90°C. AFCs use a variety of metals to speed up the reactions at the anode and cathode, with Nickel being the most commonly used catalyst. 

In the Soviet Union, the power plant Photon was developed jointly for the Buran space shuttle by the Urals Integrated Electrochemical Plant (which had also been concerned with problems of nuclear energy) and the S. P. Korolev Rocket and Space Corporation. The Photon power plant weighed 160 kg and had a sustained power of 10 kW (with a maximum load of 15 kW). The alkaline fuel cells in this plant were of the matrix type and had hydrophobized electrodes with a porous nickel support and 20 mg/cm of platinum catalysts. Because of discontinuation of the Buran project, the experience gained when developing the Photon battery was used subsequently in building power plants for test models of electric cars (Korovin, 2005). 

The anode electrode-catalyst is one of the important components of the alkaline fuel cell as it helps in the electro-oxidation of fuel. It is desirable that the anode electrode-catalyst provides faster reaction kinetics and 100% oxidation of fuels to CO2 and H2O. The most widely used catalyst, without doubt, is platinum. Platinum seems to be the best choice for acidic solutions, but other metallic alloy with platinum or other metals can match its performance in alkaline medium because of the favorable fuel oxidation in alkaline medium. Different anode materials based on Pt (Prabhuram et al. 1998, Moralldn et al. 1995, Tripkivic et al. 1996), Pt-Ru (Wang et al. 2003, Manoharan et al. 2001), Co-W alloys (Shobba et al. 2002), sintered Ag/ PdO (Koscher et al. 2003), spent carbon electrodes impregnated with Fe, Fe" or Ag (Verma 2000), nickel impregnated silicate-1 (Khalil et al. 2005) and nickel dimethylglyoxime complex (Golikand et al. 2005) are some of the catalysts studied for the electro-oxidation of methanol in alkaline medium. 

The hydrogen-oxygen cell used in the space shuttle is called an alkali fuel cell, because it has an alkaline electrolyte. Both electrodes are nickel, but in some versions a platinum catalyst is used. 

Alkaline. Fuels are hydrogen and oxygen in a concentrated solution of potassium hydroxide at room temperature. The possible advantage is the use of non-platinum catalysts such as Raney nickel and silver on carbon supports. This is at an earlier stage of development than the other cells. 

The endothermic reaction is favored by high temperature and low pressure and is accelerated by the presence of nickel or iron catalysts. NH3 can be burned directly in combustion engines or used in solid oxide fuel cells without preprocessing [238]. In alkaline and PEM fuel cells, the ammonia has first to be decomposed according to the above reaction. For the PEM cell, even trace amounts of ammonia left in the gas after decomposition must be removed [239]. 

The faster kinetics of alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells opens up the possibility of using less expensive Pt-free catalysts, as nickel, gold, palladium and their alloys [30]. Thus, the cost of ADAFC could be potentially lower compared to the acid DAFC technology if non-precious metal alloys are used for the alcohol electrooxidation, being the nanoparticulated Ni-Fe-Co alloys developed by Acta (Italy) with the trade name of HYPERMEC a good example. 

Abstract The faster kinetics of the alcohol oxidation reaction in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel, and palladium, makes the alkaline direct alcohol fuel cell a potentially low-cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. In this work an overview of catalysts for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol, and ethylene glycol, formed by these materials, is presented. 

However, for technical use of AFC, the long-term behavior of AFC components is important, especially that of the electrodes. Nickel can be used for the hydrogen oxidation reaction (catalyst in the anode) and on the cathode silver can be used as catalyst (see next section), no expensive noble metal (platinum) is necessary, because the oxygen reduction reaction kinetics are more rapid in alkaline electrolytes than in acids and the alkaline electrochanical environment in AFC is less corrosive compared to acid fuel cell conditions. Both catalysts and electrolyte represents a big cost advantage. The advantages of AFC are not restricted only to the cheaper components, as shown by Giilzow [1996]. 

In 1923, Schmid [8, 9] improved fuel-cells electrode, and Scharf [10] developed the hydrogen diffusion electrode. A major advance in alkaline electrochemistry was achieved by Raney [11], who developed the weU-known Raney nickel (high surface-area Ni) catalyst. With this high surface-area electrode, it was possible to achieve a technically relevant performance with a simple catalyst material. 

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