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Hydrogen-Oxygen Fuel Cells: Case Study

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Introduction

HSC Chemistry Research Assignment Topic: The Production of Materials Lloyd Ruz Cell Type: Hydrogen-Oxygen Fuel Cell The structure of the cell The Hydrogen-Oxygen Fuel cell uses hydrogen as its fuel source. The basic structure of such a fuel cell is outlined below: Figure 8A The chemistry of this cell will be outlined below. The chemistry and function of the cell Two separate half-cell reactions occur to produce a flow of electrons (current): * At the Anode, Hydrogen gas is oxidised, allowing protons (H+) to enter the proton exchange membrane (or polymer electrolyte membrane, coincidentally, both mean the same thing, in this case, and have the same abbreviation: PEM) and electrons (e-) to travel around a circuit to the cathode. Hence the following oxidation reaction takes place: * At the Cathode, protons that have permeated through the membrane and oxygen molecule which has dissolved through the electrode are reduced by electrons that have completed the circuit. Hence, the following reduction reaction takes place: � . . . . . . . . (1,5,6,7,8) These reactions and the flow of electrons are shown in Figure 8A (above) and again below in Figure 9 Figure 9 When the electrolyte is an alkaline (as in a Alkaline fuel cell with an anion exchange membrane), such as in Figure 6A (below), the following half reactions take place: Anode: H2(g) + 2OH-(aq) � 2H2O(l) ...read more.

Middle

Military Technologies PEM, AEM and others -Efficiency -Versatility -Length of Running Time -Quiet Operation (3,4,7) Cost considerations There are a variety of cost considerations that arise in the production and application of Hydrogen-Oxygen Fuel Cells: * Cost of Catalyst - The oxidations and reduction half-reactions require the use of a precious metal catalyst, usually platinum or an alloy of platinum, palladium, or ruthenium. And as these metals are in scarce supply and high demand, the cost of obtaining them is quite high.(1) * Cost of Hydrogen Production The production of Hydrogen can be achieved in a number of ways: (a) Electrolysis of water is the most effective way of producing hydrogen gas. However, this reaction requires electricity. There are two possibilities for producing hydrogen this way: immediate cell regeneration and solar electrolysis plants. Neither of these is currently very efficient for the following reasons: To minimise the amount of energy needed and hence create an efficient regenerative cell, a catalyst is needed to lower the activation energy of the electrolysis. The catalyst used is a manufactured compound called Rubippy similar to chlorophyllwith a metal centre (in chlorophyll it's a magnesium ion, in rubippy it's a ruthenium ion) and an attached system of organic rings (in chlorophyll its a porphyrin derivative, in rubippy its a pyridine derivative). ...read more.

Conclusion

+ H2O (g) � 3H2(g) + CO (g) (10) The other impact comes from the steam, which is produced through the burning of fossil fuels. For this reason, Hydrogen extraction from methane (or any other hydrocarbon) is not an acceptable method as it defeats or undermines the 'clean' functioning of the fuel cell. (10) Large scale electrolysis with non-renewable energy sources undermines the fuel cell function in the same way. For this reason, research is being conducted into another type of PEM fuel cell: the regenerative fuel cell. (2) Cost considerations above (catalyst and energy needed) are merely proof of the fact that research in this field is young. NASA and other scientific (and commercial) organizations all around the world are conducting research into this type of cell in the hope of creating a truly 'clean' energy source with little to no negative environmental impact. (2,4,5,10) Another Type of fuel cell, the solid oxide fuel cell uses methanol-like fuels to extract hydrogen for fuel. This produces carbon dioxide and hence offsets the environmental benefit of fuel cells, however, the use of this type of fuel cell (as it is more convenient than a PEM, using a hydrocarbon fuel) may make fuel-cell-powered cars more common. This could eventually result in a replacement of Solid Oxide fuel cells with PEM fuel cells (in individual cars) once the technology is more developed and 'get the ball rolling' for fuel cell cars becoming commonplace. (4) ...read more.

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