Operation of the Fuel Cell

The dynamic behavior of fuel cells is of importance to insure the stable operation of the fuel cells under various operating conditions. Among a few different fuel cell types, the direct methanol fuel cell (DMFC) has been known to have advantages especially for portable... 

Figure 24. Typical power curve for a fuel cell. The voltage drops quickly from the OCV due to the formation of the peroxide intermediate. Operation of the fuel cell at the knee of the curve where concentration is limiting performance can damage the electrodes and lead to rapid deterioration of cell operation.

The electrolyte is the heart of any fuel cell. Ideally, this component effectively separates the anode and cathode gases and/or liquids and mediates the electrochemical reaction occurring at the electrodes through conducting a specific ion at very high rates during the operation of the fuel cell. In other words,... 

Electrolysis of water, mentioned above, had been described by the British chemists WilUam Nicholson (1753-1815) and Sir Anthony Carlisle (1768-1842) in 1800. But Grove s experiment seemed to go in the opposite direction. This reverse eleoctrolysis is the basic operation of the fuel cell—the combination of hydrogen gas (H ) and oxygen gas (O ) to produce water and energy, as described in the following chemical equation ... 

The end use defines the quality and quantity of the gas needed. For our purposes, the end use for the hydrogen generated is a fuel for fuel cells. Most commercial hydrogen generating units incorporate a drying mechanism that removes much of the moisture from the gas. This is not appropriate for a fuel cell system. Free water will be abundant and should be removed by a water filter or series of water filters, but it is not necessary to remove very fine aerosols by coalescer or to use water absorption techniques. The reason is that the hydrogen side of the fuel cell membrane needs to remain hydrated (moist at a certain level) to aid and maintain proton transport for the operation of the fuel cell. 

The backing layers also assist in water management during the operation of the fuel cell too little or too much water can cause the cell to cease operation. The correct backing material allows the... 

A planar design allows a passive, full self-breathing operation of the fuel cell. Additional fans or air movers are not needed. 

The proper construction of a stable, well-dispersed, three-dimensional catalyst layer is one of the most critical determinants of performance for a PEM fuel cell. The membrane isolates the reactants from one another and provides an ionic current path from one electrode to another, and the flow fields and gas-diffusion layers distribute the reactants to the catalyst layer, but all of the relevant electrochemical reactions are carried out in the catalyst layers themselves. It is the proper construction of the so-called three-phase interface that allows the reactants and products to be brought into intimate contact and makes possible the operation of the fuel cell. Indeed, it is the tailoring of this layer by Raistrick et al. [1] in 1991 that demonstrated the practical feasibility of lowering precious metal loadings by a faetor of 40 over previous designs and helped to usher in the past deeade of inereased activity and investment in fuel cell development. 

Use of a high methanol concentration but maintaining an adequate concentration in the anode catalyst layer at a given current density to maximize the system specific energy and cell performance. For achieving this aim it is fundamental an optimum design of the fuel supply system (that allows the orientation-independent operation of the fuel cell), the anode current-collector, and the anode diffusion layer. 

Another species generated in situ during operation of the fuel cell is H2O2 produced by incomplete reduction of O2 at the cathode. The presence of H2O2,... 

Fuel cells are developed as a viable alternative for clean energy generation. The rational operation of the fuel cell units is closely related to the development of very active, selective, and poison-resistant catalysts. 

A fuel cell will provide power as long as the reactants are supplied. When multiple high-pressure H2 cylinders are used to supply the H2/ the empty cylinders can be hot-swapped while the other cylinders still supply H2 to the fuel cell stack, and thus the cylinder replacement process does not interrupt the operation of the fuel cell system. The replacement process may only take a few minutes. In contrast, when a secondary battery becomes empty, the recharging process will take hours. When the H2 is supplied by pipelines in the future, the use of H2 will become extremely convenient. 

Preventing drying up of such ultra thin CLs should be carefully considered during the operation of the fuel cell. 

When used to provide H2 for a fuel cell, the liquid circulation loop for the metal hydride H2 storage device is best coimected with the liquid circulation loop for the fuel cell stack. During the operation of the fuel cell, the heat generated will help the metal hydride maintain the temperature. At the same time, the heat taken by the metal hydride helps control the temperature of the stack. With such a configuration, the heat exchanger incorporated in the fuel cell system can be reduced, which in turn lowers the parasitic power consumed by the fan moimted on the heat exchanger. 

In 1839, the English lawyer, judge, and physical scientist WiUiam R. Grove (1811-1896) [3, 4] described the operation of the fuel cell. His invention is closely related to the work of the German chemist Christian Friedrich Schonbein (1799-1868) [5], who described the principle of fuel cells for the first time and who was in contact with Grove. Because of their close interaction, both scientists should be recognized as the discoverers of the fiiU cell. 

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