Fuel cell advantages

High PEM Fuel Cell Advantage and Characteristics of its AC Impedance PEM fuel cells operated at high temperatures (> 100°C) have several advantages over those operated at lower temperatures (1) faster electrochemical kinetics, (2) improved and simplified water management, (3) effective thermal management,... 

The industrial economy depends heavily on electrochemical processes. Electrochemical systems have inherent advantages such as ambient temperature operation, easily controlled reaction rates, and minimal environmental impact (qv). Electrosynthesis is used in a number of commercial processes. Batteries and fuel cells, used for the interconversion and storage of energy, are not limited by the Carnot efficiency of thermal devices. Corrosion, another electrochemical process, is estimated to cost hundreds of millions of dollars aimuaUy in the United States alone (see Corrosion and CORROSION control). Electrochemical systems can be described using the fundamental principles of thermodynamics, kinetics, and transport phenomena. 

The great disadvantage of any battery, however advanced, for automobile power trains, is the long time required to charge a battery, and in my view this will be decisive. Here, fuel cells have an enormous advantage over batteries, and so I turn to fuel cells next. 

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. 

It is expected that the fuel cell should be able to compete with an IC engine in terms of size and weight. As an added advantage, many fuel cell components can be configured into a relatively wide array of shapes to take advantage of space onboard the vehicle. 

While hydrogen engines have some advantages over natural-gas engines, the hydrogen fuel cell offers a true quantum leap in both emissions and efficiency. 

Natural gas also has an efficiency advantage in electricity generation. The economic and operational superiority of gas-fired combustion turbines and combined-cycle machines (and prospectively, the superiority of gas-powered fuel cells) relative to coal-and nuclear-powered steam turbines made the combination of natural gas and natural gas turbines the supply favorite of most electric utilities in the 1990s. 

Note that fuel cells do not provide a new source of energy. They are designed to use conventional, currently available fuels. Their main advantage lies in the efficiency of their operation, which creates fewer byproducts to threaten the environment. 

Fuel cells such as the one shown on Fig. 3.4a convert H2 to H20 and produce electrical power with no intermediate combustion cycle. Thus their thermodynamic efficiency compares favorably with thermal power generation which is limited by Carnot-type constraints. One important advantage of solid electrolyte fuel cells is that, due to their high operating temperature (typically 700° to 1100°C), they offer the possibility of "internal reforming" which permits the use of fuels such as methane without a separate external reformer.33 36... 

Qualitatively similar behaviour for methanol oxidation on Pt/YSZ was reported by Cavalca, Larsen, Vayenas and Haller51 who used the single chamber design51 instead of the fuel-cell type design of the earlier study of Neophytides and Vayenas.50 Cavalca et al51 took advantage of the electrophobic... 

This reaction is of great technological interest in the area of solid oxide fuel cells (SOFC) since it is catalyzed by the Ni surface of the Ni-stabilized Zr02 cermet used as the anode material in power-producing SOFC units.60,61 The ability of SOFC units to reform methane "internally", i.e. in the anode compartment, permits the direct use of methane or natural gas as the fuel, without a separate external reformer, and thus constitutes a significant advantage of SOFC in relation to low temperature fuel cells. 

The problem was solved by Francis Bacon, a British scientist and engineer, who developed an idea proposed by Sir William Grove in 18.39. A fuel cell generates electricity directly from a chemical reaction, as in a battery, but uses reactants that are supplied continuously, as in an engine. A fuel cell that runs on hydrogen and oxygen is currently installed on the space shuttle (see Fig. L.l). An advantage of this fuel cell is that the only product of the cell reaction, water, can be used for life support. 

Conversely, the use of elevated temperatures will be most advantageous when the current is determined by the rate of a preceding chemical reaction or when the electron transfer occurs via an indirect route involving a rate-determining chemical process. An example of the latter is the oxidation of amines at a nickel anode where the limiting current shows marked temperature dependence (Fleischmann et al., 1972a). The complete anodic oxidation of organic compounds to carbon dioxide is favoured by an increase in temperature and much fuel cell research has been carried out at temperatures up to 700°C. 

This type of cell operates at the highest temperature (1000 °C) of all current fuel cell types. This high operating temperature has many advantages including producing steam suitable for co-generation, the ability to reform many fuels efficiently and the overall fast kinetics of the... 

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... 

The advantage of a fuel cell over a conventional battery is that the fuel for electrical power can be replenished easily. Just as we pull into a service station to refill the gas tank, owners of automobiles powered by fuel cells will refill their fiiel tanks with hydrogen or butane. 

Figure 8.33. Schematic of the efficiencies of a fuel cell driven car and a conventional car with a combustion engine. Note the advantage of the fuel cell car at low load, prevailing under urban driving conditions.

---