Energy efficiency fuel cell systems

Mazumder, S.K., Burra, R.K., and Acharya, K. (2007) A ripple-mitigating and energy-efficient fuel cell power-conditioning system. IEEE Trans. Power Electron., 22, 1437-1452. 

Wilson, M. S., S. Moeller-Holst, D. M. Webb, and C. Zawodzinski, Efficient Fuel Cell Systems, 1999 Annual Progress Report Fuel Cells for Transportation (U.S. Department of Energy, Washington D.C., 1999) pp. 80-83. 

Fuel Cell Catalysts. Euel cells (qv) are electrochemical devices that convert the chemical energy of a fuel direcdy into electrical and thermal energy. The fuel cell, an environmentally clean method of power generation (qv), is more efficient than most other energy conversion systems. The main by-product is pure water. 

The utilization principles are shown in Figure 6, where the typical examples are enumerated. Hydrogen turbine has been studied by Japanese WE-NET project and the achieved energy efficiency was as high as about 60 %, which can be competitive with fuel cell system. One of the typical direct energy conversion systems, which have no movable parts and no noise, is fuel cell. Today topics of clean cars have been focused to the cars with PEMFC as was mentioned previously. 

Hagey, G., Marinetti, D., Mueller, E.A., Status of fuel cell system development/Commercialisation and future systems energy, environmental, and economic benefits, pre-prints International Conference, Next Generation Technologies for Efficient Energy End Uses and Fuel Switching, Dortmund, 7-9. April 1992. 

For road transport, fuel cells are the most efficient conversion devices for using hydrogen. For the average drive cycle, which is dominated by a power demand that is only a fraction of the maximum available power, hybrid fuel cell systems offer a clear advantage over internal combustion engines, hybridized or not, when energy use, CO2 emissions and non-greenhouse pollutants are considered. 

One of the applications for hydrogen is for Polymer Electrolyte Membrane (PEM) fuel cells. As mentioned earlier, one application is a hydrogen fuelled hybrid fuel cell / ultra-capacitor transit bus program where significant energy efficiencies can be demonstrated. Another commercial application is for fuel cell powered forklifts and other such fleet applications that requires mobile electrical power with the additional environmental benefits this system provides. Other commercial applications being developed by Canadian industry is for remote back-up power such as the telecommunications industry and for portable fuel cell systems. 

Numerous demonstrations in recent years have shown that the level of performance of present-day polymer electrolyte fuel cells can compete with current energy conversion technologies in power densities and energy efficiencies. However, for large-scale commercialization in automobile and portable applications, the merit function of fuel cell systems—namely, the ratio of power density to cost—must be improved by a factor of 10 or more. Clever engineering and empirical optimization of cells and stacks alone cannot achieve such ambitious performance and cost targets. 

Hence these three key points will determine the energy efficiency and the specific power of the elementary fuel cell an improvement in each component of the cell will increase the power density from 0.175 to 1.05 Wcm, that is, an increase by a factor of 6. As a consequence, for the fuel cell systems the weight and volume will be decreased by a similar factor, for a given power of the system, and presumably the overall cost will be diminished. The improvement in the components of the elementary fuel cell thus has a direct effect on the system technology and therefore on the overall cost. 

Hydrogen as the most efficient and cleanest energy source for fuel-cell power is produced by partial oxidation followed by the water gas-shift reaction and reforming of hydrocarbons or methanol [58]. A small amount of CO (0.3-1%) in the so-produced H2 must be selectively removed because CO greatly poisons Pt/C and Pt-M/C electrocatalysts in proton-exchange-membrane (PEM) fuel cells [59, 60]. PROX of CO in excess H2 is a key reaction in the practical use of H2 in PEM fuel-cell systems. 

Many fuel cell systems have been developed since the first discovery of Sir William Grove. Fuel cell systems can produce electricity from several fuels (hydrogen, natural gas, alcohols, etc.) for many applications stationary power plants, power train sources, APU, and electronic portable devices, with nearly the same energy efficiency (around 40% in electric energy), irrespective of their size (from tens of MW for power plants to a few W for portable electronics). 

Fig. 13.31. Fuel cell efficiency vs. power (International Fuel Cells 50-kWe PEM fuel cell system). (Reprinted from Fuel Cells for Transportation, U.S. Dept, of Energy, 1996.)...

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