Stationary power PEMFC

The PEMFC is nowadays the most advanced low-temperature fuel cell technology [19, 20], because it can be used in several applications (space programs, electric vehicles, stationary power plants, auxiliary power units, portable electronics). The progress made in one application is greatly beneficial to the others. 

Table 3.3.1 also indicates suitable power ranges of the various fuel cell types and some of their typical applications. PEMFCs are clearly the most versatile class with strong focus on portable and automotive applications. High-temperature fuel cells are more often employed for stationary power generation. 

Stationary power generation on a large scale may use either low- or high-temperature fuel cell systems, and several systems rated at up to a few hundred kW have been operated (Barbir, 2003 Bischoff et ah, 2003 Veyo et ah, 2003). The systems comprise the basic units of PEMFC, MCFC or SOFC as described in Chapter 3, combined with fuel preparation and exhaust clean-... 

Applications. For transport applications, as already noted, only Synthetic liquid fuels does not require onboard storage. All the scenarios require fuel cells, DMFCs for Synthetic liquid fuels, and (probably) PEMFCs for the other three scenarios. For stationary power, Electricity store and Ubiquitous hydrogen require fuel cells for combined heat and power (CHP), which could be PEMFCs for residential applications with low... 

Proton exchange membrane fuel cell (PEMFC) Proton conductive polymer membrane H2 O2 (in air) 60-90 Transportation vehicles, stationary power plants, cogeneration plants, portable power supplies... 

PEMFCs are characterized by low operative temperature (80-100°C), high current density, compactness, fast start-up and suitability for discontinuous operation [21]. These features make PEMFCs the most promising and attractive candidate for a wide variety of power applications ranging from portable/micropower and transport to large-scale stationary power systems for buildings and distributed generation [22], as shown in Fig. 2.6. 

General Motors Set a new world record for power density in a PEMFC stack which generates 1.75 kW per liter. Teamed up with Hydrogenics Corporation and unveiled a demonstration stationary power unit to provide backup power to cellular towers during power outages. 

MEAs in PEM fuel cells require sufficient lifetimes for applications in transportation and/or stationary power generation. During lifetime testing, the PEMFC performance should be stable and the operation behavior reliable. However, PEM fuel cells at present cannot guarantee lifetimes of 5,000 hours for mobile or transportation applications and 40,000 hours for stationary applications. The durability of the fuel cell, strictly related to the lifetime, is defined as the ability of a cell to resist permanent change in performance over time. Normally, lifetime degradation is not a catastrophic failure. However, it does indicate that the MEA degradation is not recoverable or reversible. 

At present, in addition to the United States, PEMFCs and power plants based on them have been developed in many other countries, including China, France, Germany, South Korea, and the United Kingdom. Most of the power plants delivered in 2006 (about 60%) were for power supply to portable equipment. A secondary use (about 26%) was as small stationary power plants for an uninterruptible power supply. 

Figures for the time of smooth operation of PEMFCs (and other fuel cells used in the same applications) are given variously as 2000 to 3000 hours for power plants in portable devices, as up to 3000 hours over a period of five to six years for power plants in electric cars, and as five to 10 years for stationary power plants. Much time will, of course, be required to collect statistical data for the potential lifetime of different types of fuel cells. Research efforts are therefore concentrated on finding reasons for the gradual decline of performance indicators and for premature failure of fuel cells. In recent years, many studies have been conducted in this area.

Phosphoric acid fuel cell - PAFC is the first fuel cell to have reached commercialization. Phosphoric acid is used as the electrolyte. More than 75 MW PAFC systems are in operation in 85 cities in 19 countries so far. Similar to the high temperature PEMFC, the operating temperature of a PAFC is higher than 200°C. This helps increase the tolerance of the Pt catalyst against carbon monoxide. Hydrocarbon reforming gas is a promising fuel source for PAFC. The overall efficiency of PAFC can reach 80% if the cogenerated heat is harnessed. Due to these characteristics of the PAFC, its main apphcation focuses on stationary power source. 

The PEMFC has been under development for the last two decades primarily as a potential replacement for internal combustion engines in electric passenger vehicles with power needs of 50-100 kW. However, PEMFCs have also been considered for larger vehicles of few hundred kilowatts for buses and trucks, as auxiliary power units, for small-scale stationary power generations of few kilowatts for combined heat and power of residential buildings, and even in smaller units of few watts for portable power electronics applications (Li, 2008 O Hayre et al, 2006). 

Polymer electrolyte membrane or proton exchange membrane fuel cells (PEMFC) use a thin (s50 im) proton conductive polymer membrane (such as perfluorosulfonated acid polymer) as the electrolyte. The catalyst is typically platinum supported on carbon with loadings of about 0.3mg/cm, or, if the hydrogen feed contains minute amounts of CO, Pt-Ru alloys are used. Operating temperature is typically between 60 and 80°C. PEM fuel cells are a serious candidate for automotive applications, but also for small-scale distributed stationary power generation, and for portable power applications as well. 

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