Technological Applications PEFC

Atomistic MD models can be extended to the coarse-grained level introduced in the previous section, which is determined by the dimension of the backbone chain and branch. For the precise description of water molecular behavior, simple point charge (SPC) model was adopted (Krishnan et al., 2001), which can be used to simulate complex composition systems and quantitatively express vibrational spectra of water molecules in vapor, liquid, and solid states. The six-parameter (Doh, o , fi, Lye, Lyy, and Lee) SPC potential used for the water molecules is shown in Equation (24)  

---

PEFCs are an attractive alternative power source for mobile and stationary applications characterized by low emissions, good energy conversion efficiency and high power density. One of the main obstacles towards the commercialization of this technology is the high cost of component materials (catalyst, membrane, etc.) [160-162]. 

Active technology development efforts in both PEFC and planar SOFC technology, driven primarily by the interest in distributed generation and automotive propulsion markets, have achieved significant progress in the development of these technologies. For distributed power applications refined and even early commercial prototypes are being constructed. 

Several developers, including Nuvera, Honeywell, and Plug Power are active in the development for residential PEFC power systems. Most of the PEM system technology can be adapted for APU application, except that a fuel processor capable of handling transportation fuels is required. However, most of the players in the residential PEFC field are also engaged in the... 

There has been an accelerated interest in polymer electrolyte fuel cells within the last few years, which has led to improvements in both cost and performance. Development has reached the point where motive power applications appear achievable at an acceptable cost for commercial markets. Noticeable accomplishments in the technology, which have been published, have been made at Ballard Power Systems. PEFC operation at ambient pressure has been validated for over 25,000 hours with a six-cell stack without forced air flow, humidification, or active cooling (17). Complete fuel cell systems have been demonstrated for a number of transportation applications including public transit buses and passenger automobiles. Recent development has focused on cost reduction and high volume manufacture for the catalyst, membranes, and bipolar plates. 

As mentioned, the primary motivation for the PEFC development was the anticipated applicability in transportation. However, the economics of stationary use are more forgiving, and commercialization of the technology will likely begin as grid-independent power supphes. Figure 24-51 shows a 5-kW PEFC system operating on natural gas. 

The application to fuel cells was reopened by Ballard stacks using a new Dow membrane that is characterized by short side chains. The extremely high power density of the polymer electrolyte fuel cell (PEFC) stacks was actiieved not only by the higher proton conductance of the membrane, but also by the usage of PFSA polymer dispersed solution, serpentine flow separators, the structure of the thin catalyst layer, and the gas diffusion layer. Although PFSA membranes remain the most commonly employed electrolyte up to now, their drawbacks, such as decrease in mechanical strength at elevated temperature and necessity for humidification to keep the proton conductance, caused the development of various types of new electrolytes and technologies [7], as shown in Fig. 2. 

Within the past 20 years, tremendous progress has been achieved in PEFC technology, in particular since the automotive industry has joined forces to fmther develop this energy conversion technology with its advantages in efficiency and environmental friendliness. This development has brought about a much deeper understanding of the various functions of the polymer electrolyte in the cell, particularly under duty cycle conditions of automotive applications. As a further and utmost prerequisite, the cost issue came to every one s attention. 

SOFC and PEFC are competing in several stationary markets, with advantages to SOFC technology when reformed hydrocarbon or alcohol fuels are used. PEFC systems however have some distinct advantages in applications where frequent start-stop-cycles and extended periods of standstill are required such as in residential CHP applications. Therefore, more PEFC than SOFC units are ciurently in the field in Japan where market introduction of residential fuel cell systems has already taken place. SOFC systems are in the early phase of deployment. 

---