Fuel cell technical limitations

A number of technical and cost issues facing polymer electrolyte fuel cells at the present stage of development have been recognized by managers and researchers (6, 27, 28, 29). These issues concern the cell membrane, cathode performance, and cell heating limits. 

In more detail, it is evident that there still exist technical problems on hydrogen technology equipment (especially on fuel cells) that need to be solved before such equipment becomes commercially available. Reliability, lifetime and guarantees of hydrogen energy equipment and limited experience on the integration of such equipment into a complete power system are currently considered the most important drawbacks towards commercialisation. 

Although EIS offers many advantages for diagnosing fuel cell properties, clear difficulties exist for applying impedance methods and fitting the data to the model to extract the relevant electrochemical parameters. The limitations of the EIS technique derive from the several requirements required to obtain a valid impedance spectrum, because the accuracy of EIS measurement depends not only on the technical precision of the instrumentation but also on the operating procedures. Theoretically, there are three basic requirements for AC impedance measurements linearity, stability, and causality. 

Consuming patterns have over recent years seen a dramatic increase in the use of portable equipment for entertainment and work (such as music and video players, laptop computers and mobile phones with multi-functionality). This has increased the demand for batteries, but at the same time found limitations of the battery technology that seem difficult to avoid even with increasing conversion efficiencies. Fuel cells with small-scale stores are an obvious solution to these problems, because the technical performance is already far beyond that of batteries (e.g., operating a state-of-the-art laptop computer for a few days rather than a few hours). The difference between these otherwise similar technologies is the external storage of chemicals for a fuel cell versus the internal storage in batteries. 

Technical Efficiency—major improvement potential with fuel cells Environmental advantage—no emissions of pollutants and C02 Overcome the thermodynamic limitations of combustion systems... 

Chapters 6 and 7 refer to two practical case studies, in particular two fuel cell propulsion systems of different size. Here the technical characteristics of all individual components are described, and the results of an experimental characterization carried out on laboratory dynamic test benches are discussed. The findings of these two chapters evidence the limitations and potentialities of fuel cell power trains at the present state of development, in terms of performance, efficiency, environmental impact and durability. 

The limited supply of fossil energy resources means that new automotive concepts are essential. Electric vehicles are a promising alternative, especially electric vehicles with a fuel cell, which have a number of advantages [34]. This technical overview presents some examples of fuel cell-driven passenger cars and buses. 

A number of technical and cost issues face polymer electrolyte fuel cells at the present stage of development (35, 38, 39, 40, 41). These concern the cell membrane, cathode performance, and cell heating limits. The membranes used in present cells are expensive, and available only in limited ranges of thickness and specific ionic conductivity. Lower-cost membranes that exhibit low resistivity are needed. This is particularly important for transportation applications characterized by high current density operation. Less expensive membranes promote lower-cost PEFCs, and thinner membranes with lower resistivities could contribute to power density improvement (41). It is estimated that the present cost of membranes could fall (by a factor of 5) if market demand increased significantly (to millions of square meters per year) (33). 

A fuel cell stack has to be surrounded with actuators and devices which are necessary for its operation. The ensemble is called a fuel-cell system. It is not easy to genetically define a fuel-cell system and its limitations. Indeed, on the one hand, the elements contained in the system depend on the fuel-cell technology being used, the apphcation in question and the technical specifications pursued. On the other hand, a fuel-cell system is a multi-physical system because it involves chemical, electrical, fluidic and thermal phenomena whose effects are closely interrelated. Thus, the interactions between the different elements of the system and the environment are significant. Figure 3.12 offers a generic description of the elements of the system and sets the general outlines of the system [CAN 07 PER 07 HIS 09]. Besides the stack, which is the heart of the system, we can identify various different circuits ... 

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