1 Background

Growing concerns over energy supply and surrounding security and environmental issues have placed considerable emphasis on the development of alternatives to conventional energy sources. Much of the world’s energy is derived from fossil fuels; coal, petroleum, and natural gas. In the United States, for example, in 2009 over 50% of the country’s electricity was generated by coal-fired power plants, which consequently contributed 40% of the nation’s carbon dioxide (CO2) emissions [1]. Figure 1.1(a) shows recent world wide consumption of the top five energy sources, with non-renewables (such as petroleum, coal, and natural gas) displaying a more dramatic increase than renewables (such as hydroelectricity). The demand for energy – petroleum in particular – has been on the rise since the early 1980s, following the 1970s oil crisis. In 2009 over 84 million barrels of oil were consumed internationally each day, compared to 58 million in 1983 [2]. All regions of the world have seen significant growth in oil demand, but this trend has been most notable in Asia (Fig. 1.1(b)).

FIGURE 1.1 (a) World consumption of primary energy by energy type, 1980–2006 [2]. (b) Petroleum consumption by region, 1980–2008 [2].

The increase in fossil fuel consumption over the past 40 years and the accompanying rise in carbon emissions have provided a substantial driving force for the development of alternative energy systems. Fuel cells are an alternative energy technology which show great potential, as they have the ability to alleviate both consumption and emissions concerns. They can be utilized for transportation, residential and commercial power, electronic devices, and so forth.

Due to their numerous benefits and wide range of application areas, they have attracted significant research and investment; specifically in polymer electrolyte fuel cells (PEFCs). This forms the main emphasis of this book. PEFC technology is highly efficient (83% theoretical, at room temperature [4]), produces near-zero detrimental greenhouse gas emissions, operates at low temperatures (generally less than 100°C), and features rapid start-up and transient response characteristics. In addition to stationary and portable power applications, PEFCs are a very promising alternative to internal combustion engines for transportation applications. All of these reasons mean that the technology has attracted much attention from governments, industrial developers, and research institutions, resulting in a focused, collective effort aimed at the development and commercialization of PEFC systems [3].

In order to be truly competitive, PEFCs must meet or exceed the technological advantages of heat engines and other conventional power systems, on both the small and large scale. This includes balancing power output, system lifetime, and cost for a specific application of interest. Current research efforts are focused on improving each of these aspects, while recognizing the complex and coupled relationships between these characteristics. For example, increasing the membrane thickness will increase its durability and lifetime, but this requires more membrane material and lowers the cell’s performance via higher protonic resistance, both of which elevate the overall cost [3]. A relatively limited lifetime is currently one of the greatest shortcomings of PEFCs compared to heat engines and other competing technologies. In order to improve cell lifetime without sacrificing cost and/or performance, much attention is now focused on identifying and investigating the factors that impact PEFC durability.

2 Durability Targets for PEFC Technology

Despite the present cost and durability challenges of PEFC technology, there is a strong consensus that it is a practical, marketable, alternative energy technology. This factor, along with the impressive advantages of PEFCs, has led to the establishment of several government programs which have been designed to facilitate the development and implementation of PEFC power systems. Most notable are the efforts of the United States Department of Energy, the European Commission, and Japan’s Ministry of Economy, Trade and Industry, each of which has established targets and timelines for the commercialization of PEFCs for a range of applications. The technical targets established by each of these organizations will be presented in Sections 2.1–2.3 and compared in Section 3 at the conclusion of the chapter. While the focus of this book is PEFC durability, due to the coupling between durability, cost, and performance, other relevant targets are also presented to provide the reader with the complete context in which these targets must be achieved.