Gas‐diffusion media (also known as gas diffusers and gas‐diffusion backings) are required in most polymer electrolyte fuel cell (PEFC) designs. Their function is to provide uniform reactant (H 2 , O 2 , and electrons) access to and product (H 2 O) removal from the electrodes, efficient heat removal from the membrane electrode assembly (MEA), and mechanical support to the MEA. The vast majority of gas‐diffusion media are based on carbon‐fiber materials; a variety of forms are used, with carbon‐fiber paper and carbon cloth receiving widest application. This chapter describes the production and properties of currently available and emerging materials. Commonly employed treatments and coatings used to tailor the wicking and hydrophobic properties of diffusion media for efficient water removal are discussed. Finally, ex‐situ and in‐situ methods for characterizing diffusion media are described.

This intriguing volume provides a thorough examination of the historical roots of global climate change as a field of inquiry, from the Enlightenment to the late twentieth century. Based on primary and archival sources, the book is filled with interesting perspectives on what people have understood, experienced, and feared about the climate and its changes in the past. Chapters explore climate and culture in Enlightenment thought; climate debates in early America; the development of international networks of observation; the scientific transformation of climate discourse; and early contributions to understanding terrestrial temperature changes, infrared radiation, and the carbon dioxide theory of climate. But perhaps most important, this book shows what a study of the past has to offer the interdisciplinary investigation of current environmental problems.

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