Proton channels.

The structure of Nafion, the polymer electrolyte membrane used in some fuel cells, has been extensively debated over recent decades. Now, a newly proposed model reveals the nanoscale arrangement that could explain the excellent transport properties of the material. Transport is a major source of pollution in cities. As a result, the development of cars and buses which generate low or negligible level emissions of greenhouse gases is an environmental priority. Two promising technologies compete for this niche: Batteries and fuel cells. The latter, and the topic of discussion here, are based on scientific principles known for about two centuries, but the technology has emerged only recently. 1,2 Among the few established fuel cell designs, 1,2 those based on a polymer electrolyte membrane (PEM) and di-hydrogen are promising candidates as power sources for cars as they function in the appropriate operating temperature range (80-120°C) (Figure 1). To date, the best performing PEMs in H 2 /O 2 fuel cells have been composed of Nafion, a perfluoro-sulfonated copolymer developed by DuPont in the 1960s. 3,4 Despite all the attention Nafion has received in the industry, however, the hierarchical structure of the membrane remains a mystery and, as a result, the mechanisms of the reactions involved are not well understood. On page XX of this issue Klaus Schmidt-Rohr and Qiang Chen enter this structural debate and, by the proposal of a new model which supports the analysis of published X-ray scattering curves, show convincing support for the tubular structure of Nafion. 5 This model gives some interesting arguments for solving, where previous ones have failed, the excellent transport properties of hydrated Nafion. A fuel cell is an electrochemical converter – chemical energy from the fuel, hydrogen, is converted into electrical energy in the presence of atmospheric oxygen. More specifically, a PEM fuel cell operates using the following simple principles (Figure 1): a hydrogen molecule