Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

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The spectrally selective optical properties of wavelength selective radiation emitters and ® lters based on periodically microstructured metal surfaces were investigated. Metal surfaces were structured by the use of a holographic mask and subsequent etching processes. Due to the microstructure, thermally excited surface plasmons couple to electromagnetic radiation. Therefore a structured tungsten surface can act as a selective radiation emitter. The calculation of the absorptance by a rigorous diå raction theory allows the prediction of the emissivity of such structures. The angle dependent emissivity of tungsten gratings with periods of 1.4 m m and 2.0 m m was measured. A peak emissivity of 70%at a wavelength of 1.6 m m was achieved. Band pass ® lters for the near infrared spectral range based on perforated metal ® lms were investigated theoretically and experimentally. Filters with a grating period of 2.0 m m were produced. A peak transmittance of 80% at a wavelength 2.9 m m was achieved. The optical properties of the diå ractive elements described partly show a strong angle dependence IntroductionIn this contribution we investigate the optical properties of periodically microstructured metallic surfaces. The goal is to manufacture radiation ® lters and emitters for the near infrared (NIR) spectral range, that show wavelengthselective optical properties based on resonance eå ects.Our work was initially motivated by the use of selective emitters and bandpass ® lters in thermophotovoltaic (TPV) systems [1]. In a TPV generator, a thermal emitter is driven by any heat source with a suae cient temperature. The radiation of the emitter is converted into electrical energy by a photovoltaic (PV) cell. One of the major challenges of current research work on TPV systems is to reduce the mismatch between the emission spectrum and the spectral sensitivity of the PV cell. This can be done by increasing the emissivity of the emitter at convertible photon energies and by ® ltering the radiation.The selective emitters which we investigated are based on the eå ect that on structured surfaces thermally excited surface plasmons can be converted to electromagnetic radiation. This leads to an increase of the emittance of a metallic surface in a limited spectral range. The kind of surface structure determines the spectral range of the emissivity maxima. Towards longer wavelengths the grating