A quasi-two-dimensional, along-the-channel mass and heat-transfer model for a proton exchange membrane fuel cell (PEFC) is described and validated against experimental current distribution data. The model is formulated in a 1+1 dimensional manner, i.e., local transport phenomena are treated one-dimensional in through-plane direction and coupled in-plane by convective transport in the gas and coolant channels. Thus, a two-dimensional slice running through the repetitive unit of a cell from the anode channel via membrane-electrode assembly (MEA) and cathode channel to the coolant channel and from inlet to outlet is modeled. The aim of the work is to elucidate the influence of operating conditions such as feed gas humidities and stoichiometric ratios on the along-the-channel current density distribution and to identify the distinct underlying voltage loss mechanisms. Furthermore, a complicated technical flow field is modeled by a combination of co- and counterflow subdomains and compared with experimental current densities.

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The analysis of the complete H2/air polymer electrolyte fuel cell system shows that process air humidification is one of the biggest obstacles for a high performance portable system in the kW range. Therefore, a new concept, with passive process air humidification integrated into the stack, has been developed. Humidification in each cell makes the process independent from the number of cells and the operation mode, thus making the concept fully scalable. Without external humidification the system is simpler, smaller, and cheaper. The humidification of the process air is achieved by transfer of product water from the exhaust air, through part of the membrane, to the dry intake air. Tests have shown that cells using the concept of internal humidification and operated with dry air at 70 ° have almost the same performance as when operated with external humidification. A 42‐cell stack with this internal humidification concept was built and integrated into a portable 1 kW power generator system.

This article gives an overview on the research and development activities pursued in the area of polymer electrolyte fuel cell stacks and systems in Switzerland in 2004. Work is pursued on several different levels for stacks and systems from portable to automotive applications, in the academic as well as in the industrial area. Today's work focuses on the improvement of specific power and cost efficiency of stacks and systems by development and optimization of new concepts for water management and cooling. This is achieved through function integration i.e. of the gas humidification into the stack and adaptation of the cooling concepts for the specific application.