Search Results

A novel reversible proton exchange membrane fuel cell system that is based upon micro-sized membrane and electrode assemblies is discussed. The resulting micro-fuel cell has a reduced size and mass due to an improved design of the bipolar plates and current collectors. Bipolar plates often contribute over 75% of the fuel cell stack mass and volume in traditional fuel cell and electrolyzer designs that results in power densities near 0.1 kW/kg and 0.1 kW/liter. The micro-sized membrane and electrodes allow us to minimize the size of the gas-channels that feed reactants to the electrodes. Physical Sciences Inc.’s (PSI) micro-design approach minimizes stack features resulting in power densities greater than 1 kW/liter and specific power densities greater than 1 kW/kg.

Developing unmanned aerial vehicles (UAVs) with an electric propulsion system that combines photovoltaic modules with an energy storage system has been an ongoing goal of the aeronautics community. A closed-loop energy storage system using a fuel cell and electrolyzer will enable the UAV to operate at high altitudes (> 20 km) and for mission durations over a year. However, the specific energy of the energy storage system must be increased beyond present 150W-hr/kg levels. A high capacity fuel cell and electrolyzer unit under development at Physical Sciences Inc. (PSI) is aiming to improve the energy storage capability to values much greater than 500 W-hr/kg.

A mathematical model of the two-phase flow in a fuel cell gas channel is developed and used to predict the mass, momentum, and thermal distributions of a multi-component gas and liquid water mixture on the cathode side. Regions where flooding may occur are demonstrated by using the model evaluated with various operating conditions typical of fuel cell operations. Conditions where dry, saturated, and two-phase flows are introduced into the channel are demonstrated and the results compared. These results show the distribution of water and heat in the channel which may be used to design better flow channels.

PEM stacks are under evaluation as candidates for future space power technology. Results of long-term operation on a set of contemporary stacks fitted with different proton exchange membrane materials are given. Data on water balances show effects of membrane materials on stack performance.