On Power Density and Efficiency of H2/O2 Polymer Electrolyte Fuel Cell Systems

When storing fluctuating renewable electricity by water electrolysis hydrogen and oxygen are obtained. Up to a scale in the order of Megawatt-hours the concurrent storage of oxygen and hydrogen gas is technically feasible. This opens up the possibility to use hydrogen/pure oxygen fuel cells for the efficient conversion of hydrogen back to electric power.

The oxygen reduction reaction is responsible for the largest voltage loss in the operation of polymer electrolyte fuel cells. The sluggish reaction rate of the four-electron reduction, even on the best platinum based catalysts, is aggravated by the low partial pressure of oxygen in air. When using pure oxygen the partial pressure can typically be increased by an order of magnitude.

 On the cell level, not only the reduced electro catalytic loss but also voltage gain from lower transport overvoltage and reduced ohmic loss at same gas humidification as with air operation are observed. At the same time very high specific power densities of up to 2 W/cm²can be realized.

 In addition to the advantages on the cell level, low parasitic power consumption in the balance of plant (no compressor/blower) also contributes to high system efficiencies of up to 69% (LHV).