Water Transport and Accumulation during Air Electrode Testing for Phosphoric Acid Fuel Cells

Abstract

This paper presents experimental studies and analytic considerations on water transport and accumulation phenomena in an electrode during air electrode performance testing for phosphoric acid fuel cells.
Humidity of exhausted air and its response time are measured with varying air flow rate, current density, temperature and concentration of phosphoric acid. Quantity of water vapour exhausted from the electrode at a no load condition depends on concentration of phosphoric acid and test temperature. When current flows, a large amount of water generated by the electrochemical reaction is added to the exhausted water at the no load condition, while a small amount of water seems to diffuse to the oposite side and dilute the phosphoric acid. Accumulated water in the electrode is estimated by integrating exhausted water after current shutdown. It increases with current density and decreases with air flow rate.
These phenomena can be explained by analyzing an equivalent circuit model in which water transport and accumulation in the electrode is proportional to water vapour pressure.