The Autohumidification Polymer Electrolyte Membrane Fuel Cell

Abstract

A PEM fuel cell was specially constructed to determine kinetics under conditions of welldefined gas phase composition and cell temperature. Steady state multiplicity was discovered in the autohumidification PEM fuel cell, resulting from a balance between water production and water removal. Ignition was observed in the PEM fuel cell for a critical water activity of ~0.1. Ignition is a consequence of the exponential increase of proton conductivity with water activity, which creates an autocatalytic feedback between the water production and the proton conduction. The steady state current in the ignited state decreases with increasing temperature between 50-105°C. At temperatures of >70°C five steady states were observed in the PEM fuel cell. The steady state performance has been followed with variable load resistance and hysteresis loops have been mapped. The dynamics of transitions between steady states are slow ~103 – 104 s. These slow dynamics are suggested to result from a coupling of mechanical and chemical properties of the membrane electrode assembly due to swelling of the membrane with water absorption.