Oxidant starvation under various operating conditions on local and transient performance of proton exchange membrane fuel cells

Abstract

Oxidant starvation in proton exchange membrane fuel cells could cause severe fluctuation on dynamic performance and the significant reduction in durability. In this work, dynamic transfer and distribution characteristics of reactants and water under oxidant starvation are studied by measuring local current densities, temperatures, and the cell voltage in situ. Besides, high frequency resistance and pressure drop along the flow channel at the cathode are obtained to determine the membrane hydration state, and mass transfer and distribution. The effects of cathode humidity, cell temperature and operating modes on the local and overall transient behavior of the cell under oxidant starvation are analyzed. The experimental results show that with the air stoichiometry of 0.8, the current fluctuation distribution is much non-uniform and hydrogen pumping occurs in the downstream. When oxidant starvation occurs under potentiostatic mode, current densities in the upstream gradually increase to the steady-state; while under galvanostatic mode, local current densities in the upstream show overshoots and current variations coefficient along the flow channel are about two times of potentiostatic mode. As cell temperature increases, severe oxygen starvation occurs in the downstream and local temperature differences tend to be larger. When the unhumidified air is supplied into the cell, the combined effect of local membrane hydration state and local oxygen concentration plays a dominant role, leading to greater magnitudes of current fluctuation and higher change rate of current variation coefficient in the downstream.