Effects of Supplied Gas Humidity Change on PEFC Transient Power Generation(Thermal Engineering)

Abstract

Polymer Electrolyte Fuel cell (PEFC) gained wider interest as a clean and efficient energy conversion device. Proper water management is needed, because vapor and liquid transport effects strongly on PEFC power generation characteristics and efficiency. However, water transport factors have not been well understood especially during unsteady operation, which is often observed in uses of vehicles or distributed stationary power generators. In this paper, to grasp and generalized effects of the local water transport on the PEFC performance, we have developed unsteady numerical model considering water transports and compared its calculated results with experimental responses to verify the model adequacy and discuss water transport factors. In the numerical model, mass conservation equations and charge conservation equations in gas channel, GDL and MEA were solved. As necessary parameters for developing them, we measured membrane resistivity, activation over-voltage etc by ourselves. The membrane resistivity increases extremely as relative humidity decrease, and activation over-voltage is also affected by relative humidity, not only by current density and oxygen activity. The measured and calculated transient responses were agreed well in most operating conditions, then adequacy of our measurement methods of water transport properties and numerical model have been confirmed. Then, we have discussed the effects of transport resistance at MEA surfaces on PEFC transient power generation.