New insights into steady-state multiplicity in polymer electrolyte membrane fuel cell

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) is a potential candidate as power source for electrified transportation. Technically speaking, PEMFC is an energy conversion device involving complicated physico-chemical processes and its highly non-linear characteristic is very likely to cause unpredictability and non-repeatability, causing confusions about performance test, operation conditions optimization, etc. Steady state multiplicity is one of the most interesting types for PEMFC's non-linear characteristic, however, few works comprehensively investigates the underlying mechanisms. In this work, taking a counter-flow automotive size fuel cell as an example, the PEMFC's steady state multiplicity are experimentally discovered and, by developing numerical model, the internal states evolution are reconstructed and model-based sensitivity analysis is conducted to reveal the multi-physics coupling mechanisms inside, which would help us to have a deeper understanding on PEMFC as a complex physical system: (a) the water content in the middle area (in-plane direction) are more likely to have multi steady states, which dominates the bulk steady-state multiplicity (b) PEMFC's steady state multiplicity is more obvious under the condition of low cathode RH, low hydrogen stoichiometry and large current density. (c) For the same output voltage, PEMFC operates at higher current under galvanostatic mode than potentiostatic mode.