Self-humidification characteristics of steady-state operation and startup for humidifier-free polymer electrolyte membrane fuel cell

Abstract

Escalating the self-humidification ability of polymer electrolyte membrane fuel cell is of paramount significance to automobile and portable applications, particularly for ambitious humidifier-free goal. In this study, detailed humidification mechanisms are explored for steady-state and startup scenarios through three-dimensional multiphase modeling. Model validations for different inlet humidities and current density evolutions of startup are strictly performed, five proposed operating strategies are quantitatively compared, in which the crucial influence of anode and cathode self-humidification cycles are evaluated. The dynamic characteristics of both preheating and self-heating modes during startup are also investigated under humidifier-free design. The results indicate that anode self-humidification cycle plays a more important role than the cathode one. The thin membrane fuel cell performance is insensitive to the anode relative humidity due to enhanced self-humidification. Additionally, the observed current density overshoot after startup is attributed to rapid oxygen consumption, followed by a gradual increase due to continuous electrolyte hydration. The fundamentals of dynamic self-humidification during different voltage/current-density startups are similar, determined by transient water accumulation and current density evolution. Moreover, self-heating mode shows lower output voltage due to sluggish catalyst activity, while it can alleviate the steep oxygen concentration drop during startup, compared with the preheating one.