Hydrogen emission characterization for proton exchange membrane fuel cell during oxygen starvation – Part 1: Low oxygen concentration

• Hydrogen emission in oxygen-starved PEM fuel-cell is characterized.
• Once oxygen stoichiometry is below 1.0, hydrogen emission starts.
• A near-linear increase in emissions is seen versus reducing oxygen concentration.
• The effect of produced liquid water in the cells on emission rates is indirectly revealed.
• A guideline for system start-up is proposed to control current demand and emission.

Hydrogen emissions during low oxygen concentration appear in the cathode exhaust of a PEM fuel cell stack. In this paper, the hydrogen emission rates for a stack containing cells without hydrogen crossover leaks are characterized. A Ballard 9-cell Mk1100 stack under standard FCvelocity®1-HD6 bus module operating conditions is employed, and extensive experiments are conducted under current demand to evaluate individual cell voltages and quantify hydrogen emissions. The results indicate that the emission rates are a strong function of current demands.In parallel, a model is developed to estimate the amount of hydrogen in the cathode outlet. To illustrate the accuracy of the developed model, the simulation results and the measured hydrogen emission rates in the cathode exhaust are compared for two current demands. It is acknowledged that the proposed model can be a reliable emulator for the hydrogen sensor in the cathode exhaust, where catalytic sensors cannot perform correctly because of the lack of proper oxygen concentrations, or other types of sensor may fail due to wetting or sensor degradation. Moreover, the proposed model provides a user-friendly tool for systems engineers to design reliable start-up procedures for the control of hydrogen emissions.