Influence of ageing on the dynamic behaviour and the electrochemical characteristics of a 500 We PEMFC stack

• Short time stack/cell dynamic showed voltage under/overshoot at current step-up/down.
• Short time dynamic is ruled by charge transfer and then water content adjustment.
• Ageing or step level have no impact on charge transfer time constant.
• Except at start-up, where it is higher, step level has no impact on resistivity.
• Resistivity is unaffected by ageing.

In this study, a 500 We 19 cells Proton exchange membrane fuel cell (PEMFC) stack was aged for ∼1200 h and submitted to current steps between different operating levels. Using two different multi-channel data acquisition systems (one at 100 kHz and one at 1 Hz). the evolution with ageing of individual cells and full stack's short term (∼10 s) and medium term (∼4 min) dynamic performances was followed. Undershoots and overshoots behaviours were observed for respective current step-up and step-down. It appeared that, in studied operating conditions, the first time constant was related to the charge transfer at electrode/electrolyte interfaces. After the first “plateau”, the voltage evolution was explained by a membrane water content evolution.With the very fast data acquisition system, the evolutions of stack and individual cells' electrochemical characteristics (ohmic resistivities, charge transfer time constant) were also followed. Except for one cell which ohmic resistivity increases and which performance strongly decreases at the end of ageing, ageing doesn't affect the resistivities. Moreover, except for start-up step, no influence of step level was observed on ohmic resistivities. The higher resistivity obtained at start-up was attributed to the initiation of membrane drying related to an interruption of water production while gases still flow. Besides, the charge transfer time constant remains unaffected by ageing or step level.