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This paper presents investigations into the chronoamperometric experiments performed on polybenzimidazole/phosphoric acid based high temperature polymer electrolyte membrane fuel cells. Electrolyte loadings in the membrane electrode assembly are varied to realise three different degrees of flooding of the electrode. Steady state as well as dynamic measurements at three different temperatures (160, 120 and 80 °C) is made via chronoamperometry on these cells. The transient current behaviour resulting from a voltage step change from open circuit voltage (∼1 V) to low voltages (0.1 V) are recorded and analysed. Analysis using the Cottrell plot depicts the underlying mass transport processes in the three different electrodes, catalyst utilisation as well as a better description of the three phase boundary reaction zone. An extension of the Cottrell equation is deduced to describe a regular commercial fuel cell behaviour.

Dynamic testing of a phosphoric acid‐based high temperature PEM fuel cell shows a peculiar phenomenon. A certain current loss is observed after temperature cycling at constant voltage. This loss is incidentally recovered by applying a cell voltage spike to open circuit voltage. Experimental investigations into temperature, cell voltage, and ageing effects show that this phenomenon might occur due to the orientation of the adsorbed phosphate species on the platinum catalyst surface. Along with some supporting literature and experimental results, a hypothesis is presented in order to explain this occurrence. Phosphoric acid adsorption hysteresis on platinum catalyst due to temperature cycling could cause the temporary cell current loss. Electrode potential‐dependent molecule symmetry of adsorbed phosphate ions could bring about the cell current recovery.