Poly(pentafluorstyrene) based ionomers for electrochemical hydrogen pumps II – Probing the electrode processes by distribution of relaxation times

The properties of different poly (pentafluorstyrene) (PPFSt) based ionomers implemented into full-cell electrochemical hydrogen pumps (EHPs) are investigated by electrochemical impedance spectroscopy (EIS) coupled with the distribution of relaxation times (DRT) analysis. Thereby, the resistances of the proton transport (PT) in the electrodes, the hydrogen evolution reaction (HER) on the cathode, the hydrogen oxidation reaction (HOR) on the anode, and the mass transport (MT) in each EHP are quantified. Phosphonated PPFSt (PWN70) ionomer exhibits superior performance with a polybenzimidazole membrane, demonstrating excellent PT and kinetics. A novel PPFSt ionomer functionalized with an imidazole group also outperforms commonly utilized PTFE binder by improving the PT and the HER, reducing the power consumption by 25% at 1.0 A cm$^{−2}$ and 200°C. Both ionomers demonstrate a MT resistance comparable to the PTFE catalyst layer, caused by the high porosity of PWN70 and the high hydrophobicity of the imidazole binder.