EIS study of the service life of activated cathodes for the hydrogen evolution reaction in the chlor–alkali membrane cell process

Electrochemical impedance spectroscopy (EIS) has been used, in conjunction with steady-state and voltammetric techniques, to test the service life of the following activated cathodes for the hydrogen evolution reaction (h.e.r.): thermal Pt-based cathodes with high noble metal loading, modified thermal Pt-based cathodes with low noble metal loading and composite Ni + RuO2 cathodes of large effective area. Ni mesh electrodes were also tested for comparison, since the Pt-based electrodes were supported on Ni meshes. The service life test was especially designed to highlight the robustness of the cathodes under conditions of polarity inversion and involved a sequence of galvanostatic polarisations in the h.e.r. range (to activate the electrodes), cyclic voltammetries taking the electrodes to potentials positive enough to evolve oxygen, slow potentiodynamic sweeps (to obtain pseudo-steady-state curves, and hence Tafel plots) and EIS measurements at various potentials in the h.e.r. range.EIS and steady-state results converged to indicate the strong activity and very good stability of the modified thermal Pt-based cathodes which underwent very little degradation upon polarity inversion. Composite Ni + RuO2 cathodes were not as active as Pt-based electrodes, but withstood polarity inversion with very limited loss of their activity.