EIS Study of the Service Life of Activated Cathodes for the Hydrogen Evolution 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.