Advanced characterization of alkaline water electrolysis through electrochemical impedance spectroscopy and polarization curves

• EIS enables distinction between anodic and cathodic processes. • Tafel slopes can be derived from charge transfer resistances. • Capacitances can potentially provide information on number of active sites. Improved electrolyzer components are needed to make alkaline water electrolyzers more flexible and durable. The performance of these new components can be assessed through in situ electrochemical characterization in the form of polarization curves and electrochemical impedance spectroscopy (EIS). Presently, EIS is still mostly used for the IR-correction of the polarization curve, but more valuable information can be extracted. In this work we show how EIS data can be used to determine the dependence of ohmic resistance on current density, to derive anodic and cathodic Tafel slopes and exchange current densities from fitted charge transfer resistances and to derive anodic and cathodic capacitances from fitted constant phase elements. We do this for both a two electrode alkaline electrolysis flow cell setup as well as for a three electrode beaker type setup with 2D nickel electrodes. The presented tools can be used in performance studies of new and existing electrodes and membranes in alkaline water electrolysis.