(307h) Estimating Overpotentials in Alkaline Water Electrolysis Based on Chronopotentiometry and Electrochemical Impedance Spectroscopy

For a water electrolyzer, the operating voltage to achieve a certain current density is a key performance indicator. It is composed of an equilibrium potential given by thermodynamics and additional overpotentials, due to effects including reaction kinetics, ohmic resistances, and mass transfer limitations. In water electrolysis, gas bubbles can lead to additional overpotentials by increasing the ohmic resistance of the electrolyte or by covering part of the electrode surface, thus reducing the available electrochemically active surface area. Several literature articles use empiric models to estimate the overpotentials due to these different effects [1,2]. However, these models were often derived for a specific material and material structure and neglect material dependencies. Therefore, they generally cannot be used for reliable prediction of overpotentials for other materials.

We investigate how well overpotentials in alkaline water electrolysis due to different effects can be estimated through non-invasive electrochemical measurement techniques. We consider chronopotentiometry and electrochemical impedance spectroscopy measurements performed in a three-electrode beaker cell setup under typical laboratory and industrial conditions. We model the chronopotentiometry experiments using a steady-state model and the electrochemical impedance spectroscopy experiments with an equivalent electric circuit. Using both models and data sets, we estimate model parameters and overpotentials and perform an identifiability analysis to derive respective confidence intervals. We then compare the obtained results with estimates based on available often empiric, non-material dependent, literature models. The results allow to understand how well solely electrochemical measurement techniques can be used to estimate different overpotentials. These estimates help to understand which effects are mainly responsible for an operating voltage, and thus potentially highlight ways to improve the material and electrolyzer design and operation to achieve higher voltage efficiencies.

[1] Hammoudi et al., 2012, Int. J. Hydrogen Energy, 37(19), 13895–13913.

[2] Dominici & Gabriel, 2022, Int. J. Energy Res., 46(3), 3295–3323.