The nonlinear frequency response method for the diagnosis of PEM water electrolyzer performance

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A better grasp of the underlying phenomena occurring in electrochemical technologies is crucial for their further development and, consequently, a much-needed step forward to a greener economy. Diagnostic methods that can reliably determine the state of health and causes of the performance shortcomings are indispensable. The ease of obtaining electrochemical data makes the analysis of current and voltage responses the preferred diagnostic approach. Traditional techniques, like steady-state polarization and electrochemical impedance spectroscopy are limited by their inability to distinguish between different processes due to the constraints of steady-state and linearity of system response, respectively. The nonlinear frequency response (NFR) method is an advanced diagnostic method that has the potential to overcome these issues. In this work, the NFR method was applied both experimentally and theoretically to study polymer electrolyte membrane water electrolysis (PEMWE). The model-based analysis provides insights into the losses in the PEMWE at different current densities. It shows that the contributions of the cathode to the overpotential losses at high current densities cannot be neglected. This has been much discussed in the literature and was often attributed only to mass transport losses. The contribution of mass transport has also been identified at higher current densities but is less pronounced than the kinetic contributions. Furthermore, we show that including the nonlinear dynamics in the analysis was crucial for identifying the appropriate parameter set. Overall, this work showed a considerable potential of the NFR method for the diagnosis of PEMWE due to its prospects of identifying different processes occurring within.