Water electrolysis under dynamic conditions: diagnosis and process enhancement

Proton exchange membrane water electrolysis (PEMWE) is a key technology for storing excess electrical energy produced by renewables in the form of hydrogen (Figure 1). To achieve high productivity of hydrogen, operation at high current density is necessary. However, for this operating condition, high performance losses appear. Currently, a significant part of voltage losses at high current densities is assigned to mass transfer resistances in the anode porous transport layer. In addition to the mass transport, ohmic and kinetic resistances are present in the system. The contributions of different resistances to the total losses, as well as the influence of the operating and design parameters on the individual losses, are not understood yet.

Figure 1: Water electrolysis is a key technology for storing excess electrical energy produced by renewables in the form of hydrogen — **Figure 1:** Water electrolysis is a key technology for storing excess electrical energy produced by renewables in the form of hydrogen

**Figure 1:** Water electrolysis is a key technology for storing excess electrical energy produced by renewables in the form of hydrogen

In this work, we aim to employ a close combination of modeling and dynamic experiments for the discrimination of processes occurring in PEMWE. A complex combination of the processes occurring at different scales requires the implementation of multiscale modeling for describing the operation of the PEMWE. Therefore, the macroscopic model describing the electrolyzer performance was developed [1], as well as the mesoscale models: the pore network model (PNM) [2] and the Lattice-Boltzmann model [3]. PNM and LBM were shown to be suitable approaches for the systematic optimization and understanding of the PTLs, and in this work were used to parametrize the macro-scale model. Secondly, the experimental analysis allowed for the validation of the developed models. On one hand, neutron and optical imaging experiments were used to study the two-phase transport in the electrolyzer, especially within anode PTL [4, 5]. ]. Additionally, dynamic methods were developed and employed for electrochemical analysis of the water electrolyzer [6, 7]. The most common dynamic method in electrochemistry is electrochemical impedance spectroscopy (EIS), but its limitation lies in its inability to differentiate processes occurring at similar time scales. To address this, we applied nonlinear frequency response (NFR) analysis, which generalizes traditional EIS by extending it into the nonlinear domain, providing additional insights into the system. The application of NFR analysis for diagnosing PEMWE is illustrated in Figure 2 [7]. Moreover, we will explore the potential of this method for process improvement through forced periodic operation and assess its degradation.
The final goal of this work is to understand different processes occurring in the PEMWE and to determine operating and design conditions that would lead to process improvement.

Figure 2: The application of the nonlinear frequency response analysis for the diagnosis of the proton exchange membrane water electrolyzer performance. Based on [7]. — **Figure 2:** The application of the nonlinear frequency response analysis for the diagnosis of the proton exchange membrane water electrolyzer performance. Based on [7].

**Figure 2:** The application of the nonlinear frequency response analysis for the diagnosis of the proton exchange membrane water electrolyzer performance. Based on [7].

Funding: IMPRS, CDS and EFRE (Power-to-X-Systemmodulen Staßfurt project), MWU Sachsen-Anhalt (Research Initiative SmartProSys)

Collaborations:

Prof. Evangelos Tsotsas, Dr. Nicole Vorhauer-Huget, OVGU, Magdeburg, Germany
Asst. Prof. Tobias K. S. Ritschel, DTU, Denmark
Dr. Ingo Manke, Dr. Tobias Arlt, Dr. Nikolay Kardjilov, HZB, Berlin, Germany
Assoc. Prof. Alessandro Tengatitini, Dr. Lukas Helfen, ILL, Grenoble, France
Dr. Georgios Papakonstantiou, Prof. Kai Sundmacher, PSE group, MPI Magdeburg, Germany

Selected recent publications:

[1] Miličić, T., Altaf, H., Vorhauer, N., Živković, L.A., Tsotsas, E., & Vidaković-Koch, T. (2022) Modeling and Analysis of Mass Transport Losses of Proton Exchange Membrane Water Electrolyzer. Processes, 10, 2417, doi:10.3390/pr10112417.

[2] Vorhauer-Huget, N, Altaf, H., Dürr, R., Tsotsas, E., & Vidaković-Koch, T. (2020) Computational Optimization of Porous Structures for Electrochemical Processes. Processes, 8 (10), 1205, doi:10.3390/pr8101205

[3] Bhaskaran, S., Pandey, D., Surasani, V.K., Tsotsas, E., Vidaković-Koch, T., & Vorhauer-Huget, N. (2022) LBM studies at pore scale for graded anodic porous transport layer (PTL) of PEM water electrolyzer. International Journal of Hydrogen Energy, 74, 31551-32656, doi:10.1016/j.ijhydene.2022.07.079.

[4] Altaf, H., Miličić, T., Vidaković-Koch, T., Tsotsas, E., Tengattini, A., Kardjilov, N., Arlt, T., Manke, I., & Vorhauer-Huget, N. (2023) Neutron Imaging Experiments to Study Mass Transport in Commercial Titanium Felt Porous Transport Layers, Journal of The Electrochemical Society, 170, 064507, doi:10.1149/1945-7111/acd7a8

[5] Bhaskaran, S., Miličić, T., Vidaković-Koch, T., Surasani, V.K. , Tsotsas, E., & Vorhauer-Huget, N. (2024) Model PEM water electrolyzer cell for studies of periodically alternating drainage/imbibition cycles. International Journal of Hydrogen Energy, 77, 1432-1442, doi:10.1016/j.ijhydene.2024.06.268

[6] Vidaković-Koch, T., Miličić, T., Živković, L. A., Chan, H. S., Krewer, U., & Petkovska, M. (2021) Nonlinear frequency response analysis: a recent review and perspectives. Current Opinion in Electrochemistry, 30, 100851. doi:10.1016/j.coelec.2021.100851.

[7] Miličić, T., Muthunayakage, K., Vu, T.H., Ritschel, T.K.S., Živković, L.A., Tsotsas, E., & Vidaković-Koch, T. (2024) The nonlinear frequency response method for the diagnosis of PEM water electrolyzer performance. Chemical Engineering Journal, 496, 153889, doi:10.1016/j.cej.2024.153889.