Impact of Multiphase Mass and Energy Transport Processes on Water Electrolysis in Polymer Electrolyte Membrane Cells
Final Report Abstract
Subject of the project was the development of scientifically solid fundamentals for the design and operation management of large PEM water electrolyzers. Special focus was on the investigation of the effect of the anode two-phase flow on the performance of PEM water electrolyzers in case of cell size enlargement and water feed reduction. Experimental as well as theoretical analyses were conducted in collaboration with the project partners. In the course of the project a special electrochemical reactor setup was used that allows spatially distributed measurement of current density and temperature. This more than 50 cm long single channel cell (active area 22.6 cm2) depicts the flow regime in large scale electrolyzers. Comparative experiments with commercial and lab-made membrane electrode assemblies showed that the performance of the cell is in accordance with a 63.5 cm2 circular and a 4 cm2 quadratic cell. Main focus of the project was the observation of the cells response regarding local current density, cell voltage and temperature under variation of the anode feed water stoichiometry. The experiments showed that for water feed stoichiometry down to λH2O = 5 no significant influence on the cell performance could be observed. Using galvanostatic operation, below this stoichiometry a strong increase in current density in the rear of the channel is induced, whereas the current density increases in the channel front. Together with a rapid increase in cell voltage, this indicates a lack of reactant water in the channel rear, due to which in turn a temperature inhomogeneity arises. This quite small lower boundary of feed water stoichiometry was confirmed in theoretical studies. A model of the anode porous transport layer was used for the theoretical investigation of the two-phase flow orthogonal to the channel coordinate. The parameter variations showed water depletion in the catalyst only in case of very low channel saturation or very low permeability of the porous transport layer. By use of the along-the-channel model it was shown that the channel orientation has no significant influence on the channel saturation or pressure drop. Additionally, further analysis with regard to the origin of the voltage drop was conducted. A voltage breakdown showed that the related performance losses cannot be attributed to kinetic effects. Local impedance spectra indicate that the voltage increase originated partly from Ohmic losses and mass transfer losses. The former can be attributed to changes of the membrane conductivity. Therefore, it is likely that internal water transport along the membrane serves for the water supply in case of low feed water stoichiometry. The remaining losses seem to be attributable to transport losses within the catalyst layer. It can be concluded that the results of the project quantify the effect of low feed water stoichiometry. The analysis shows that transport resistances in porous transport layers due to two phase flow only appear at operating conditions beyond normal cell operation. However, it unveils that internal transport phenomena within the membrane electrode assemblies of PEM water electrolyzers may play a significant role for water distribution. This aspect should be further analyzed, since it may become relevant, e.g. in case of highly transient operation of PEM cells.
Publications
- (2016) Hydrogen Permeation in PEM Electrolyzer Cells Operated at Asymmetric Pressure Conditions, J. Electrochem. Soc., 163(11):F3164-70
P. Trinke, B. Bensmann, S. Reichstein, R. Hanke-Rauschenbach, K. Sundmacher
(See online at https://doi.org/10.1149/2.0221611jes) - (2016) Impact of Pressure and Temperature on Hydrogen Permeation in PEM Water Electrolyzers Operated at Asymmetric Pressure Conditions, ECS Trans., 75(14):1081-94
P. Trinke, B. Bensmann, S. Reichstein, R. Hanke-Rauschenbach, K. Sundmacher
(See online at https://doi.org/10.1149/07514.1081ecst) - (2017) Anodic microporous layer for polymer electrolyte membrane water electrolyzers, J. Appl. Electrochem., 47(10):1137-46
J. Polonský, R. Kodým, P. Vágner, M. Paidar, B. Bensmann, K. Bouzek
(See online at https://doi.org/10.1007/s10800-017-1110-1) - (2017) Experimental characterization of inhomogeneity in current density and temperature distribution along a single-channel PEM water electrolysis cell, ICE2017, Copenhagen
C. Immerz, M. Schweins, P. Trinke, B. Bensmann, M. Paidar, T. Bystroň, K. Bouzek, R. Hanke-Rauschenbach
- (2018) Effect of the MEA design on the performance of PEMWE single cells with different sizes, J. Appl. Electrochem., 48:701–11
C. Immerz, M. Paidar, G. Papakonstantinou, B. Bensmann, T. Bystroň, T. Vidakovic-Koch, K. Bouzek, K. Sundmacher, R. Hanke-Rauschenbach
(See online at https://doi.org/10.1007/s10800-018-1178-2) - (2018) Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation, J. Appl. Electrochem., 48: 713–23
T. Bystroň, M. Vesely, M. Paidar, G. Papakonstantinou, K. Sundmacher, B. Bensmann, R. Hanke-Rauschenbach, K. Bouzek
(See online at https://doi.org/10.1007/s10800-018-1174-6) - (2018) Experimental characterization of inhomogeneity in current density and temperature distribution along a single-channel PEM water electrolysis cell, Electrochim. Acta, 260:582-8
C. Immerz, M. Schweins, P. Trinke, B. Bensmann, M. Paidar, T. Bystroň, K. Bouzek, R. Hanke-Rauschenbach
(See online at https://doi.org/10.1016/j.electacta.2017.12.087)
