Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell

Abstract

The present analysis shows the local distribution of current density and EIS measurements along a 50 cm single-channel proton exchange membrane water electrolysis (PEMWE) cell. Measurements for operating modes with one sufficiently high and one insufficiently low stoichiometric water ratio (λ) were carried out to observe effects on the current density distribution. Furthermore, global and local EIS measurements were performed to distinguish between the cell voltage loss differences in the two cases. The mass transport losses η mtx and the Ohmic voltage losses η show a strong increase, when the stoichiometric water ratio falls below a level of λ ≈ 5. The reduction of the inlet water flux of the anode reduces both the proton conductivity of the ionomer within the catalyst layer and the membrane, increasing transport and Ohmic resistances, respectively. The local analysis has shown that the level of membrane and catalyst hydration under low stoichiometric conditions can be distributed highly non-homogeneous in along-the-channel direction, with the most pronounced dehydration toward the end of the channel.

Model-Based Analysis of Low Stoichiometry Operation in Proton Exchange Membrane Water Electrolysis

“…In the following, a detailed analysis of the model results is given with a focus on the qualitative comprehension of experimental and model data. First, simulation results are investigated under both high and low stoichiometry operation modes and validated with the experimental findings from our previous work [5]. Furthermore, a deeper analysis of the local phenomena is provided, analyzing the local water flow rates in the channel and sandwich direction complemented by a local overpotential analysis under low stoichiometry operations.…”

“…In (b): CDD for high (blue) and low (red line) stoichiometry operations at a common mean current density ofī ≤ 0.85 A cm −2 are shown along the channel coordinate (ζ). The experimental setup is briefly described in the Appendix C. Data and comprehensive experiment description in Immerz et al [5].…”

“…In this work, critically low water stoichiometric ratios are modeled and analyzed with a more-dimensional model. A particular focus is on (i) the description and enlightening of the experimental findings of previous works on low stoichiometry operation (e.g., [4,5,[12][13][14]), (ii) the analysis of the water management in PEMWE in low stoichiometry operation and (iii) the assessment of the low stoichiometry operation mode in context of general use cases and thermal issues. As a starting point, the 1-dimensional sandwich model of Trinke [15] is used and reasonably simplified in order to describe the sandwich direction of a PEMWE cell and extended by a 1-dimensional channel model, that can describe local effects of the low stoichiometry operation.…”

“…In the following, the sandwich model is described in detail, focusing on the simplifications in comparison to the model of Trinke [15] first. In a second step the channel model is presented, enabling a local analysis similar to the experimental results from Immerz et al [5]. The experimental setup is briefly described in the Appendix C. , sandwich flux densities as j dsw,k for dissolved water and j w,k for liquid water.…”

“…In the present study, we analyzed low water flow rates in PEMWE cells focusing on the influences of low stoichiometry on local cell behavior. For this purpose, a mathematical model is developed to describe and analyze the experimental findings that were observed in previous studies for a PEMWE cell of 50 cm channel length [4,5]. The main results from these experimental findings are summarized in Figure 1, showing the polarization curves (a) and current density distributions (CDD) (b) for high and low stoichiometry operations, which will be described with the herein developed model.…”