A Robust and Quantified Analysis of Mass Transport and Its Application in Designing Next Generation Architecture for Polymer Electrolyte Water Electrolysis Cells

Investigations to better understand the nature of mass transport and two-phase flow within a polymer electrolyte water electrolyzer (PEWE) have gained popularity as researchers strive to improve system performance and efficiency. Along with traditional polarization experiments, the use of in-situ spatial and temporal current distribution measurement techniques has proven to be very attractive. Different methods for spatial current distribution measurements include the use of resistor networks, potential probes, and printed circuit boards (PCB) [1–3]. Using such techniques, Mench and co-workers have previously demonstrated [4–7] that, under mass transport limited conditions for any combination of flow-field and diffusion media, the current density distributions consistently exhibit a gradient – with high current towards the inlet and low towards the outlet. These contour plots showed certain dissimilarities; however, they serve as a qualitative picture to gauge cell performance and characterize mass transport. Therefore, in this work a robust analysis was developed that provides a quantitative understanding and better characterization of the mass transport limitation within the electrolyzer. A mass transport number (MTN) was defined and used to further characterize the influence of mass transport limitation experienced within an electrolyzer. Applying this new analysis to our the investigations revealed that the PEWE system performance using high-performance micro-patterned Ti-foil liquid-gas-diffusion-layer (LGDL) [8,9] was highly sensitive to the cell architecture and exhibited poor mass transport behavior using traditional channel based flow-fields. Compared with the conventional porous transport layer (PTL) morphology, the lack of in-plane permeability of the LGDLs caused faster onset of mass transport limitations at lower flowrates, local increase in HFR, and poor area utilization. Therefore, a unitized single flow-field-LDGL component that mitigates these problems has been designed. Through this work it will be shown that the flow-field is designed to have pins that allow for greater in-plane transport. The staggered pattern reduces pressure drop and promotes exchange in-between channels that assist in efficient bubble removal. Additionally, the cross-section of the pin, the pitch, and aspect-ratios are adjustable to maximize porosity for different LGDLs. Finally, making this into a single unitized component having a permanently attached LGDL will decrease interfacial contact resistances and improve cell performance (as shown in Figure 1). [1] T. V. Reshetenko, G. Bender, K. Bethune, R. 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Roenning, D. Aaron, M.M. Mench, Quantifying Lateral Current Spread While Measuring Performance Using a Segmented Polymer Electrolyte Water Electrolysis Cell, ECS Meet. Abstr. MA2020-02 (2020) 2458–2458. https://doi.org/10.1149/MA2020-02382458mtgabs. [6] A. Roy, F. Roenning, D. Aaron, M.M. Mench, Local Two-Phase Flow and Performance in Polymer Electrolyte Water Electrolysis Cells, ECS Meet. Abstr. MA2021-01 (2021) 1190–1190. https://doi.org/10.1149/MA2021-01381190mtgabs. [7] A.Z. Weber, R.L. Borup, R.M. Darling, P.K. Das, T.J. Dursch, W. Gu, D. Harvey, A. Kusoglu, S. Litster, M.M. Mench, R. Mukundan, J.P. Owejan, J.G. Pharoah, M. Secanell, I. V. Zenyuk, A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells, J. Electrochem. Soc. 161 (2014) F1254–F1299. https://doi.org/10.1149/2.0751412jes. [8] J. Mo, Z. Kang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green, M.M. Mench, F.-Y. Zhang, Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting, Sci. Adv. 2 (2016) e1600690. https://doi.org/10.1126/sciadv.1600690. [9] Y. Li, Z. Kang, X. Deng, G. Yang, S. Yu, J. Mo, D.A. Talley, G.K. Jennings, F.-Y. Zhang, Wettability effects of thin titanium liquid/gas diffusion layers in proton exchange membrane electrolyzer cells, Electrochim. Acta. 298 (2019) 704–708. https://doi.org/10.1016/j.electacta.2018.12.162. Figure 1