Transient Gas Saturation in Porous Transport Layers of Polymer Electrolyte Membrane Electrolyzers
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Intermittency of renewable energy sources, such as wind and solar, remains as a major barrier to the establishment of a sustainable energy infrastructure (1). Balancing the supply of intermittent energy with demand requires an energy storage technology capable of operating under dynamic conditions. Over the last decade, polymer electrolyte membrane (PEM) electrolyzers attracted much attention as the ideal energy storage technology for renewable energy generators (2). PEM electrolyzers are favorable due to their wide operating current density range (0.6 – 2.0 A/cm2) and rapid response to dynamic changes (3). However, PEM electrolyzers need to become significantly more efficient to become commercially-viable energy storage technology (4). A major source of inefficiency stems from the undesired accumulation of oxygen gas in the anode porous transport layers (PTLs), which leads to blockage of reaction sites and water transport pathways in the PTL (5). The overpotential associated with this effect is termed mass transport overpotential, and it can contribute up to 25% of the total overpotential (6). Furthermore, mass transport overpotential could increase exponentially at higher current densities (7). Despite the extensive studies on gas transport in the PTL over the last decade, the effect of dynamic operating condition on the transient gas distribution in the PTL remains unknown. Understanding the transient gas transport through the PTL is an important first step for coupling PEM electrolyzer systems with intermittent renewable energy sources. In this work, we studied gas transport through the PTL under dynamic operating conditions via in operando synchrotron X-ray imaging. Specifically, we used synchrotron X-ray imaging with high spatial (6.5 µm/pixel) and temporal (2.5 frames per second) resolution to quantify the change in gas volume in the PTL under changing current densities. We observed that the gas volume oscillated at a constant amplitude with a similar frequency over a series of repeating step currents (Fig. 1). We also operated the electrolyzer using a real output power profile acquired from a wind turbine. The results provide insights on the transient behaviour of gas distribution in the PTL of PEM electrolyzers coupled with renewable energy sources. References J. A. Turner, Science.,285, 5428 (1999).O. Schmidt, A. Gambhir, I. Staffell, A. Hawkes, J. Nelson and S. Few, Int J Hydrogen Energy.,42, 52 (2017).M. Carmo, D. L. Fritz, J. Mergel and D. Stolten, Int J Hydrogen Energy.,38, 12 (2013).C. K. Mittelsteadt, ECS Transactions.,69, 17 (2015).Ö F. Selamet, M. C. Acar, M. D. Mat and Y. Kaplan, Int.J.Energy Res.,37, 5 (2013).M. Suermann, T. J. Schmidt and F. N. Büchi, Electrochim.Acta.,211(2016).S. Sun, Y. Xiao, D. Liang, Z. Shao, H. Yu, M. Hou and B. Yi, RSC Adv.,5(2015).Figure 1
