Transient Gas Distribution in Porous Transport Layers of Polymer Electrolyte Membrane Electrolyzers

Abstract

Here, we elucidated the dynamic gas transport behavior in the anode porous transport layer (PTL) of polymer electrolyte membrane (PEM) electrolyzers via in operando synchrotron X-ray imaging. The imaging results showed that the gas saturation in the PTL reached steady state more rapidly with a steep current density ramp-up and a shallow ramp-down (compared to a shallow ramp-up and a steep ramp-down, respectively). Additionally, the gas accumulation was characterized by a faster response time compared to that of the gas removal due to the relatively slow migration of residual gas from the catalyst layer-PTL interface to the flow channels. Furthermore, we investigated the impact of gas response behavior on gas saturation during intermittent electrolyzer operation. Intermittent operation led to an increase in residual gas accumulation, which negatively impacted the electrolyzer performance. Our results are key for informing design and operating strategies for mitigating such hysteresis effects and improving the performance of PEM electrolyzers when coupled with intermittent renewable energy sources.

Computational Optimization of Porous Structures for Electrochemical Processes

“…When the gas pressure is further increased after breakthrough of the gas phase, a water-gas barrier is formed in the 3D pore networks. The striking differences between the two simulations are the final saturations with liquid and gas phases at breakthrough, as well as the invasion behavior after breakthrough, if it is assumed that the gas phase can be forced to further invade the porous structure by increasing the gas pressure, e.g., provoked by the very low gas permeability in the studied case of laminar, incompressible gas flow (Figure 10) or based on diffusion resistances [49]. The pore network simulations indicate that the gas saturation at the top side can be reduced from around 50% to around 30% by application of a pore size gradient (Figure 9).…”

“…Apart from the optimization of mass transfer properties, the change of the ohmic resistances for charge transfer must also be considered to achieve the optimal structural design [35]. Experimental studies in the literature indicate that the realization of the connectivity of the PTL with the catalyst layer and the degradation of material properties play major roles in performance enhancement [35,49,55], while other studies reveal the impacts of temperature and pressure [47].…”

Interfacial analysis of a PEM electrolyzer using X-ray computed tomography

“…Their observations surprising at a time, suggested that the PTL would always be saturated with water, regardless of the current density and that oxygen saturation did not change with current density in the regime of 0.1 -2.5 A/cm 2 . Lee et al (C. Lee et al, 2020) have investigated the dynamic gas transport behavior in the anode PTL by using operando synchrotron x-ray imaging. When they applied the current with a steep ramp-up and a shallow ramp-down.…”

Observation of Preferential Pathways for Oxygen Removal through Porous Transport Layers of Polymer Electrolyte Water Electrolyzers

“…As an effort to better understand the two-phase transport behavior in the PTL, studies ( Abdin et al., 2015 ; Dedigama et al., 2014 ; García-Valverde et al., 2012 ; Han et al., 2016 ; Kadyk et al., 2016 ; Kang et al., 2018 ; 2017 ; Kim et al., 2020 ; Lee et al., 2020a ; Lee et al., 2017 ; Leonard et al., 2020 ; 2018 ; Lopata et al., 2020 ; Schuler et al., 2019 ; Seweryn et al., 2016 ; Suermann et al., 2017 ; Zlobinski et al., 2020 ) have focused on using imaging techniques to investigate the evolution and transport of oxygen in electrolyzers, including optical, neutron, or X-ray imaging, as well as computational studies. Optical microscopy was utilized by Dedigama et al.…”

“…Lee et al. ( Lee et al., 2020a ) have investigated the dynamic gas transport behavior in the anode PTL by using operando synchrotron X-ray imaging. When they applied the current with a steep ramp-up and a shallow ramp-down, they concluded that the oxygen responds more rapidly, which means that the gas saturation in the PTL reached a steady state quickly.…”