Flow and Mass Transport for Polymer Electrolyte Membrane Electrolyzers

Effective two-phase transport is a prerequisite for achieving high efficiency operation for polymer electrolyte membrane electrolyzers since the undesired accumulation of gaseous oxygen leads to mass transport losses. In this thesis, two-phase flow in the PTL and flow channels were investigated via experimental and numerical techniques to inform new designs and optimize operating conditions. The effect of gas compressibility on displacement behaviour in the PTL was elucidated by studying gas invasion in liquid-saturated microfluidic cells. Smaller pore throat sizes led to larger pore burst velocities, which inspired a new PTL design with engineered pore throat sizes for enhanced gas removal. Next, the gas transport behaviour in the PTL was investigated via a custom microfluidic cell that was based on a realistic PTL microstructure. A unique pore throat was identified where gas snap-off occurred, and the location of this pore throat governed the average gas saturation in the PTL. Next, the temperature-dependent gas saturation in the PTL was investigated using in operando neutron imaging. Increasing the operating temperature led to lower gas saturation near the catalyst layer and PTL interface, resulting in a decrease in mass transport overpotential. To increase the accuracy of anode flow channel visualizations, the nitrogen purging rate was optimized to minimize the impact of purging on cell performance. Excessive cathode purging led to undesired changes in performance, and a minimal purge rate was recommended to achieve accurate through-plane imaging. Lastly, temperature effects on two-phase quality in the anode flow channels were investigated via neutron imaging. A more uniform reactant distribution across the flow channels was observed at higher temperatures, enabling a uniform operating current density across the active area. The main findings in this thesis inform the design of novel PTL microstructure and explain the benefits of higher operating temperature for enhanced mass transport in PEM electrolyzers.Ph.D