Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields

Abstract

A novel interdigitated flow field design for polymer electrolyte electrolysis cells (proton exchange membrane water electrolysis cells) composed of oxygen exhaust channels apart from liquid water feed channels has been developed for ground and space applications because the design is advantageous in terms of oxygen/water separation without buoyancy, and dispenses with water circulators for bubble removal in a cell and external separators by natural or centrifugal buoyancy. Finite element modeling of water transport in the polymer electrolyte (proton exchange) membrane in a cell with the interdigitated flow fields is conducted. Current-voltage (I–V) measurement of the cell is also performed for comparison with numerical modeling. Deviation of the experimental I–V characteristics from those of the numerical model indicates a possible water transport path in the in-plane direction of hydrophobic microporous layers (MPLs) coated on gas diffusion layers installed between the anode catalyst layers (CLs) and oxygen flow channels in the cell. Analysis of the deviation associated with the limitation of water transport also suggests fractional bubble coverage of produced oxygen gas at the CLs. The hydrophobic MPL acts to separate oxygen gas and pressurized liquid water due to the capillary pressure, while it determines the limitation of water transport to the CLs with the oxygen bubble coverage.

Keywords

• water electrolyzer
• gas/liquid separation
• interdigitated flow field
• microporous layer