Water starvation phenomena in a segmented along the channel PEM water electrolysis cell

Proton exchange membrane water electrolyzers are typically operated with high water stoichiometry since the water, as a reactant, is also used as cooling agent for heat management. Water starvation phenomena are therefore not a pressing issue. However, in large industrial cell designs with challenging flow distribution, some areas of the cell may not be properly supplied with water.

This study investigates water starvation in a segmented test cell with 30 cm long flow field channels. By varying the water flow rate close to the stoichiometric level, local membrane dry-out and mass transport issues are investigated. To achieve this, the distribution of current density, temperature, and impedance are analyzed up to 5 A∙cm⁻² mean cell current density. Distribution of Relaxation Time is used to analyze the local impedance.

Our findings reveal that undersupply of water drastically affects the high frequency resistance coupled with increasing low-frequency capacitive features of the impedance, which we refer to as membrane dry-out due to mass transport limitations. However, mass transport issues, without a significant influence on membrane resistance, seem not to be relevant. By varying the gas pressure, membrane dry-out effects can be reduced which emphasizes the importance of oxygen removal at the anode.