Water Crossover in Proton Exchange Membrane Water Electrolysis

Abstract

Water management is critical for high performance of polymer electrolyte membrane water electrolysis (PEMWE). In this work, we investigated the water crossover for 5 cm2 PEMWE single cell by varying the temperature (40 – 80 °C), current density (0 – 2 A cm-2 geo), cathode pressure (ambient, 310 kPagauge,inlet), and nitrogen purge rate (50, 100 nccm). Using an advanced gravimetric method, water crossover to the cathode could be established very accurately and also corrected by the water vapor fraction. We pointed out that the cathode exhaust gas is saturated with water vapor, either from diffusion or by proton drag at low or high current densities, respectively. Very importantly, water crossover at high current density is controlled by proton drag and are used to extract the temperature-dependent proton drag coefficient at 1 A cm-2geo. Our results reveal that the proton drag coefficient increases from 2.5 ± 0.2 at 40 °C to 3.2 ± 0.2 at 80 °C (+28 %). Altogether, we have developed a sophisticated gravimetric method to accurately determine water crossover under PEMWE operatingconditions and proposed a model of the temperature-dependent proton drag coefficient. Unravelling the proton drag and diffusion is very important for modeling of water transport in PEMWE.