Understanding of Mass Transport Limitation in Near-Neutral Anion-Exchange-Membrane Water Electrolysis

Anion-exchange-membrane water electrolysis (AEMWE) is a nascent green hydrogen production technology which combines the advantages of proton-exchange-membrane water electrolysis (PEMWE) and alkaline water electrolysis (AWE). Using less-concentrated KOH feed is preferable and an active area of research. However, it is generally known that AEMWE’s performance suffers greatly from using near-neutral pH feeds (e.g., pure water), which is attributed to kinetic losses and the poor conductivity of water. Mass-transport limitations are also observed in a low pH condition, which introduces another loss at high current density. However, mass transport in these systems has not been described extensively in the literature. To improve the understanding of mass transport phenomena in AEMWE in-operando, we have developed an asymmetric feed system to probe the impacts of KOH transport in the mass-transport-limited region. The cell is constructed using a membrane electrode assembly (MEA) fabricated by Pt/C catalyst coated directly on the membrane as the cathode and iridium oxide (IrOx) sprayed on a stainless-steel porous transport layer (PTL) as the anode. PiperION is used as the anion exchange membrane. Cells constructed in this way are able to reach a high current density, even in pure water conditions, in which the mass transport limitation region is observed. Through combination with mathematical modeling, we have shown that, by utilizing various combinations of feeds, it is possible to elucidate the cause of mass transport limitations in different systems. As a result, this work paves a way for moving towards pure water electrolysis.