(550c) The Role of Water in Vapor-Fed Proton-Exchange-Membrane Electrolysis

Electrolytic devices provide a carbon-free option for producing hydrogen, with many advantages such as modular, scalable design and flexibility of operating parameters (temperature, pressure, etc.). Typically, electrolyzers are run under conditions that require a significant amount of clean, liquid water and are run at several A/cm². Using liquid water mitigates transport issues at these high current densities, but introduces multiphase flow when liquid water and oxygen gas are present simultaneously. These challenges can be surmounted using a vapor-fed electrolyzer, where water vapor is split to oxygen and hydrogen directly. While removing multiphase flow, vapor-fed electrolysis introduces a myriad of other considerations when investigating the water, ion, and gas transport within the system.

In this talk, we explore water vapor electrolysis, both with experiments and with a mathematical model, to elucidate the local transport in the cell. Applied voltage breakdowns are used to analyze the losses are occurring and how they differ from the transport in liquid-phase systems. The major limitations within the vapor-fed electrolyzer are caused by a decreased water content within the membrane phase, indicated by increased Ohmic and mass transport losses seen in applied voltage breakdowns. Detailed explanation of other transport, including the water within the gas phase and in the membrane, provides a further understanding of transport limitations for these vapor-fed cells. The performance, though limited compared to liquid systems, has the potential to satisfy niche applications for future study.

J.C.F. would like to acknowledge support from National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400. This work was partially funded by the Energy & Biosciences Institute through the EBI-Shell program.