Effects of porous transport layer wettability on performance of proton exchange membrane water electrolyzer: Mass transport overvoltage and visualization of oxygen bubble dynamics with high-speed camera

For producing hydrogen from renewable energy, a proton exchange membrane water electrolyzer (PEMWE) is an appealing method offering higher current density and purity of generated hydrogen than other electrolyzers. However, this technique should be further developed to have higher efficiency for utilization. The main issue on reducing the PEMWE performance is the management of generated oxygen bubbles near the reaction site. They persist near the reaction site, inhibit the water supply, and significantly reduce the reaction efficiency. Therefore, how oxygen bubbles are removed from the reaction site should be optimized, however, the mechanism of transport phenomena of oxygen bubbles through the porous transport layer (PTL) has not been clarified. Therefore, in this study, an original cell was developed which allowed us to observe bubble movements inside PTL with a high-speed camera, and the effects of PTL wettability on the oxygen bubble movement were investigated. The PTL wettability drastically affected the PEMWE performance and bubble movement, and hydrophobic PTL reduced the PEMWE performance. The oxygen bubbles tended to stay inside hydrophobic PTL, which might cause lower PEMWE performance.