Mass transport losses ultimately suppress gas evolving electrochemical energy conversion technologies, such as fuel cells and carbon dioxide electrolyzers, from reaching the high current densities needed to realize commercial success. In this work, we reach ultrahigh current densities up to 9 A/cm 2 in a polymer electrolyte membrane (PEM) water electrolyzer with the application of custom porous transport layers (PTLs) with patterned through-pores (PTPs), and we reduce the mass transport overpotentials of the electrolyzer by up to 76.7 %. This dramatic performance improvement stems from the 43.5 % reduction in gas saturation at the catalyst layer-PTL interface region. Moreover, the presence of PTPs leads to more rapid bubble coalescence and subsequently more frequent bubble snap-off (∼3.3 Hz), thereby enhancing the rate of gas removal and liquid water reactant delivery to the reaction sites. This work is highly informative for designing PTLs for optimal gas removal for a wide range of gas evolving electrochemical energy conversion technologies.

No abstract

Carbon dioxide (CO 2 ) reduction flow cells, coupled with renewable energy sources, are a promising means of curtailing anthropogenic CO 2 emissions by reducing CO 2 to generate useful carbon fuels. However, unstable mass transport overpotential due to gas evolution impedes high current density operation (>200 mA cm −2 ), preventing wide-scale commercialization. Here, we identify a real-time correlation between the electrolyte layer gas content and the cathode potential in an operating flow cell via concurrent galvanostatic operation and subsecond X-ray synchrotron imaging, whereby gas accumulation directly corresponds to increasing cathode overpotentials and gas removal corresponds to decreasing cathode overpotentials. Specifically, at 125 mA cm −2 , a 5% decrease in gas volume near the interface of the cathode gas diffusion electrode (GDE) and the electrolyte layer corresponds to a 12% decrease in the cathode overpotential. Moreover, gas saturation becomes more stable at high current densities (>175 mA cm −2 ) due to more frequent gas removal, consequently stabilizing cell performance. The findings from our work suggest that enhancing gas removal from the electrolyte layer minimizes cathode potential instability and enables current density operation greater than 200 mA cm −2 in alkaline flow cells for CO 2 reduction.

No abstract

No abstract