Vapor Phase Water Electrolysis or Pocket Mediated Water Electrolysis?

In this article, we show that adventitious water/electrolyte coming from various processing steps can obscure the assessment of results for a fully vapor-fed water electrolyzer. A couple hundreds of μl per cm 2 of water can sustain typical operating current densities of 10 mA cm −2 geo for tens of hours, thereby not reflecting the true vapor-phase performance. This is a serious problem, especially for catalyst coated substrate architecture where surface non-uniformities behave as water pockets. We demonstrate that these water-pockets mediate the electrolysis process which can run for up to 30 h at 10 mA cm −2 geo with or without the supply of humidity. Interestingly, the vapor-fed device stops functioning at a particular charge density that corresponds to the consumption of liquid water present in these pockets.