Electrochemical water-splitting devices can contribute to increase the share of renewable sources in today’s energy landscape. Simplifying the operation of state-of-the-art electrolysis systems could help drive their large scale deployment. One alternative for the simplification of electrolyzers is the implementation of systems that can operate directly with water vapor feeds. Operation under vapor conditions brings with it several advantages: a reduced water-splitting potential, the elimination of catalysis limitations from bubble formation, and a slow-down of the degradation processes of the materials involved in the water-splitting process. In this study, we introduce a microstructured device that can produce hydrogen from humid ambient air streams.¹ The device is composed of interdigitated microelectrodes that are covered by a thin ionomer film (Nafion^®) (< 1 µm). Water diffuses through this film and is oxidized at the anode interface to generate oxygen and protons. Protons then migrate through the film towards the cathode side and are reduced to produce hydrogen. This presentation will provide insights into the multiple transport and electrochemical processes taking place inside of the ionomer and that affect the overall device performance. The effects of parameters such as electrodes dimensions, interelectrode separation, electrocatalysts selection and ionomer processing were studied, and their effects in the operation of the device will be discussed. We demonstrate that large ionic resistances in the devices limit the current densities achievable, and that minimizing the pathways for proton transport can result in current densities higher than 10 mA/cm²at 1.8 V. Lastly, strategies towards the integration of these air-based electrolysis components into solar-hydrogen generators will be presented. 

1. M. A. Modestino, M. Dumortier, M. Hashemi, S. Haussener, C. Moser and D. Psaltis, Lab on a Chip, 2015, 15, 2287-2296.