Floating membraneless PV-electrolyzer based on buoyancy-driven product separation

This paper describes the design and performance of a scalable, stand-alone photovoltaic (PV) electrolysis device used for hydrogen (H2) production by solar-driven water electrolysis. The electrolyzer component of this device is based on a simple, membraneless design that enables efficient operation with high product purity and without active pumping of the electrolyte. Key to the operation of this PV-electrolyzer is a novel electrode configuration comprised of mesh flow-through electrodes that are coated with catalyst on only one side. These asymmetric electrodes promote the evolution of gaseous H2 and O2 products on the outer surfaces of the electrodes, followed by buoyancy-driven separation of the detached bubbles into separate overhead collection chambers. The successful demonstration of this concept was verified with high-speed video and analysis of product gas composition with gas chromatography. While the device based on asymmetric electrodes achieved product cross-over rates as low as 1%, a control device based on mesh electrodes that were coated on both sides with catalyst had cross-over rates typically exceeding 7%. The asymmetric electrode configuration was then incorporated into a standalone, floating PV-electrolyzer and shown to achieve a solar-to-hydrogen efficiency of 5.3% for 1 sun illumination intensity. The simplicity of this membraneless prototype, as characterized by the lack of a membrane, scaffolding, or actively pumped electrolyte, makes it attractive for low-cost production of hydrogen.