This paper describes the design and performance of a scalable, stand-alone photovoltaic (PV) electrolysis device used for hydrogen (H 2 ) 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 H 2 and O 2 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.