Toward orientation-independent design for gas recombination in closed-loop electroosmotic pumps

Direct current operation of electroosmotic pumps consumes water and generates electrolysis gas bubbles that can block the working electrode and build up pressure in the pump housing. The formation of the electrolysis gases can degrade pump performance and can lead to failure. Although catalysts have been used to recombine the electrolytic gases, current designs are sensitive to orientation relative to gravity making them inappropriate for many portable applications. Here we propose a gas recombination system design that operates independent of pump orientation. The design uses Nafion-sheathed electrodes, a catalyst chamber, and an osmotic membrane to capture and recombine electrolytic gases as well as return the liquid recombination products to the electrolyte reservoir. The pump was tested for 24 h at six major orientations with constant current fluxes. The measured gas chamber pressures and applied pump potentials suggest that the recombination system is functional at all orientations for driving currents of 3 mA and less.