A Stable Ag/Ceramic-Membrane/Ag₂O Electroosmotic Pump Built with a Mesoporous Phosphosilicate-on-Silica Frit Membrane

Low-voltage non-gassing electro-osmotic pumps were built of phosphorylated silica frit membranes, formed meso-porous silica particles of 0.7-1.0 μm diameter, sandwiched between porous, consumable, Nafion-coated Ag/Ag 2 O electrodes. The flow rates of pumps with membranes formed of the meso-porous silica particles were stable, remaining constant within ±12% until ≥80% of the 2.6 coulomb capacity of the Ag or Ag 2 O electrodes, sufficient for pumping about 5 mL water, was exhausted. The cause of the decay of the flow in these pumps is Ag + -accumulation at the non-mesoporous membrane surface, observed by metallic silver precipitation caused blackening of the light-exposed non-mesoporous membranes. When the membranes were made with the mesoporous particles, there was no silver precipitate on the membrane; instead, all of the silver was electrodeposited at the cathode. The stability of the flow of pumps made with meso-porous silica membranes is thus attributed to the rapid transport of Ag + -transport to the cathode.