Voltage charging enhances ionic conductivity in gold nanotube membranes

Ionically conductive membranes are used in many electrochemical processes and devices, including batteries, fuel cells, and electrolyzers. In all such applications, it is advantageous to use membranes with high ionic conductivity because membrane resistance causes a voltage loss suffered by the cell. We describe here a method for enhancing ionic conductivity in membranes containing small diameter (4 nm) gold nanotubes. This entails making the gold nanotube membrane the working electrode in an electrochemical cell and applying a voltage to the membrane. We show here that voltage charging in this way can increase membrane ionic conductivity by over an order of magnitude. When expressed in terms of the ionic conductivity of the electrolyte, κ, within an individual voltage-charged tube, the most negative applied voltage yielded a κ comparable to that of 1 M aqueous KCl, over 2 orders of magnitude higher than κ of the 0.01 M KCl solution contacting the membrane.