Polarity-dependent electrochemically controlled transport of water through carbon nanotube membranes

We demonstrate here that water can be efficiently wet and pumped through superhydrophobic aligned multiwalled nanotube membranes by application of a small positive dc bias. At a critical bias (∼1.7 V), with the membrane acting as anode, there is an abrupt transition from a superhydrophobic to hydrophilic state. Interestingly, this phenomenon is strongly polarity dependent; for a negative bias applied to the membrane, 2 orders of magnitude higher bias is required for the transition. The polarity and voltage-dependent wetting that we report could be used to controllably wick fluids through nanotube membranes and could find various applications.