Characterization and application of carbon nanotube sheet as electrode for capacitive deionization

Desalination of seawater provides a viable solution to counteract the shortage of drinking water that affects a great share of the world’s population. In this regard, capacitive deionization has proven to be a promising alternative for the desalination of seawater with a low or moderate salt concentration. High performance of the capacitive deionization cell requires high quality electrode materials with very specific requirements such as low wettability, good conductivity, high specific area, low pore radius, non-faradaic reactions and good capacitance: nanostructured materials can improve the process efficiency and reduce energy consumption. The electrode employed in this study was a multi-walled carbon nanotube sheet produced by Lockheed Martin, and the experimental characterization was performed in the Laboratory of Energy and NanoSciences (LENS) of Masdar Institute of Science and Technology (Abu Dhabi, UAE). Three different types of fundamental characterization were performed initially. Morphology was investigated by the use of different microscopy techniques (SEM, AFM, BET). The wettability behavior was studied by contact angle machine and ESEM. Finally, the electrical homogeneity of the electrode and its conductivity were tested by the use of 4-probe and 2-probe techniques. The characteristics identified allowed to indicate the material as good candidate for capacitive deionization electrodes. Its electrochemical behavior was then investigated by means of three different techniques, which are cyclic voltammetry in different environmental conditions, galvanostatic charge/discharge and electrochemical impedance spectroscopy, in order to determine the types of phenomena occurring during electrosorption, the specific capacitance and the possible degradation of the material during the charge/discharge cycles in repeated uses.