Self-supporting macroscopic carbon/Ni-Fiber hybrid electrodes prepared by catalytic chemical vapor deposition using various carbonaceous compounds and their capacitive deionization performance

We prepared a series of self-supported macroscopic C/Ni-fiber hybrid electrodes by catalytic chemical vapor deposition (CCVD) using methane, ethylene, ethanol and n-butanol as carbon sources to embed carbon onto a three-dimensional network of sinter-locked conductive 8 μm-nickel fibers. For the as-prepared hybrid electrodes, the Ni-microfibrous network serves as a current collector and the carbons as ion storage media while the macroporous void space serves as an electrolyte reservoir. We characterized the hybrid electrodes using scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), N₂ isothermal adsorptiondesorption, cyclic voltammetry and electrochemical impedance spectroscopy. The desalination performance of the C/Ni-fiber hybrids was evaluated as electrodes in a capacitive deionization system. The carbon morphology is dependent on the carbonaceous compounds used in CCVD: carbon nanotubes (CNTs) with fishbone-like structure, CNTs with inclined graphene layers parallel to the tube axis, rod-likecarbon nanofibers (CNFs) and worm-like CNFs for ethylene, methane, n-butanol and ethanol. The desalination performance of these hybrid electrodes with respect to the carbonaceous compounds decreases as follows: ethylene>n-butanol>methane>ethanol, which correlates with their electrochemical features, pore structures and their carbon nanostructures. The hybrid electrodes obtained using ethylene as the carbon source gave a maximum electrosorption capacity of 159 μmol·g^-1 using a direct current voltage of 1.2 V and a 100 mg·L^-1 NaCl aqueous solution as raw water.