Synthesis of single and bimetallic oxide-doped rGO as a possible electrode for capacitive deionization

Porous carbon doped with transition metal oxides is rapidly becoming a key research topic in capacitive deionization desalination. This work reports a simple method for the synthesis of rGO doped with different ratios of nickel and cobalt oxides, i.e., 0, 10, 15, 25, 50, 75, and 100 wt%. The nanocomposite material was prepared via a modified Hammer`s method, followed by a hydrothermal doping process. The prepared samples were characterized using the X-Ray diffractometer (XRD), scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy. TEM images revealed the arbitrary distribution of nickel and cobalt oxides in the rGO layer with an average particle size of 13 nm. The performance of the prepared materials was investigated ex situ, i.e., using a typical three-electrode cell. Also, it was verified in situ during the cell operation, i.e., using a two-electrode cell. Results showed that the performance of rGO was improved in the presence of Co 3 O 4 and NiO nanoparticles as they form ternary Co 3 O 4 /NiO/rGO composites. Both XRD and EDX analyses confirmed the presence of Ni and Co in oxide form and attached to the rGO. The three-electrode cell measurements were from − 0.6 to 0.6 V in 1 M aqueous NaCl. The electrochemical measurements demonstrated that the rGO-25Ni, rGO-25Co, and rGO-15(50Ni-50Co) electrodes exhibited the best capacitive performance. Those samples achieved specific capacitances as high as 357 F g −1 , 368.7 F g −1 , and 461.5 F g −1 , respectively. Such values are higher than those of electrodes based on rGO (82.77 F g −1 ), nickel oxide (2.98 F g −1 ), and cobalt oxide (3.8 F g −1 ). Better performance has been achieved using an equal ratio of bimetallic oxide loaded into the rGO than the single oxides or other ratios. Graphic abstract