Fabrication of porous polyphosphate carbon composite on nickel foam as an efficient binder-less electrode for symmetric capacitive deionization

• A porous Polyphosphate/RGO/CNT composite was prepared. • Simple binder-free route was used to prepare the electrodes on Ni substrate. • The electrode reveals specific capacitance of 122F/g at scan rate of 2 mV/s in 1 M of NaCl. • Eelectrochemical adsorption capacity of the electrode is 19.7 mg/g in 500 ppm NaCl. • Electrodes preserved 67% of the initial sorption capacity after 300 cycles (13 days). An efficient and commercially available method is introduced for preparation of a binder-free electrode for capacitive deionization (CDI) application. An interconnected porous composite consisting of polyphosphate (PPO), graphene (Gr) and multi-walled carbon nanotube (CNT) is fabricated and assembled on a Ni foam substrate to prepare a binder-free electrode (Ni/PPOGrCNT). The resulting electrodes were characterized using various instrumental techniques such as TEM, SEM, EDS, XRD, FT-IR, Raman, XPS and XRF. Characterization results indicated that a mesoporous PPO structure is formed on a 3D assembly of carbon backbone. Accordingly, the 3-D porous structure facilitates the ion diffusion into the composite structure. In addition, the PPO texture enhances the pseudocapacitive electrosorption mechanism and extend the life cycle stability of the prepared electrodes. The performance of the fabricated electrodes was studied for CDI application. In this regard, the cyclic voltammograms and galvanostatic life cycle stabilities of the electrode are surveyed in NaCl solution. Also, the electrosorption capacity and the lifetime of the electrode are surveyed in constant voltage regime. The results indicated that the fabricated electrode had a good specific capacitance of 122F g −1 , an ion removal capacitance of 19.7 mg g −1 , and an acceptable life cyclic performance of 67% after 13 days.