g-C(3)N(4)/Chlorocobaloxime Nanocomposites as Multifunctional Electrocatalysts for Water Splitting and Energy Storage

[Image: see text] Due to environmental contamination and the depletion of energy supplies, it is very important to develop low-cost, high-performance, multifunctional electrocatalysts for energy conversion and storage systems. Herein, we report the development of cost-effective modified electrodes containing g-C(3)N(4)/chlorocobaloxime composites (C1–C4) and their electrocatalytic behavior toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), followed by their energy-storage applications. A series of chlorocobaloximes {ClCo(dpgH)(2)B} with diphenylglyoxime (dpgH) and neutral bases (B) containing a carboxylic acid moiety (isonicotinic acid, pyridine-3,5-dicarboxylic acid, indole-2-carboxylic acid, and p-aminobenzoic acid) have been synthesized and characterized by spectroscopic techniques. The nanocomposites of g-C(3)N(4)/chlorocobaloximes are prepared and characterized by Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), particle size distribution analysis (PSA), Brunauer–Emmett–Teller (BET), and energy dispersive X-ray analysis (EDAX) techniques. The composite coatings exhibit enhanced HER performance at lower overpotential and with a lower Tafel slope. When the water-splitting reactions are studied using 0.5 M H(2)SO(4) and 0.5 M KOH as electrolytic solutions, the composite g-C(3)N(4)/C2 containing pyridine-3,5-dicarboxylic acid as a neutral base shows excellent HER activity with a lower overpotential of 173 mV at −10 mA cm(–2) and OER activity with a lower overpotential of 303 mV. The HER reaction takes place through the Volmer–Heyrovský mechanism, where the desorption step is the rate-determining step. Among the synthesized nanocomposites, the nanocomposite g-C(3)N(4)/C2 shows higher efficiency toward both HER and OER reactions, with a lower Tafel slope of 55 mV dec(–1) for HER and 114 mV dec(–1) for OER than the other nanocomposites. The overall water-splitting studies of the composite g-C(3)N(4)/C2 in 0.5 M KOH indicate that the evolution of hydrogen and oxygen occurs constantly up to 120 h. The supercapacitance applications studied using cyclic voltammetry and charge–discharge studies indicate that the nanocomposite g-C(3)N(4)/C1 shows a good specific capacitance of 236 F g(–1) at 0.5 A g(–1) compared to others. The increased electrochemical performance of the synthesized nanocomposites is due to the incorporation of electron-withdrawing carboxylic-acid-functionalized neutral bases present in cobaloximes, which increases electron mobility. The incorporation of a cobaloxime complex into a g-C(3)N(4) nanosheet enhances the electrocatalytic behavior of the nanosheet, and its performance can further be fine-tuned by systematic variation in the structure of cobaloxime by changing the halide ion, dioxime, the neutral base ligand, or the substituent.