Graphitic Carbon Nitride-Induced Multifold Enhancement in Electrochemical Charge Storage of CoS–NiCo2S4 for All-Solid-State Hybrid Supercapacitors

In order to improve the electro-microstructural physiognomics of electrode materials for applications in better efficiency supercapacitors, herein graphitic carbon nitride (GCN)-heterostructurized CoS-NiCo2S4 is designed using a controlled material growth synthesis procedure. The developed CoS-NiCo2S4/GCN possesses ample hydrophilicity, possible charge transfer between GCN and CoS-NiCo2S4, uniform phase distribution, and distinctive microstructural characteristics. The preliminary electrochemical studies in the three-electrode setup show GCN-induced lower charge transfer resistance and very unique Warburg profile corresponding to extremely low diffusion resistance in CoS-NiCo2S4/GCN as compared to pristine CoS-NiCo2S4. Furthermore, GCN is found to significantly induce surface-controlled (capacitive-type) charge storage and frequency-independent specific capacitance up to 10 Hz in CoS-NiCo2S4. Furthermore, the CoS-NiCo2S4||N-rGO and CoS-NiCo2S4/GCN||N-rGO all-solid-state hybrid supercapacitor (ASSHSC) devices were fabricated using N-rGO as the negative electrode material, and the inducing effect of GCN on the supercapacitive charge storage performance of the devices is thoroughly studied. Results demonstrate that the mass specific capacitance and areal capacitance of CoS-NiCo2S4/GCN||N-rGO are ∼2 and ∼4 times more than those of the CoS-NiCo2S4||N-rGO ASSHSC device, respectively. Furthermore, the CoS-NiCo2S4/GCN||N-rGO offers more energy density, rate energy density, and additional charge-discharge durability (over ∼10,000 cycles) than the CoS-NiCo2S4||N-rGO ASSHSC device. The multifold performance improvement of CoS-NiCo2S4 with GCN heterostructurization is ascribed to GCN-induced supplemented porosity and pore widening, ionic nonstoichiometry (Ni2±δ, Co2±δ, and Co3±δ), wettability, integrated enhancement in the conductivity, and electroactive-ion accessibility in the CoS-NiCo2S4/GCN heterocomposite. The present study offers vital physicoelectrochemical insights toward the future development of low cost and high-performance electrode materials, and their implementation in high-rate and operationally stable all-solid-state hybrid supercapacitor devices, for application in the next-generation front-line technologies.