Solvothermal synthesis of nickel cobalt sulfide nanostructures for high-performance electrochemical supercapacitors an integrated experimental, computational and machine learning approach

This complete investigation presents a combined experimental and computational Approach to emergent high-performance nickel cobalt sulfide (NiCo2S4) nanostructures for Supercapacitor applications. NiCo2S4 samples were synthesised via a two-step solvothermal Method at temperatures of 120–180 °C (designated NCS1-NCS4) and scientifically characterised using XRD, BET, SEM, XPS and FTIR. The optimised NCS4 electrode exhibited a notable specific capacitance of 920.04 Fg− 1 from cyclic voltammetry and 375 Fg− 1 from galvanostatic Charge-discharge measurements. DFT calculations revealed that the (111) surface has the lowest surface energy (0.85 Jm− 2) and the highest electrochemical activity, while nickel vacancies have the lowest formation energy (1.8 eV) under Ni-poor conditions. ML models achieved R2 = 0.97 in predicting capacitance, with synthesis temperature identified as the most critical parameter (importance: 0.28). A Comparative analysis of simulated and experimental results showed excellent agreement (average deviation < 5%). The symmetric supercapacitor device achieved an exceptional specific capacitance of 1234.89 Fg− 1, an energy density of 42.9 Whkg− 1, a power density of 735 Wkg− 1, and 82.82% capacitance retention after 5000 cycles. Pre-fabrication analysis indicated optimal mass loading of 1.5 mg cm− 2 and electrode thickness of 200 nm for device development. This integrated methodology provides a comprehensive framework for the rational design of transition metal sulfide electrodes, with applications in electric automobiles, portable semiconductor technology, renewable energy storage, and industrial power systems.