High-performance of Ni2CoS4 as Pt-free counter electrode for advanced flexible dye sensitized solar cell (FDSSC) and symmetric supercapacitors

In this work, we used a hydrothermal process to synthesize NiCo 2 O 4 and Ni 2 CoS 4 for flexible dye sensitized solar cell (FDSSC) and supercapacitor. The phase structures, functional groups and optical features of synthesized samples were confirmed by different characterization analytical techniques. The morphologies of NiCo 2 O 4 are formed as nanoflakes and Ni 2 CoS 4 formed as multiple interconnected nanosheets and nanoparticles, which were confirmed by FE-SEM and HR-TEM analysis. The fabricated FDSSC performances were analysed and the J sc , V oc and FF% were obtained from J-V curves and were 6.7455 mA cm −2 , 0.6 V and 0.7209% for NiCo 2 O 4 and 8.1275 mA cm −2 , 0.7 V and 0.7325% for Ni 2 CoS 4 , respectively. The fabricated FDSSC displays a power conversion efficiency (PCE %) of 2.91 for NiCo 2 O 4 and 4.16% for Ni 2 CoS 4 . After 50 bends and twists of the FDSSC the PCE% of the FDSSC remained at 70% (3.39%) and 74% (3.21%). Moreover, Ni 2 CoS 4 showed exceptional photovoltaic activity in the reduction of triiodide (I − /I ₃ − ) due to enhanced electronic conductivity and synergistic effects at the interfaces of NiCo 2 O 4 and Na 2 S. Electrochemical performance of Ni 2 CoS 4 electrodes in 1 M KOH showed a specific capacitance of 517.8 F/g at 1 A/g. A symmetric supercapacitor assembled with Ni 2 CoS 4 attained an energy density of 26.85 Wh/kg, a power density of 699.9 W/kg and maintained 98.5% capacitance retention after 7000 cycles, highlighting its potential for energy storage applications. This study aims to provide novel synthesis and rational design of highly efficient NiCo 2 O 4 and Ni 2 CoS 4 materials for prospective FDSSC solar cell and supercapacitor applications.