Unlocking the synergetic potential of cobalt iron phosphate and multiwalled carbon nanotube composites towards supercapacitor application

Abstract

To date, bimetallic phosphates have not been much explored in supercapacitor applications. Interestingly, these materials hold significant potential for energy storage due to the existence of multiple oxidation states and the presence of numerous phosphorus atoms, each contributing to a substantial number of electron clouds. Present research emphasises the electrochemical performance of composite electrodes consisting of multiwalled carbon nanotubes (MWCNTs) and cobalt iron phosphate (Co₃Fe₄(PO₄)₆). These electrodes have demonstrated exceptional performance and achieved a specific capacity of 3320 C g⁻¹ (3688 F g⁻¹) at a scan rate of 5 mV s⁻¹ maintaining 87% stability even after 5000 cyclic voltammetry (CV) cycles. The electrochemical active surface area (ECSA) was estimated to be 700 cm² for Co₃Fe₄(PO₄)₆ and 1625 cm² for MWCNTs/Co₃Fe₄(PO₄)₆ composites. Additionally, the designed and tested large-area (10 × 4 cm²) liquid-configured symmetric device exhibited an impressive energy density (ED) of 52.3 W h kg⁻¹ and power density (PD) of 3.5 kW kg⁻¹. The fabricated device showed outstanding stability with a 98% capacity retention after 5000 cycles, reflecting the remarkable durability of the designed system. To illustrate its real-world applicability, the constructed device underwent a 10 s charging to power a DC fan for 110 s.