Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

Abstract

Metal–organic frameworks (MOFs) serve as expedient self-templated precursors to derive hybrid materials with various functionalities. This study develops a bimetallic MOF-derived approach for the facile synthesis of nitrogen-doped carbon integrated nickel–cobalt mixed metal phosphide (NiCoP/NC) using a controlled experimental procedure for supercapacitors. Here, the nitrogen-doped carbon nanosheet functions as a conductive framework and protective layer for NiCoP nanostructures and offers facile pathways for easy charge transfer, abundant surface active sites and improves the stability of the electrode. The marigold flower-like morphology of NiCoP nanostructures stores a large number of ions in their petals and shortens the ion diffusion length. The electrochemical analysis demonstrates that the as-designed NiCoP/NC electrode possesses a high specific capacity of 690.6 mA h g⁻¹ (6.22 F cm⁻²) at 1 A g⁻¹, high rate capability and excellent cycling stability. Additionally, a hybrid supercapacitor built with NiCoP/NC and activated carbon as positive and negative electrodes shows a maximum specific energy of 47 W h kg⁻¹ at a specific power of 1666 W kg⁻¹ and good capacity retention over 10 000 charge–discharge cycles. The present multicomponent approach combines the virtues of efficient redox chemistries of each element and N-doped carbon providing abundant surface active sites while stabilizing the active electrode material during repeated cycling.