Morphology tailoring and improved electrochemical performance of hexagonal boron nitride (h-BN) for symmetric supercapacitor applications

Abstract

Correlations among the crystal structure, electronic structure, morphology, and electrochemical performance of hexagonal boron nitride (h-BN) are a matter of debate and need systematic investigation of their implications on the energy storage assets. This work explores the morphology-controlled synthesis of h-BN nanostructures and their influence on the structural, electronic, and electrochemical properties toward the development of a symmetric supercapacitor device. h-BN nanostructures were synthesized via a nitridation process at 900 °C using boric acid with urea, melamine, and a urea–melamine mixture precursors. Scanning electron microscopy revealed that urea-derived h-BN exhibits a faceted and porous morphology, whereas the melamine-derived sample predominantly forms nanorod-like structures. X-ray diffraction (XRD) confirmed morphology-dependent XRD line shape changes and variations in the lattice parameters. X-ray photoelectron spectroscopy (XPS) results conveyed σ-type sp² hybridization between B and N atoms in all the samples, while a higher sp2/sp3 ratio in the melamine-derived h-BN indicated reduced oxygen functionalization associated with the rod-like morphology. Electrochemical measurements, conducted in three electrode configurations with 1 M KOH electrolyte, confirmed pseudocapacitive behaviour and delivered high specific capacitance of 455.0 F/g, 516.8 F/g , and 493.3 F/g (at a scan rate of 2 mV/s) from the urea, melamine, and mixed-precursor-derived samples, respectively, highlighting morphology-dependent charge-storage characteristics. Furthermore, a symmetric supercapacitor assembled using nanorod-based h-BN electrodes in a Swagelok configuration delivered an energy density of 8.74 Wh/kg and a power density of 4500 W/kg, along with excellent cycling stability, retaining 77.1% of its initial capacitance after 10,000 charge-discharge cycles.