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 for 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 as 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 changes in the XRD line shape and variations in the lattice parameters. X-ray photoelectron spectroscopy (XPS) results revealed 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 values of 455.0 F g⁻¹, 516.8 F g⁻¹, and 493.3 F g⁻¹ (at a scan rate of 2 mV s⁻¹) 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⁻¹ and a power density of 4500 W kg⁻¹, along with excellent cycling stability, retaining 77.1% of its initial capacitance after 10 000 charge–discharge cycles.