Morphology-Dependent Electrochemical Performance of Boron Carbide for Energy Storage: A Comparison of Whisker and Equiaxed Morphologies

Abstract

Enhancing the electrochemical performance and structural durability of electrode materials is a critical frontier in energy storage research. Boron carbide (B₄C), characterized by its exceptional chemical stability and mechanical robustness, emerges as a promising candidate for next-generation supercapacitor electrodes. In this study, B₄C was synthesized in two distinct morphologies equiaxed and whisker via a sol–gel method. Phase and morphological analyses via X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) verified the successful synthesis of crystalline B₄C with different morphologies. Complementary electron spin resonance (ESR) spectroscopy analysis revealed a stronger paramagnetic defect-related signal for the equiaxed particles than for the whisker-type particles. The influence of these morphological and atomic-scale variations on electrochemical behavior was systematically investigated in a three-electrode configuration using 1 and 6 M potassium hydroxide (KOH) electrolytes. Cyclic voltammetry (CV) analysis revealed clear redox peaks, indicating a Faradaic contribution to the overall charge-storage response. The 6 M KOH electrolyte produced an enhanced charge-storage response, as evidenced by larger CV areas and longer discharge times and supported by the lower solution and charge-transfer resistances obtained from electrochemical impedance spectroscopy (EIS). The whisker-type B₄C outperformed the equiaxed morphology, delivering a maximum specific capacitance of 348.3 F g⁻¹ at 5 mV s⁻¹ in 6 M KOH, surpassing the 285.56 F g⁻¹ attained by its equiaxed counterpart. Furthermore, a symmetric supercapacitor device fabricated with whisker-type B₄C in 6 M KOH achieved an energy density of 0.376 Wh kg⁻¹ and a power density of 407.64 W kg⁻¹. The device demonstrated good long-term stability, retaining 97.7% of its initial capacitance after 10,000 cycles at 4 A g⁻¹, highlighting the potential of whisker-type B₄C for stable aqueous supercapacitor operation.