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

Enhancing the electrochemical performance and structural durability of electrode materials is a critical frontier in energy storage research. Boron carbide (B ₄ C), characterized by its exceptional chemical stability and mechanical robustness, emerges as a promising candidate for next‐generation supercapacitor electrodes. In this study, B ₄ C 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 B ₄ C 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 B ₄ C 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 B ₄ C 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 B ₄ C for stable aqueous supercapacitor operation.