Engineering oxygen defects in the boron nanosheet for stabilizing complex bonding structure: An approach for high-performance supercapacitor

Boron is a highly pursued advance charge storage material ascribed to its lighter weight and metallic nature. However, vastly reactive bonding structure of boron is impeding its application as supercapacitive material, especially in aqueous electrolyte. Here, an energetically favourable oxidation approach is engineered to enforce the lattice distortion of β-rhombohedral phase that results in oxygen defect. This approach causes the oxidative exfoliation (few layers ∼ 8.5 nm thickness) to maximize the electroactive surface area and also stabilizes the structure in aqueous electrolytes. These attributes combining with large conductivity (96.12 S m−1) results in an excellent cycling stability (>80%) and rate capability (>59%) in aqueous electrolytes. Among different pH electrolytes, oxygen defective boron nanosheet with KOH (τ ∼ 0.83 s; 107.63 mF cm−2@2 A g−1) and H2SO4 (τ ∼ 1.78 s; 141.55 mF cm−2@2 A g−1) shows extremely splendid pseudocapacitive charge storage. From the mechanistic study, governance of pseudocapacitive contribution is verified. Moreover, the fabricated symmetric cell (3 V, BMIMBF4) with slight decline of discharge voltage (2.85 to 2.4 V) on current density increment (5 fold) exhibits a maximum specific energy of 25.1 Wh kg−1@636.13 W kg−1. This work provides a cornerstone to the upcoming studies for further advancement of highly conductive boron based capacitive electrodes.