Mn-doped 2D hexagonal boron nitride: Boosting supercapacitor performance via point defects

Hexagonal boron nitride (h-BN) is chemically robust but intrinsically insulating, which limits its direct use as an electrochemically active electrode material. Here, Mn-doped h-BN powders were synthesized via high-energy ball milling, followed by solution-assisted mixing with an Mn precursor, and annealing under N 2 at 700–900 °C. Structural and defect evolution were investigated using XRD, Raman spectroscopy, photoluminescence (PL), and electron paramagnetic resonance (EPR). Increasing annealing temperature and Mn content induce measurable lattice modifications and phonon softening, as evidenced by a redshift of the E 2 g Raman mode and the emergence of additional defect-activated bands. PL reveals a systematic enhancement of blue emission with increasing processing severity, consistent with the creation of dopant- and defect-related radiative recombination pathways and concomitant band-structure perturbation. EPR directly confirms Mn incorporation through the M n 2 + hyperfine sextet and shows temperature-dependent linewidth broadening, indicating stronger Mn–Mn interactions and partial clustering at higher annealing temperatures, while a carbon-related signal near 𝑔 ≈ 2 . 0 0 5 is suppressed upon annealing. Electrochemical testing in symmetric supercapacitor cells demonstrates a transition from predominantly electric double-layer behavior at 700 °C to a pronounced pseudocapacitive response at higher temperatures, with the best overall performance achieved at intermediate thermal activation (800 °C) and moderate Mn loading ( ∼ 3%). For this best-performing composition, the maximum specific capacitance reaches 566.73 F/g at a scan rate of 10 mV/s, and the Ragone plot yields an energy density of 78.7 Wh/kg at a power density of 15.7 kW/kg. These results show that Mn-assisted defect engineering provides a viable route to activate h-BN and tailor its charge-storage mechanism for energy-storage applications.