Boron-doped MnO₂/carbon fiber composite electrode for supercapacitor

Highlights: • Interstitial ion in MnO₂ lattice. • Porous film composed by interlocking worm-like nanostructure. • Boron-doped birnessite-type MnO₂/carbon fiber composite electrode. • Enhanced capacitive properties through nonmetal element doping. - Abstract: The boron-doped MnO₂/carbon fiber composite electrode has been prepared via in situ redox reaction between potassium permanganate and carbon fibers in the presence of boric acid. The addition of boron as dopant results in the increase of growth-rate of MnO₂ crystal and the formation of worm-like nanostructure. Based on the analysis of binding energy, element boron incorporates into the MnO₂ lattice through interstitial mode. The doped electrode with porous framework is beneficial to pseudocapacitive reaction and surface charge storage, leading to higher specific capacitance and superior rate capability. After experienced 1000 cycles, the boron-doped MnO₂ still retain a higher specific capacitance by about 80% of its initial value. The fall in capacitance is blamed to be the combination of the formation of soluble Mn²⁺ and the absence of active site on the outer surface