Boosting internal accessibility via 50-nm-diameter channels in NiO@nitrogen-containing carbon for high rate performance and high contribution of electric double layer capacitance

Loading metal oxides on carbon nanotubes (CNTs) is a commonly used method to enhance the pseudocapacitance (PC) of metal oxides via the improved electrical conductivity. However, the small nanometer-sized tube of CNTs is factually an inaccessible internal channel for the diffusion of large hydrated ions, which reduces the contribution of electric double layer capacitance (EDLC) of CNTs and limits the rate capability of composites. To address this challenge, a 50-nm-diameter channel is here constructed in NiO@nitrogen-containing carbon (NC) by high-temperature calcination of Ni(OH)₂/polypyrrole nanotube composite. The large-sized NC channel produced from decomposed polypyrrole significantly boosts the internal accessibility and accelerates the flow and penetration of electrolyte into the NC tube, enhancing the EDLC contribution of NCs and improving rate performance. The obtained worm-like NiO@NC shows high ion diffusion coefficient and impressive specific capacitance (SC). The assembled NiO@NC||graphene aerogel asymmetric supercapacitor offers high EDLC contribution of 65 % and exhibits a high SC of 763F g⁻¹, with outstanding retention of 93.40 % after 50,000 cycles at large current density. This study demonstrates an innovative approach to effectively combat the issue of internal inaccessibility of tubular carbon materials, marking an enormous progression in supercapacitor technology.