Sonochemically manganese doped activated carbon from Bauhinia variegata for dual energy application

Abstract

Activated carbon (AC) remains a foundational electrode material in electrochemical double-layer capacitors (EDLCs) owing to its high specific surface area, tunable pore structure, and robust charge–discharge cycling. The performance of EDLCs is closely linked to the physicochemical properties of the carbonaceous electrodes, with an optimal pore-size distribution facilitating rapid electrolyte-ion access while mitigating resistive losses. Recent machine-learning-guided design of biomass-derived activated carbons has predicted electrodes with surface areas approaching ~ 2822 m 2 g −1 and gravimetric capacitances around ~ 322 F g −1 at 1 A g −1 in aqueous KOH, illustrating the dramatic influence of synthesis variables such as activation temperature and chemical activation ratio on capacitive performance [ 1 ]. Parallel efforts in surface functionalization underscore how elemental doping can further unlock performance gains by enhancing wettability and electronic interactions. For example, nitrogen-doped ordered mesoporous carbons derived via hard templating not only achieve ~ 100 F g −1 gravimetric capacitance but also break conventional areal limits for activated carbons with ~ 9.2 µF cm −2 , attributing performance to the creation of highly adsorptive sites for electrolyte ions [ 2 ]. Doped porous carbons also find relevance in hybrid devices, where synergistic charge storage mechanisms combine EDLC and pseudocapacitance contributions. Nitrogen and phosphorus co-doped porous AC electrodes achieve energy densities of ~ 49 Wh kg −1 and power densities up to ~ 13.8 kW kg −1 in ionic liquid and water-in-salt electrolytes, indicating that heteroatom incorporation can tailor ion dynamics for both EDLCs and emerging zinc-ion hybrid capacitors [ 3 ]. Phosphorus-doped AC also enables symmetric pouch-cell supercapacitors with energy densities of ~ 36 Wh kg −1 and outstanding cycle retention (~ 93.7% after 30,000 cycles) by modulating adsorption/desorption dynamics of organic electrolytes [ 4 ]. Biomass-derived heteroatom-rich ACs produced via natural doping deliver ~ 202 F g −1 and specific energy of ~ 28.7 Wh kg −1 in symmetric devices, demonstrating that inherent dopants can combine EDLC and pseudocapacitive behaviour [ 5 ]. Additionally, hierarchical loofah sponge-derived porous carbons exhibit exceptional specific capacitances up to ~ 344 F g −1 and robust cycling stability (> 10,000 cycles), further validating the importance of macro-/mesopore architecture coupled with functional surfaces [ 6 ].