Interface-engineered MnCO3 nanocrystals anchored on lignite-derived nitrogen/oxygen co-doped hierarchical porous carbon for high-performance supercapacitors

Lignite-derived sodium humate was converted into N/O co-doped hierarchical porous carbon. • MnCO 3 nanocrystals were grown in situ on NHAC via a one-step hydrothermal route. • Surface carboxylate groups promoted Mn 2+ anchoring, localized nucleation, and MnCO 3 dispersion. • The optimized NHAC/Mn-0.01 electrode delivered 458.3 F/g at 0.5 A/g. • The symmetric supercapacitor achieved 14.21 Wh/kg and retained 69.57% after 20000 cycles. Transition metal carbonates are promising pseudocapacitive materials, but MnCO 3 suffers from low conductivity and severe agglomeration. Herein, sodium humate from lignite is used to construct nitrogen/oxygen co-doped hierarchical porous carbon (NHAC) via urea-assisted carbonization and low-dosage KOH activation. NHAC features a high specific surface area (2323 m 2 /g), hierarchical micro/mesopores, and abundant oxygen groups. MnCO 3 nanocrystals are then grown in situ on NHAC through a one-step hydrothermal process. The NHAC matrix acts as both a conductive scaffold and an interfacial regulator: its porous framework facilitates ion/electron transport, and surface carboxylate groups anchor Mn 2+ ions, promoting uniform nucleation and preventing aggregation. The resulting NHAC/Mn-0.01 electrode delivers a high specific capacitance of 458.3 F/g at 0.5 A/g in 6 M KOH, with an 88% capacitive contribution at 30 mV/s. The assembled symmetric supercapacitor achieves an energy density of 14.21 Wh/kg at 175 W/kg and retains 69.57% of its initial capacitance after 20000 cycles. This work offers an effective interfacial engineering strategy to unlock the pseudocapacitive potential of MnCO 3 and provides a sustainable route for high-value utilization of lignite-derived carbon. Download: Download high-res image (421KB) Download: Download full-size image