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[Display omitted] • A facile "chemical blowing" strategy is developed to expand the dense and micron-scale thickness walls into interconnected carbon nanosheets. • Zn(NO 3) 2 is proved to functioned as blowing agent, precursor of template, activator, and nitrogen dopant. • The optimized thick carbon monolith with high-mass loading (∼30 mg cm−2) delivers encouraging capacitive performance in low-temperature. Biomass-derived carbon materials are promising electrode materials for capacitive energy storage. Herein, inspired by the hierarchical structure of natural wood, carbon monoliths built up by interconnected porous carbon nanosheets with enriched vertical channels were obtained via zinc nitrate (Zn(NO 3) 2)-assisted synthesis and served as thick electrodes for capacitive energy storage. Zn(NO 3) 2 is proved to function as expansion agent, activator, dopant, and precursor of the template. The dense and micron-scale thickness walls of wood were expanded by Zn(NO 3) 2 into porous and interconnected nanosheets. The pore volume and specific surface area were increased by more than 430 %. The initial specific capacitance and rate performance of the optimized carbon monolith was approximately three times that of the pristine dense carbon framework. The assembled symmetric supercapacitor possessed a high initial specific capacitance of 4564 mF cm−2 (0–1.7 V) at −40 °C. Impressively, the robust device could be cycled more than 100,000 times with little capacitance attenuation. The assembled zinc-ion hybrid capacitor (0.2–2 V) delivered a large specific capacitance of 4500 mF cm−2 at −40 °C, approximately 74 % of its specific capacitance at 25 °C. Our research paves a new avenue to design thick carbon electrodes with high capacitive performance by multifunctional Zn(NO 3) 2 for low-temperature applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen, sulfur co-doped PCG composite has been fabricated via a facile co-pyrolysis method. • Pollen-derived carbon with inherited charge-transfer structure can serve as as effective "porous spacer". • The optimized PCG-0.5 electrode exhibits excellent specific capacitance, rate performance and stability. • The symmetrical PCG-0.5//PCG-0.5 device displays a remarkable energy density in neutral medium. • The "sphere-in-layer" interconnection and heteroatoms doping may be the key factors for high performance. Rational design of electrode with hierarchical charge-transfer structure and good electronic conductivity is important to achieve high specific capacitance and energy density for supercapacitor, but it still remains a challenge. Herein, a nitrogen, sulfur co-doped pollen-derived carbon/graphene (PCG) composite with interconnected "sphere-in-layer" structure was fabricated, in which hierarchically pollen-derived carbon microspheres can serve as "porous spacers" to prevent the agglomeration of graphene nanosheets. The optimized PCG composite prepared with 0.5 wt% of graphene oxide (PCG-0.5) exhibited high specific capacitance (420 F g−1 at 1 A g−1), rate performance (280 F g−1 at 20 A g−1), and excellent cycling stability with 94% of capacitance retention after 10,000 cycles. The symmetrical device delivered a remarkable energy density of 31.3 Wh kg−1 in neutral medium. Moreover, density functional theory calculation revealed that PCG electrode possessed the accelerated charge transfer and enhanced electronic conductivity, thus ensuring a remarkable electrochemical performance. This work may afford an effective strategy for the development of biomass-derived carbon electrodes with novel charge-transfer structure toward supercapacitor applications. [ABSTRACT FROM AUTHOR]