Hierarchical structural carbon with properly modulated compositions and porosity is essential for energy storage capacity. Here, N-doped porous carbon was synthesized using abundant rice straw under the sequential hydrothermal treatment and calcination by KHCO 3 in the presence of melamine. The activation with KHCO 3 resulted in about a 50% increase in the yields of porous carbons and performance comparable to that of KOH. The extra additional melamine not only introduces the N-containing functional groups but also enhances the mesoporosity and specific surface area (2786.5 m 2 g −1 ). Meanwhile, wettability and conductivity are improved. The obtained N-doped porous carbon exhibits outstanding capacitance of 317 F g −1 at 1 A g −1 . The fabricated symmetric supercapacitor displays a stable cycling performance (99.4% retention after 5000 cycles), a reasonable rate performance, and the maximum specific energy of 18.4 W h kg −1 . Our research provides a promising method for effectively converting biowaste into energy storage materials through green synthetic strategy.

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Designing low-cost and sustainable electrode materials for energy storage devices with large energy density and capacitance is still a formidable challenge. Herein, a green, template-free, and facile Fe-decorated porous carbon synthesis strategy derived from bamboo was proposed. This strategy includes hydrothermal carbonization pretreatment, which can tune the carbon morphology and dope iron elements in one step, and a mild KHCO3 activation to improve porosity while retaining the spherical morphology. The optimized Fe-decorated porous carbon exhibited a high surface area (1509.5 m2 g–1) with a carbon sphere/nanosheet architecture, which is beneficial for ion/electrolyte diffusion and increasing the accessibility between the surface area and electrolyte ions. Moreover, the introduced Fe oxides can provide extra pseudocapacitance, which comes from the reversible faradaic reaction between Fe3+ and Fe2+. The resulting carbon material presented a high capacitance of 467 F g–1 at 0.5 A g–1. The assembled KOH-based symmetric supercapacitor displayed a superb cycling performance that can output 99.8% of the initial capacitance after 5000 cycles, and the Na2SO4-based device showed the maximum energy density of 20.31 W h kg–1. Meanwhile, different behaviors in different electrolytes were further analyzed. This work demonstrated that the modification of hydrochar is an effective way to convert biomass into high-performance electrode materials, which has potential for advanced storage device applications.

Corncob, as a sustainable biomass waste, is mainly composed of hemicellulose. Herein, on the basis of natural corncob as substrates, Fe/N co-doped porous carbon spheres were designed via a consecutive FeCl3-mediated hydrothermal reaction and mild KHCO3 activation route for supercapacitor electrode materials. Owing to the low hydrolysis temperature of hemicellulose and hydrolysis promotion of Fe3+, the corncob-derived hydrochar exhibited special carbon sphere morphology. Interestingly, the carbon sphere morphology was well-preserved upon the melamine-mediated KHCO3 activation. As a result of the short ion diffusion distance, unique packing architecture, and developed micro–mesoporous structure of the carbon spheres, optimized CCAC-Fe-M-50% manifested superior ion transfer kinetics and rate performances (87% up to 20 A g–1). Meanwhile, the electrochemical investigation of CCAC-Fe-M-50% in a three-electrode setup illustrated high capacitance (338 F g–1 at 1 A g–1). In a two-electrode setup, the CCAC-Fe-M-50%||CCAC-Fe-M-50% device revealed supreme cyclability (102.7% retention after 5000 cycles) and extremely low R ct (0.59 Ω) and R s (4.54 Ω). These superior properties were attributed to the large S BET (2305.7 m2 g–1), the multiple redox possibilities (Fe3+, Fe2+, and N functional groups), and the carbon sphere morphology with a micro–mesoporous structure, which enhanced ion physisorption, pseudocapacitance, and electrolyte/ion diffusion, respectively. Besides, the fabricated CCAC-Fe-M-50%||CCAC-Fe-M-50% device in a neutral electrolyte demonstrated a superb energy density (E D) of 18.60 Wh kg–1 at the power density (P D) of 455 W kg–1. The currently presented strategy with superior results might lead to the novel development of biomass-based ultraperformance electrode materials for supercapacitors and other high-tech applications.

Lignocellulose is a key starting material for the production of biofuels, biochemicals, and biomaterials. This review discusses various catalytic systems, including homogeneous and heterogeneous catalytic systems, for biomass valorization. Different strategies of biomass‐derived catalyst systems for value‐added chemicals are evaluated. Novel strategies for using biomass‐derived carbon‐based catalysts are proposed as a potential way to make the valorization process economically viable. This review also provides a comprehensive assessment of the fabrication of biomass‐derived carbon as catalytic support for biorefinery applications and discussion about mechanism of the synergistic catalytic effect between the biochar and catalyst. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd