Biomass derived carbons via hydrothermal carbonization (HTC) are critically important for different applications due to their low cost, eco-friendly properties, light weight and potential for the catalysis research field. However, standard HTC carbons commonly present amorphous and spherical morphology with low surface areas and large particle size. Here we report a 2D morphology of crystalline carbons via a HTC method by employing the biomolecule guanine and diverse carbohydrates (glucose, fructose and cellulose) as carbon precursors. Importantly, the addition of guanine to the HTC process plays a significant role in producing the 2D-morphology of carbon materials from the diverse carbohydrates. Hierarchical porous nitrogen-doped carbons with high surface areas up to 974 m² g⁻¹ and nitrogen contents as high as 2.39 at% are made by further high temperature carbonization. The current 2D carbons are found to be highly active toward the oxygen reduction reaction (ORR) with a rather positive half-wave potential of 0.87 V (vs. the RHE) and a large limiting current density of 5.9 mA cm⁻². These catalysts outperform most other equivalent benchmarks as well as Pt-based electrocatalysts, meanwhile being efficient for the hydrogen evolution reaction (HER) with a very low overpotential of 0.35 V to achieve 10 mA cm⁻² in alkaline medium. It is expected that our synthetic protocol can be extended to various bio-nucleobases, yielding all-sustainable bio-based electrocatalysts with a tunable structure, elemental composition, porosity and electronic properties.

High mass energy density coupled with high power density is highly desired for electrical double-layer capacitors. Usually the capacitive performance is improved by optimizing the pore size and volume distribution. Herein, the authors report an efficient approach to optimize the porous structure through a facile ionothermal carbonization method. A series of hierarchical porous carbons with unique sub-micrometer sized morphology, high surface area and abundant mesopores (e.g. S_BET = 2532 m² g⁻¹ and V_meso = 1.077 cm³ g⁻¹) have been synthesized, using Jujun grass as a nitrogen-containing precursor. The ionic liquid acts not only as a reaction medium for the conversion of biomass to carbon but also as a porogenic agent for inducing mesoporosity. The results indicate that the ionothermal method can balance the micro- and mesoporosity of the optimized porous carbon, making it one of the competent alternatives to the state-of-the-art electrodes for ultra-high energy density supercapacitors. The optimized ionothermal carbon (ITC-JG-900) shows an impressively high specific capacitance of 336 F g⁻¹ at 1 A g⁻¹ in 6 M KOH, and even retained a capacitance of 222 F g⁻¹ at 10 A g⁻¹, which is 66% of the initial capacitance. The maximum energy density of ITC-JG-900 as a supercapacitor is found to be over 72.7 W h kg⁻¹ when the power density is 1204 W kg⁻¹, which is higher than those of most of the equivalent benchmarks tested in aqueous electrolytes.