Rapid motion of electrolyte ions is a crucial requirement to ensure the fast charging/discharging and the high power densities of supercapacitor devices. This motion is primarily determined by the pore size and connectivity of the used porous carbon electrodes. Here, the diffusion characteristics of each individual electrolyte component, that is, anion, cation, and solvent confined to model carbons with uniform and well‐defined pore sizes are quantified. As a result, the contributions of micropores, mesopores, and hierarchical pore architectures to the overall transport of adsorbed mobile species are rationalized. Unexpectedly, it is observed that the presence of a network of mesopores, in addition to smaller micropores—the concept widely used in heterogeneous catalysis to promote diffusion of sorbates—does not necessarily enhance ionic transport in carbon materials. The observed phenomenon is explained by the stripping off the surrounding solvent shell from the electrolyte ions entering the micropores of the hierarchical material, and the resulting enrichment of solvent molecules preferably in the mesopores. It is believed that the presented findings serve to provide fundamental understanding of the mechanisms of electrolyte diffusion in carbon materials and depict a quantitative platform for the future designing of supercapacitor electrodes on a rational basis.
Nitrogen‐doped carbons were synthesized by a solvent‐free mechanochemically induced one‐pot synthesis by using renewable biomass waste. Three solid materials are used: sawdust as a carbon source, urea and/or melamine as a nitrogen source, and potassium carbonate as an activation agent. The resulting nitrogen‐doped porous carbons offer a very high specific surface area of up to 3000 m2 g−1 and a large pore volume up to 2 cm3 g−1. Also, a high nitrogen content of 4 wt % (urea only) up to 12 wt % (melamine only) is generated, depending on the nitrogen and carbon sources. The mechanochemical reaction and the impact of different wood components on the porosity and surface functionalities are investigated by nitrogen physisorption and high‐resolution X‐ray photoelectron spectroscopy (XPS). These N‐doped carbons are highly suitable as cathode materials for Li–S batteries, showing high initial discharge capacities of up to 1300 mAh gsulfur−1 (95 % coulombic efficiency) and >75 % capacity retention within the first 50 cycles at low electrolyte volume.
Nanoimprint lithography is proposed as a highly versatile method for the production of nanostructured supercapacitors (micro-supercapacitors, MSC). Liquid sucrose- and lignin-precursor printing produces patterns with high quality and a line width down to 500 nm. The liquid-carbon-precursor NIL-printing approach enables nitrogen doping to achieve an increased supercapacitor performance for aqueous electrolytes (Li2SO4). The lines are interconverted into nanoporous carbon materials (d ≈ 1 nm) with high specific surface area (>1000 m2 g-1) to form stable structures reaching specific resistivities as low as ρ = 3.5 × 10-5 Ωm and capacitances up to 7 F cm-3.
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