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We report the influence of structural features on the properties of porous carbonaceous materials obtained using soft-templating coupled with hydrothermal carbonisation. Our results demonstrate that using d - glucose with Pluronic P123 results in a more homogeneous particle size distribution of carbon spheres compared with d - fructose. The textural properties of the carbon materials, both surface area and pore volume, have improved when the carbonisation temperature was increased from 550 °C to 900 °C, while the amount of C C bonds was also increased. Physical activation with CO 2 was found to open the pores and thereby improve textural properties, including total pore volume, micropore volume, and surface area. Concomitantly, the CO 2 and H 2 S uptake also underwent significant enhancement, achieving a maximum CO 2 adsorption capacity of 8.37 mmol/g at 0 °C and 1 bar, and ca. 6 mmol/g at room temperature and 1 bar. The same samples showed about 25.7 mmol/g adsorption capacity for H 2 S at room temperature and atmospheric pressure, with approximately 32% process efficiency. Image 1 • Soft templating strategy coupled with hydrothermal carbonisation (HTC) resulted in improved porosity. • The highest CO 2 uptake has been obtained after physical activation. • H 2 S adsorption efficiency was boosted after physical activation step. [ABSTRACT FROM AUTHOR]

After being undervalued for a long-time, the potential use of lignins have gained interest as a source of wealth from waste. Despite the complexity of lignins chemical structure, its high carbon content compared to cellulose and sugars makes lignin a very promising precursor for the development of nanocarbons for broad range applications, including supercapacitors for energy storage. High performing supercapacitors have been made using dimensionally different nanocarbon entities (zero-to three), such as carbon nanoparticles, carbon nanodots, carbon fibers, and carbon nanosheets with modular and interconnected pore structures, which are prepared from lignins of various types with and without use of templates, porogens and chemical agents. Control of physicochemical and electrochemical properties in such nanocarbons remains the key for their high energy density, flexibility, and long-term stability. To this end, nanocarbons conductivity, porosity and surface areas are controlled by various synthesis approaches while detailed adjustment of pore structure, pore width and pore distribution have been made to improve electrolyte access, ions confinement, and transportation. To compare performances of nanocarbons made from different lignin types, we must do meaningful investigations on the lignin's structure, composition, and purity to understand how their structure-property relationships are influenced by pyrolysis, carbonization and activation methods/conditions used. In this review, a clear overview of the lignins structure, classification, and properties is presented, wherein we compared the structure-property-performance relationships of nanostructured carbons from lignins for improvement of supercapacitor device performances with recent advances. Separation processes of lignin from wood, steps involved in preparing dimensionally different nanocarbon entities (zero -to three), and electrolytes for the fabrication of sustainable and flexible supercapacitor devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Alkali metal ion batteries are instrumental in the widespread implementation of electric vehicles, portable electronics, and grid energy storage. From experimental characterisation of hard carbons, these carbon anodes were shown to contain a variety of functional groups. Through density functional theory simulations, the effect of functional groups (O, OH, NH 2 , and COOH) on edges and basal plane surfaces of carbonaceous materials on the adsorption of lithium, sodium, and potassium are investigated. These simulations show that the functionalisation of H-terminated edges and curved surfaces rather than basal planes is more energetically favourable and thus more likely to be present. Comparison of experimental FTIR and computational vibrational frequency analysis confirmed the occurrence of the investigated functional groups (O, OH, NH 2 , and COOH) in the synthesised hard carbon materials. Metal adsorption on the functionalised models showed that adsorption energies were stronger on the functionalised basal plane in comparison to the functionalised edge sites and contribute to the metal ion immobilization and consequent irreversible capacity loss. The metal adsorption on the curved surface was further improved by the addition of functional groups, benefitting the initial lithiation/sodiation/potassiation of the carbon anode. Hence, the morphology of the functionalised carbon systems plays an important role in the charge/discharge performance of carbonaceous anodes. [Display omitted] • XPS and FTIR identify functional groups in hard carbon. • Functional groups can adsorb at different carbon motifs. • DFT simulations show that functional groups bind strongly to edge sites. • Li, Na, and K bind strongly to hydroxyl groups. • Functional group type and site play important roles in the charge/discharge process. [ABSTRACT FROM AUTHOR]

Pyridinic-N configurations and intrinsic defects on nanocarbons have been regarded as potentially active-sites for the oxygen reduction reaction (ORR). In this work, a facile strategy is demonstrated to achieve pyridinic-N dominated porous carbon nanosheets with edge-enriched defective nature through the selection of the bio-precursor guanine as C/N sources. It is able to achieve high contents of pyridinic-N dominated (48.1% from gross N) species and the few-layers carbon architectures with hierarchical porosity by a template-free carbonization method. These 2D carbon structures are of low cost, scalable and economically attractive while based on renewable and highly abundant resources. As a result, the optimized catalyst delivers a significantly enhanced electrocatalytic performance for ORR under wide range of pH from alkaline to acid, i. e. possessing a 30 mV more positive half-wave potential (0.885 V) than Pt/C (0.855 V) catalyst in 0.1 M KOH, and very close activities to Pt/C in 0.1 M PBS and 0.1 M HClO 4 solution. This ORR performance is attributed to the synergistic effects of unique graphene-like architecture, high porosity, and coexistences of high contents of pyridinic-N species and abundant edge/defect sites. Image 1 A facile strategy is demonstrated to achieve pyridinic-N dominated porous carbon nanosheets with edge-enriched defective nature through the selection of the biological nucleobase precursor as C/N sources. [ABSTRACT FROM AUTHOR]

Pure eucalyptus Kraft lignin derived carbon fiber mats were produced based on a model workflow. It covers the preparation and characterization of the lignin precursor and the carbon materials and its testing in the final application (supercapacitor). Sequential solvent extraction was employed to produce a eucalyptus Kraft lignin precursor which could be electrospun into lignin fibers without any additives. The fiber formation from low molecular weight lignin is assigned to strong intermolecular interactions via hydrogen bonding and π-π-stacking between individual lignin macromolecules which gives rise to association complexes in the electrospinning solution. By stabilization in air, carbonization in N 2 and an activation step in CO 2 , free-standing microporous carbon fiber mats could be produced. These fiber mats possess mainly basic oxygen functional groups which proved to be beneficial when tested as free-standing electrodes in symmetric supercapacitors. Consequently, the CO 2 -activated fiber mats showed a high specific gravimetric capacitance of 155 F/g at 0.1 A/g, excellent rate capability with 113 F/g at 250 A/g and good capacitance retention of 94% after 6000 cycles when tested in 6 M KOH electrolyte. Therefore, we conclude that lignin itself is a promising precursor to produce microporous, oxygen functionalized carbon fibers serving as free-standing electrodes in aqueous supercapacitors. Image 1 [ABSTRACT FROM AUTHOR]

Abstract In order to compensate for cracking, brittleness and low electrical conductivity of polymer-derived silicon oxycarbide (SiOC), graphene was successfully introduced into a SiOC matrix by phase transfer of graphene oxide (GO) from an aqueous (GO dispersed in water) to organic phase (copolymer as SiOC precursor in diethyl ether). Spark plasma sintering (SPS) was used to fully densify composites to ∼2.3g/cm3. The prepared materials were comprehensively characterized and exhibited significant enhancement in the mechanical properties, electrical conductivity and electrochemical performance. Self-assembled lamellar structure of graphene in the SiOC-matrix was achieved, leading to anisotropy in the properties of the composites. The fracture toughness of the SiOC-2vol%GO composite was increased by ∼91%, at the expense of a slight decrease in the flexural strength, compared to the SiOC-matrix. Moreover, the composites exhibited three orders higher electrical conductivity than the SiOC-matrix. The electrical conductivity in the perpendicular direction (σ ┴ = 3 × 10−1S/cm) of SiOC-2vol%GO composites was two orders of magnitude higher than that in the parallel direction (σ ‖ = 4.7 × 10−3S/cm), owing to the self-assembled lamellar graphene in the SiOC-matrix. The SiOC-2vol%GO composites further showed better electrochemical performance of oxygen reduction reaction (ORR) than pure graphene, exhibiting an onset potential (∼0.75 V vs RHE) and more positive half-wave potential (∼0.6 V vs RHE). Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Chitosan, glucosamine, a glucose-melamine mixture, a glucose polyvinylpyrrolidone mixture, and a glucose poly(vinylpyrrolidone- co -vinylimidazole) mixture are examined in a hydrothermal carbonization and calcining process to investigate effects of nitrogen additives on incorporation of nitrogen into the carbon products and the effects of such additives on morphology and porosity. The resulting calcined hydrothermal carbons are examined for their aqueous dispersibility using a nanolatex (NL) stabilizer based on an ionic liquid imidazolium acrylate monomer. Sonication of water, nanolatex, and carbon mixtures shows that ease of dispersion and friability increase with carbon porosity. This is the first report connecting friability with porosity on μm to nm length scales. Scanning electron microscopy of carbon dispersions in excess NL suggests adsorption of NL from suspension is random and irreversible, and accompanied by conformational equilibration and spreading. Thin films made from aqueous dispersions and from sediments obtained by centrifugation of such dispersions exhibit electrical and thermal conductivities that can be understood in terms of how the carbon particles pack in a gravitational or centrifugal field. The most porous carbon is found to produce an optical extinction in the visible on the order of that exhibited by single wall carbon nanotubes. Carbon produced hydrothermally from glucose and melamine appears to be a layered material that is electrically insulating while appreciably thermally conducting. [ABSTRACT FROM AUTHOR]

A simple, cost-effective and scalable approach for the synthesis of N-doped mesoporous carbons that are effective as ORR catalysts is reported. The synthesis procedure involves two steps: a) production of mesoporous carbons using a template-free approach based on the carbonization of citrate salts of zinc and calcium, and b) N-doping by heat treatment in the presence of melamine. The resulting N-doped carbon possess a high specific surface area, a porosity made up exclusively of mesopores and a large amount of nitrogen functionalities (∼8–9 wt%). When used as an electrocatalyst for the oxygen reduction reaction (ORR), the metal-free carbon materials predominantly catalyze the 4 e − process, with an onset potential of 0.9 V ( vs. RHE) and a superior kinetic current density (∼17 mA cm −2 ) to that of Pt/C at ∼0.6 V under basic conditions. In addition, the developed catalysts show a higher stability than commercial Pt/C and excellent electrocatalytic selectivity against methanol crossover. [ABSTRACT FROM AUTHOR]

Herein we presented, for the first time, facile fabrication of nitrogen doped (0.5–4 wt.%) porous carbon aerogels using biomass derivatives ( i.e. glucose or cellulose) as the carbon precursor and soy protein as both the nitrogen precursor and the structure directing agent. Through post thermal treatment to improve the electrical conductivity and porosity, the obtained materials showed excellent oxygen reduction reaction (ORR) catalytic activity. The electrochemical performance was further enhanced after platinum impregnation, combining the advantages of small over-potential from platinum catalyst and high limiting current density from the carbon substrate. Therefore, we demonstrated here not only a novel and low cost hydrothermal synthesis route to achieve high-performing metal-free ORR catalyst or carbon substrate for additional metal catalyst, but also a general principle on how to develop metal nanoparticles/carbon hybrids for ORR. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen-doped carbons were produced using hydrothermal carbonization of nitrogen-containing carbohydrates under mild temperature (180°C). The resulting materials contain significant amounts of nitrogen and display a high degree of aromatization. The nitrogen contents are also retained after further calcination at higher temperatures. All the resulting materials have been thoroughly characterized using X-ray photoelectron spectroscopy, solid state 15N and 13C-nuclear magnetic resonance, elemental chemical analysis, nitrogen adsorption, scanning and transmission electron microscopy. The nitrogen-doped materials proved to have superior performance with respect to their nitrogen-free counterparts in terms of electrical conductivity. [ABSTRACT FROM AUTHOR]