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Sodium‐ion batteries as a prospective alternative to lithium‐ion batteries are facing the challenge of developing high‐performance, low‐cost and sustainable anode materials. Hard carbons are appropriate to store sodium ions, but major energy and environmental concerns during their fabrication process (i.e., high‐temperature carbonization) have not been properly assessed. Furthermore, the rational design of high‐performing hard carbon anodes is usually limited by the conventional direct carbonization of organic precursors. Here, the hydrothermal carbonization process is employed as a versatile pre‐treatment method of renewable precursors, followed by high‐temperature carbonization, for producing advanced hard carbon anodes. The critical role of hydrothermal pre‐treatment in regulating the structure for an optimized performance of hard carbon anodes is elucidated, while revealing the sodium‐ion storage mechanism using electrochemical kinetic calculations, advanced characterization and multi‐scale modeling. Furthermore, the environmental impacts of hydrothermal pre‐treatment and subsequent carbonization are evaluated using life cycle assessment compared to direct carbonization. By comparing hard carbon anodes with and without the hydrothermal pre‐treatment, it is verified that the additional hydrothermal process is responsible for enhanced electrochemical performance, increased carbon yields and reduced carbon emissions. The work provides a systematic understanding of functions and energy consumptions of hydrothermal systems to achieve next‐generation sustainable sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Summary: The thermal treatment of an activated carbon/chars with a nitrogen precursor is not a sustainable nor an efficient method for the incorporation of N into the carbon structure. This study proposes the use of hydrothermal carbonization (HTC) as an environmentally friendly method for the incorporation of N into the bulk of carbon materials. The authors propose the following sequence for the synthesis of N‐enriched carbon materials (NCM) for energy storage applications: HTC of the N precursor and biomass → activation of N‐hydrochar (N‐HC). To investigate the proposed method, HTCs of spent coffee grounds (SCG) with N precursors (urea and alanine) were conducted at 220°C for 5 hours. The resulted N‐HCs were subjected to a mild thermal activation via pyrolysis at 600°C for 2 hours. The results showed that HTC enhances the incorporation of N into the carbon matrix via many reactions, for example, the Maillard reaction (MR) or the Mannich reaction, which may accompany the formation of HC via the solved‐intermediate pathway or the solid‐to‐solid pathway, respectively. However, adjusting some parameters before HTC, for example, the concentration of the N precursor and the pH value of the slurry is important to avoid a significant reduction in the N‐HC yield. The proposed method led to the synthesis of NCM with a N content of 10.3wt% The X‐ray photoelectron spectroscopy (XPS) confirmed the incorporation of N into the bulk of NCM and showed a significant increase in the content of heterocyclic N compounds (pyridinic N, pyrrolic N, and graphitic N) in the NCM. The incorporation of N via the proposed method significantly improved the electrochemical properties of NCM as the values of the specific capacitance and the electrical conductivity in the NCM increased by five times and four times, respectively. [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal‐nitrogen‐carbon catalysts are emerging as low‐cost electrocatalysts for the oxygen reduction reaction in fuel cells. However, a cost‐effective and scalable synthesis strategy for these catalysts is still required, as well as a greater understanding of their mechanisms. Herein, iron, nitrogen co‐doped carbon spheres (Fe@NCS) have been prepared via hydrothermal carbonization and high‐temperature post carbonization. It is determined that FeN4 is the main form of iron existing in the obtained Fe@NCS. Two different precursors containing Fe2+ and Fe3+ are compared. Both chemical and structural differences have been observed in catalysts starting from Fe2+ and Fe3+ precursors. Fe2+@NCS‐A (starting with Fe2+ precursor) shows better catalytic activity for the oxygen reduction reaction. This catalyst is studied in an anion exchange membrane fuel cell. The high open‐circuit voltage demonstrates the potential approach for developing high‐performance, low‐cost fuel cell catalysts. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) has demonstrated that it is an effective technique for the production of functionalized carbon materials from simple carbohydrates, such as monosaccharides and disaccharides. The chemical structure of the HTC carbon has been identified in detail by means of solid-state MAS 13C NMR investigations. However, it has not yet been clearly shown what the effects are of the processing temperature and time on the chemical structure and morphology of the generated HTC carbon. This study shows, with the help of SEM, elemental and yield analysis and solid-state MAS 13C NMR, the effects of these two key variables on the final nature of the produced material, allowing the development of a mechanistic model. According to the chosen set of processing parameters, the chemical structure of the HTC carbon can be tuned from polyfuran rich in oxygen containing functional groups to a carbon network of extensive aromatic domains. The same kind of investigation using lignocellulosic biomass as a carbon precursor shows a striking difference between the HTC mechanism of glucose and cellulose. The biopolymer, when it is treated under mild hydrothermal conditions (180–280 °C), tends to react according to a reaction scheme which leads to its direct transformation into an aromatic carbon network and which has strong similarities with classical pyrolysis. [ABSTRACT FROM AUTHOR]

Dye sensitized solar cells have emerged as an attractive alternative to conventional solar cells due to their easy processing and the abundance and low cost of their materials. However, the counter electrode in these cells employs platinum which significantly impacts their cost. Here, we report biomass-derived, nitrogen-doped carbon aerogel as an effective alternative to conventional platinum-based counter electrodes for dye sensitized solar cells. A stable suspension of biomass-derived, nitrogen-doped carbon aerogel was prepared in DMF by using oleylamine as a binder. The nitrogen-doped carbon aerogel electrode was annealed at different temperatures, and its impact on photovoltaic performance is investigated. I-V measurements confirm that the annealing temperature substantially enhances the photovoltaic parameters of these devices; these enhancements are linked to the removal of the organic binders. Electrochemical impedance spectra of the counter electrodes confirm that removal of oleylamine in nitrogen-doped carbon aerogels reduces the series resistance of the resulting electrodes. The power conversion efficiency of the solar cells from optimized nitrogen-doped carbon aerogel exhibited comparable efficiency to that of a cell fabricated using a platinum-based counter electrode. This study demonstrates the potential of biomass-derived carbon aerogels as a cheap and sustainable replacement of platinum in DSSCs. [ABSTRACT FROM AUTHOR]

The hydrothermal carbonization (HTC) technique has shown a great ability in the synthesis of carbon materials with special properties for a wide range of different applications. Here, a hypersaline salt mixture (LiCl–ZnCl2) combined with hydrothermal carbonization was applied in order to obtain sulfur containing micro- and mesoporous (0.3–40 nm) monolithic carbons with high surface areas (400–550 m2 g−1) and well developed porosity (0.4–1.2 cm3 g−1). Fructose was used as a carbon source and sulfur was introduced in an aromatic configuration as 2-thiophenecarboxaldehyde. The resulting carbon materials showed a promising removal capacity (qe = 0.3 mmol g−1) towards methylene blue and the adsorption followed the Sips isotherm independent of the pH. Intraparticle diffusion appeared to control the adsorption kinetics. Carbon materials could be easily regenerated with simple ethanol washing. The dye pollutant could be completely desorbed from the adsorbent's surface, while the adsorbent still maintained removal efficiency of above 90% during three cycles. [ABSTRACT FROM AUTHOR]

A simple and efficient polymer grafting onto hydrothermal carbonization (HTC)-derived materials is described. The method pertains to the Diels-Alder cycloaddition reaction of furan moieties present on the surface of a HTC material with the maleimide groups stemming from a maleimide protected poly(ethylene glycol) (Me-PEG-MI) by a retro Diels-Alder reaction. The precursor polymer, HTC material, and final product are characterized. Successful grafting is confirmed by elemental analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and dispersion studies. [ABSTRACT FROM AUTHOR]

Abstract: Greenhouse gas mitigation options include the production of carbonized materials and their addition to soils for longer term storage. Hydrothermal carbonization (HTC) is a novel way to produce carbonized materials. The goal here was to test if HTC material, in our case derived from beet root chips, has adverse effects on plant growth or that of root associated symbionts such as arbuscular mycorrhizal fungi. We carried out several studies, and found that increasing concentrations of HTC material could be deleterious for plant growth of Taraxacum, starting at 10vol% additions. Conversely, root colonization of the fungal symbiont was stimulated at an addition of 20vol%. Soil pH changes occurring during the study could be traced to microbial reduction reactions, and these led to a pH increase of the medium despite the quite acidic nature of the HTC material itself. In separate assays, we showed that spore germination of the AM fungus Glomus intraradices was stimulated by the HTC material, suggesting that direct effects on the fungi are likely in addition to those mediated by the host plant. A third experiment with a different plant species (Trifolium repens) confirmed the major conclusions, and showed also neutral to stimulatory effect on nodulation. Our results suggest that HTC materials should be carefully tested and optimized to reduce negative effects on plant growth before applications in the field are undertaken, particularly at high addition rates. [Copyright &y& Elsevier]

Abstract: We describe the production and catalytic application of highly functionalized mesoporous carbonaceous materials, obtained via a one step green and cheap process relying on the hydrothermal carbonization of carbohydrates (e.g. glucose) in the presence of functional organic monomers (e.g. vinyl imidazole). The resulting materials could be further functionalized to feature imidazolium bromides on their surface and be used for various transesterification, Knoevenagel and Aldol reactions. [Copyright &y& Elsevier]

The growing importance of bio-based products, combined with the desire to decrease the production of wastes, boosts the necessity to use wastes as raw materials for bio-based products. A waste material with a large potential is spent sugar beets, which are mainly used as animal feeds or fertilizers. After hydrothermal treatment, the produced chars exhibited an H/C ratio of 1.2 and a higher heating value of 22.7 MJ/kg, which were similar to that of subbituminous coal and higher than that of lignite. Moreover, the treatment of 25 g/L of glucose and 22 g/L of fructose by heating up to 160 °C led to a possible application of spent sugar beets for the production of 5-hydroxymethylfurfural. In the present study, the maximum concentration of 5-hydroxymethylfurfural was 3.4 g/L after heating up to 200 °C. [ABSTRACT FROM AUTHOR]

Brewer's spent grains (BSG) represent a highly abundant byproduct generated in the beer industry. Owing to abundant availability and high water content, BSG constitutes a raw material of interest for thermochemical conversion via hydrothermal carbonization (HTC). Nevertheless, the phyto-toxic effect and low-porosity of hydrochars limit the possible application. Therefore, coupling HTC and pyrolysis may overcome these obstacles. HTC experiments were carried out at 180, 220, and 260 °C and pyrolysis was performed at 400, 600, 800, and 1000 °C to investigate the influence of HTC on the pyrolysis of BSG. Pyrolyzed hydrochars showed lower ash content and higher carbon content compared to char obtained from BSG. The highest surface area (139.5 m2 g−1) was obtained for hydrochar produced at 180 °C and then pyrolyzed at 600 °C. This value was 70% higher compared to BSG pyrolyzed at the same temperature (82 m2 g−1). The coupling of HTC and pyrolysis showed synergies in the char yield, reduction of ash, increasing of carbon content, and porosity. The promising results proved that at selected process conditions, the novel route is beneficial for carbon materials production due to the improvement of the physicochemical properties of pyrochar at similar mass and carbon yields. Image 1 • One-step pyrolysis and two-step HTC coupled with pyrolysis was investigated. • Low-temperature HTC in two-step process resulted in similar char yield as pyrolysis. • Coupling of HTC and pyrolysis improved physicochemical properties of pyrochars. • Highest S BET was achieved for hydrochar obtained at 180 °C and pyrolyzed at 600 °C. [ABSTRACT FROM AUTHOR]

Na‐ion hybrid capacitors consisting of battery‐type anodes and capacitor‐style cathodes are attracting increasing attention on account of the abundance of sodium‐based resources as well as the potential to bridge the gap between batteries (high energy) and supercapacitors (high power). Herein, hierarchically structured carbon materials inspired by multiscale building units of cellulose from nature are assembled with cellulose‐based gel electrolytes into Na‐ion capacitors. Nonporous hard carbon anodes are obtained through the direct thermal pyrolysis of cellulose nanocrystals. Nitrogen‐doped carbon cathodes with a coral‐like hierarchically porous architecture are prepared via hydrothermal carbonization and activation of cellulose microfibrils. The reversible charge capacity of the anode is 256.9 mAh g−1 when operating at 0.1 A g−1 from 0 to 1.5 V versus Na+/Na, and the discharge capacitance of cathodes tested within 1.5 to 4.2 V versus Na+/Na is 212.4 F g−1 at 0.1 A g−1. Utilizing Na+ and ClO4− as charge carriers, the energy density of the full Na‐ion capacitor with two asymmetric carbon electrodes can reach 181 Wh kg−1 at 250 W kg−1, which is one of the highest energy devices reported until now. Combined with macrocellulose‐based gel electrolytes, all‐cellulose‐based quasi‐solid‐state devices are demonstrated possessing additional advantages in terms of overall sustainability. [ABSTRACT FROM AUTHOR]