Abstract:Activated carbons (ACs) are actively researched as electrode materials for supercapacitors and there is a significant interest to produce ACs from sustainable and low cost precursors. In this study, various ACs were prepared from hydrothermally carbonized sugars by KOH activation. Both the hydrothermal carbonization and activation processes were optimized to tailor the properties (e.g. textural properties, chemical composition, N-doping, electrical conductivity) of the ACs. For instance, the BrunauerEmmett-Tel… Show more
“…As during electrode manufacturing for EDLCs, additives are added to the active material (Lee et al., ; Liu & Cao, ; Pandolfo & Hollenkamp, ; Zhu et al., ), and the influence of these additives on the EC performance is of great interest. The graphs in Figure show the EC values obtained with M1 (Figure a) and M2 (Figure b) for the pure activated carbon AC‐600‐800 and the same AC plus additives.…”
This study focusses on the assessment of the electrical conductivity (EC) of biobased electrode materials for the application in energy storage devices and presents a simple and reproducible method to measure the EC of carbonaceous powders under moderate pressure (10–50 N). Based on the pyrolysis of corncob at three different temperatures (600, 800, and 900°C) and further treatments of the biochar obtained at 600°C, 11 different carbonaceous powder materials were produced including biochars, activated carbons, and composites. Composite materials were obtained by adding either metal oxide (RuO2 or Fe3O4) in different proportions or additives which are commonly used in electrode production (5 wt% binder and 15 wt% conductive additive). Furthermore, one physically activated commercial AC based on peat with a known EC of 33 S/m was treated with additives and used as a reference. For all materials, an increase of applied pressure resulted in higher EC values due to closer particle contact. The comparison of two methods (with and without preload) showed that a prepelletization of the samples is not necessary to obtain reliable results. By analyzing the obtained EC values while taking mechanical and physicochemical properties into account, it could be shown that a high carbonization temperature and high specific surface area favor the increase of EC. Furthermore, certain proportions of metal oxides lead to an improvement of EC (40 wt% RuO2, 10 wt% Fe3O4), while the treatment with additives leads to a decrease of EC. The EC values among all samples varied between 0.8 S/m (biochar) and 408 S/m (AC/RuO2 composite) at the highest pressure level (637 kPa). Thus, promising biobased electrode materials for environmentally friendly energy storage technologies are presented with the aim of contributing to the establishment of a biobased resource and product platform for bioeconomy.
“…As during electrode manufacturing for EDLCs, additives are added to the active material (Lee et al., ; Liu & Cao, ; Pandolfo & Hollenkamp, ; Zhu et al., ), and the influence of these additives on the EC performance is of great interest. The graphs in Figure show the EC values obtained with M1 (Figure a) and M2 (Figure b) for the pure activated carbon AC‐600‐800 and the same AC plus additives.…”
This study focusses on the assessment of the electrical conductivity (EC) of biobased electrode materials for the application in energy storage devices and presents a simple and reproducible method to measure the EC of carbonaceous powders under moderate pressure (10–50 N). Based on the pyrolysis of corncob at three different temperatures (600, 800, and 900°C) and further treatments of the biochar obtained at 600°C, 11 different carbonaceous powder materials were produced including biochars, activated carbons, and composites. Composite materials were obtained by adding either metal oxide (RuO2 or Fe3O4) in different proportions or additives which are commonly used in electrode production (5 wt% binder and 15 wt% conductive additive). Furthermore, one physically activated commercial AC based on peat with a known EC of 33 S/m was treated with additives and used as a reference. For all materials, an increase of applied pressure resulted in higher EC values due to closer particle contact. The comparison of two methods (with and without preload) showed that a prepelletization of the samples is not necessary to obtain reliable results. By analyzing the obtained EC values while taking mechanical and physicochemical properties into account, it could be shown that a high carbonization temperature and high specific surface area favor the increase of EC. Furthermore, certain proportions of metal oxides lead to an improvement of EC (40 wt% RuO2, 10 wt% Fe3O4), while the treatment with additives leads to a decrease of EC. The EC values among all samples varied between 0.8 S/m (biochar) and 408 S/m (AC/RuO2 composite) at the highest pressure level (637 kPa). Thus, promising biobased electrode materials for environmentally friendly energy storage technologies are presented with the aim of contributing to the establishment of a biobased resource and product platform for bioeconomy.
“…Previous reports have shown that KOH activation can destroy the morphology of a precursor to varying degrees. 35,55 Here, the morphologies of the ACs activated in KOH ranged from foam-like (AC-700-K1) to flake-like (AC-800-K4). The foamy morphology of AC-700-K1 could speculatively relate to an activation of the colloidal spheres of HTC-RNA from the inside out, leaving a negative imprint.…”
Section: ■ Results and Discussionmentioning
confidence: 96%
“…The resulting ACs, labeled AC-X-KY, where X is the activation temperature, and Y is the mass loading of KOH to HTC-RNA, displayed pore textural properties (Table 1) similar to those of KOH-activated ACs prepared from HTC-glucose and HTC-biomass. 28,34,35,38,39,63 AC-700-K1 and -K4, obtained in 33 and 14% yield, respectively, both displayed Activated carbons were derived from hydrothermally carbonized ribonucleic acid (HTC-RNA) by activation for 2 h under flowing N 2 . Samples activated with KOH and KHCO 3 are labeled AC-X-KY and AC-X-KCY, respectively, where X is the activation temperature, and Y is the mass ratio of activating agent to HTC-RNA.…”
Activated carbons (ACs) have applications in gas separation and power storage, and N-doped ACs in particular can be promising supercapacitors. In this context, we studied ACs produced from yeast-derived ribonucleic acid (RNA), which contains aza-aromatic bases and phosphate-linked ribose units, and is surprisingly inexpensive. The RNA was hydrothermally carbonized to produce hydrochars that were subsequently activated with CO 2 , KOH, or KHCO 3 to give ACs. The ACs adsorbed up to ∼7 mmol/g at 0 °C and 1 bar and had capacitances as high as ∼300 F/g in a three-electrode cell and a 6 M KOH(aq) electrolyte. The material that displayed the best capacitance was tested in a two-electrode cell, which displayed a specific capacitance of 181 F/g even at a current density of 10 A/g. The ACs with the highest uptake of CO 2 and the highest capacitance were those activated with KOH and KHCO 3 ; however, CO 2 activation is arguably less expensive and more suitable for industrialization.
“…S2b). We have previously observed Fe in activated carbons generated from hydrochars, even when no Fe precursor was added; this is derived from the stainless steel reactor used during the activation 39 .Figure 3Scanning electron microscope images of activated carbons (ACs) generated from a hydrochar formed in milk without solid precursors. For each sample, a smaller particle is shown on the left, and a larger one on the right.…”
Hydrothermal carbonization converts organics in aqueous suspension to a mixture of liquid components and carbon-rich solids (hydrochars), which in turn can be processed into activated carbons. We investigated whether milk could be used as a medium for hydrothermal carbonization, and found that hydrochars prepared from milk, with or without an added fibrous biomass, contained more carbon (particularly aliphatic carbon), less oxygen, and more mineral components than those prepared from fibrous biomass in water. Activated carbons produced from hydrochars generated in milk had lower specific surface areas and CO2 capacities than those from hydrochars formed in water; however, these differences disappeared upon normalizing to the combustible mass of the solid. Thus, in the context of N2 and CO2 uptake on activated carbons, the primary effect of using milk rather than water to form the hydrochar precursor was to contribute inorganic mass that adsorbed little CO2. Nevertheless, some of the activated carbons generated from hydrochars formed in milk had specific CO2 uptake capacities in the normal range for activated carbons prepared by activation in CO2 (here, up to 1.6 mmol g−1 CO2 at 15 kPa and 0 °C). Thus, hydrothermal carbonization could be used to convert waste milk to hydrochars and activated carbons.
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