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- Iakunkov, Artem, et al.
(författare)
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Activated graphene as a material for supercapacitor electrodes : effects of surface area, pore size distribution and hydrophilicity
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : RSC Publishing. - 1463-9076 .- 1463-9084. ; 21:32, s. 17901-17912
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Tidskriftsartikel (refereegranskat)abstract
- Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.
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| 2. |
- Grimm, Alejandro, et al.
(författare)
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Slagging and fouling characteristics during co-combustion of Scots pine bark with low-temperature dried pulp and paper mill chemical sludge
- 2019
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Ingår i: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 193, s. 282-294
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows how chemical sludge (CS) generated during wastewater treatment at a paperboard mill can be quickly dried at low-temperature and employed in bark-fired boilers to reduce slagging and corrosion problems. By using a cyclone-dryer operated at an inlet-air velocity of 110 m/s and a temperature of 90 degrees C, the dry-matter content of CS was increased from approximately 19 to 82%. The residence time of CS inside the cyclone was approximately 2 s when using the inlet-air velocity mentioned above. Disaggregation of the feedstock caused by collisions with the cyclone wall and between particles played a crucial role in enhancing the efficiency of heat and mass transfer. Three co-pelletized mixtures of Scots pine bark (SPB) and dried-CS were combusted in a 40 kW fixed-bed burner. Flue gas analysis was performed with a gas analyser. Coarse and fine ash were analysed by SEM-EDS and XRD. NOx, and SO2 emissions increased with increasing amount of CS in the mixtures. Mono combustion of SPB resulted in a large quantity of slag (i.e., molten ash) with a high degree of sintering (i.e., hardness of the slag), and ash deposits formed on heat transfer surfaces were rich in K2SO4 and KCI. Mixtures of SPB and CS were less prone to slagging, and the amount of alkali chloride in the deposits was reduced in favour of alkali sulphate formation.
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