Micropore-rich activated carbon with high surface area and pore volume was prepared by alkali activation of azulmic carbon (AZC) precursor as nitrogen-doped carbon; AZC was a carbonized product from azulmic acid. We successfully loaded a large amount of sulfur (S) into micropores of the activated AZC. Our two kinds of activated AZC (BET surface area: 1,747 and 2,319 m2 g−1) can include S up to 55 and 62 wt%, respectively. The former activated AZC including S can be charged and discharged with lithium (Li) ion transfer stably and reversibly in glyme-based and carbonate-based electrolytes. The latter activated AZC can be charged and discharged in a glyme-based electrolyte. These different characteristics are due to a difference in fine pore structure between them. Our microporous activated AZC with high S loading is promising material as positive S electrode for rechargeable Li-S batteries.
He SUN, Lina SUN, Takashi SUGIURA, Matthew S. WHITE, Philipp STADLER, Niyazi S. SARICIFTCI, Akito MASUHARA, Tsukasa YOSHIDA
Microwave-assisted hydrothermal synthesis of ZnO nanocrystals has resulted in two distinctive structures: hexagonal bi-pyramidal (HBP) and nano-sheet (NS) shapes from Zn(CH3COO)2 solutions containing triethanolamine or benzene tetracarboxylic acid as structure directing agents, respectively. Observation by field-emission scanning electron microscope, high resolution transmission electron microscope as well as analysis of selected area electron beam diffraction patterns revealed that the predominantly exposed facets of HBP and NS ZnO are (102) and (100) faces, occupying 84 and 76% of the total surface area, respectively. Adsorption of D149 and eosin Y photosensitizer dyes onto HBP and NS ZnO was studied in comparison with a randomly structured commercial ZnO nanocrystal (MZ). Density of dye packing was found to be in the order of HBP > MZ > NS, for which HBP was 2 to 5 times higher than NS. Consequently, dye-sensitized solar cells employing HBP ZnO exhibited the highest short circuit photocurrent, but also the lowest open circuit voltage. By contrast, the DSSCs employing NS ZnO exhibited the highest voltage among the three.
From the viewpoint of the cost and safety, aqueous sodium-ion batteries are attractive candidate for large-scale energy storage. Although the operating voltage range of the aqueous battery is theoretically limited to 1.23 V by the electrochemical decomposition of water, the voltage restriction is a little bit eased in real aqueous battery system by the charge/discharge overvoltage. Effect of the concentrated electrolyte on the operation voltage was studied in aqueous Na-ion battery with Na2MnFe(CN)6 hexacyanoferrates cathode and NaTi2(PO4)3 NASICON-type anode, in order to increase the discharge voltage. According to the cyclic voltammetry, the electrochemical window of diluted 1 mol kg−1 NaClO4 aqueous electrolyte is only 1.9 V, whereas the corresponding electrochemical window of concentrated 17 mol kg−1 NaClO4 aqueous electrolyte is widen to 2.8 V. This wide electrochemical window of the concentrated aqueous electrolyte allows the Na2MnFe(CN)6//NaTi2(PO4)3 aqueous sodium-ion system to work reversibly. By contrast, the framework of Na2MnFe(CN)6 cathode was destroyed by the hydroxide anion generated in diluted 1 mol kg−1 electrolyte.