Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.
γ-Graphyne is the most symmetric sp 2 /sp 1 allotrope of carbon, which can be viewed as graphene uniformly expanded through the insertion of two-carbon acetylenic units between all the aromatic rings. To date, synthesis of bulk γ-graphyne has remained a challenge. We here report the synthesis of multilayer γ-graphyne through crystallization-assisted irreversible cross-coupling polymerization. A comprehensive characterization of this new carbon phase is described, including synchrotron powder X-ray diffraction, electron diffraction, lateral force microscopy, Raman spectroscopy, infrared spectroscopy, and cyclic voltammetry. Experiments indicate that γ-graphyne is a 0.48 eV band gap semiconductor, with a hexagonal a-axis spacing of 6.88 Å and an interlayer spacing of 3.48 Å, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 °C but undergoes transformation at higher temperatures. While conventional 2D polymerization and reticular chemistry rely on error correction through reversibility, we demonstrate that a periodic covalent lattice can be synthesized under purely kinetic control. The reported methodology is scalable and inspires extension to other allotropes of the graphyne family.
The mediated electrochemical method characterized by the combinational utilization of two double mediator systems was proposed to assess the fermentation efficiency of three yeasts. The mediator systems selected were the menadione/ferricyanide system and the 2,6-dichlorophenolindophenol (DCPIP)/ferricyanide system. Both the electrochemical responses and succinate dehydrogenase assay suggested that the menadione/ferricyanide system made the yeasts switch to anaerobic respiration and, the DCPIP/ferricyanide system let the yeasts remain in theirs fermentative mode. The ethanol yields (g ethanol/g glucose) and the R D /R M (R D and R M refer to the electrochemical response from the menadione/ferricyanide system and the DCPIP/ferricyanide system, respectively) values are 0.47 and 0.38, 0.24 and 0.75, 0.23 and 0.81, respectively, for Saccharomyces cerevisiae, Pachysolen tannophilus and Pichia stipitis. The results showed that there was a negative correlation between the ethanol yields and the R D /R M values of the three yeasts, which showed the feasibility of the mediated electrochemical method in rapid fermentation ability assay.
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