Relaxation analysis has been carried out on fresh and charge-discharge cycled graphites to evaluate the effect of cycle process on the relaxation behavior after lithium insertion. While the formed stage I at charging partly transforms into stage II during relaxation, the cycled samples exhibit smaller fraction of transformation. The charge-discharge cycles also restrict the relaxation variation in c-axis of stage II, even though lithium occupation ordering similarly occurs between the fresh and cycled samples. Variation in c-length of stage II would be the results of stage transformation from I into II, and charge-discharge process enables to follow the equilibrium stages rapidly at charging.
New porous carbon materials are proposed in which washi, the Japanese paper as well as cotton and other cellulose materials are carbonized by new method, retaining their original fibrous structures. Porous carbon sheets thus fabricated are used as gas diffusion layer in fuel cells. Fuel cell testing is conducted and the optimum conditions of fabrication are investigated. Low cost and superior characteristics of new carbon structure are demonstrated based on morphological study and fuel cell polarization data.
This study reports a novel electrochemical sensing technique based on electro-deposited Pt particles on glassy carbon electrodes modified with nitrogen atoms containing functional groups (PtNF-GC) electrode for detecting sulfite in aqueous solution. PtNF-GC electrodes have a favorable electrocatalytic activity of sulfite oxidation, which moves the oxidation peak potential to the negative direction of potential unlike Pt disk, a bare glassy carbon electrode and electro-deposited Pt particles on glassy carbon (Pt-GC) electrode. The linear relationship between the oxidation current peak and sulfite concentration is over the range up to 10 mM with a detection limit of 100 µM. Our prepared PtNF-GC electrode was applied for the sulfite detection in sample solution with favorite recovery of sulfite. Additionally, a possible reaction mechanism of sulfite was discussed.
Three types of widely used carbon materials were examined as scaffolds for the direct-electron-transfer (DET)-type bioelectrocatalysis of bilirubin oxidase (BOD) as an electrocatalyst for a 4-electron reduction of oxygen (O2). The carbon materials used were: Ketjen Black EC300J (KB) with a primary particle size (ϕp) of ca. 40 nm and a hollow structure, Vulcan XC-72R (Vulcan) with ϕp of 37 nm and a filled structure, and high purity graphite SP series (JSP) with ϕp of 10 µm and well-developed micropore structures. For the three carbon materials, the rotating disk steady-state limiting catalytic current density of the O2-reduction (|jc,lim|) increased with the non-Faradaic current (|jb|) at small |jb| values and was saturated at large |jb| values. The |jc,lim/jb| ratio in low |jb| range was in the following order: JSP ≫ Vulcan > KB. Electrochemical and microscopic data suggested that microporous structures of JSP are highly effective for the DET-type reaction of BOD. Gaps between several primary particles in the KB and Vulcan aggregates play important roles as scaffolds for BOD. The inner surface of partially broken KB particles is electrochemically active to give large |jb| but not effective as BOD scaffolds.
The novel one-pot pyrolysis method with ionic liquid (IL one-pot pyrolysis method) was developed in our previous study to prepare a PtNi alloy nanoparticle-supported multi-walled carbon nanotube (PtNi/MWCNT) composite. Herein, it was found that the PtNi/MWCNT composite could be prepared by IL one-pot pyrolysis method even if an insoluble nickel precursor with crystal water, nickel(II) oxalate dihydrate (NiC2O4·2H2O), was used. The Ni content and crystal structure of the resulting PtNi/MWCNT composites were similar to those of the composites produced under dehydrated and homogeneous conditions. It means that solubility of Ni precursor and existence of crystal water in the precursor had an insignificant effect on the production of the PtNi/MWCNT composite.
The fabrication of low-temperature waste heat power conversion modules will require the development of thermoelectric materials based on mass-produced nanotubes such as super-growth carbon nanotubes (SGCNTs), rather than high-quality nanotubes generated on the laboratory scale. In this work, SGCNT films co-loaded with colloidal ZnO (which has a high Seebeck coefficient) and Ag (which enhances electrical conductivity) were prepared to optimize both carrier concentration and mobility. The resulting carbon-based hybrid films were found to have a p-type power factor of 100.4 µW m−1 K−2 at 383 K, which represented one of the highest values yet reported for a SGCNT system.
Graphene-like graphite prepared by heating graphite oxide under vacuum at 800°C was fluorinated by elemental fluorine in the presence of HF at room temperature. The interlayer spacing of the resulting material was 0.639 nm and it showed CxF type characteristics. The fluorine content of it (x = 1.7) was higher than that obtained from natural graphite (x = 2.3). The discharge capacity of it as a cathode of lithium primary battery reached 940 mAh g−1 at a low current density, which was 50% larger than the theoretical capacity based on the 100% discharge of fluorine.
Ni-doped covalent triazine frameworks (Ni-CTF) has been known as an efficient electrocatalysts that achieve conversion of carbon dioxide (CO2) to carbon monoxide (CO) with the faradaic efficiency (FE) exceeding 90% in neutral electrolytes. Here we report that the FE can reach 60% even in acidic electrolytes, where the hydrogen evolution can proceed competitively, by loading Ni-CTF on gas diffusion electrode (GDE). In the presence of Zn(II) ions, zinc hydroxide analogues that can be formed only in alkaline conditions were deposited on the GDE during the CO2 reduction in an electrolyte with a bulk pH of 2. On the other hand, when a normal plate electrode (PE) was used, the FE was only 1.2% in an electrolyte with the same pH, and the zinc hydroxide analogues were not formed. These results indicate that the local pH around GDE increased during the cathodic process, which led to an increasing FE of CO2 reduction even in an acidic electrolyte.
The performance of the graphite anode of lithium-ion batteries is greatly affected by the solid electrolyte interphase (SEI) generated at the first charge. However, there are few studies on the kinetics of the lithium-ion intercalation/de-intercalation reaction in graphite to investigate the effect of SEI. In this study, the correlation between the interfacial lithium-ion transfer resistance (Rct) and the double layer capacitance (Cdl) of graphite composite electrodes coated with various SEIs was investigated. It was found that the value of 1/RctCdl was different for each SEI, that is, the frequency (or rate) of intercalation and de-intercalation of lithium ions into graphite was different for each SEI. The activation energy of Rct was almost the same for all the electrolyte solutions. These results indicate that the pre-exponential factor of the Arrhenius equation governing the rate of interfacial ion transfer in a practical graphite anode is dependent on the nature of SEI.
Voltammetric properties of chlorine dioxide (ClO2) obtained by using a glassy carbon (GC) electrode fabricated by electrolyzing in ammonium carbamate aqueous solution were first reported. GC electrode surface was covalently modified with nitrogen atoms containing functional groups, which were introduced onto GC surfaces by electrochemical oxidation process in ammonium carbamate aqueous solution. The introduction of nitrogen into the GC surface structure enhanced the electrocatalytic activities of GC electrode towards the electro-oxidation of ClO2 in an acidic medium more than a bare GC electrode does. A favorable linearity for the peak current signals in cyclic voltammograms was exhibited in the concentration range from 2.0 to 100 ppm.
To achieve an efficient hole injection into triphenylamine derivatives cast on an Au electrode, we focused on the use of Fullerene (C60)-doped triphenylamine derivative as a buffer layer. After measuring the current-voltage properties of a layered device with the Au/C60-doped triphenylamine derivative/triphenylamine derivative/Au, hole injection was improved only at the interface where C60 was introduced. In addition, when 1 mol% of C60 was doped, the energy barrier for the hole injection decreased to 0.06 eV from 0.43 eV. Overall, we successfully developed a device with enhanced rectification properties.
Recently, the single-walled carbon nanotube (SWCNT) has been the focus as a durable electrode with a high rate performance for the electric double layer capacitor (EDLC). However, it has not yet been clarified whether these reported outstanding properties are universal for all SWCNTs. The authors compared various self-standing SWCNT membranes (buckypapers) as the EDLC electrode to evaluate their stability to a floating high-voltage charge. Some SWCNTs exhibited an excellent rate performance even after the floating durability test, but other electrodes were degraded and showed a lower capacitance-retention. This variability in the durability for the SWCNTs can be attributed to the presence of residual metal impurities. Thus, it should be noted that the purity is a significant factor when using SWCNTs as the EDLC electrode, in addition to the nano-structure design from the viewpoint of operation stability.