Non-covalent interacting porphyrin/Graphene Oxide (GO) nanohybrids were formed in water and confirmed by TEM, Raman, FT-IR, XRD, UV-vis and fluorescence spectroscopy. The binding constant between porphyrin and GO is 2.38 × 103 L mol−1 calculated by Benesi-Hildebrand equation based on absorbance plot, which confirmed a robust porphyrin/GO nanohybrid formation. Fluorescence of porphyrin was effectively quenched by GO indicated the efficient photoinduced electron transfer (PET) from porphyrin moieties to GO, which porphyrin acts as energy absorbing and electron transferring antennae and GO serves as an efficient electron acceptor of the system. The photoelectrical response measurements of porphyrin/GO nanohybrid showed a rapid and reversible on/off photovoltage and photocurrent by the alternative white light. The PET from porphyrin to GO is energetically favorable deduced by calculating free Gibbs energy. Non-covalent porphyrin/GO nanohybrid may be used as photovoltaic conversion materials for photoelectronic applications.
Multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (Au NPs) were assembled on glassy carbon electrode (GCE) to form homogeneous and stable multilayer films using a layer-by-layer assembled method by electrostatic interaction. Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Ultraviolet–visible absorption spectroscopy (UV) were used for characterization of multilayer films. Electrocatalytic activity of uric acid (UA) was studied. UA and ascorbic acid (AA) of electrochemical signals were well separated on the modified electrode in pH 7.0 phosphate buffered solution (PBS). The oxidation peak potential of AA and UA was appeared at −91 and 247 mV vs. SCE on differential pulse voltammograms (DPVs), respectively. Response of UA was linear in the range from 4.0 × 10−6 mol/L to 3.0 × 10−3 mol/L and linear regression equation was ipa (µA) = 1.027 + 0.037 C (µmol/L) with a correlation coefficient of 0.992, the limit of detection for UA was 2.0 × 10−6 mol/L.
The tubular cathode bodies of a direct ethanol fuel cell (DEFC) are shaped by the gelcasting technology and the tubular cathode is prepared by spraying the diffusion layer and the Pt/C catalyst layer after the sintering process based on raw material of mesocarbon microbead (MCMB) and graphite. The process of mass transfer in DEFC is simulated using CFD software including the concentration of oxygen, liquid water saturation inside the tubular cathode and the cell performance under different operating temperature, inlet pressure and porosity. The results show that proper increase in operating temperature and porosity have obvious improvements on mass transfer process and the cell performance, while inlet pressure has little impact on cell performance.
The HFBI protein, a type of hydrophobin, from Trichoderma reesei self-organizes in an orderly manner at either air/water or water/solid interfaces. The structural and electrochemical properties of self-organized membranes on different types of solid substrates (electrode materials) were investigated. Two types of substrates, highly oriented pyrolytic graphite (HOPG) and single crystal Au(111), were used for this study. Atomic force microscopy (AFM) showed that the self-organized HFBI membranes (prepared at the air/water interface) exhibited different structures on the two types of electrodes. In terms of the electrochemical results, both HFBI/HOPG and HFBI/Au(111) electrodes performed electrochemical reactions. Self-organized HFBI membranes did not provide insulation from electron transfer. Our findings that HFBI can be tagged with functional proteins, such as enzymes, by genetic fusion and utilized as a molecular carrier to fabricate molecular interfaces on an electrode.
An α-PbO2 layer were synthesized on the Pb-0.3%(mass proportion)Ag alloy substrates by constant current electrosynthesis from an alkaline solution, and Pb-0.3%Ag/α-PbO2 composite inert anode materials were obtained. An electrochemical investigation of α-PbO2 deposition process on the Pb-0.3%Ag alloy substrates, using anodic polarization technique, galvanostatic polarization technique and steady state polarization technique, has been carried out. The phase composition and surface microstructures of α-PbO2 layers in different synthesizing times were tested by means of XRD and SEM, respectively. The experimental data have shown that the process of α-PbO2 formation on Pb-0.3%Ag alloy substrates have several stages. The optimized conditions can be effectively improving the formation rate of α-PbO2 and avoid the occurrence of oxygen evolution reaction. The α-PbO2 deposition layer obtained in alkaline solution possesses compact structure, and it is composed of well developed spherical grains.
Layer-by-layer assembly of hemoglobin (Hb) with DNA functionalized singlewall carbon nanotubes (DNA-SWCNTs) was achieved on glassy carbon electrode surface based on the electrostatic attraction between positively charged Hb and negatively charged DNA-SWCNTs hybrids. Cyclic voltammogram of (Hb/DNA-SWCNTs)n films modified electrodes showed a pair of well-defined and quasireversible redox peaks for Hb Fe(III)/Fe(II), indicating that direct electrochemistry of Hb was achieved. The dependence of the formal potential on solution pH indicated that one-proton transfer was coupled to each electron transfer in the direct electron transfer reaction. Additionally, Hb in the multilayer films retained its bioactivity and showed excellent electrocatalytic activity toward H2O2, suggesting that such multilayer films could be used as reagentless biosensors. The electrocatalytic current values were linear with increasing concentration of H2O2 in a wide range of 1–80 µM, with a low detection limit of 0.2 µM. The layer-by-layer assembly of enzymes with DNA-SWCNTs hybrids provided a general and useful way to construct sensitive biosensors without using mediators. On the other hand, this would be used as an easily prepared experimental model to fabricate functional nanostructured biointerfaces.
A comparative study of composite electrodes consisting of nanoparticles of iron compounds with fibrous nano-carbon in alkaline electrolyte was conducted to ascertain the morphological or composition factors that can increase the iron capacity. The preparation method and the iron content of a composite electrode affect the capacity per unit of iron mass. Particularly by increasing the iron content using a solution process, the capacity can be increased considerably up to ca. 460 mAh (g Fe)−1 for an Fe(OH)x/carbon composite. Such improved iron utilization in these composites suggests a catalytic effect of some intermediate species. Addition of a model candidate of an intermediate species, FeOOH, even of only 3 wt%, can improve the iron utilization in a Fe(OH)x/carbon composite.
In order to design a safe and practical Na-ion cell, the electrochemical properties of a conduction additive-free Li4Ti5O12 (LTO) electrode were investigated. The charge-discharge properties of LTO electrodes with/without conductive carbon additives are similar to each other in half-cell experiments, while the irreversible capacity fading of the carbon-free electrode is much smaller than that of the carbon-added electrode. A full cell consisting of α-NaFeO2 and carbon-free LTO electrodes shows a capacity of more than 90 mAh g−1 after 50 cycles without Na-metal deposition. The current density capabilities of both electrodes are comparable, indicating that the rate-determining process of the charge-discharge reaction is the ionic conduction of Na+ in the Li4Ti5O12 crystal, not electronic conduction.
A novel in situ Raman imaging technique has been developed to visualize the Li-ion battery reaction during the charge/discharge operation. A specially designed cell enables to measure Raman spectra at high speed so that the in situ measurements are carried out during the reaction. The distribution of the state of charge in cross-section of LiCoO2 cathode has been visualized as a demonstration. Inhomogeneous state of charge distribution is observed and there are some active materials where Li+ does not completely return after discharging. This technique enables to evaluate not only the electrode performance but also battery degradation, and thus may promote the realization of the next generation batteries.
The electrochemical performance of two electrolytes, containing 1 mol L−1 spiro structure quaternary ammonium salts, spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBP-BF4) and piperidine-1-spiro-1′-pyrrolidinium (PSP-BF4), in acetonitrile (AN), are investigated in commercial 7500F electric double layer capacitors (EDLC). Compared with conventional tetraethylammonium tetrafluoroborate (TEA-BF4) electrolyte in AN, the cell using SBP-BF4/AN electrolyte have a larger capacitance and an equivalent equivalent series resistance (ESR). The cells with electrolytes containing spiro structure quaternary ammonium salts have great advantages in capacitance and ESR remained in floating test at 70°C and 2.85 V.