Ferrocene clicked poly(3,4-ethylenedioxythiophene) conducting polymer: Characterization, electrochemical and electrochromic properties

The “click” chemistry, Cu(I)-catalyzed azide–alkyne cycloaddition reaction, was applied to covalently functionalize the poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer film with an excellent electron transfer mediator (ferrocene). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used to characterize the ferrocene-grafted PEDOT conducting polymer film, and it was proved that the grafting procedure via click reaction had a high efficiency. The ferrocene groups covalently grafted in the polymer films turned out to own a relatively fast electron transfer rate and show multi-color states via adjusting applied potential.     

氧化还原导电水凝胶制备及其在微生物燃料电池的应用

微生物细胞与微生物燃料电池阳极之间的电子传递效率是影响产电性能的关键因素.借助阳极修饰可以促进电子转移速率,提高电池的性能.本文合成了一种以聚4-乙烯基吡啶为骨架,中性红单体为氧化还原活性中心、具有良好导电性和生物兼容性的氧化还原水凝胶材料.其中通过共价键合固定氧化还原中介体,避免了对外界环境的二次污染.以该材料修饰碳纸作为阳极组装电池,实验表明经过修饰的生物阳极驯化周期缩短,阳极电势更接近NADH/NAD的平衡电位.该电池的功率密度较未修饰的电极的电池有明显的提高.     

Quantum Size Effects in the Photonics of Semiconductor Nanoparticles

The appearance of quantum size effects in ultradisperse semiconductors, their quantitative analysis, and their effect on the absorption of light and on the photophysical (vibrational relaxation of photogenerated “hot” charge carriers, band-band and “defect” luminescence) and certain primary photochemical processes (the accumulation of excess negative charge by the semiconductor nanoparticles, interphase electron transfer, etc.) are discussed.__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 2, pp. 67–87, March–April, 2005.     

Solar-microbial hybrid device based on oxygen-deficient niobium pentoxide anodes for sustainable hydrogen production

Hydrogen gas is emerging as an attractive fuel with high energy density for the direction of energy resources in the future. Designing integrated devices based on a photoelectrochemical (PEC) cell and a microbial fuel cell (MFC) represents a promising strategy to produce hydrogen fuel at a low price. In this work, we demonstrate a new solar-microbial (PEC–MFC) hybrid device based on the oxygen-deficient Nb₂O₅ nanoporous (Nb₂O_5–x NPs) anodes for sustainable hydrogen generation without external bias for the first time. Owing to the improved conductivity and porous structure, the as-prepared Nb₂O_5–x NPs film yields a remarkable photocurrent density of 0.9 mA cm^–2 at 0.6 V (vs. SCE) in 1 M KOH aqueous solution under light irradiation, and can achieve a maximum power density of 1196 mW m^–2 when used as an anode in a MFC device. More importantly, a solar-microbial hybrid system by combining a PEC cell with a MFC is designed, in which the Nb₂O_5–x NPs electrodes function as both anodes. The as-fabricated PEC–MFC hybrid device can simultaneously realize electricity and hydrogen using organic matter and solar light at zero external bias. This novel design and attempt might provide guidance for other materials to convert and store energy.     

Polyvinyl alcohol–ionic liquid composition for promoting the direct electron transfer and electrocatalysis of hemoglobin

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in polyvinyl alcohol (PVA)–room temperature ionic liquid (i.e., 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM]PF₆) composition has been investigated by using cyclic voltammetry and chronocoulometry. It is found that the composition can promote the direct electron transfer of Hb and the heterogeneous electron transfer rate constant (k_s) of immobilized Hb is enhanced to 19.9 s⁻¹. The immobilized Hb also shows high electro-catalytic activity towards the redox of oxygen, hydrogen peroxide and nitrite. The Michaelis constants (K_m) decrease to 1.2 × 10⁻⁴ M (for hydrogen peroxide) and 9.4 × 10⁻³ M (for nitrite). The surface concentration of electroactive Hb is estimated and it is ca. 1.4 × 10⁻¹⁰ mol cm⁻², meaning that several layers of immobilized Hb take part in the electrochemical reaction. When gold nanoparticles (GNP) is introduced into the composition, the resulting PVA–GNP–[OMIM]PF₆ composition presents better performance. The electrochemical characteristic of immobilized Hb is improved further. Thus PVA–GNP–[OMIM]PF₆ composition is more suitable for the immobilization of Hb. Therefore, it is a good strategy to prepare novel composition for protein immobilization by using several materials with different function.     

Investigation of coherence transfer between “CH3” and “CH2” groups in ethanol with time-resolved multiplex CARS technique

The coherence transfer between stretching vibration modes of C–H bonds in the ethanol is detected by time-resolved multiplex CARS technique and it occurs via “through-bond transfer” pathway. The time scale and velocity of coherence transfer are estimated at 90 fs and 1670 m/s. Moreover, coherence transfer process requires vibrational modes of acceptor and donor are different.     

Effects of anionic surfactant SDS on the photophysical properties of two fluorescent molecular sensors

Two fluorescent molecular sensors CS1 and CS2 were designed and synthesized to probe the aggregate behavior of anionic surfactant SDS. CS1 was based on the photo-induced electron transfer (PET) mechanism, while CS2 was founded on the intramolecular charge transfer (ICT) mechanism. The photophysical properties of CS1–2 in anionic surfactant sodium dodecyl sulfate (SDS) solution were studied by fluorescence and UV–vis methods. The experimental results show that significant absorption and emission spectral responses of CS1 were observed with the addition of SDS: the absorbance and fluorescence intensity decreased first and then increased. The plot of fluorescence intensity of CS1 versus SDS concentration showed two break points, which might be ascribed to the critical micellar concentration (cmc) and the formation of premicelle (cac) aggregate, respectively. But the solution’s color of CS2 changed from yellow to red with increasing SDS concentrations. The large red-shift in both absorption (50 nm) and emission (55 nm) spectra of CS2 was resulted from the protonation of the electron accepting moiety (NC nitrogen), which enhanced the “push–pull” interaction of the ICT fluorophore. This was facilitated by the increase of local H⁺ concentration around SDS premicelle and micelle. As a consequence, pK_a values of CS1 and CS2 were elevated in SDS micelle.     

Anodic electron shuttle mechanism based on 1-hydroxy-4-aminoanthraquinone in microbial fuel cells

In microbial fuel cells (MFCs), the electron transfer from microorganisms to the cell anode is a decisive factor on the power output. Though quinone derivatives can function as electron shuttles, the electron shuttle pathways have so far not been demonstrated. In this paper, the mechanism of electron shuttle via an exogenous mediator was studied in MFCs using Geobacter metallireducens (G. metallireducens). 1-hydroxy-4-aminoanthraquinone was labeled by fluorescamine and the product (HAQ-F) showed strong and stable fluorescence. The addition of HAQ-F into MFCs increased cell voltage from 170 mV to 290 mV, suggesting that the redox mediator could facilitate electron transfer from bacteria to anode. Further, confocal laser scanning microscopy imaging indicated that HAQ-F was present in microbial cells, demonstrating that the redox mediator shuttled across the membranes to get reduced within cells.     

Electrochemical and spectroelectrochemical properties of manganese reconstituted myoglobin

Electrochemical and spectroelectrochemical properties of manganese(III) reconstituted myoglobin (Mn(III)–Mb) have been investigated. No redox wave of Mn(III)–Mb was observed at a highly hydrophilic indium oxide electrode on which rapid direct electron transfer of native myoglobin took place, suggesting the electron transfer reaction of Mn(III)–Mb at an indium oxide electrode is very slow. The rate constant of the chemical reduction of Mn(III)–Mb with dithionite was ca. 20 times smaller than that of native Mb. Using an optically transparent thin layer electrode (OTTLE) cell and Oxazine-170 perchlorate, 5,9-bis(diethylamino)-10-methyl-benzo[a]phenoxazonium perchlorate, as an electron transfer mediator, the redox potential for the Mn(III) Mn(II)–Mb couple was estimated to be −0.32 V versus Ag AgCl (sat. KCl) at 25°C.     

Reduction of cytochrome c at a lipid bilayer modified electrode

The reduction of horse heart cytochrome c has been investigated at a platinum electrode modified with a lipid bilayer membrane (BLM) which immobilized vinyl ferrocene as an electron mediator. The current—voltage curves show that the direct electrochemistry of cytochrome c at the metal electrode occurs quite efficiently. An adsorption equilibrium constant for cytochrome at the BLM surface, as well as an electron transfer rate constant between the protein and the modified electrode have been estimated from these results. The values of both parameters are much higher than those reported with other types of electrode modifications, indicating that a lipid bilayer-modified platinum electrode system using vinyl ferrocene as a mediator provides substantial improvements in electrochemical activity of cytochrome c at metal electrodes. The potential for modifying and utilizing this new class of “biomembrane-like” electrode surface for metalloprotein electrochemistry is briefly discussed.     

CO electrooxidation on a polycrystalline Pt electrode: A wall-jet EQCN study

Pre-adsorbed and bulk (continuous) CO oxidation on a polycrystalline Pt electrode were examined in a wall-jet electrochemical quartz crystal nanobalance (EQCN) setup, using both differential and integral evaluation of the EQCN data, to get further insights into the kinetics and mechanism of this important fuel-cell related electrocatalytic reaction. The hydrogen underpotential adsorption–desorption features in the base cyclic voltammogram of a Pt film are accompanied by significant changes in the electrode mass due H-upd induced desorption–adsorption of anion. In the double-layer region small capacitive currents are accompanied by comparatively large reversible mass changes indicating anion adsorption/desorption (96.5 g mol⁻¹ assigned to bisulfate). OH and oxygen electrosorption from water at potentials more positive of 1.0 V result in relatively small variations in the electrode mass (16 g mol⁻¹ for PtOH and ca. 9 g mol⁻¹ for PtO formation, respectively). The CO-adlayer stripping first leads to the electrode mass decrease in the “pre-peak” region, followed by a fast mass increase within the main stripping peak due to re-adsorption of bisulfate anion (91 g mol⁻¹). A mass-transport limited current for bulk CO oxidation under continuous flow of CO-saturated electrolyte leads to negligible mass changes (0–1 g mol⁻¹) in the PtO region, suggesting that bulk CO oxidation is mediated by electroformed PtO.     

“In situ” ESR and UV-visible spectroscopic studies of iron phthalocyanine films deposited on gold electrodes

The electrochemical behaviour of iron phthalocyanine (Fe^IIPc) films, supported on gold substrates, was studied in 3.5 M NaOH solution, using cyclic voltammetry and coupled “in situ” ESR and UV-visible spectroscopic techniques. Two types of electron transfer were observed in the potential range from −0.45 to −1.0 V vs. Hg/HgO. According to the “in situ” spectroscopy investigations, these two processes were assigned respectively to electron transfers involving first the ligand ring, and then the centre iron ion.     

Silicon–air batteries

A new “metal”–air battery based on silicon–oxygen couple is described. Silicon–air battery employing EMI·2.3HF·F room temperature ionic liquid (RTIL) as an electrolyte and highly-doped silicon wafers as anodes (fuels) has an undetectable self-discharge rate and high tolerance to the environment (extreme moisture/dry conditions). Such a battery yields an effectively infinite shelf life with an average working voltage of 1–1.2 V. Silicon–air battery can support relatively high current densities (up to 0.3 mA/cm²) drawn from flat polished silicon wafers anodes. Such batteries may find immediate applications, as they can provide an internal, built-in autonomous and self sustained energy source.     

Nitrate as an Oxidant in the Cathode Chamber of a Microbial Fuel Cell for Both Power Generation and Nutrient Removal Purposes

Nitrate ions were used as the oxidant in the cathode chamber of a microbial fuel cell (MFC) to generate electricity from organic compounds with simultaneous nitrate removal. The MFC using nitrate as oxidant could generate a voltage of 111 mV (1,000 Ω) with a plain carbon cathode. The maximum power density achieved was 7.2 mW m⁻² with a 470 Ω resistor. Nitrate was reduced from an initial concentration of 49 to 25 mg (NO₃⁻−N) L⁻¹ during 42-day operation. The daily removal rate was 0.57 mg (NO₃⁻–N) L⁻¹ day⁻¹ with a voltage generation of 96 mV. In the presence of Pt catalyst dispersed on cathode, the cell voltage was significantly increased up to 450 mV and the power density was 117.7 mW m⁻², which was 16 times higher than the value without Pt catalyst. Significant nitrate removal was also observed with a daily removal rate of 2 mg (NO₃⁻–N) L⁻¹ day⁻¹, which was 3.5 times higher compared with the operation without catalyst. Nitrate was reduced to nitrite and ammonia in the liquid phase at a ratio of 0.6% and 51.8% of the total nitrate amount. These results suggest that nitrate can be successfully used as an oxidant for power generation without aeration and also nitrate removal from water in MFC. However, control of the process would be needed to reduce nitrate to only nitrogen gas, and avoid further reduction to ammonia.     

Breaking the barrier to fast electron transfer

A study of the electron transfer for a non-glycosylated redox variant of GOx is reported, immobilised onto an electrode via a polyhistidine tag. The non-glycosylated variant allows the enzyme to be brought closer to the electrode, and within charge transfer distances predicted by Marcus' theory. The enzyme-electrode-hybrid shows direct very fast reversible electrochemical electron transfer, with a rate constant of ~ 350 s^− 1 under anaerobic conditions. This is 2 orders of magnitude faster than the enzyme-free flavin adenine dinucleotide (FAD). These results are discussed in the context of the conformation of FAD in the active site of GOx. Further data, presented in the presence of oxygen, show a reduced electron transfer rate (~ 160 s^− 1) that may be associated with the oxygen interaction with the histidines in the active site. These residues are implicated in the proton transfer mechanism and thus suggest that the presence of oxygen may have a profound effect in attenuating the direct electron transfer rate and thus moderating ‘short-circuit’ incidental electron transfer between proteins.     

Kinetics and mechanism of oxidation of copper(I) ions with thiuram disulfide

The kinetics of the oxidation of copper(I) perchlorate with thiuram disulfide (tds) in acetonitrile and its mixtures with benzene or ethyl bromide have been investigated. It has been shown that the rate of the reaction is limited by the inner-sphere transfer of an electron from the copper(I) ion to tds in a complex of the type [Cu^I(tds)]⁺. The subsequent dissociation of the anionradical tds —proceeds rapidly and leads to the formation of copper(II) dithiocarbamate which is recorded in the absorption spectra and by EPR. The rate constant of electron transfer has been determined (3·10^–4sec^–1) and it was found that it is practically independent of the polarity of the medium. The absence of such a correlation is attributed to the negligible energies of reorganization of the solvent in the inner-sphere electron transfer.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 450–455, July–August, 1988.     

Enhanced electricity production from microbial fuel cells with plasma-modified carbon paper anode

Microbial fuel cells (MFC) provide a new opportunity for simultaneous electricity generation and waste treatment. An improvement in the anode capacity of MFCs is essential for their scale-up and commercialization. In this work we demonstrate, for the first time, that plasma-based ion implantation could be used as an effective approach to modify carbon paper as an anode for MFC to improve its electricity-generating capacity. After the N(+) ion implantation, a decreased charge-transfer resistance is achieved, which is attributed to the increased C-N bonds after N(+) ion implantation. In addition, the surface roughness and hydrophobicity are also changed, which favor microbial adhesion on the anode surface. The cyclic voltammetry results show that both the electrochemical activity and the electron transfer are enhanced remarkably, leading to better MFC performance compared to the control. Such a plasma surface modification technique provides an effective way to modify the electrode for enhancing MFC performance for power generation.     

Simultaneous processes of electricity generation and p-nitrophenol degradation in a microbial fuel cell

This study initially demonstrates that the electricity generated by a microbial fuel cell (MFC) can be used to in situ generate H₂O₂ at a carbon felt cathode. In the presence of scrap iron, H₂O₂ further reacts with Fe²⁺ to produce hydroxyl radicals. Attributed to the oxidation of H₂O₂ and hydroxyl radicals, and the oxidation–reduction of scrap iron, p-nitrophenol was significantly removed in the cathode chamber of the MFC. The p-nitrophenol was completely degraded after 12 h, and about 85% of TOC was removed after 96 h. Simultaneously, a maximum power density (143 mW m^?2) was generated by the MFC. It is concluded that a MFC not only can generate electricity and degrade biodegradable compounds, but also remove bio-refractory pollutants.     

EPR study of the feasibility of anisotropy in the electron transfer in the photoreduction of molybdenum(VI) complexes in hydrochloric acid

Conclusions The formation of oriented Cl₂ ^– radical-ions in the coordination sphere of a Mo(V) complex is observed upon the irradiation of glassy solutions at 77 K using partially polarized light. Anisotropy of the electron transfer in the photoreduction of Mo(VI) was proposed. The kinetic curve for the disordering of Cl₂ ^– was measured.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1427–1429, June, 1988.     

100-femtosecond MeV electron source for ultrafast electron diffraction

A near-relativistic 100-fs MeV electron beam is developed by using a photocathode rf gun for revealing the hidden ultrafast dynamics of intricate molecular and atomic processes in materials through experimentation of ultrafast time-resolved electron diffraction (UED). The transverse and longitudinal dynamics of femtosecond electron beam in the rf gun were studied theoretically by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf and space charge effects were investigated by changing the laser parameters, field gradient and electron charge. The theoretical studies indicate that a 100-fs MeV electron beam with the transverse emittance of 0.1 mm mrad and the relative energy spread of 10⁻³–10⁻⁴ at bunch charge of 0.1–2 pC (10⁶–10⁷ electrons per pulse) is achievable for UED, in which the intensity is three orders of magnitude higher than that produced by the conventional dc or pulsed guns.