High-surface-area microporous carbon as the efficient photocathode of dye-sensitized solar cells

This paper reports on the application of cornstalks-derived high-surface-area microporous carbon (MC) as the efficient photocathode of dye-sensitized solar cells (DSCs). The photocathode, which contains MC active material, Vulcan XC–72 carbon black conductive agent, and TiO₂ binder, was obtained by a doctor blade method. Electronic impedance spectroscopy (EIS) of the MC film uniformly coated on fluorine doped SnO₂ (FTO) glass displayed a low charge-transfer resistance of 1.32 Ω cm². Cyclic voltammetry (CV) analysis of the as-prepared MC film exhibited excellent catalytic activity for I₃^?/I^? redox reactions. The DSCs assembled with the MC film photocathode presented a short-circuit photocurrent density (J_sc) of 14.8 mA cm^?2, an open-circuit photovoltage (V_oc) of 798 mV, and a fill factor (FF) of 62.3%, corresponding to an overall conversion efficiency of 7.36% under AM 1.5 irradiation (100 mW cm^?2), which is comparable to that of DSCs with Pt photocathode obtained by conventional thermal decomposition.     

Electrophoretic deposition of ZnO photoanode for plastic dye-sensitized solar cells

Plastic dye-sensitized solar cells have been fabricated based on an organic dye (D 149) and ZnO photoanode prepared via room temperature electrophoretic deposition (EPD) to yield a conversion efficiency of 4.17% under 100 mW cm^?2 AM 1.5 illumination. Intensity modulated photocurrent spectroscopy analyses reveal that the fabricated ZnO electrodes have adequate interparticle connection, even in the absence of any post-treatment. This study demonstrates that EPD is a convenient method for photoanode fabrication and ZnO photoelectrodes obtained via EPD are promising for efficient plastic solar cells.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

Nonenzymatic glucose fuel cells with an anion exchange membrane as an electrolyte

Nonenzymatic glucose fuel cells were prepared by using a polymer electrolyte membrane and Pt-based metal catalysts. A fuel cell with a cation exchange membrane (CEM), which is often used for conventional polymer electrolyte fuel cells, shows an open circuit voltage (OCV) of 0.86 V and a maximum power density (P_max) of 1.5 mW cm^?2 with 0.5 M d-glucose and humidified O₂ at room temperature. The performance significantly increased to show an OCV of 0.97 V and P_max of 20 mW cm^?2 with 0.5 M d-glucose in 0.5 M KOH solution when the electrolyte membrane was changed from a CEM to an anion exchange membrane (AEM). This is due to the superior catalytic activity for both glucose oxidation and oxygen reduction in alkaline medium than in acidic medium. The anodic reaction of the fuel cell can be estimated to be the oxidation of glucose to gluconic acid via a two-electron process under these experimental conditions. The crossover of glucose through an electrolyte membrane was negligibly small compared with methanol and may not represent a serious technical problem due to the cross-reaction.     

Photovoltaic characteristics of dye-sensitized surface-modified nanocrystalline SnO2 solar cells

Zinc-modified nanocrystalline SnO₂ electrodes are prepared by chemical treatment of the commercial SnO₂ colloid with zinc acetate and their thickness effects on photovoltaic characteristics are investigated. Open-circuit voltage (V_oc) and fill factor increase with increasing zinc concentration, while short-circuit photocurrent (J_sc) decreases. The normalized incident photon-to-current conversion efficiency (IPCE) shows that increase of zinc concentration utilizes long wavelength light. Concerning the conversion efficiency, optimal concentration within the present experiment is found to be 10 mol.% Zn²⁺ with respect to Sn⁴⁺. As increasing thickness of the films based on 10 mol.% zinc-modified SnO₂ ranging from 0.76 to 8.12 μm, J_sc increases, reaches maximum and then decreases without change in V_oc. The highest conversion efficiency of about 3.4% is achieved under 1 sun of AM 1.5 irradiation for the ∼6.3 μm-thick 10 mol.% zinc-modified SnO₂ film with J_sc of 9.09 mA/cm², V_oc 600 mV and fill factor 62%.     

Photovoltaic performance of dye-sensitized solar cells assembled by in-situ chemical cross-linking

Quasi-solid state dye-sensitized solar cells (DSSCs) were assembled by in-situ chemical cross-linking of a gel electrolyte precursor containing liquid electrolyte. The DSSCs assembled with this cross-linked gel polymer electrolyte showed higher open circuit voltage and lower short-circuit photocurrent density than those of DSSCs with liquid electrolyte. Addition of SiO₂ nanoparticles into the cross-linked gel polymer electrolyte significantly improved the photovoltaic performance and long-term stability of the DSSCs. The optimized quasi-solid state DSSC showed high conversion efficiency, 6.2% at 100 mW cm^?2 with good durability.     

Synthesis and photovoltaic properties of organic sensitizers containing electron-deficient and electron-rich fused thiophene for dye-sensitized solar cells

Diverse fused thiophenes with electron-rich and electron-deficient blocks have been synthesized and employed as the π-conjugated spacers of organic dyes for the dye-sensitized solar cells (DSSCs). The effects of these fused thiophenes were investigated by their absorption spectra, electrochemical and photovoltaic properties. For a typical device a maximum power conversion efficiency of 6.11% was obtained under simulated AM 1.5 irradiation (100 mW cm^?2): a short-circuit current (J_SC) of 14.47 mA cm^?2, an open-circuit voltage (V_OC) of 670 mV, and a fill factor (FF) of 0.63.     

Highly efficient dye-sensitized SnO2 solar cells having sufficient electron diffusion length

Dye-sensitized solar cells (DSCs) were fabricated from mesoporous SnO₂ electrodes, which were prepared from nano-sized SnO₂ particles. Current–voltage characteristics of the DSCs were compared with DSCs prepared from conventional TiO₂ electrodes, which have similar amount of adsorbed dye with the SnO₂. As a result, short-circuit current of the SnO₂DSC were comparable with that of the TiO₂DSCs, and more than 15 mA/cm² was obtained with the SnO₂ at the thickness of 10 μm under one sun conditions. Electron diffusion coefficients and lifetimes in the SnO₂ and TiO₂ electrodes were measured, showing slower diffusion and longer lifetime in the SnO₂DSC than in the TiO₂. The results imply that the electron transport and transfer dynamics in such electrodes is dominated by the influence of intra-band charge traps, and the control of the trap conditions would be the key strategy to employ various metal oxides for such solar cells.     

Amphiphilic ruthenium dye as an ideal sensitizer in conversion of light to electricity using ionic liquid crystal electrolyte

The optimization of interfacial charge transfer between the dye and the electrolyte is crucial to the design of dye-sensitized solar cells. In this paper, we address the combined use of an ionic liquid crystal electrolyte and amphiphilic ruthenium dyes in dye-sensitized solar cells. The solar cell with an amphiphilic ruthenium dye [Ru(H₂dcbpy)(tdbpy)(NCS)2] (H₂dcbpy = 4,4′-dicarboxy-2,2′-bipyridine, tdbpy = 4,4′-tridecyl-2,2′-bipyridine), exhibited a short-circuit photocurrent density of 9.1 mA/cm², an open-circuit voltage of 665 mV and a fill factor of 0.58, corresponding to an overall conversion efficiency of 3.51%. We find that increasing dye alkyl chain length to octadecyl from tridecyl results in lower short-circuit photocurrent density and open-circuit voltage, and the suitable dyes for ionic liquid crystal electrolyte differed completely from those used in liquid and ionic liquid electrolyte cells.     

Electrochemical performances of LaBaCuFeO5+x and LaBaCuCoO5+x as potential cathode materials for intermediate-temperature solid oxide fuel cells

Layered perovskite-structure oxides LaBaCuFeO_5+x (LBCFO) and LaBaCuCoO_5+x (LBCCO) were prepared and the electrical conductivity and electrochemical performance were investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity of LBCCO is much higher than that of LBCFO. Area specific resistances of LBCFO and LBCCO cathode materials on Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte are as low as 0.21 Ω cm² and 0.11 Ω cm² at 700 °C, respectively. The maximum power density of the LBCFO/SDC/Ni-SDC and LBCCO/SDC/Ni-SDC cells with 300 μm thick electrolytes attains 557 mW cm^?2 and 603 mW cm^?2 at 800 ^oC, respectively. Preliminary results demonstrated that the layered perovskite-structure oxides LBCFO and LBCCO are very promising cathode materials for application in IT-SOFCs.     

NADH oxidation on screen-printed electrode modified with a new phenothiazine diazonium salt

NADH oxidation catalysts are extremely important in the field of electrochemical biosensors and enzymatic biofuel cells. Based on the growing diazonium chemistry, we synthesized the diazonium salt of the well-known NADH mediator toluidine blue O. The electrochemical reduction of the diazonium moiety by cyclic voltammetry onto a screen-printed electrode leads to an electrocatalyst suitable for the oxidation of NADH. The amperometric response for its oxidation shows a maximal current of 1.2 μA ([NADH] = 100 μM). Based on electrochemical measurements, the surface coverage is found to be 3.78 × 10^? 11 mol cm^? 2 and the heterogeneous standard rate constant k_h is 1.21 ± 0.16 s^? 1. The sensitive layer for the oxidation of NADH is improved by electrografting the diazonium salt with a potentiostatic method. Both the surface coverage and the heterogeneous standard rate constant k_h are improved and found to be 6.08 ± 0.63 × 10^? 11 mol cm^? 2 and ~ 5.02 s^? 1, respectively. The amperometric response is also improved by an 8 fold factor, reaching 9.87 μA ([NADH] = 120 μM). These remarkably high values for screen-printed electrodes are comparable to glassy carbon electrodes making this method suitable for low-cost bioelectronical devices.     

Optical and electrical conducting properties of Polyaniline/Tin oxide nanocomposite

Polyaniline(PANI)/Tin oxide (SnO₂) hybrid nanocomposite with a diameter 20–30 nm was prepared by co-precipitation process of SnO₂ through in situ chemical polymerization of aniline using ammonium persulphate as an oxidizing agent. The resulting nanocomposite material was characterized by different techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared spectroscopy (FT-IR) and Ultraviolet–Visible spectroscopy (UV–Vis), which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the nanocomposite materials and the distribution of the metal particles in the nanocomposite material. SEM observation showed that the prepared SnO₂ nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer nanocomposite material. UV–Vis absorption spectra of PANI/SnO₂ nanocomposites were studied to explore the optical behavior after doping of nanoparticles into PANI matrix. The incorporation of SnO₂ nanoparticles gives rise to the red shift of π–π¹ transition of polyaniline. Thermal stability of PANI and PANI/SnO₂ nanocomposite was investigated by thermogravimetric analysis (TGA). PANI/SnO₂ nanocomposite observed maximum conductivity (6.4 × 10^?3 scm^?1) was found 9 wt% loading of PANI in SnO₂.     

Enhancement of the performances of a single concentric glucose/O2 biofuel cell by combination of bilirubin oxidase/Nafion cathode and Au–Pt anode

This work deals with a novel preparation method of bilirubin oxidase/2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid electrode. The enzyme and its mediator were adsorbed on carbon Vulcan XC-72R before their immobilization into a Nafion^® matrix. Promising results were obtained when this biocathode was associated with Au₇₀Pt₃₀ nanoparticles as anode in a single concentric glucose/O₂ biofuel cell (BFC). The latter BFC delivered at 37 °C a power density of 90 μW cm^?2 for a cell voltage of 0.4 V in phosphate buffer (pH 7.4) containing 0.01 M glucose. Moreover, the electrical performances were increased with the concentration of glucose by generating up to 190 μW cm^?2 for a cell voltage of 0.52 V when the concentration of the renewable fuel reached 0.7 M.     

Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO₂ nanocrystalline mesoporous membrane with carotenoid 8′-apo-β-caroten-8′-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm²) and immersed in an aqueous 10 mM hydroquinone (H₂Q), 0.1 M NaH₂PO₄ solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm²) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 μA/cm² upon a 40 μW/cm² incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40 μW/cm² illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO₂ membrane with a maximum near 426 nm. No decay of the ACOA on the TiO₂ surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA⁺ at the surface by electron transfer from H₂Q.     

In situ growth of polymer electrolytes on lithium ion electrode surfaces

Polyacrylonitrile (PAN) films were grown on glassy carbon, nickel foam and MnO₂ substrates by cathodic electropolymerisation of acrylonitrile in acetonitrile with tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. The electronic barrier properties of the films were confirmed by impedance spectroscopy of carbon |PAN| Hg cells while the ionic resistance of the films varied from 200 kΩ cm² in the dry state to 1.4 Ω cm² when plasticised with 1 M LiPF₆ in propylene carbonate. A galvanic cell was prepared by successive electrodepositions of MnO₂ and PAN on a carbon substrate, using liquid lithium amalgam as the top contact. The cell showed a stable open circuit potential and behaved normally under the galvanostatic intermittent titration technique (GITT).     

Temperature dependent Raman study of SB → SC transition in liquid crystalline compound N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7)

Temperature dependent Raman study of C–H in-plane bending mode (～1163 cm^?1 and ～1190 cm^?1) and C–C stretching mode of phenyl ring (～1571 cm^?1 and ～1594 cm^?1) of N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7) has been done. Vibrational assignment and potential energy distribution (PED) of individual modes have been calculated employing density functional theory (DFT) for the first time. The S_B → S_C transition is nicely depicted in the variation of the linewidth of the ～1163 cm^?1 band and the peak position of ～1594 cm^?1 band with temperature. Because of a small amount of charge density transfer from the core part to the alkyl chain region, the ～1163 cm^?1 band shifts towards lower wavenumber side whereas the ～1190 cm^?1 band towards higher wavenumber side at S_B → S_C transition. The ～1571 cm^?1 and ～1594 cm^?1 bands are assigned as 8a and 8b modes, whose relative intensity variation with temperature gives the evidence of increased possibility of C–H bending motion of the linking group and the C–C stretching of the alkyl chain in S_C phase.     

Organic dyes with a novel anchoring group for dye-sensitized solar cell applications

Two novel trialkylsilyl-containing organic sensitizers (JK-53 and JK-54) have been designed and synthesized. Nanocrystalline TiO₂–silica-based dye-sensitized solar cells (DSSCs) were fabricated using these dyes. Under standard global AM 1.5 solar conditions, the JK-53-sensitized cell gave a short-circuit photocurrent density (J_sc) of 6.37 mA cm^?2, an open-circuit voltage (V_oc) of 0.70 V, and a fill factor of 0.74. These values correspond to an overall conversion efficiency (η) of 3.31%. By comparison, the JK-54-sensitized cell resulted in a J_sc of 7.52 mA cm^?2, a V_oc of 0.71 V, and a fill factor of 0.75. These values give an overall conversion efficiency of 4.01%.     

Field emission investigation of single Fe-doped SnO2 wire

Tin oxide submicronwires doped with Fe element were prepared by the thermal evaporation method. Morphological and structural characterizations revealed wires with sub micron size and crystalline in nature. The field electron emission from the single Fe:SnO₂ wire was carried out in conventional field emission microscope. The Fowler–Nordheim plot obtained from I–V characteristics of the wire showed a linear behavior typical that of metal. The field enhancement factor estimated from the slope of the F–N plot is 7455 cm^?1, indicating that the field emission is from nanometric features of the emitter. A current density of 10 A/cm² has been obtained at an applied field of 4.845 × 10³ V/μm. The field emission current–time record at a current level of 1 μA for more than 3 h duration is promising for various field emissions based applications.     

Mesoporous organo-silica nanoarray for energy storage media

A SnO₂–mesoporous organo-silica nanoarray (MOSN) composite was prepared by surfactant mediated synthesis combined with a sol–gel vacuum suction method in which SnO₂ has been successfully incorporated inside the periodic nanoholes in the MOSN or coated on its surface. The MOSN with a high aspect ratio of length to width could not only maintain its structure but also effectively accommodate the volume expansion of the SnO₂ during electrochemical reactions with Li⁺. The SnO₂–MOSN composite showed a higher reversible capacity of 420 mA h g⁻¹ with greatly improved capacity retention and lower initial irreversible capacity compared to SnO₂ powder. This interesting anodic performance of SnO₂–MOSN composite supports the potential use of MOSN for lithium ion batteries.     

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes,and enhanced photoelectrocatalytic degradation of indigo carmine dye

Photoanodes based on Ti/TiO₂ thin films were prepared by the sol–gel method, using either tetraisopropoxide (Ti(OPri)₄) or modified tetraisopropoxide, producing electrodes with different sized nanoparticle coatings, termed nanoporous (20 nm) or nanoparticulated (10 nm) electrodes. The anatase form dominated the composition of the nanoparticulated electrode, which presented a higher surface area, a flat band potential shift of ?160 mV and a 50% improvement in photoactivity, compared to the nanoporous electrode. 100% color removal, and 75% mineralization, of indigo carmine dye were achieved after 15 min of photoelectrocatalytic treatment using a nanoparticulated Ti/TiO₂ electrode operated at a current density of 0.4 mA cm^?2. Our findings indicate that the use of nanoparticulated electrodes, under UV irradiation and with controlled current density, is an efficient alternative for the removal of food dye contaminants during wastewater treatment.