H2S oxidation by multi-wall carbon nanotubes decorated with tungsten sulfide

Tungsten sulfide catalysts decorated on single and multiwall carbon nanotubes (SWNTs & MWNTs) and activated carbon were synthesized, and XRD, ICP, SEM, TEM and ASAP analyses were employed to acquire the characteristics of each catalyst. Afterwards a gas flow containing 5,000 ppm of H₂S was passed over the catalyst in gas hour space velocity (GHSV) of 5,000 h^?1, temperature of 65 °C, steam volume percent of 20 and O₂/H₂S ratio equal to 2. The results revealed that the catalyst supported on MWNTs exhibited higher conversion amongst its counterparts. Then effects of GHSV, steam volume percent in the feed, catalyst loading and temperature were investigated on conversion of hydrogen sulfide to elemental sulfur for tungsten sulfide catalyst decorated on MWNTs.     

A flexible carbon counter electrode for dye-sensitized solar cells

A pure carbon counter electrode (CE) for dye-sensitized solar cells (DSCs), has been fabricated using an industrial flexible graphite sheet as substrate and activated carbon as the catalytic material. The CE shows very low series resistance (Rs) and charge-transfer resistance (Rct) by combining the high conductivity of the flexible graphite with the high catalytic property of activated carbon. The Rs and Rct for the CE are respectively only a quarter and two-thirds of those for a platinized fluorine-doped tin oxide glass (Pt/FTO). DSCs with cell areas of 0.15 and 1 cm² fabricated with this CE show higher solar-to-electricity conversion efficiencies. The respective values are 6.46% and 5%, compared with 6.37% and 2.91% for the Pt/FTO based devices.     

Graphene films decorated with metal sulfide nanoparticles for use as counter electrodes of dye-sensitized solar cells

The composite films of metal sulfide (MS, M = Ni, Co) nanoparticles (NPs)/graphene films were proposed to be novel transparent conductive oxide- and platinum (Pt)-free counter electrodes with high electrocatalytic activity for dye-sensitized solar cells (DSSCs). Such DSSCs show higher photovoltaic conversion efficiencies of 5.25% (NiS/graphene) and 5.04% (CoS/graphene), compared with 5.00% for (Pt/fluorine-doped tin oxide). The excellent DSSC efficiencies are mainly due to the superior electrocatalytic activity of the MS and graphene films, and highly electrical properties of graphene films (9.57 Ω/sq). The excellent charge transfer between MS NPs and graphene films is due to the unique MS NPs and high surface area graphene structure. The graphene films were directly grown on dielectric SiO₂ substrates by chemical vapor deposition. MS NPs were uniformly implanted on the graphene films by dip coating of MS precursors M(C₃H₅OS₂)₂, and further annealed at 400 °C for 30 min under Ar.     

Graphene-based counter electrode for dye-sensitized solar cells

Graphene nanosheets (GNs) were synthesized and used as a substitute for platinum as counter-electrode materials for dye-sensitized solar cells (DSSCs). The as-synthesized GNs were dispersed in a mixture of terpineol and ethyl cellulose. GN films were screen-printed on fluorine-doped tin oxide (FTO) slides using the formed GN dispersions. GN counter-electrodes were produced by annealing the GN films at different temperatures. The annealed GN films revealed an unusual 3D network structure. Structural and electrochemical properties of the formed GN counter-electrodes were examined by field emission scanning electron microscopy, Raman spectroscopy and electrochemical impedance spectroscopy. It was found that the annealing temperature of GN materials played an important role in the quality of the GN counter-electrode and the photovoltaic performance of the resultant DSSC. The grown DSSCs with graphene-based counter-electrodes exhibited a conversion efficiency high up to 6.81%.     

A novel high-performance counter electrode for dye-sensitized solar cells

A novel Pt counter electrode for dye-sensitized solar cells (DSC) was prepared by thermal decomposition of H₂PtCl₆ on NiP-plated glass substrate. The charge-transfer kinetic properties of the platinized NiP-plated glass electrode (Pt/NiP electrode) for triiodide reduction were studied by electrochemical impedance spectroscopy. Pt/NiP electrode has the advantage over the platinized FTO conducting glass electrode (Pt/FTO electrode) in increasing the light reflectance and reducing the sheet resistance leading to improve the light harvest efficiency and the fill factor of the dye-sensitized solar cells effectively. The photon-to-current efficiency and the overall conversion efficiency of DSC using Pt/NiP counter electrode is increased by 20% and 33%, respectively, compared to that of using Pt/FTO counter electrode. Examination of the anodic dissolution and the long-term test on the variation of charge-transfer resistance indicates the good stability of the Pt/NiP electrode in the electrolyte containing iodide/triiodide.     

Wurtzite copper-zinc-tin sulfide as a superior counter electrode material for dye-sensitized solar cells

Wurtzite and kesterite Cu₂ZnSnS₄ (CZTS) nanocrystals were employed as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Compared to kesterite CZTS, the wurtzite CZTS exhibited higher electrocatalytic activity for catalyzing reduction of iodide electrolyte and better conductivity. Accordingly, the DSSC with wurtzite CZTS CE generated higher power conversion efficiency (6.89%) than that of Pt (6.23%) and kesterite CZTS (4.89%) CEs.     

Highly efficient bio-based porous carbon hybridized with tungsten carbide as counter electrode for dye-sensitized solar cell

Bio-based porous carbon (C_MA and C_TA) are successfully prepared from waste carton via microwave-assisted activation (MA) and two-step chemical activation (TA) methods, respectively. The as-prepared C_TA sample exhibits higher specific surface area (824.16 m² g⁻¹) and larger total pore volume (0.71 cm³ g⁻¹), as compared with those of the C_MA sample (655.36 m² g⁻¹ and 0.62 cm³ g⁻¹, correspondingly). The higher specific surface area could provide more catalytic sites; thus, the dye-sensitized solar cell (DSSC) assembled with a C_TA counter electrode (CE) deliver a power conversion efficiency (PCE) of 6.76%, surpass the C_MA-based DSSC (6.19%). Further, tungsten carbide (WC) are introduced into C_TA and C_MA to form hybrid catalysts (WC/C_TA and WC/C_MA, respectively) in order to improve their catalytic activities. Benefitting from the synergistic effect of bio-based porous carbon and WC, the DSSCs with WC/C_TA and WC/C_MA CEs exhibit superior PCE values of 7.32% and 6.85%, respectively, close to Pt (7.51%). This work provides an effective strategy for synthesizing low-cost and high-performance hybrid catalysts from bio-based carbon to achieve resource utilization of biomass waste in new energy fields.     

Electrophoretic deposition of carbon nanotubes films as counter electrodes of dye-sensitized solar cells

Carbon nanotubes (CNTs) films have been successfully fabricated by electrophoretic deposition (EPD) technique and used as counter electrodes of dye-sensitized solar cells (DSSCs). The CNTs counter electrodes consisting of a large number of bamboo-like structures with defect-rich edge planes exhibit a highly interconnected network structure with high electrical conductivity and good catalytic activity. A high photovoltaic conversion efficiency of 7.03% is achieved for DSSCs based on the CNTs counter electrodes, which is comparable to the cell based on conventional Pt counter electrode at one sun (AM 1.5G, 100 mW cm⁻²). The results suggest that the present synthetic strategy provides a potential feasibility for the fabrication of low-cost flexible counter electrodes of DSSCs using a facile deposition technique from an environmentally “friendly” solution at low temperature.     

Rutile TiO2-modified multi-wall carbon nanotubes in TiO2 film electrodes for dye-sensitized solar cells

The beneficial influence of incorporation of acid-treated and rutile TiO₂ (r-TiO₂)-modified multi-wall carbon nanotubes (MWNTs) in TiO₂ films on photocurrent–voltage characteristics of dye-sensitized solar cells (DSSCs) was studied. Two different routes were adopted for the modification of acid-treated MWNTs (a-MWNTs) with r-TiO₂. The films and MWNTs were characterized by electron microscopy, energy dispersive X-ray spectroscopy, XRD and Raman spectroscopy. In the case of incorporation of a-MWNTs with r-TiO₂ modification, short-circuit photocurrent (J _sc) of the pertinent DSSC increased by 35% compared with that of a cell with bare TiO₂ film. The open-circuit voltage remained almost the same for all cases. The enhanced J _sc is explained by the increased surface area of the film, enhanced cluster formation of TiO₂ particles around a-MWNTs, and improved interconnectivity of TiO₂ particles in the presence of a-MWNTs.     

Micro–meso hierarchical porous carbon as low-cost counter electrode for dye-sensitized solar cells

A micro–meso hierarchical porous carbon with low crystallinity was prepared by a combination of self-assembly and post activation and explored as a counter electrode in dye-sensitized solar cells. Pore structure analysis showed that the pristine mesopores were basically preserved during activation and the micropores were mainly generated within the mesopore wall. Due to its low crystallinity and unique pore-structure including both mesopores and micropores, hierarchical porous carbon exhibited a relatively higher electrocatalytic activity for triiodide reduction, as compared with the pristine mesoporous carbon electrode. This enhanced electrocatalytic activity is beneficial for improving the photovoltaic performance of dye-sensitized solar cells. Under irradiation of 100 mW cm⁻², the dye-sensitized solar cell with hierarchical porous carbon counter electrode showed an overall conversion efficiency of 6.48%, which was 11.5% higher than that of the cell with pristine mesoporous carbon counter electrode.     

Carbon nanotube counter electrode for high-efficient fibrous dye-sensitized solar cells

ABSTRACT: High-efficient fibrous dye-sensitized solar cell with carbon nanotube (CNT) thin films as counter electrodes has been reported. The CNT films were fabricated by coating CNT paste or spraying CNT suspension solution on Ti wires. A fluorine tin oxide-coated CNT underlayer was used to improve the adherence of the CNT layer on Ti substrate for sprayed samples. The charge transfer catalytic behavior of fibrous CNT/Ti counter electrodes to the iodide/triiodide redox pair was carefully studied by electrochemical impedance and current-voltage measurement. The catalytic activity can be enhanced by increasing the amount of CNT loading on substrate. Both the efficiencies of fibrous dye-sensitized solar cells using paste coated and sprayed CNT films as counter electrodes are comparative to that using Pt wires, indicating the feasibility of CNT/Ti wires as fibrous counter electrode for superseding Pt wires.     

A study of TiO2/carbon black composition as counter electrode materials for dye-sensitized solar cells

This study describes a systematic approach of TiO₂/carbon black nanoparticles with respect to the loading amount in order to optimize the catalytic ability of triiodide reduction for dye-sensitized solar cells. In particular, the cell using an optimized TiO₂ and carbon black electrode presents an energy conversion efficiency of 7.4% with a 5:1 ratio of a 40-nm TiO₂ to carbon black. Based on the electrochemical analysis, the charge-transfer resistance of the carbon counter electrode changed based on the carbon black powder content. Electrochemical impedance spectroscopy and cyclic voltammetry study show lower resistance compared to the Pt counter electrode. The obtained nanostructures and photo electrochemical study were characterized.     

Improvement of performance of dye-sensitized solar cells based on electrodeposited-platinum counter electrode

Platinum nanoparticle was electrodeposited on FTO conducting glass substrate as counter electrode for application in dye-sensitized solar cells (DSSCs). Images of transmission electron microscope (TEM) and Scanning Electron Microscope (SEM) showed that platinum nanoparticle was with the mean size of 20-30 nm and was homogeneously distributed on the surface of the FTO conductive glass sheet. Using such a counter electrode, DSSC showed a 6.40% overall energy conversion efficiency under one sun illumination. It exhibited the same high-performance as the DSSC with a platinum counter electrode prepared by electroplating. Furthermore, the present preparation method for the platinum counter electrode has the advantage of low platinum loading and transparence.     

Soft-template synthesized ordered mesoporous carbon counter electrodes for dye-sensitized solar cells

Ordered mesoporous carbon (OMC) with a high surface area (∼1575 m²/g) and bimodal pores (2.5 and 6.1 nm) was synthesized using a soft-template method employing triblock copolymer F127 as the structure directing agent and then applied as a low-temperature processable counter electrode for dye-sensitized solar cell (DSSC). The OMC counter electrode-based DSSC shows an energy conversion efficiency of 7.46%, whereas that of a Vulcan counter electrode is 4.30%. Electrochemical impedance spectroscopy analysis reveals decreased charge transfer resistance at the OMC counter electrode–electrolyte interface, thus improved fill factor and energy conversion efficiency.     

Enhanced performance in dye-sensitized solar cells via carbon nanofibers-platinum composite counter electrodes

A composite counter electrode (CE) made of electrospun carbon nanofibers (ECNs) and platinum (Pt) nanoparticles has been demonstrated for the first time to improve the performance of dye-sensitized solar cells (DSCs). The new ECN-Pt composite CE exhibited a more efficient electro-catalytic performance with lower charge transfer resistance (R(ct)), larger surface area, and faster reaction rate than those of conventional Pt. It reduced the overall series resistance (R(se)), decreased dark saturation current density (J(0)) and increased shunt resistance (R(sh)) of the DSCs, thereby leading to a higher fill factor (FF) and larger open circuit voltage (V(oc)). The reduced electron transport resistance (R(s)) and faster charge transfer rate in the CE led to a smaller overall cell series resistance (R(se)) in the ECN-Pt composite based DSCs. The DSCs based on an ECN-Pt CE achieved a η of ～8%, which was improved over those of pure Pt or ECN based cells.     

染料敏化太阳能电池非铂对电极研究进展

对电极作为染料敏化太阳能电池（dye-sensitized solar cell,DSSC）的重要组成部分,对电极材料性能的好坏直接影响着染料敏化太阳能电池的光电转化效率。最常使用的对电极电催化材料是贵金属铂,而铂十分稀少而且价格昂贵,并且铂很容易被碘电解液腐蚀,不利于染料敏化太阳能电池的产业化发展。本文重点综述了2010年以来染料敏化太阳能电池非铂对电极的研究成果,简要说明了对电极在染料敏化太阳能电池中的作用,详细介绍了非铂金属、碳材料、导电聚合物和无机化合物等对电极材料,分析了各类非铂对电极材料的特点、制备工艺、发展前景、优缺点和改进措施。最后提出,继续开发各种成本低、原料易得以及稳定高效的新型非金属对电极材料仍是今后染料敏化太阳能电池研究的一个重要方向。     

Graphene aerogels as a highly efficient counter electrode material for dye-sensitized solar cells

Graphene aerogels (GAs) prepared with an organic sol–gel process, possessing a high specific surface area of 814 m²/g and a high electric conductivity of 850 S/m, are applied as a counter electrode material for dye-sensitized solar cells (DSSCs). The performance of the GA as the counter electrode material is found to be dependent on its film thickness, with thicker films offering more surface areas for the involved catalytic reduction reaction but at the same time increasing the charge and mass transport resistances. At an optimum GA film thickness of 4.9 μm, a power conversion efficiency of 96% of that achieved with a Pt counter electrode based DSSC is obtained. In addition, a thinner GA film of 1.7 μm, when loaded with Pt of 1 mol% through a photo-reduction process, achieves a power conversion efficiency of 98% of that obtained with a Pt counter electrode based DSSC. The excellent performances of the GA-based counter electrodes are manifested with electrochemical impedance analyses and cyclic voltammetry based catalytic activity analyses.     

Enhanced performance of a dye-sensitized solar cell with an electrodeposited-platinum counter electrode

A counter electrode was prepared for a dye-sensitized solar cell (DSSC) through electrochemical deposition of mesoporous platinum on fluorine-doped tin oxide glass in the presence of a structure-directing nonionic surfactant, octaethylene glycol monohexadecyl ether (C₁₆EO₈). The DSSC fabricated with the electrochemically deposited Pt (ED-Pt) counter electrode rendered a higher solar-to-electricity conversion efficiency of 7.6%, compared with approximately 6.4% of the cells fabricated with the sputter-deposited or most commonly-employed thermal deposited Pt counter electrodes. This enhanced efficiency is attributed to the higher short-circuit photocurrent arising from the increases in the active surface area and light reflection as well as the decrease in the sheet resistance of the ED-Pt film, relative to those of the Pt films prepared by the other two deposition methods. The sputter-deposited Pt film yielded almost the same photovoltaic characteristics as the thermal deposited Pt film. The Pt films were characterized by FE-SEM, AFM, cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, sheet resistance measurements, adhesion tests, and light reflection tests.