Hollow nanostructured materials have attracted considerable interest as lithium ion battery electrodes because of their good electrochemical properties. In this study, we developed a general procedure for the synthesis of hollow... more
Hollow nanostructured materials have attracted considerable interest as lithium ion battery electrodes because of their good electrochemical properties. In this study, we developed a general procedure for the synthesis of hollow nanostructured metal silicates via a hydrothermal process using silica nanoparticles as templates. The morphology and composition of hollow nanostructured metal silicates could be controlled by changing the metal precursor. The as-prepared hierarchical hollow nanostructures with diameters of about 100~200 nm were composed of various shaped primary particles such as hollow nanospheres, solid nanoparticles, and thin nanosheets. Furthermore, different primary nanoparticles could be combined to form hybrid hierarchical hollow nanostructures. When hollow nanostructured metal silicates were applied as anode materials for lithium ion batteries, all samples exhibited good cyclic stability during 300 cycles, as well as tunable electrochemical properties.
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The synthesis of urchin-like Pt-Ni bimetallic nanostructures is achieved by a controlled one-pot synthesis. Pt-Ni nanostructures have superior oxygen reduction reaction activities in both with and without specific anion adsorption... more
The synthesis of urchin-like Pt-Ni bimetallic nanostructures is achieved by a controlled one-pot synthesis. Pt-Ni nanostructures have superior oxygen reduction reaction activities in both with and without specific anion adsorption electrolytes due to the geometric and alloying effects.
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We report a simple synthetic method of carbon-based hybrid cellular nanosheets that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The nanosheets consist of close-packed cubic... more
We report a simple synthetic method of carbon-based hybrid cellular nanosheets that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The nanosheets consist of close-packed cubic cavity cells partitioned by carbon walls, resembling plant leaf tissue. We loaded carbon cellular nanosheets with SnO2 nanoparticles by vapor deposition method and tested the performance of the resulting SnO2-carbon nanosheets as anode materials. The specific capacity is 914 mAh g(-1) on average with a retention of 97.0% during 300 cycles, and the reversible capacity is decreased by only 20% as the current density is increased from 200 to 3000 mA g(-1). In order to explain the excellent electrochemical performance, the hybrid cellular nanosheets were analyzed with cyclic voltammetry, in situ X-ray absorption spectroscopy, and transmission electron microscopy. We found that the high packing density, large interior surface area, and rigid carbon wall netwo...
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The electronic properties of quantum dots can be tuned by changing the size of particles without any change in their chemical composition. CdSe quantum dots, the sizes of which were controlled by changing the con-centrations of Cd and Se... more
The electronic properties of quantum dots can be tuned by changing the size of particles without any change in their chemical composition. CdSe quantum dots, the sizes of which were controlled by changing the con-centrations of Cd and Se precursors, were adsorbed on TiO 2 photoelectrodes and used as sensitizers for photovoltaic cells. For applications of CdSe quantum dot as sensitizers, CdSe/TiO 2 films on conducting glass were employed in a sandwich-type cell that incorporated a platinum-coated conductive glass and an electrolyte consisting of an I − /I 3 − redox. The fill factor (FF) and efficiency for energy conversion (ç) of the photovoltaic cell was 62 % and 0.32 %, respectively.
The origin of the excellent electrocatalytic performance of PtRu alloy catalysts supported on newly synthesized carbon nanocoil supports was investigated. Among three commercially available carbon materials Vulcan XC-72, multiwall carbon... more
The origin of the excellent electrocatalytic performance of PtRu alloy catalysts supported on newly synthesized carbon nanocoil supports was investigated. Among three commercially available carbon materials Vulcan XC-72, multiwall carbon nanotube, and activated carbon, the ...
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Core-shell structure nanoparticles have been the subject of many studies over the past few years and continue to be studied as electrocatalysts for fuel cells. Therefore, many excellent core-shell catalysts have been fabricated, but few... more
Core-shell structure nanoparticles have been the subject of many studies over the past few years and continue to be studied as electrocatalysts for fuel cells. Therefore, many excellent core-shell catalysts have been fabricated, but few studies have reported the real application of these catalysts in a practical device actual application. In this paper, we demonstrate the use of platinum (Pt)-exoskeleton structure nanoparticles as cathode catalysts with high stability and remarkable Pt mass activity and report the outstanding performance of these materials when used in membrane-electrode assemblies (MEAs) within a polymer electrolyte membrane fuel cell. The stability and degradation characteristics of these materials were also investigated in single cells in an accelerated degradation test using load cycling, which is similar to the drive cycle of a polymer electrolyte membrane fuel cell used in vehicles. The MEAs with Pt-exoskeleton structure catalysts showed enhanced performance t...
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Nickel nitride electrodes were prepared by reactive sputtering of nickel under a N2 atmosphere at room temperature for application in mesoscopic dye- or quantum dot- sensitized solar cells. This facile and reliable method led to the... more
Nickel nitride electrodes were prepared by reactive sputtering of nickel under a N2 atmosphere at room temperature for application in mesoscopic dye- or quantum dot- sensitized solar cells. This facile and reliable method led to the formation of a Ni2N film with a cauliflower-like nanostructure and tetrahedral crystal lattice. The prepared nickel nitride electrodes exhibited an excellent chemical stability toward both iodide and polysulfide redox electrolytes. Compared to conventional Pt electrodes, the nickel nitride electrodes showed an inferior electrocatalytic activity for the iodide redox electrolyte; however, it displayed a considerably superior electrocatalytic activity for the polysulfide redox electrolyte. As a result, compared to dye-sensitized solar cells (DSCs), with a conversion efficiency (η) = 7.62%, and CdSe-based quantum dot-sensitized solar cells (QDSCs, η = 2.01%) employing Pt counter electrodes (CEs), the nickel nitride CEs exhibited a lower conversion efficiency (η = 3.75%) when applied to DSCs, but an enhanced conversion efficiency (η = 2.80%) when applied to CdSe-based QDSCs.
An all-solid-state supercapacitor is fabricated and optimized using a Nafion ® membrane and an ionomer. The device shows good capacitance (ca. 200 F g −1 ) as demonstrated by cyclic voltammograms (CVs) and chargedischarge curves. The... more
An all-solid-state supercapacitor is fabricated and optimized using a Nafion ® membrane and an ionomer. The device shows good capacitance (ca. 200 F g −1 ) as demonstrated by cyclic voltammograms (CVs) and chargedischarge curves. The supercapacitor exhibits a ...
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Although numerous reports on nonprecious metal catalysts for replacing expensive Pt-based catalysts have been published, few of these studies have demonstrated their practical application in fuel cells. In this work, we report graphitic... more
Although numerous reports on nonprecious metal catalysts for replacing expensive Pt-based catalysts have been published, few of these studies have demonstrated their practical application in fuel cells. In this work, we report graphitic carbon nitride and carbon nanofiber hybrid materials synthesized by a facile and gram-scale method via liquid-based reactions, without the use of toxic materials or a high pressure-high temperature reactor, for use as fuel cell cathodes. The resulting materials exhibited remarkable methanol tolerance, selectivity, and stability even without a metal dopant. Furthermore, these completely metal-free catalysts exhibited outstanding performance as cathode materials in an actual fuel cell device: a membrane electrode assembly with both acidic and alkaline polymer electrolytes. The fabrication method and remarkable performance of the single cell produced in this study represent progressive steps toward the realistic application of metal-free cathode electrocatalysts in fuel cells.
Pt-based binary or ternary catalysts containing Rh for use as anodes in direct methanol fuel cells (DMFC) were synthesized by borohydride reduction method combined with freeze-drying. The resulting catalysts had a specific surface area of... more
Pt-based binary or ternary catalysts containing Rh for use as anodes in direct methanol fuel cells (DMFC) were synthesized by borohydride reduction method combined with freeze-drying. The resulting catalysts had a specific surface area of approximately 65–75m2/g. X-ray diffraction (XRD) patterns indicated that the catalysts were well alloyed and the average size of alloy catalysts was confirmed by transmission electron
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... S BET : BET surface area; S micro : micropore area; S meso/macro :meso and macropore area; V totoal : total ... Figure 5 Cyclic voltammograms for supported Pt 50 Ru 50 alloy catalysts. Figure 6 shows the unit cell performance of... more
... S BET : BET surface area; S micro : micropore area; S meso/macro :meso and macropore area; V totoal : total ... Figure 5 Cyclic voltammograms for supported Pt 50 Ru 50 alloy catalysts. Figure 6 shows the unit cell performance of direct methanol fuel cell at 30 and 70 °C by the ...
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Solvothermal processes are considered efficient approaches for the gram-scale production of graphene. Further modification of graphene by chemical doping is an important approach to tailor its properties. In this work, we successfully... more
Solvothermal processes are considered efficient approaches for the gram-scale production of graphene. Further modification of graphene by chemical doping is an important approach to tailor its properties. In this work, we successfully synthesized sulfur-doped graphene by using a solvothermal method with dimethyl sulfoxide as a precursor, which is a common laboratory reagent. Nitrogen-doped graphene was produced to demonstrate the generality of this process. These heteroatom-doped graphene materials exhibited high surface areas and high contents of heteroatoms. Furthermore, the lithium-ion storage properties and oxygen reduction reaction catalytic activity of these materials were also investigated. The success of this approach might facilitate the development of other advanced graphene-based materials with relative simplicity, scalability, and cost effectiveness for use in various potential applications.
We propose a method to enhance the fuel cell efficiency with the simultaneous removal of toxic heavy metal ions. Carbon monoxide (CO), an intermediate of methanol oxidation that is primarily responsible for Pt catalyst deactivation, can... more
We propose a method to enhance the fuel cell efficiency with the simultaneous removal of toxic heavy metal ions. Carbon monoxide (CO), an intermediate of methanol oxidation that is primarily responsible for Pt catalyst deactivation, can be used as an in-situ reducing agent for hexavalent chromium (Cr (VI)) with reactivating the CO-poisoned Pt catalyst. Using electro-oxidation measurements, the oxidation of adsorbed CO molecules coupled with the concurrent conversion of Cr (VI) to Cr (III) was confirmed. This concept was also successfully applied to a methanol fuel cell to enhance its performance efficiency and to remove toxic Cr (VI) at the same time.
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Columnar-structured rutile TiO2 film with a thickness of 1.4μm is prepared using the radio-frequency (RF) magnetron sputtering technique, for application in dye-sensitized solar cells (DSSCs). Pure rutile TiO2 films are fabricated by... more
Columnar-structured rutile TiO2 film with a thickness of 1.4μm is prepared using the radio-frequency (RF) magnetron sputtering technique, for application in dye-sensitized solar cells (DSSCs). Pure rutile TiO2 films are fabricated by controlling the substrate temperature during sputtering and using a substrate with a rough surface morphology. Successive substrate heating to 623K induces the growth of a rutile TiO2 film
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Pt/Ru (1:1), Pt/Ni (1:1), and Pt/Ru/Ni (5:4:1) electrocatalysts for use in direct methanol fuel cells (DMFCs) were synthesized by reduction with combined with freeze-drying and their activity as a methanol oxidation catalyst was examined... more
Pt/Ru (1:1), Pt/Ni (1:1), and Pt/Ru/Ni (5:4:1) electrocatalysts for use in direct methanol fuel cells (DMFCs) were synthesized by reduction with combined with freeze-drying and their activity as a methanol oxidation catalyst was examined at different temperatures. The onset potential ...
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Pt/Ni thin-film electrodes were fabricated by e-beam evaporation of metal layers and rapid thermal annealing (RTA), to achieve alloy formation between the Pt and Ni layers. The structural, chemical, and electronic properties of thin-film... more
Pt/Ni thin-film electrodes were fabricated by e-beam evaporation of metal layers and rapid thermal annealing (RTA), to achieve alloy formation between the Pt and Ni layers. The structural, chemical, and electronic properties of thin-film electrodes annealed at 200, 300, and 500 ...
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PtRu alloy and PtRu−WO 3 nanocomposite thin-film electrodes for methanol electrooxidation were fabricated by means of a sputtering method. The structural and electrochemical properties of well-defined PtRu alloy thin-film electrodes were... more
PtRu alloy and PtRu−WO 3 nanocomposite thin-film electrodes for methanol electrooxidation were fabricated by means of a sputtering method. The structural and electrochemical properties of well-defined PtRu alloy thin-film electrodes were characterized using X-ray diffraction ( ...
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A Pt−WO x nanophase electrode showed a considerably more enhanced electrocatalytic activity than Pt itself for methanol oxidation and exactly the reverse change in optical signal intensity with respect to electrochemical cell potential,... more
A Pt−WO x nanophase electrode showed a considerably more enhanced electrocatalytic activity than Pt itself for methanol oxidation and exactly the reverse change in optical signal intensity with respect to electrochemical cell potential, compared with an electrochromic WO x ...
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The role of defects on the electrochromic response time of sputter-deposited Ni oxide films grown by RF magnetron sputtering system was examined. In order to create an excess interstitial oxygens and voids, the sputter-deposited Ni oxides... more
The role of defects on the electrochromic response time of sputter-deposited Ni oxide films grown by RF magnetron sputtering system was examined. In order to create an excess interstitial oxygens and voids, the sputter-deposited Ni oxides were grown at varying Ar/O2 ambient ratios and RF power, respectively. The electrochromic response time was evaluated by an in situ transmittance measurement during
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... Appl. Phys. Lett., 75 (1999), p. 1541. [5] SH Lee, HM Cheong, CE Tracy, A. Mascarenhas, JR Pitts, G. Jorgensen and SK Deb. Appl. Phys. ... J. Electroanal. Chem., 511 (2001), p. 79. [9] KS Ahn, YC Nah, JH Yum and Y.-E. Sung. Jpn. J.... more
... Appl. Phys. Lett., 75 (1999), p. 1541. [5] SH Lee, HM Cheong, CE Tracy, A. Mascarenhas, JR Pitts, G. Jorgensen and SK Deb. Appl. Phys. ... J. Electroanal. Chem., 511 (2001), p. 79. [9] KS Ahn, YC Nah, JH Yum and Y.-E. Sung. Jpn. J. Appl. Phys., 41 (2002), p. L212. ...
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The effects of tantalum oxide (Ta2O5) films deposited on tungsten oxide (WO3) films were investigated since unmodified WO3 films have a tendency to be soluble in the acidic electrolyte. The electrochromic properties of the resulting... more
The effects of tantalum oxide (Ta2O5) films deposited on tungsten oxide (WO3) films were investigated since unmodified WO3 films have a tendency to be soluble in the acidic electrolyte. The electrochromic properties of the resulting Ta2O5/WO3 films were then compared to those of unmodified WO3 films by means of in situ transmittance measurements. In the case of WO3 films, electrochromic
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... The electrospun tungsten oxide NWs electrode and solgel spin-coated WO 3 thin film ... cathodic electrochromic material in this work were fabricated by the electrospinning method under ... the FESEM images, size distribution and... more
... The electrospun tungsten oxide NWs electrode and solgel spin-coated WO 3 thin film ... cathodic electrochromic material in this work were fabricated by the electrospinning method under ... the FESEM images, size distribution and crystalline characteristics of as-electrospun WO x ...
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... In this study, a dye-modified TiO 2 /ZnO electrode was prepared by the one-step cathodic electrodeposition of dye and ZnO on a TiO 2 -coated ITO glass substrate and used in a DSSC. ... Fig. 1(b) shows the results. The solution had a... more
... In this study, a dye-modified TiO 2 /ZnO electrode was prepared by the one-step cathodic electrodeposition of dye and ZnO on a TiO 2 -coated ITO glass substrate and used in a DSSC. ... Fig. 1(b) shows the results. The solution had a pH of ca. ...
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This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO2 nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier... more
This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO2 nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier between TONTs and the Q dot sensitizer increased the short-circuit current under illumination and also reduced the dark current in a dark environment. The power conversion efficiency of Q dot-sensitized TONT solar cells increased by 25.9% in the presence of the ZnO thin layer due to improved charge-collecting efficiency and reduced recombination.
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The intercalation/deintercalation of lithium ions into the heat-treated mesophase pitch-based carbon fibers (MPCF) was carried out in 1 M LiPF6ethylene carbonate (EC)/diethyl carbonate (DEC)(1: 1, volume ratio) solution at room... more
The intercalation/deintercalation of lithium ions into the heat-treated mesophase pitch-based carbon fibers (MPCF) was carried out in 1 M LiPF6ethylene carbonate (EC)/diethyl carbonate (DEC)(1: 1, volume ratio) solution at room temperature. LiC6 became ...
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Thickness-dependent microstructural and electrochromic properties of sputter-deposited Ni oxide films were investigated as a function of growth time using x-ray diffraction, in situ transmittance measurements, and x-ray photoelectron... more
Thickness-dependent microstructural and electrochromic properties of sputter-deposited Ni oxide films were investigated as a function of growth time using x-ray diffraction, in situ transmittance measurements, and x-ray photoelectron spectroscopy. By increasing the thickness of the Ni oxide, the transmittance or optical differences during coloring/bleaching process were increased. However, thick Ni oxides showed a lower maximum bleached transmittance and coloration efficiency
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Nitrogen (n)-doped titanium dioxide (TiO2) was prepared with varying doping extent by a general sol–gel process with a pure TiO2 film as the control sample. The n-doped-2 electrode showed the maximum conversion efficiency with an... more
Nitrogen (n)-doped titanium dioxide (TiO2) was prepared with varying doping extent by a general sol–gel process with a pure TiO2 film as the control sample. The n-doped-2 electrode showed the maximum conversion efficiency with an open-circuit voltage (Voc) of 0.726V, a photocurrent (Jsc) of 10.52mAcm−2, a fill factor of 63.6%, and an efficiency of 4.86%, compared to 0.751V, 7.4mAcm−2, 67.1%, and 3.73%, respectively, for the undoped (u-doped) TiO2 electrode. The approximate 23% enhancement in the conversion efficiency of the n-doped-2 TiO2 electrode-based dye-sensitized solar cells (DSSCs) was mostly ascribed to the increase of light absorption in the near-vis absorbance and partially to the morphological characteristics of the n-doped TiO2 film. Additionally, the doping type of nitrogen in the TiO2 lattice was closely studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The relation between the doping type and the electron behavior in the DSSCs was also ...
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... A Nafion 112 membrane (DuPont) was used as the polymer electrolyte membrane. The membrane was treated with 3 wt.% H 2 O 2 (Junsei Chemical Co. ... [17] M. Uchida, Y. Fujuoka, Y. Sugawara, N. Eda and A. Otha, J. Electrochem. Soc. 143... more
... A Nafion 112 membrane (DuPont) was used as the polymer electrolyte membrane. The membrane was treated with 3 wt.% H 2 O 2 (Junsei Chemical Co. ... [17] M. Uchida, Y. Fujuoka, Y. Sugawara, N. Eda and A. Otha, J. Electrochem. Soc. 143 (1996), p. 2247. ...
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The initial capacity irreversibility caused by film formation on a mesophase pitch-based carbon fibre (MPCF) electrode surface is studied with the goal of improving the performance of a lithium-ion battery. The addition of Li2CO3 to a... more
The initial capacity irreversibility caused by film formation on a mesophase pitch-based carbon fibre (MPCF) electrode surface is studied with the goal of improving the performance of a lithium-ion battery. The addition of Li2CO3 to a solution of 1M LiPF6/EC:DFC (1:1, v/v) results in a decrease in the initial irreversible capacity caused by solvent decomposition and the passivation film on
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TiCl4-treated, nanoporous-layer-covered TiO2 (Type II) nanotube arrays are fabricated through a two-step anodization process followed by treatment with TiCl4. A dye-sensitized solar cell (DSSC) with TiCl4-treated, nanoporous-layer-covered... more
TiCl4-treated, nanoporous-layer-covered TiO2 (Type II) nanotube arrays are fabricated through a two-step anodization process followed by treatment with TiCl4. A dye-sensitized solar cell (DSSC) with TiCl4-treated, nanoporous-layer-covered Type II TiO2 nanotubes is compared with other DSSCs based on untreated Type II and both untreated and TiCl4-treated, conventional TiO2 (Type I) nanotube arrays. The TiCl4 surface treatment's effects on dye adsorption, charge transport, and electron lifetime are dependent on the morphologies of the TiO2 nanotubes. The TiCl4-treated Type I nanotubes allow higher dye adsorption, whilst the TiCl4-treated Type II nanotubes provide much faster electron transport and enhanced electron lifetime. This is because there are fewer defect traps in the nanostructure well-aligned without bundling, which contributes to the significantly improved cell performance over the DSSC with the TiCl4-treated Type I nanotubes.
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Solid-state dye-sensitized TiO2 solar cells using commercially available ruthenium dye (Z907) as an hydrophobic sensitizing dye and poly (3, 4-ethylenedioxythiophene)(PEDOT) as a hole conductor and a platinum-free counter electrodes were... more
Solid-state dye-sensitized TiO2 solar cells using commercially available ruthenium dye (Z907) as an hydrophobic sensitizing dye and poly (3, 4-ethylenedioxythiophene)(PEDOT) as a hole conductor and a platinum-free counter electrodes were fabricated. The ...
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ABSTRACT Quasi-solid-state transparent TiO2 solar cells using aniline oligomer as a hole conducting material and PEDOT on FTO as a counter cathode catalyst were newly developed. The pore of the nanoporous TiO2 layer was filled with... more
ABSTRACT Quasi-solid-state transparent TiO2 solar cells using aniline oligomer as a hole conducting material and PEDOT on FTO as a counter cathode catalyst were newly developed. The pore of the nanoporous TiO2 layer was filled with aniline oligomer as a hole conductor through the in situ photoelectrochemical oxidative polymerization of aniline under photo-excitation of TiO2 layers. The best efficiency of 0.36% with high open circuit voltage 0.83 V was obtained under simulated 1-sun conditions even though the cells absorb only UV light, containing only 5% photon energy to the total in solar light. The photoelectrochemical synthesis of a conjugated polymer (p-type electron donor) is an effective way to fill the porous structure of inorganic n-type electron acceptor like nanoporous TiO2 and to obtain the molecular level contact between them.
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A nanoporous electrode was prepared by incorporating various amounts of carbon powder (Vulcan X-72) into TiO2 paste. To remove the black-colored carbon elements, high-temperature (550°C) thermal treatment was required for a long period of... more
A nanoporous electrode was prepared by incorporating various amounts of carbon powder (Vulcan X-72) into TiO2 paste. To remove the black-colored carbon elements, high-temperature (550°C) thermal treatment was required for a long period of time (from 30 to 50min). In this way, a nanoporous TiO2 electrode with a high specific surface area and high porosity was formed after the incorporation