Chung-Wei Kung

CoS Acicular Nanorod Arrays for the Counter Electrode of an Efficient Dye-Sensitized Solar Cell

One-dimensional cobalt sulfide (CoS) acicular nanorod arrays (ANRAs) were obtained on a fluorine-doped tin oxide (FTO) substrate by a two-step approach. First, Co(3)O(4) ANRAs were synthesized, and then they were converted to CoS ANRAs for various periods. The compositions of the films obtained after various conversion periods were verified by X-ray diffraction, UV-visible spectrophotometry, and X-ray photoelectron spectroscopy; their morphologies were examined at different periods by scanning electron microscopic and transmission electron microscopic images. Electrocatalytic abilities of the films toward I(-)/I(3)(-) were verified through cyclic voltammetry (CV) and Tafel polarization curves. Long-term stability of the films in I(-)/I(3)(-) electrolyte was studied by CV. The FTO substrates with CoS ANRAs were used as the counter electrodes for dye-sensitized solar cells; a maximum power conversion efficiency of 7.67% was achieved for a cell with CoS ANRAs, under 100 mW/cm(2), which is nearly the same as that of a cell with a sputtered Pt counter electrode (7.70%). Electrochemical impedance spectroscopy was used to substantiate the photovoltaic parameters.

Cobalt oxide acicular nanorods with high sensitivity for the non-enzymatic detection of glucose

Acicular cobalt oxide nanorods (CoONRs) were prepared for the non-enzymatic detection of glucose, first by directly growing layered cobalt carbonate hydroxide (LCCH) on a conducting fluorine-doped tin oxide (FTO) substrate using a simple chemical bath deposition (CBD) technique and then by transforming the LCCH into CoONRs through pyrolysis. The composition and grain size of the films of LCCH and CoONRs were verified by X-ray diffraction (XRD); their morphologies were examined by scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images. CoONRs showed high electrocatalytic activity for the electro-oxidation of glucose in alkaline media, and the activity was strongly influenced by NaOH concentration, annealing temperature of CoONRs, and thickness of CoONRs film. The pertinent sensor could be successfully used for the quantification of glucose by amperometric method. The sensing parameters include wide linear range up to 3.5 mM, a high sensitivity of 571.8 μA/(cm(2) mM), and a remarkable low detection limit of 0.058 μM. The CoONRs modified electrode exhibited a high selectivity for glucose in human serum, against ascorbic acid, uric acid, and acetaminophen.

Highly efficient dye-sensitized solar cell with a ZnO nanosheet-based photoanode

Zinc oxide (ZnO) nanosheets (ZnO-NS) were prepared for the photoanode of a dye-sensitized solar cell (DSSC), first by directly growing layered hydroxide zinc carbonate (LHZC) on an FTO substrate using a chemical bath deposition (CBD) method and then by transforming the LHZC into ZnO through pyrolysis at 300 °C. A light-to-electricity conversion efficiency (η) of 6.06% was achieved for the DSSC with ZnO-NS as its photoanode, under 100 mW cm−2 illumination, and this (η) was found to be much higher than that of the DSSC with ZnO nanoparticles (ZnO-NP) as the photoanode (2.92%). The far superior performance of the DSSC with ZnO-NS is essentially attributed to (i) higher effective electron diffusion coefficient of ZnO-NS (3.59 × 10−3 cm2s−1) than that of ZnO-NP (1.12 × 10−3 cm2s−1), and to (ii) higher dye loading on ZnO-NS (2.66 × 10−7 mol cm−2) than that on ZnO-NP (1.99 × 10−7 mol cm−2); this higher electron diffusion coefficient and dye-loading are attributed to the specific morphology of the ZnO-NS. A further improvement in the efficiency of the DSSC with ZnO-NS could be achieved through the electrophoretic deposition (EPD) of a very thin layer (3 μm) of titanium dioxide nanoparticles (TiO2-NPs of average size 14 nm) onto the ZnO-NS layer (12 μm). Notwithstanding a decrease in the effective electron diffusion coefficient (3.07 × 10−3 cm2s−1) in the TiO2-NP/ZnO-NS film, with reference to that in the ZnO-NS film (3.59 × 10−3 cm2s−1), a far higher cell efficiency was obtained in favor of the cell with TiO2-NP/ZnO-NS (7.07%), compared to that of the cell with bare ZnO-NS (6.06%); this enhancement in the η of the cell with TiO2-NP/ZnO-NS is ascribed to an increased dye-loading in favor of its cell (3.92 × 10−7 mol cm−2), with reference to that in the case of the cell with bare ZnO-NS (2.66 × 10−7 mol cm−2). As against the common ruthenium dyes, such as N3 and N-719, a metal-free dye, coded as D149, was used in this research. The efficiency achieved for the best DSSC in this work is the highest ever reported for a DSSC with ZnO as the main semiconductor material.

Directed Growth of Electroactive Metal-Organic Framework Thin Films Using Electrophoretic Deposition

Electrophoretic deposition (EPD) is used to assemble metal-organic framework (MOF) materials in nano- and micro-particulate, thin-film form. The flexibility of the method is demonstrated by the successful deposition of 4 types of MOFs: NU-1000, UiO-66, HKUST-1, and Al-MIL-53. Additionally, EPD is used to pattern the growth of NU-1000 thin films that exhibit full electrochemical activity.

A porous proton-relaying metal-organic framework material that accelerates electrochemical hydrogen evolution

The availability of efficient hydrogen evolution reaction (HER) catalysts is of high importance for solar fuel technologies aimed at reducing future carbon emissions. Even though Pt electrodes are excellent HER electrocatalysts, commercialization of large-scale hydrogen production technology requires finding an equally efficient, low-cost, earth-abundant alternative. Here, high porosity, metal-organic framework (MOF) films have been used as scaffolds for the deposition of a Ni-S electrocatalyst. Compared with an MOF-free Ni-S, the resulting hybrid materials exhibit significantly enhanced performance for HER from aqueous acid, decreasing the kinetic overpotential by more than 200 mV at a benchmark current density of 10 mA cm−2. Although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst.

Metal–Organic Framework Thin Films as Platforms for Atomic Layer Deposition of Cobalt Ions To Enable Electrocatalytic Water Oxidation

Thin films of the metal-organic framework (MOF) NU-1000 were grown on conducting glass substrates. The films uniformly cover the conducting glass substrates and are composed of free-standing sub-micrometer rods. Subsequently, atomic layer deposition (ALD) was utilized to deposit Co(2+) ions throughout the entire MOF film via self-limiting surface-mediated reaction chemistry. The Co ions bind at aqua and hydroxo sites lining the channels of NU-1000, resulting in three-dimensional arrays of separated Co ions in the MOF thin film. The Co-modified MOF thin films demonstrate promising electrocatalytic activity for water oxidation.

MOF Functionalization via Solvent-Assisted Ligand Incorporation: Phosphonates vs Carboxylates

Solvent-assisted ligand incorporation (SALI) is useful for functionalizing the channels of metal-organic framework (MOF) materials such as NU-1000 that offer substitutionally labile zirconium(IV) coordination sites for nonbridging ligands. Each of the 30 or so previous examples relied upon coordination of a carboxylate ligand to achieve incorporation. Here we show that, with appropriate attention to ligand/node stoichiometry, SALI can also be achieved with phosphonate-terminated ligands. Consistent with stronger M(IV) coordination of phosphonates versus carboxylates, this change extends the pH range for retention of incorporated ligands. The difference in coordination strength can be exploited to achieve stepwise incorporation of pairs of ligands-specifically, phosphonates species followed by carboxylate species-without danger of displacement of the first ligand type by the second. Diffuse reflectance infrared Fourier-transform spectroscopy suggests that the phosphonate ligands are connected to the MOF node as RPO2(OH)¯ species in a moiety that leaves a base-accessible -OH moiety on each bound phosphonate.

A highly efficient dye-sensitized solar cell with a platinum nanoflowers counter electrode

This study applied the pulse reversal electrodeposition (PRE) technique to deposit a platinum film having a nanoflowers (PtNFs) structure onto an indium tin oxide (ITO) glass. The physical characteristics and electro-catalytic abilities of the PtNF-CEs were analyzed by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) patterns, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). A double layer theory and a crystal facet formation mechanism are used to explain the catalytic abilities of the PtNFs. Scanning electron microscopy (SEM) images depict a dramatic transformation in the surface structure of the Pt clusters. The ITO glass with the PtNFs was used as the counter electrode (CE) of a dye-sensitized solar cell (DSSC). The DSSC assembled with the as-prepared PtNF-CE exhibits a high power conversion efficiency (η) of 7.74%, while the cell with an additional thin (2 nm) sputtered layer of platinum on the PtNF film shows much higher η of 8.13%, both at 1 sun conditions. The performances of the DSSCs are further substantiated by the data from electrochemical impedance spectroscopy (EIS) and UV-Vis reflectance spectra.

Planar Heterojunction Perovskite Solar Cells Incorporating Metal–Organic Framework Nanocrystals

Zr-based porphyrin metal-organic framework (MOF-525) nanocrystals with a crystal size of about 140 nm are synthesized and incorporated into perovskite solar cells. The morphology and crystallinity of the perovskite thin film are enhanced since the micropores of MOF-525 allow the crystallization of perovskite to occur inside; this observation results in a higher cell efficiency of the obtained MOF/perovskite solar cell.

A high performance electrochemical sensor for acetaminophen based on a rGO–PEDOT nanotube composite modified electrode

In this study, we perform an electrochemical sensing using a conductive composite film containing reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene) nanotubes (PEDOT NTs) as an electrode modifier on a glassy carbon electrode (GCE). Scanning electron microscopy suggests that the rGO covers the surface of GCE uniformly and the PEDOT NTs act as a conducting bridge to connect the isolated rGO sheets. By combining these two materials, the conductivity and the surface coverage of the film can be enhanced, which is beneficial for electrochemical sensing. The rGO–PEDOT NT composite modified electrode is applied for an effective sensor to analyze acetaminophen. The obtained electrochemical activity is much higher than those obtained by the rGO- and PEDOT NT-modified electrodes; the higher electrochemical activity may be attributed to the higher conductivity and greater coverage of the rGO–PEDOT NT composite film on the GCE. Furthermore, interference tests indicate that the rGO–PEDOT NT composite modified electrode exhibits high selectivity toward the analyte. This novel method for combining the rGO and PEDOT NTs establishes a new class of carbon material-based electrodes for electrochemical sensors.