Tetrachlorocobaltate-Catalyzed Methane Oxidation to Methyl Trifluoroacetate

In ongoing attempts to efficiently utilize abundant natural gas, there has been steady scientific and industrial interest in using an environmentally benign and inexpensive oxidant (dioxygen O2) for the direct catalytic oxidation of methane to oxygenate products under mild conditions. Here, we report the homogeneous bis(tetramethylammonium) tetrachlorocobaltate ([Me4N]2CoCl4)-catalyzed methane oxidation to methyl trifluoroacetate (MeTFA) with dioxygen O2 in trifluoroacetic acid (HTFA) media. [Me4N]2CoCl4 had the highest catalytic activity among previously reported homogeneous cobalt-based catalyst systems; the turnover of methane to MeTFA reached 8.26 molester molmetal−1h−1 at 180 °C. Results suggest that the ionic form of the catalyst makes the Co species more soluble in the HTFA media; consequently, an active catalyst form, [CoTFAxCly]2−, can form very rapidly. Furthermore, chloride anions dissociated from CoCl42− appear to suppress oxidation of the solvent HTFA, thereby driving the reaction toward methane oxidation. The effects of reaction time, catalyst concentration, O2 and methane pressure, and reaction temperature on MeTFA production were also investigated

Solution processed WO3 layer for the replacement of PEDOT:PSS layer in organic photovoltaic cells

Tungsten oxide layer is formed uniformly by a sol-gel technique on top of indium tin oxide as a neutral and photo-stable hole extraction layer (HEL). The solution processed tungsten oxide layer (sWO(3)) is fully characterized by UV-Vis, XPS, UPS, XRD, AFM, and TEM. Optical transmission of ITO/sWO(3) substrates is nearly identical to ITOs. In addition, the sWO(3) layer induces nearly ohmic contact to P3HT as PEDOT: PSS layer does, which is determined by UPS measurement. In case that an optimized thickness (similar to 10 nm) of the sWO(3) layer is incorporated in the organic photovoltaic devices (OPVs) with a structure of ITO/sWO(3)/P3HT: PCBM/Al, the power conversion efficiency (PCE) is 3.4%, comparable to that of devices utilizing PEDOT: PSS as HEL. Furthermore, the stability of OPV utilizing sWO3 is significantly enhanced due to the air-and photo-stability of the sWO(3) layer itself. PCEs are decreased to 40% and 0% of initial values, when PEDOT: PSS layers are exposed to air and light for 192 h, respectively. In contrast, PCEs are maintained to 90% and 87% of initial PCEs respectively, when sWO(3) layers are exposed to the same conditions. Conclusively, we find that solution processed tungsten oxide layers can be prepared easily, act as an efficient hole extraction layer, and afford a much higher stability than PEDOT: PSS layers

Tetrachlorocobaltate-Catalyzed Methane Oxidation to Methyl Trifluoroacetate

In ongoing attempts to efficiently utilize abundant natural gas, there has been steady scientific and industrial interest in using an environmentally benign and inexpensive oxidant (dioxygen O2) for the direct catalytic oxidation of methane to oxygenate products under mild conditions. Here, we report the homogeneous bis(tetramethylammonium) tetrachlorocobaltate ([Me4N]2CoCl4)-catalyzed methane oxidation to methyl trifluoroacetate (MeTFA) with dioxygen O2 in trifluoroacetic acid (HTFA) media. [Me4N]2CoCl4 had the highest catalytic activity among previously reported homogeneous cobalt-based catalyst systems; the turnover of methane to MeTFA reached 8.26 molester molmetal−1h−1 at 180 °C. Results suggest that the ionic form of the catalyst makes the Co species more soluble in the HTFA media; consequently, an active catalyst form, [CoTFAxCly]2−, can form very rapidly. Furthermore, chloride anions dissociated from CoCl42− appear to suppress oxidation of the solvent HTFA, thereby driving the reaction toward methane oxidation. The effects of reaction time, catalyst concentration, O2 and methane pressure, and reaction temperature on MeTFA production were also investigated

Suppression of photocorrosion in CdS/CdSe quantum dot-sensitized solar cells: Formation of a thin polymer layer on the photoelectrode surface

Suppression of the photocorrosion process is an important subject for quantum dot-sensitized solar cells (QSSCs). A method is reported to suppress the substitution and anodic oxidation reaction in the photocorrosion process of CdS/CdSe QSSCs through the addition of poly(ethyleneoxide) (PEO) to liquid polysulfide electrolyte. In the presence of PEO in the electrolyte, a thin PEO layer is formed on the quantum dot (QDs) film using coordination bonding between the ether group in the PEO and Cd metal ions in the QDs, acting as passivation layer to suppress substitution reaction and anodic oxidation. Due to the passivation effect of PEO thin film, the photostability of QSSCs is significantly improved compared to the liquid polysulfide electrolyte without PEO

Photovoltaic properties of high efficiency plastic dye-sensitized solar cells employing interparticle binding agent "nanoglue"

An interparticle binding agent, or nanoglue, was synthesized by a sol-gel process, which facilitated the preparation of well-interconnected TiO2 electrodes at low-temperatures for plastic dye-sensitized solar cells. The viscosity of the nanoglue-based pastes was seven times higher than that obtained in pastes without any nanoglue. The increased viscosity was sufficiently high enough for coating thick films to fabricate TiO2 electrodes. The structural and photovoltaic properties of the films were extensively investigated by varying the amounts of nanoglue. A reduced pore size and greatly enhanced surface area were observed in the nanoglue-based films. Improved interparticle connectivity, resulting in faster electron transport, was confirmed by photocurrent transient spectroscopy and electrochemical impedance measurements of the nanoglue-based films. The electron diffusion length and charge collection efficiency were also enhanced in these nanoglue-based films. A maximum conversion efficiency of 5.43% was achieved in films containing 20 wt% nanoglue fabricated on a plastic substrate under one-sun illumination, even without any additional treatment

Hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer

We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In. order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V-OC = 1.041 V, J(SC) = 2.97 mA/cm(2), FF = 32.3%) to 2.6%. (V-OC = 1.336 V, J(SC) = 4.65 mA/cm(2), FF = 41.98%) due to the eliminated interfacial series resistance