ZnO@Ni foam photoelectrode modified with heteroatom doped graphitic carbon for enhanced photoelectrochemical water splitting under solar light

In this study, an electrocatalyticaly inactive ZnO@Ni foam photoelectrode was modified with heteroatom doped graphitic carbon to achieve enhanced photoelectrochemical (PEC) water splitting performance. The O, S and N doped graphitic carbon was simultaneously deposited with ZnO on Ni foam substrate under hydrothermal deposition. One dimensional ZnO nanorods with flower-like graphitic carbon on their surface were obtained on the Ni foam substrate, which was directly used as photoelectrode to derive photoelectrochemical water splitting under solar light irradiation. The pristine ZnO@NF exhibit unattractive PEC performance evidenced by the high overpotential required for the oxygen evolution reaction (OER) couple of water splitting reaction (398 mV vs. RHE). The carbon modified ZnO–C@NF photoelectrode lowers the overpotential required to 317 mV. This enhancement was attributed to the carbon modification which serves as both active site and photoelectron reservoir; facilitating the sluggish kinetics of OER couple reaction and promoting separation of photogenerated charge carriers.     

Preparation and characterization of poly(lactic acid)/recycled polypropylene blends with and without the coupling agent,n-(6-aminohexyl)aminomethyltriethoxysilane

Blends of polylactide (PLA) and recycled polypropylene (rPP) were prepared by melt-processing using a corotating twin-screw extruder and subsequent pelletizing of the extrudates for injection molding. The PLA/rPP blends were characterized by Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), rheometer (MCR-102), scanning electron microscopy(SEM), tensile tests, and impact measurements. The results indicate that the PLA/rPP blend is immiscible and has a two-phase structure. TGA revealed enhancement of the thermal stability of the blends upon addition of rPP. The storage modulus, loss modulus, and complex viscosity of the blends increased with rPP concentration. Mechanical studies showed that introduction of rPP results in a decrease in tensile strength and modulus and enhancement of the impact strength of PLA in the blends. The effects of a silane coupling agent on the morphology and on the tensile and impact properties of the rPP blends of silane-modified PLA were also examined. SEM studies suggest that silane is an effective interfacial modifier. Thus, better interfacial adhesion was observed with silane-modified blends as compared with unmodified blends. Silane also improved the mechanical properties of the modified blends. The blends reached maximum tensile strength at 1.5 wt.% silane (relative to modified PLA content), and impact strength increased with increasing silane concentration. These results confirm the enhancing effect of silane on modified PLA/rPP blends.     

Improvements of fill factor in solar cells based on blends of polyfluorene copolymers as electron donors

The photovoltaic characteristics of solar cells based on alternating polyfluorene copolymers, poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-3), and poly(2,7-(9,9-didodecyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-4), blended with an electron acceptor fullerene molecule [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), have been investigated and compared. The two copolymers have the same aromatic backbone structure but differ by the length of their alkyl side chain. The overall photovoltaic performance of the solar cells is comparable irrespective of the copolymer used in the active layer. However, the fill factor (FF) values of the devices are strongly affected by the copolymer type. Higher FF values were realized in solar cells with APFO-4 (with longer alkyl side chain)/PCBM bulk heterojunction active layer. On the other hand, devices with blends of APFO-3/APFO-4/PCBM were found to render fill factor values that are intermediate between the values obtained in solar cells with APFO-3/PCBM and APFO-4/PCBM active film. Upon using APFO-3/APFO-4 blends as electron donors, the cell efficiency can be enhanced by about 16% as compared to cells with either APFO-3 or APFO-4. The transport of holes in each polymer obeys the model of hopping transport in disordered media. However, the degree of energetic barrier against hopping was found to be larger in APFO-3. The tuning of the photovoltaic parameters will be discussed based on studies of hole transport in the pure polymer films, and morphology of blend layers. The effect of bipolar transport in PCBM will also be discussed.     

A New Donor–Acceptor–Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility

A new alternating polyfluorene copolymer poly[2,7‐(9,9‐dioctylfluoren)‐alt‐5,5‐(5′,8′‐di‐2‐thienyl‐(2′,3′‐bis‐(3′′‐octyloxyphenyl)‐quinoxaline))] (APFO‐15), which has electron donor–acceptor–donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photoluminescence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5 % have been realized from blends of APFO‐15 and an electron acceptor molecule, a methanofullerene [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). It has also been observed that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto‐electronic devices.     

New low band gap alternating polyfluorene copolymer-based photovoltaic cells

New low band gap alternating polyfluorene copolymers were synthesized for use in plastic solar cells and their optical, electrochemical, and photovoltaic characteristics were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor–acceptor–donor (DAD) sequence to achieve the lowering of band gaps. The HOMO–LUMO values were estimated from electrochemical studies. By varying the donor and acceptor strength and position of the solubilizing substituents, similar HOMO values were obtained. These values were also found to correlate well with the open circuit voltage (V_OC) values determined from photovoltaic data of the polymers blended with the acceptor PCBM. Despite similar HOMO values, the absorption spectra of the polymers differ significantly. This prompted the preparation of photovoltaic devices consisting of blends of two polymers with complementary absorptions in combination with PCBM to harvest more photons in the polymer solar cells.     

Electrothermal investigation of the switching effect in p-Type TllnSe2, TllnTe2, and TIGaTe2 chain chalcogenide semiconductors

Large p-type TlInSe₂, TlInTe₂, and TlGaTe₂ single crystals have been grown by the Bridgman-Stockbarger method, starting from stoichiometric melts. The first observations of the switching process in p-type TlGaTe₂ single crystal are reported. Current-voltage (I-V) characteristics of symmetrical In/p-TlInSe₂/In, In/p-TlInTe₂/In, and In/p-TlGaTe₂/In structures exhibit two distinct regions: an ohmic region at low current densities and nonlinear regions (S-shape) having negative differential resistance (NDR) at moderate and higher current densities. An electrothermal model was used to explain the nonlinear behavior. The nonlinear behavior of the I–V curves was studied at different ambient temperatures in the 100–340K region; the sample temperature and the threshold voltage of the NDR region were examined as a function of the current density and the ambient temperature, respectively. The electrothermal model is a satisfactory explanation.     

Finite element analysis of couple stress micropolar nanofluid flow by non‐Fourier's law heat flux model past stretching surface

Numerical analysis has been done to investigate magnetohydrodynamics nonlinear convective flow of couple stress micropolar nanofluid with Catteneo‐Christov heat flux model past stretching surface with the effects of heat generation/absorption term, chemical reaction rate, first‐order slip, and convective boundary conditions. The coupled highly nonlinear differential equation governing the steady incompressible laminar flow has been solved by a powerful numerical technique called finite element method. The impacts of diverse parameters on linear velocity, angular velocity (microrotation), temperature, concentration profile, local skin friction coefficient, local wall couple stress, local Nusselt number, and Sherwood number are presented in graphical and tabular form. The result pointed out that the enhancement in material parameter β increases the velocity of the fluid while the couple stress parameter K has quite opposite effect. Heat and mass transfer rate of the fluid are enhanced by increasing material parameter while couple stress parameter shows the opposite influence. Moreover, heat and mass transfer rate are higher with the Catteneo‐Christov heat flux model than Fourier's law of heat conduction. The accuracy of the present method has been confirmed by comparing with previously published works.     

Revealing the Impact of F4‐TCNQ as Additive on Morphology and Performance of High‐Efficiency Nonfullerene Organic Solar Cells

Fluorinated molecule 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ) and its derivatives have been used in polymer:fullerene solar cells primarily as a dopant to optimize the electrical properties and device performance. However, the underlying mechanism and generality of how F4‐TCNQ affects device operation and possibly the morphology is poorly understood, particularly for emerging nonfullerene organic solar cells. In this work, the influence of F4‐TCNQ on the blend film morphology and photovoltaic performance of nonfullerene solar cells processed by a single halogen‐free solvent is systematically investigated using a set of morphological and electrical characterizations. In solar cells with a high‐performance polymer:small molecule blend FTAZ:IT‐M, F4‐TCNQ has a negligibly small effect on the molecular packing and surface characteristics, while it clearly affects the electronic properties and mean‐square composition variation of the bulk. In comparison to the control devices with an average power conversion efficiency (PCE) of 11.8%, inclusion of a trace amount of F4‐TCNQ in the active layer has improved device fill factor and current density, which has resulted into a PCE of 12.4%. Further increase in F4‐TCNQ content degrades device performance. This investigation aims at delineating the precise role of F4‐TCNQ in nonfullerene bulk heterojunction films, and thereby establishing a facile approach to fabricate highly optimized nonfullerene solar cells.     

Chemical composition of naturally fermented buttermilk

Naturally fermented buttermilk, prepared from soured cream or milk, was collected during two seasons from sixteen farms in northern Ethiopia, to study chemical composition and flavour compounds. Protein, fat, organic acids, carbohydrates and volatile compounds were quantified using Kjeldahl, Gerber, high‐pressure liquid chromatography (HPLC) and headspace GC methods, respectively. Widely differing concentrations of organic acids and volatile compounds among samples indicated variable fermentation in the products. This indicates the need for the introduction of the standardisation of the process to supply the market with homogenous buttermilk products.