Monodisperse rutheniumcopper alloy nanoparticles decorated on reduced graphene oxide for dehydrogenation of DMAB

In this study, we report a superior dehydrogenation catalyst for dimethylamine borane, which exhibited one of the best catalytic activities. The newly formed catalyst system contains well dispersed ruthenium-copper nanomaterials on reduced graphene oxide (3.86 ± 0.47 nm), which was prepared by using the ultrasonic double reduction technique. The characterization of monodisperse ruthenium-copper alloy nanoparticles was performed using some advanced analytical methods such as TEM, HRTEM, XPS, Raman spectroscopic analysis. The experiments results revealed that the monodisperse ruthenium-copper alloy catalyst (RuCu@rGO) has one of the highest catalytic activity compared to previous studies, having a high turnover frequency value (256.70 h⁻¹). The detailed kinetic parameters such as activation energy, enthalpy, and entropy values were also calculated for the dehydrogenation of dimethylamine borane at room temperature. Also, the results showed that the monodisperse RuCu@rGO catalyst has high durability and reusability as retained its 81% initial catalytic activity even after 4th runs for the dehydrogenation of dimethylamine borane.     

Predicting the transient response of a serpentine flow-field PEMFC: I. Excess to normal fuel and air

A three-dimensional numerical simulation of the transient response of a polymer electrolyte membrane fuel cell (PEMFC) subjected to a variable load is presented. The model parameters are typical for a laboratory-scale cell with a serpentine flow path and a 10 cm² reactive area. The simulation uses a commercial computational fluid dynamics (CFD) solver modified to include the electrochemical behavior. The predictions are based on an isothermal set of equations and include transient responses of the cell in terms of local distributions of the current density and gas mole fractions. The predictions show transients in the current density that overshoot the final state value when the cell voltage is abruptly changed from 0.7 to 0.5 V for fixed excess initial stoichiometric flowrates. The fixed flowrates are excess because they correspond to stoichiometries of 2.6 and 4.4 at 0.7 V for the 0.35 A/cm² predicted initial current density. The percent overshoot decreases with the rate of voltage change and it is shown to change with anode gas flow rates. Also the magnitude of this overshoot and undershoot can be adjusted by changing the rate of voltage change and the operating conditions. The overshoot behavior for these excess stoichiometric flowrates is shown to depend on changes in the oxygen mole fraction distributions.     

Fabrication of a mesoporous Pt-carbon catalyst by the direct templating of mesoporous Pt-alumina for the methanol electro-oxidation

Mesoporous Pt-carbon catalysts were directly fabricated using mesoporous Pt-alumina as a template with a metal source and using poly(divinylbenzene) as a carbon precursor. Two types of mesoporous Pt-alumina templates were prepared by employing different calcination conditions (PtAl-A and PtAl-N were produced by the calcination in a stream of air and nitrogen, respectively). Both the mesoporous Pt-aluminas served as efficient templates for the fabrication of replicated Pt-carbon catalysts (PtC-A and PtC-N). The PtC catalysts showed high surface area with a narrow pore size distribution centered at ca. 4.0 nm. Together with pore-confined metal growth, the characteristic feature of the template, such as a strong interaction of metal species with the support was beneficial for the formation of highly dispersed Pt particles on the replicated mesoporous carbon catalysts. The mesoporous Pt-carbon (PtC) catalysts exhibited a higher metal dispersion than Pt catalyst impregnated on CMK-3 (Pt/CMK-3). Futhermore, the PtC-N catalyst exhibited a higher metal dispersion than the PtC-A catalyst. Methanol electro-oxidation experiments revealed the catalytic performance was closely related to the metal dispersion in the supported catalysts. The PtC-N catalyst with the highest metal dispersion exhibited the best catalytic performance in methanol electro-oxidation.     

Recent progress in stability of perovskite solar cells

Perovskite solar cells have attracted significant attention in just the past few years in solar cell research fields, where the power conversion efficiency was beyond 22.1%. Now, the most important challenge for perovskite solar cells in practical applications is the stability issue. In this mini-review, we will summarize the degradation mechanism of perovskite solar cells, including the perovskite material itself and also the interfaces. While we also provide our opinion on improving the stability of perovskite solar cells.     

Novel brominated compounds using in binary additives based organic solar cells to achieve high efficiency over 10.3%

Solvent additives have been considered as a simple and efficient method to increase the performance of bulk-heterojunction (BHJ) organic solar cells, in which, the morphology of the active layer could obtain further improvements by using the binary solvent additives. In this paper, a series of brominated compounds, 1-Bromo-4-butylbenzene (Brbb), 1-Bromo-4-n-hexylbenzene (Brbh) and 1-Bromo-4-n-octylbenzene (Brbo), have been respectively incorporated with 1, 8-diiodooctane (DIO) and regarded as binary solvent additives to fabricate highly efficient bulk heterojunction (BHJ) organic solar cells (OSCs). Compared with the BHJ film based on single additive, the binary additives contained BHJ film shows increased optical absorption, efficient charge transport and better active layer morphology, leading to an enhancement of short-circuit current (J_SC) together with a higher achieved fill factor (FF). The conventional BHJ device using PTB7: PC₇₁BM or PTB7-th: PC₇₁BM with the binary solvent additives exhibit enhanced PCE of 8.13% and 10.31%, respectively, which is much higher than that of single additive based devices (7.04% for PTB7 and 8.73% for PTB7-th). The optimized performance of BHJ devices indicates that these brominated compounds are promising additives to improve device efficiency.     

Effect of pre-calcination for modified CaO-based sorbents on multiple carbonation/calcination cycles

In the present work,the effect of pre-calcination on carbonation conversion and cyclic stability of modified CaO-based sorbent was investigated by thermogravimetric analyzer (TGA).The modified CaO-based sorbents with CaAc2 as precursor were respectively doped with different elements (Mg,Al,Ce,Zr and La).The specfic surface area,pore volume and pore size distribution were tested by N2 isothermal adsorption measurements.The phase compositions of sorbents were characterized by X-ray diffraction (XRD).The results showed that the cyclic stabilities of the sorbents were improved by pre-calcination.The pre-calcination was conducted at 900 ℃ for 5 h in air by the muffle furnace.With pre-calcination,the cyclic stabilities of sorbents could be as high as 96％after 22 cycles,such as CaO-Al,CaO-Ce and CaO-La.After contact with air,the carbonation conversions of spent sorbents with pre-calcination suddenly increased by about one-sixth due to the change of channel structure by hydration.Both the cyclic stability of sorbent and the durability of reactivation were related to the structural stability of sample,especially the stability of mesopores between 2 nm and 5.5 nm.The present work also provided an easy and low-cost method for reactivating the spent CaO-based sorbents.     

Absorption of CO2 and H2S in aqueous alkanolamine solutions using a fixed-bed reactor with cocurrent downflow operation in the pulsing flow regime: Absorption von CO2 und H2S in wäßrigen alkanolamin-lösungen in einem Festbettreaktor bei abwärtsfließendem Gleichstrombetrieb und pulsierendem Arbeiten

Absorption rates of H₂S and CO₂ in several aqueous alkanolamines in a cocurrent downflow fixed-bed reactor operated in the pulse flow regime have been measured in order to obtain information on the potential selectivity and on the mass transfer parameters. From these experiments it can be concluded that this type of reactor seems to be very suitable for the selective removal of H₂S from acid gases.It was not possible to derive correlations which are always valid for the calculation of the mass transfer parameters in laboratory-scale contactors. The results of the present study in combination with the data published in the literature were correlated with only one unknown parameter in which the influence of the physical properties of the system and the shape and material of the packing were combined. This parameter has to be determined empirically.Small amounts of acid gases in aqueous alkanolamine solutions have a pronounced effect on the properties, such as the foaming behaviour, of the liquid phase. The pressure drops measured in the cocurrently operated fixed-bed reactor were affected substantially by small amounts of acid gases present in the aqueous alkanolamine solutions and up to now this effect could not be explained satisfactorily.For the design of contactors for industrial purposes, detailed scale-up rules are required. In the present study this aspect is not investigated.     

A statistical examination of five models for preferred orientation in carbon materials

Five equations, viz. the Bacon, Bragg, Ergun, Lorentz and Ruland equations, for describing the preferred orientation of graphite-like materials were studied in combination with eleven sets of data using modern techniques for examining the behaviour of nonlinear regression models. The Bragg equation, which is based upon the normal (Gaussian) probability distribution, had the best statistical properties, in that the estimators of the parameters of the equation were close to being unbiased, normally distributed, minimum variance estimators. The other four equations were generally more erratic in their statistical behaviour, their estimators being highly biased and skewed in their distribution for at least one data set. The Bragg equation was generally the best fitting model, with the Lorentz and Ruland equations being generally the worst fitting models. The Bragg equation can therefore be recommended for general use to describe the preferred orientation of graphitic materials.