Earth-abundant materials with Fe-N-C centers have been identified as promising catalysts for oxygen reduction reaction (ORR), but these alternatives for Pt catalysts are usually the porphyrin-like ...FeN4 configuration. The density functional theory (DFT) calculations reveal that FeN2 outperforms FeN4 due to its lower interaction with *O2 and *OH intermediates and enhanced electron transport, however, achieving an optimum design of these earth-abundant materials with the enriched FeN2 catalytic centers is still a great challenge. Here, we report an intriguing template casting strategy to introduce a mass of atomically dispersed FeN2 moieties onto the surface of N-doped ordered mesoporous carbon for boosting ORR electrocatalysis. One of unique parts herein is to pre anchor Fe precursor on the surface of template (SBA-15) during catalyst synthesis, preventing Fe from penetrating into the carbon skeleton and facilitating the removal of excessive Fe-based particles during silica elimination by HF etching, resulting in a desirable model structure comprising only highly active atomically dispersed FeN2 sites, as confirmed by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), extended X-ray absorption fine structure (EXAFS) and Mößbauer spectroscopy analysis. The well-defined structure prompts us to understand the nature of the catalytic active sites, and to demonstrate that the catalyst activity is linearly proportional to the concentration of FeN2 sites. The obtained atomic electrocatalyst exhibits superior electrocatalytic performance for ORR with a more positive half-wave potential than that of Pt/C catalyst. We further establish a kinetic model to predict the ORR activity of these single-atom dispersed catalysts. The present work elaborates on a profound understanding for designing low-cost, highly efficient FeN2-based electrocatalyst for boosting ORR.
A new class of atomically FeN2 moieties dispersed on the surface of N-doped mesoporous carbon were prepared via template casting procedure as highly efficient electrocatalysts for boosting oxygen reduction. The regulation of mononuclear FeN2 moieties (an active site toward four-electron process) can linearly increase the ORR activity. Display omitted
•A template casting method to introduce ORR catalytic sites FeN2 atomically dispersed on the surface of ordered mesoporous carbon support.•A higher ORR activity with enhanced stability is achieved, and a kinetic model is established to predict the ORR activity.•Density functional theory calculations reveal higher ORR activity and enhanced electron transport of FeN2 than FeN4 moieties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The high open‐circuit voltage (Voc) loss arising from insufficient surface passivation is the main factor that limits the efficiency of current lead sulfide colloidal quantum dots (PbS CQDs) solar ...cell. Here, synergistic passivation is performed in the direct synthesis of conductive PbS CQD inks by introducing multifunctional ligands to well coordinate the complicated CQDs surface with the thermodynamically optimal configuration. The improved passivation effect is intactly delivered to the final photovoltaic device, leading to an order lower surface trap density and beneficial doping behavior compared to the control sample. The obtained CQD inks show the highest photoluminescence quantum yield (PLQY) of 24% for all photovoltaic PbS CQD inks, which is more than twice the reported average PLQY value of ≈10%. As a result, a high Voc of 0.71 V and power conversion efficiency (PCE) of 13.3% is achieved, which results in the lowest Voc loss (0.35 eV) for the reported PbS CQD solar cells with PCE >10%, comparable to that of perovskite solar cells. This work provides valuable insights into the future CQDs passivation strategies and also demonstrates the great potential for the direct‐synthesis protocol of PbS CQDs.
Synergistic passivation is performed in the direct synthesis of conductive lead sulfide colloidal quantum dot (PbS CQD) inks. The improved passivation effect is intactly delivered to the final photovoltaic device, leading a high open‐circuit voltage (Voc)) of 0.71 V and efficiency of 13.3%, which results in the lowest Voc loss (0.35 eV) for the reported PbS CQD solar cells.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Trap states in colloidal quantum dot (QD) solids significantly affect the performance of QD solar cells, because they limit the open‐circuit voltage and short circuit current. The {100} facets of PbS ...QDs are important origins of trap states due to their weak or missing passivation. However, previous investigations focused on synthesis, ligand exchange, or passivation approaches and ignored the control of {100} facets for a given dot size. Herein, trap states are suppressed from the source via facet control of PbS QDs. The {100} facets of ≈3 nm PbS QDs are minimized by tuning the balance between the growth kinetics and thermodynamics in the synthesis. The PbS QDs synthesized at a relatively low temperature with a high oversaturation follow a kinetics‐dominated growth, producing nearly octahedral nanoparticles terminated mostly by {111} facets. In contrast, the PbS QDs synthesized at a relatively high temperature follow a thermodynamics‐dominated growth. Thus, a spherical shape is preferred, producing truncated octahedral nanoparticles with more {100} facets. Compared to PbS QDs from thermodynamics‐dominated growth, the PbS QDs with less {100} facets show fewer trap states in the QD solids, leading to a better photovoltaic device performance with a power conversion efficiency of 11.5%.
The {100} facets of ≈3 nm PbS quantum dots (QDs) are minimized by tuning the balance between the growth kinetics and thermodynamics in the synthesis. Compared to PbS QDs from thermodynamics‐dominated growth, the PbS QDs with less {100} facets show fewer trap states in the QD solids, leading to a better photovoltaic device performance with a power conversion efficiency of 11.5%.
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► CHF3 can be incinerated with LNG at 1473K. ► CHF3 can be decomposed to CO2 via plasma or hydrolysis. ► CHF3 can be converted to TFE via pyrolysis. ► CHF3 can be the source material ...for the production of VDF and CF3I.
CHF3 is a potent and synthetic greenhouse gas with global warming potential of 11,700 times higher than that of CO2. It is mainly produced as a by-product during the manufacture of HCFC-22. Many methods have been proposed for the treatment of CHF3, including thermal oxidation (incineration), catalytic hydrolysis, plasma destruction and conversion to environmentally benign compounds. This review reports the recent research advances in the treatment of CHF3 waste. It has been found that pyrolysis process, especially in the presence of a catalyst, and reaction of CHF3 with I2 or CH4, has great potential for the conversion of CHF3 to valuable and environmentally benign chemicals. In this regard, the review is largely focused on the conversion of CHF3 to C2F4, CF3I and VDF, as well as the chemistry involved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The AlF
3
catalysts with controlled morphology (cubic, hexahedron and octahedron) were synthesized via hydrothermal method using different solvents. The dehydrofluorination of ...1,1,1,3,3-pentafluoropropane (HFC-245fa) was used as the model reaction to evaluate the catalytic performance of the AlF
3
catalysts with different morphology. Results showed that surface area, crystal structure, surface acidic properties together with the chemical composition of the AlF
3
catalyst were substantially influenced by the different morphology. XRD results showed that κ-AlF
3
crystalline structure was formed when using ethanol as solvent while β-AlF
3
crystalline structure was formed when using water as solvent. Among the three prepared AlF
3
samples, the AlF
3
-C catalyst with cubic shape demonstrated not only largest surface area but also most amount of medium-strength surface acid sites, resulting in enhanced reaction activity towards the dehydrofluorination reaction. The characteristic high Miller index crystal planes of (402) and (321) exposed on the cubic shaped AlF
3
-C catalyst is believed to be the main reason accounting for the high catalytic performance as there are equal amount of Al and F atoms exposed. Moreover, a reaction mechanism describing dedehydrofluorination of HFC-245fa on AlF
3
catalyst with equal amount of Al and F atoms exposed on certain crystal planes was proposed.
Graphic Abstract
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Cr₂O₃ nanoparticles were prepared by solution combustion synthesis (SCS) with chromium nitrate as the precursor and glycine as the fuel. Commercial Cr₂O₃ and Cr₂O₃ prepared by a precipitation method ...were also included for comparison. The morphology, structure, acidity and particle size of fresh and spent Cr₂O₃ catalysts were investigated by techniques such as XRD, SEM, TEM, BET and NH₃-TPD. In addition, catalytic performance was evaluated for the dehydrofluorination of 1,1,1,3,3-pentafluoropropane (CF₃CH₂CHF₂, HFC-245fa) to 1,3,3,3-tetra-fluoropropene (CF₃CH=CHF, HFO-1234ze). The catalytic reaction rate of Cr₂O₃ prepared by SCS method is as high as 6 mmol/h/g, which is about 1.5 times and 2 times higher than that of precipitated Cr₂O₃ and commercial Cr₂O₃, respectively. The selectivity to HFO-1234ze for all the catalysts maintains at about 80%. Compared with commercial and precipitated Cr₂O₃, Cr₂O₃-SCS prepared by SCS possesses higher specific surface area and acid amount. Furthermore, significant change in the crystal size of Cr₂O₃ prepared by SCS after reaction was not detected, indicating high resistance to sintering.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Autonomous underwater vehicles (AUVs) are now widely used in both civilian and military applications; however, wireless charging underwater often faces difficulties such as disturbances from ocean ...currents and errors in device positioning, making proper alignment of the charging devices challenging. Misalignment between the primary and secondary coils can significantly impact the efficiency and power of the wireless charging system energy transfer. To address the issue of misalignment in wireless charging systems, this paper proposes a multiple transfer coil wireless power transfer (MTCWPT) system based on backpropagation (BP) neural network control combined with nonsingular terminal sliding mode control (NTSMC) to enhance further the system robustness and efficiency. To achieve WPT in the ocean, a coil shielding case structure was equipped. In displacement experiments, the proposed multi-transmitting coil system could achieve stable power transfer of 40 W and efficiency of over 78.5% within a displacement range of 8 cm. The system robustness was also validated. This paper presents a new AUV energy supply solution based on MTCWPT. The proposed MTCWPT system can significantly improve the navigation performance of AUVs.
Carbon nanotubes (CNTs) with abundant surface defects are prepared by a liquid oxidation and thermal annealing method. The defective CNTs-D supported Ba–Ru/CNTs-D catalysts exhibit superior catalytic ...performance in ammonia synthesis with a TOF be increased up to 0.30 s−1, which is 2.5 times of oxidized CNTs-O supported Ba–Ru/CNTs-O catalysts and 5 times of the Ba–Ru/CNTs. The characterizations by CO chemisorption, transmission electron microscope, Raman, and X-ray photoelectron spectroscopy revealed that the uniformly well dispersed Ru NPs can be stabilized on the defective sites of CNTs-D. The great improvement of the catalytic performance and stability of the Ba–Ru/CNTs-D is contributed to the strong interaction between Ru NPs and surface defect of the CNTs.
The surface defects of CNTs-D can stabilize Ru NPs and enhance the interaction between Ru NPs and carbon, thus effectively improve the performance of the Ba–Ru/CNTs-D in ammonia synthesis. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High resolution micro-computed tomography images for multiphase flow provide us an effective tool to understand the mechanism of fluid flow in porous media, which is not only fundamental to the ...understanding of macroscopic measurements but also for providing benchmark datasets to validate pore-scale modeling. In this study, we start from two datasets of pore scale imaging of two-phase flow obtained experimentally under in situ imaging conditions at different water fractional flows under water-wet and mixed-wet conditions. Then, fractal dimension, lacunarity and succolarity are used to quantify the complexity, clustering and flow capacity of water and oil phases. The results show that with the wettability of rock surface altered from water-wet to mixed-wet, the fractal dimension for the water phase increases while for the oil phase, it decreases obviously at low water saturation. Lacunarity largely depends on the degree of wettability alteration. The more uniform wetting surfaces are distributed, the more homogeneous the fluid configuration is, which indicates smaller values for lacunarity. Moreover, succolarity is shown to well characterize the wettability effect on flow capacity. The succolarity of the oil phase in the water-wet case is larger than that in the mixed-wet case while for the water phase, the succolarity value in the water-wet is small compared with that in the mixed-wet, which show a similar trend with relative permeability curves for water-wet and mixed-wet. Our study provides a perspective into the influence that phase geometry has on relative permeability under controlled wettability and the resulting phase fractal changes under different saturations that occur during multiphase flow, which allows a means to understand phase geometric changes that occur during fluid flow.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A novel synthesis of ultrahigh molecular weight poly(methyl methacrylate) (PMMA) using organosulfur compounds combined with a catalytical amount of transition metal carboxylates as an initiator has ...been developed. The combination of 1-octanethiol with palladium trifluoroacetate (Pd(CF
COO)
) was found to be a very efficient initiator for the polymerization of methyl methacrylate (MMA). An ultrahigh molecular weight PMMA with a number-average molecular weight of 1.68 × 10
Da and a weight-average molecular weight of 5.38 × 10
Da has been synthesized at the optimal formulation of MMA:Pd(CF
COO)
:1-octanethiol = 94,300:8:23 at 70 °C. A kinetic study showed that the reaction orders with respect to Pd(CF
COO)
, 1-octanethiol, and MMA are 0.64, 1.26, and 1.46, respectively. A variety of techniques such as proton nuclear magnetic resonance spectroscopy (
H NMR), electrospray ionization mass spectroscopy (ESI-MS), size exclusion chromatography (SEC), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron paramagnetic resonance spectroscopy (EPR) were employed to characterize the produced PMMA and palladium nanoparticles (Pd NPs). The results revealed that Pd(CF
COO)
was firstly reduced by the excess of 1-octanethiol to form Pd NPs at the early stage of the polymerization, followed by the adsorption of 1-octanethiol on the surface of nanoparticles and subsequent generation of corresponding thiyl radicals to initiate the polymerization of MMA.
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