Surface passivation technology provides noble‐metal materials with limited chemical stability, especially under highly acidic condition. To design effective strategy to enhance stability of ...noble‐metal particles, an understanding of their surface anticorrosion mechanism at the atomic level is desirable by using two‐dimensional (2D) noble‐metal coordination polymer (CP) as an ideal model for their interfacial region. With the protection of 2‐thiobenzimidazole (TBI), we isolated two Ag‐based 2D CPs, {Ag14(TBI)12X2}n (S−X, where S denotes sheet and X=Cl or Br). These compounds exhibited excellent chemical stability upon immersion in various common solvents, boiling water, boiling ethanol, 10 % hydrogen peroxide, concentrated acid (12 M HCl), and concentrated alkali (19 M NaOH). Systematic characterization and DFT analyses demonstrate that the superior stability of S−X was attributed to the hydrophobic organic shell and dynamic proton buffer layer acting as a double protective “shield”.
Acid resistance (12 M HCl) was made possible for two isomorphic two‐dimensional silver‐based coordination polymers. Protection is provided by a hydrophobic organic shell and a dynamic proton buffer layer via a thiolate‐thione tautomerism of 2‐thiobenzimidazole ligands. Thus, these ligands are promising surface inhibitors, acting as a dual protective shield against metal corrosion.
Summary
Mode switching between fuel cell and water electrolyzer of a unitized regenerative fuel cell alters two‐phase flow dynamics in the channels. To fully understand the mode switching, the ...observation of two‐phase flow is necessary. In this work, experiments are conducted to investigate the two‐phase flow in the flow field of a unitized regenerative fuel cell during mode switching. A transparent window is assembled at the oxygen side to allow a direct view of the serpentine flow field. The two‐phase flow are captured by a high‐speed camera. Water has a significant effect on the mode switching. The switching from water electrolyzer to fuel cell is difficult because of the flooding problem. High temperature causes insufficient water in water electrolyzer mode without water supply and membrane dehydration in fuel cell mode. The voltage in fuel cell mode decreases more rapidly with fuel cell current density during mode switching.
Experiments on mode switching of a unitized regenerative fuel cell are conducted, and two‐phase flow in the flow field during mode switching is observed. Water has a significant effect on mode switching from water electrolyzer to fuel cell. Moderate temperature and low fuel cell current density is better for the mode switching from water electrolyzer to fuel cell.
This work provided the first example of selective hydrodeoxygenation of 5‐hydroxymethylfurfural (HMF) to 2,5‐dimethylfuran (DMF) over heterogeneous Fe catalysts. A catalyst prepared by the pyrolysis ...of an Fe‐phenanthroline complex on activated carbon at 800 °C was demonstrated to be the most active heterogeneous Fe catalyst. Under the optimal reaction conditions, complete conversion of HMF was achieved with 86.2 % selectivity to DMF. The reaction pathway was investigated thoroughly, and the hydrogenation of the C=O bond in HMF was demonstrated to be the rate‐determining step during the hydrodeoxygenation, which could be accelerated greatly by using alcohol solvents as additional H‐donors. The excellent stability of the Fe catalyst, which was probably a result of the well‐preserved active species and the pore structure of the Fe catalyst in the presence of H2, was demonstrated in batch and continuous flow fixed‐bed reactors.
Selective and stable Fe: Selective catalytic hydrodeoxygenation of 5‐hydroxymethylfurfural to 2,5‐dimethylfuran over heterogeneous Fe catalysts is demonstrated in batch and continuous flow fixed‐bed reactors. The Fe catalyst exhibited excellent stability, which is probably a result of the well‐preserved active species and the pore structure of the Fe catalyst in the presence of H2.
The interface microenvironment of doped quantum dots (QDs) is crucial in optimizing the properties associated with the photogenerated excitons. However, the imprecision of QDs' surface structures and ...compositions impedes a thorough understanding of the modulation mechanism caused by the complex interface microenvironment, particularly distinguishing the contribution of surface dopants from inner ones. Herein, we investigated interface-mediated emission using a unique model of an atomically precise chalcogenide semiconductor nanocluster containing uniform near-surface Mn
2+
dopants. Significantly, we discovered that Mn
2+
ions can directly transfer charges with hydrogen-bonding-bound electron-rich alkylamines with matched molecular configurations and electronic structures at the interface. This work provides a new pathway, the use of atomically precise nanoclusters, for analyzing and enhancing the interface-dependent properties of various doped QDs, including chalcogenides and perovskites.
Temperature distribution on the surface of a membrane electrode assembly (MEA) significantly influences the performance, lifetime, and reliability of proton exchange membrane fuel cells (PEMFCs). ...Entire temperature fields on the surface of an MEA anode side under an interdigitated flow field are experimentally measured at non-humidification conditions with a self-designed PEMFC and infrared imaging technology. The highest temperature on the surface of the MEA anode side appears in the bottom bordered two side channels, and the lowest temperature exists in the area closed to the inlet of the middle channel. The hot region on the surface of the MEA anode side is easy to locate in the infrared temperature image. The reason for the temperature distribution under the interdigitated flow field is analyzed. The temperature of the MEA, the non-uniformity of temperature distribution on the surface of the MEA anode side, and the fuel cell temperature increase with the loaded current density.
Herein we report a covalent cage TPE-Zn4 based on a tetraphenylethylene molecule via subcomponent self-assembly, which is templated by zinc ions. TPE-Zn4 features a quadrangular prismatic cage ...structure, which is characterized by NMR, mass spectrum, and single-crystal X-ray diffractions. TPE-Zn4 emitted orange fluorescence (λem = 620 nm) in DMSO solution under the irradiation of UV light (λex = 395 nm) and can be applied as a fluorescence sensor for selectively detecting Pd2+. The fluorescence of TPE-Zn4 was quenched by Pd2+ in DMSO solution, and a very low detection limit of 62.3 nM was achieved. Mechanism studies reveal that the Pd2+ can replace the Zn2+, and the heavy atom effect and chelation-enhanced quenching effect between the Pd2+ and the cage probably cause the fluorescence quenching.
A quadrangular prismatic covalent cage templated by zinc ions was synthesized, which can be used as a selective fluorescence sensor for palladium ions with a detection limit as low as 62.3 nmol/L. Display omitted
The evolution of the microstructure, texture, and microhardness of 5754 aluminum alloy subjected to high-temperature plastic deformation under different deformation conditions was studied on the ...basis of thermal simulations and electron-backscattered diffraction and Vickers microhardness experiments. The results of a misorientation angle study show that an increase in the deformation temperature and strain rate promoted the transformation of low-angle grain boundaries to high-angle grain boundaries, which contributed to dynamic recrys-tallization. The effect of the deformation parameters on the texture and its evolution during the recrystallization process was explored on the basis of the orientation distribution function. The results demonstrate that the deformed samples mainly exhibited the features of type A, B, and B textures. The formation and growth of the recrystallized grains clearly affected the texture evolution. The microhardness results show that the variation of the microhardness was closely related to the temperature, strain rate, and dynamic recrystallization.
Acoustic change complex (ACC) is a cortical auditory-evoked potential induced by a change of continuous sound stimulation. This study aimed to explore: (1) whether the change of horizontal sound ...location can elicit ACC; (2) the relationship between the change of sound location and the amplitude or latency of ACC; (3) the relationship between the behavioral measure of localization, minimum audible angle (MAA), and ACC. A total of 36 normal-hearing adults participated in this study. A 180° horizontal arc-shaped bracket with a 1.2 m radius was set in a sound field where participants sat at the center. MAA was measured in a two-alternative forced-choice setting. The objective electroencephalography recording of ACC was conducted with the location changed at four sets of positions, ±45°, ±15°, ±5°, and ±2°. The test stimulus was a 125–6,000 Hz broadband noise of 1 s at 60 ± 2 dB SPL with a 2 s interval. The N1′–P2′ amplitudes, N1′ latencies, and P2′ latencies of ACC under four positions were evaluated. The influence of electrode sites and the direction of sound position change on ACC waveform was analyzed with analysis of variance. Results suggested that (1) ACC can be elicited successfully by changing the horizontal sound location position. The elicitation rate of ACC increased with the increase of location change. (2) N1′–P2′ amplitude increased and N1′ and P2′ latencies decreased as the change of sound location increased. The effects of test angles on N1′–P2′ amplitude
F
(1.91,238.1) = 97.172,
p
< 0.001, N1′ latency
F
(1.78,221.90) = 96.96,
p
< 0.001, and P2′ latency
F
(1.87,233.11) = 79.97,
p
< 0.001 showed a statistical significance. (3) The direction of sound location change had no significant effect on any of the ACC peak amplitudes or latencies. (4) Sound location discrimination threshold by the ACC test (97.0% elicitation rate at ±5°) was higher than MAA threshold (2.08 ± 0.5°). The current study results show that though the ACC thresholds are higher than the behavioral thresholds on MAA task, ACC can be used as an objective method to evaluate sound localization ability. This article discusses the implications of this research for clinical practice and evaluation of localization skills, especially for children.
In this study, a two-dimensional full cell analytical model of a proton exchange membrane fuel cell is developed. The analytical model describes electrochemical reactions on the anode and cathode ...catalyst layer, reactants diffusion in the gas diffusion layer, and gases flow in the gas channel, etc. The analytical solution is derived according to the basic physical equations. The performance predicted by the model is in good agreement with the experimental data. The results show that the polarization mainly occurs in the cathode side of the proton exchange membrane fuel cell. The anodic overpotential cannot be neglected. The hydrogen and oxygen concentrations decrease along the channel flow direction. The hydrogen and oxygen concentrations in the catalyst layer decrease with the current density. As predicted by the model, concentration polarization mainly occurs in the cathode side.
•A 2D full cell analytical model of a proton exchange membrane fuel cell is developed.•The analytical solution is deduced according to the basic equations.•The anode overpotential is not so small that it cannot be neglected.•Species concentration distributions in the fuel cell is obtained and analyzed.
As Fe is more abundant and economic than Cu and Ni, it is probably a more attractive non‐noble alternative to precious metals in biomass conversions, for which usually require promising catalysts for ...large‐scale production. In this work, economic and environmental benign heterogeneous iron catalysts prepared by simultaneous pyrolysis of graphitic carbon nitride and iron precursors on activated carbon, were demonstrated to be active for the hydrodeoxygenation of biomass‐derived 5‐hydroxymethylfurfural to 2,5‐dimethylfuran. The effect of pyrolysis temperature, support, iron content, the type of g‐C3N4 and iron precursor, and N/Fe ratio were explored thoroughly, and reaction parameters such reaction temperature and H2 pressure were also investigated. The highest DMF yield of 85.7 % was obtained at 240 °C for 3 h, which is comparable to that obtained over iron catalysts prepared from precious iron complexes. The investigation of reaction pathway showed that 5‐methylfurfural was the possible intermediate. The stability of as‐prepared Fe‐N‐C catalyst could be improved after treatment with aqueous HCl solution.
Economic and environmental benign Fe‐N‐C catalysts, prepared by simultaneous pyrolysis of graphitic carbon nitride and iron precursors on activated carbon, were demonstrated to be active towards selective hydrodeoxygenation of biomass‐derived 5‐hydroxymethylfurfural to 2,5‐dimethylfuran. The highest DMF yield of 85.7 % was achieved at 240 °C for 3 h. The special Fe‐N structure formed through Fe‐g‐C3N4 intermediates provides remarkable active sites for the hydrodeoxygenation reaction.
