Blocking the defect sites on ultrathin Pt nanowires with Rh atoms to optimize the reaction path toward alcohol fuel oxidation

Anodic electrocatalyst plays the core role in direct alcohol fuel cells (DAFCs), while traditional Pt-catalysts suffer from limited catalytic activity, high over potential and severe CO poisoning. Herein, by selectively depositing Rh atoms on the defective-sites of Pt nanowires (NWs), we developed a new Pt@Rh NW electrocatalyst that exhibited enhanced electrocatalytic performance for both methanol oxidation (MOR) and ethanol oxidation (EOR). Both cyclic voltammetry (CV) and in-situ infrared spectroscopy revealed that the presence of Rh atoms suppressed the generation of poisonous intermediates and completely oxidized alcohols molecule into CO₂. Atomic resolusion spherical aberration corrected high-angle annular dark field scanning transmission electron microscopy (CS-HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mapping analysis revealed that Rh atoms were primarily deposited on the defective sites of Pt NWs. Meanwhile, the presence of Rh atoms also modified the electronic state of Pt atoms and therefore lowered the onset potential for alcohols oxidation potential. This work gives the first clear clue on the role of the defective sites of Pt nanocatalyst poisoning, and propose that selectively blocking these sites with trace amount of Rh is an effective strategy in designing advantageous electrocatalysts.     

Crystallization of Poly(ethylene adipate) within γ-Phase Poly(vinylidene fluoride) Matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy(OM), infrared spectroscopy(IR) and scanning electron microscopy(SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.     

Modification and application of Fe3O4 nanozymes in analytical chemistry: A review

In recent years, Fe₃O₄ nanomaterials have received much attention in analytical chemistry due to their excellent magnetic and peroxidase-like activity. As the catalytic characteristics of Fe₃O₄ nanomaterials is similar to those of horseradish peroxidase (HRP), Fe₃O₄ nanomaterials are also used as peroxidase mimics and have achieved a certain development in many fields based on latest research results. To improve the stability and catalytic ability of simple Fe₃O₄ nanomaterials, various modification strategies of Fe₃O₄ nanomaterials have been developed. The recent advances of these strategies have been presented and discussed. In addition, this paper introduces the application of Fe₃O₄ nanozymes in the detection of food and industrial pollutants, as well as in the field of biosafety.     

Transition metal decorated bismuthene for ammonia synthesis: A density functional theory study

The electrochemical nitrogen reduction reaction (NRR) for the ammonia production under ambient conditions is regarded as a sustainable alternative to the industrial Haber–Bosch process. However, the electrocatalytic systems that efficiently catalyze nitrogen reduction remain elusive. In the work, the nitrogen reduction activity of the transition metal decorated bismuthene TM@Bis is fully investigated by means of density functional theory calculations. Our results demonstrate that W@Bis delivers the best efficiency, wherein the potential-determining step is located at the last protonation step of *NH₂ + H⁺ + e^– → *NH₃ via the distal mechanism with the limiting potential U_L of 0.26 V. Furthermore, the dopants of Re and Os are also promising candidates for experimental synthesis due to its good selectivity, in despite of the slightly higher U_L of NRR with the value of 0.55 V. However, the candidates of Ti, V, Nb and Mo delivered the relative lower U_L of 0.35, 0.37, 0.41 and 0.43 V might be suffered from the side hydrogen evolution reaction. More interestingly, a volcano curve is established between U_L and valence electrons of metal elements wherein W with 4 electrons in d band located at the summit. Such phenomenon originates from the underlying acceptance-back donation mechanism. Therefore, our work provides a fundament understanding for the material design for nitrogen reduction electrocatalysis.     

The introduction of cobalt element into nickel-organic framework for enhanced supercapacitive performance

Metal-organic frameworks (MOFs) as promising electrodes for supercapacitors are attracting increasing research interest. Herein, we report an effective strategy to improve the electrochemical performance of Ni-MOF for supercapacitor by introducing a secondary Co ion. The Co substitution of Ni in Ni-MOF can improve the intrinsic reactivity and stability. As a result, the bimetallic Co/Ni-MOF-1:15 with an optimal Co/Ni ratio delivers high specific capacitance (359 F/g at 0.5 A/g), good rate performance (81.5% retention at 5 A/g) and cycling stability (81% retention after 5000 cycles). These results demonstrate that the bimetallic synergistic strategy is an effective way to improve the pseudocapacitive performance of MOFs.     

Two Low-temperature Phase Transition Compounds Based on Quinuclidine Derivatives with Fluorescence

Two phase transition materials[iPrQ]2MnBr4(1,iPrQ=N-isopropyl-quinuclidinium)and[iPrQ]₂MnCl₄(2)were synthesized and characterized.Dielectric measurements and differential scanning calorimetry showed that the two compounds underwent reversible phase transitions at ca.–47 and–37℃,respectively.Variable-temperature single-crystal X-ray diffraction suggested that the two compounds underwent the same phase transitions from space group C2/c to Cc but at different temperature.The variable crystal structures indicated that the structural phase transitions of the compound were ascribed to the torsional movement of quinuclidine ring and the disappearance of the c-slide plane.The second harmonic generation(SHG)response further proved this structural phase transition.Fluorescence tests showed that the two compounds have strong fluorescence.The strong variations in dielectric anomalies make compounds 1 and 2 suitable for promising switchable dielectric materials.     

Structural Variability and Gas Adsorption Properties of Coordination Polymers Constructed with Aromatic Multicarboxylic and Bidentate Ligands

The self‐assembly reactions of transition metal ions and 1,3,5‐benzenetricarboxylic acid (H₃btc) in the presence of auxiliary aromatic bidentate ligands 1,10‐phenanthroline (1,10‐phen) or 4,4′‐bipyridine‐N,N′‐dioxide (4,4′‐bpdo) have isolated four coordination polymers [Co₁₈(btc)₁₀(H₂O)₆(OH)₆(1,10‐phen)₆] · 14H₂O · 3DMF ( 1 ) and [M₃(btc)₂(H₂O)₄(4,4′‐bpdo)] · 2H₂O · 2DMF [M = Co ( 2 ), Mn ( 3 ), Ni ( 4 )]. Single‐crystal X‐ray diffraction analysis revealed that the M₃ clusters in the structure of 1 – 4 are connected by hydroxyl group oxygen atoms (or oxygen atoms from 4,4′‐bpdo ligands) and carboxyl groups to generate a three‐dimensional framework. The network of final assemblies can be adjusted by varying the type of auxiliary ligands (1,10‐phen, 4,4′‐bpdo). In addition, the gas adsorption properties of 2 are also investigated.