Design, Synthesis, and Analysis of Thermophysical Properties for Imidazolium-Based Geminal Dicationic Ionic Liquids

To enhance the thermal stability of ionic liquids (ILs) and increase the latent heat, the effect of amount of hydrogen bonds for geminal dicationic ionic liquids (DILs) was investigated and compared to that of monocationic analogues. A series of geminal dicationic ionic liquids with alkyl chain or electronegativity functional groups in the imidazolium were synthesized. Thermal stability was determined by TGA; melting point, heat of fusion, and heat capacity were investigated by DSC for synthetic DILs. The effect of molecular structure on the heat of fusion was examined by changes alkyl side-chain, linkage chain, C2–H of imidazole ring, and functional groups. Hydrogen bonding in DILs was studied, in the case of C₂(eim)₂(Br)₂, by single-crystal X-ray diffraction. The thermal analysis results indicate that functionalized geminal dicationic ionic liquids show excellent thermal stability. The decomposition temperatures of geminal dicationic ionic liquids can be up to 603.74 K, and the latent heat can reach 159.35 J g^–1. It is increased on average by 64.5% and 212.5%, respectively, as compared to alkyl chain ionic liquid (C₄mim)­Br. It can be expected that these geminal dicationic ionic liquids are suitable for thermal storage applications

Synthesis and Characterization of Functionalized Ionic Liquids for Thermal Storage

A series of imidazolium-based ionic liquids were synthesized by introducing functional groups in the imidazolium cation to develop new phase change materials. The structures of these ionic liquids were determined by nuclear magnetic resonance; the quantum calculation was performed based on density functional theory by Gaussian 09 to determine the number of hydrogen bonds among the ions. The heat of fusion, heat capacity, and thermal storage density of the ionic liquids were investigated by DSC; in addition, the thermal stability was determined by TGA. The thermal analysis results indicate that new functionalized ionic liquids have excellent thermal stability with decomposition temperatures higher than 475 K. In addition, the heat of fusion, heat capacity, and thermal storage density of the functionalized ionic liquids increased on average by 34, 86.5, and 100%, respectively, compared with alkyl chain ionic liquids with the same carbon numbers. These superior properties are attributed to the additional hydrogen bonds in the functionalized ionic liquids

First-Principles Study on Stability and HER Activity of Noble Metal Single Atoms on TiO₂: The Effect of Loading Density

The highly dispersed “single-atom (SA)” catalysts on oxide supports significantly alter the catalytic reaction activity and selectivity and meanwhile save the catalyst utilization. However, preparation of SA catalysts remains a challenge up to now. An approach effectively evaluating the stability and activity is required. Herein, density functional theory (DFT)-based first-principles calculations were performed to evaluate the stability and photocatalytic hydrogen evolution reaction (HER) activity of noble metal (NM = Ag, Au, Pd, and Pt) SAs loaded on TiO₂ support. The chemical potential-based thermodynamic model was employed to estimate the stability of SAs; the capability to trap photoelectrons on surface and free energy of hydrogen adsorption were used to estimate the photocatalytic HER activity of SAs. Compared to the (101) surface, the (001) surface is more feasible for preparation of NM SAs due to the “soft” structural character caused by incompletely saturated surface atoms. The stability of SAs on the (001) is getting better with the loading density lowering except for Au SA. After deposition of NM SAs on the (001), the photoelectron was extracted from the subsurface to the surface around the NM sites, facilitating the proton adsorption and reduction process. The calculated free energy of hydrogen adsorption shows that the photocatalytic HER activity of NM SAs on the (001) changes moderately with the loading density but is very different than those for the TiO₂ clean (001) and bulk NM (111). Both stability and activity evaluations dictate that Pd SA on the (001) is the most promising candidate catalyst for photocatalytic HER

Undoped and Ni-Doped CoO_<i>x</i> Surface Modification of Porous BiVO₄ Photoelectrodes for Water Oxidation

Surface modification of photoanodes with oxygen evolution reaction (OER) catalysts is an effective approach to enhance water oxidation kinetics, to reduce external bias, and to improve the energy harvesting efficiency of photoelectrochemical (PEC) water oxidation. Here, the surface of porous BiVO₄ photoanodes was modified by the deposition of undoped and Ni-doped CoO_<i>x</i> via nitrogen flow assisted electrostatic spray pyrolysis. This newly developed atmospheric pressure deposition technique allows for surface coverage throughout the porous structure with thickness and composition control. PEC testing of modified BiVO₄ photoanodes shows that after deposition of an undoped CoO_<i>x</i> surface layer, the onset potential shifts negatively by ca. 420 mV and the photocurrent density reaches 2.01 mA cm^–2 at 1.23 vs V_RHE under AM 1.5G illumination. Modification with Ni-doped CoO_<i>x</i> produces even more effective OER catalysis and yields a photocurrent density of 2.62 mA cm^–2 at 1.23 V_RHE under AM 1.5G illumination. The valence band X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption spectroscopy results show the Ni doping reduces the Fermi level of the CoO_<i>x</i> layer; the increased surface band bending produced by this effect is partially responsible for the superior PEC performance

Fe Single-Atom Catalyst for Cost-Effective yet Highly Efficient Heterogeneous Fenton Catalysis

High energy consumption in pyrolyzing precursors for catalyst preparation would limit the application of nitrogen-doped carbon-based single-atom catalysts in actual pollutant remediation. Herein, we report an Fe single atom (7.67 wt %) loaded polyaniline catalyst (Fe-PANI) prepared via a simple impregnation process without pyrolysis. Both experimental characterizations and density functional theory calculations demonstrated that isolated −N group sites can fasten Fe atoms through Fe–N coordination in PANI, leading to a high stability of Fe atoms in a heterogeneous Fenton reaction. Highly dispersive yet dense −N groups in PANI can be protonated to be adsorption sites, which largely reduce the migration distance between reactive radicals and organics. More significantly, frontier molecular orbitals and spin-density distributions reveal that electrons can transfer from reduction groups of PANI to an Fe­(III) site to accelerate its reduction. As a result, a remarkably boosted degradation behavior of organics under near-neutral conditions (pH 6), with low H2O2 concentration, was achieved. This cost-effective Fe-PANI catalyst with high catalytic activity, stability, and adsorption performance has great potential for industrial-level wastewater treatment

Significantly Enhanced Breakdown Strength and Energy Density in Nanocomposites by Synergic Modulation of Structural Design and Low-Loading Nanofibers

Polymer-based dielectric nanocomposites have attracted great attention due to the advantages of high-power density and stability. However, due to the limited breakdown strength (Eb) of the dielectrics, the unsatisfactory energy density becomes the bottleneck that restricts their applications. Here, newly designed sandwich-structured nanocomposites are proposed, which includes the introduction of low-loading 0.4BiFeO3–0.6SrTiO3 (BFSTO) nanofibers into the poly­(vinylidene fluoride-co-hexafluoropropylene) (P­(VDF-HFP)) matrix as the polarization layer (B-layer) to offer high permittivity and the selection of poly­(methylmethacrylate) (PMMA)/P­(VDF-HFP) all-organic blend film as the insulation layer (P-layer) to improve Eb of the nanocomposites. The optimized sandwich-structured PBP nanocomposite exhibits significant enhancement in Eb (668.6 MV/m), generating a discharged energy density of 17.2 J/cm3. The dielectric and Kelvin probe force microscope results corroborate that the outer P-layer has a low surface charge density, which can markedly impede the charge injection from the electrode/dielectric interface and thereby suppress the leakage current inside the nanocomposite. Furthermore, both the finite element simulations and capacitive series models demonstrate that the homogenized distribution of electric field in the PBP sandwich-structured nanocomposite favors the improvement of energy storage performance. This work not only provides insightful guidance into the in-depth understanding of the dielectric breakdown mechanism in sandwich-structured nanocomposites but also offers a novel paradigm for the development of polymer-based nanocomposites with high Eb and discharged energy density

Anomalous Capacitive Behaviors of Graphene Oxide Based Solid-State Supercapacitors

Substantial differences in charge storage mechanisms exist between dielectric capacitors (DCs) and electrochemical capacitors (ECs), resulting in orders of magnitude difference of stored charge density in them. However, if ionic diffusion, the major charge transport mechanism in ECs, is confined within nanoscale dimensions, the Helmholtz layers and diffusion layers will overlap, resulting in dismissible ionic diffusion. An interesting contradiction between appreciable energy density and unrecognizable ionic diffusion is observed in solid-state capacitors made from reduced graphene oxide films that challenge the fundamental charge storage mechanisms proposed in such devices. A new capacitive model is proposed, which combines the two distinct charge storage mechanisms of DCs and ECs, to explain the contradiction, of high storage capacity yet undetectable ionic diffusion, seen in graphene oxide based supercapacitors

Hierarchical NiFeP Nanoflowers on the MXene Film as a Self-Standing Bifunctional Electrode toward Superior Overall Water Electrolysis

The exploitation of highly active, nonprecious metal bifunctional electrodes to facilitate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for water electrolysis to produce hydrogen, but the performances are still unsatisfactory. Herein, a facile strategy was proposed to fabricate a three-dimensional (3D) bimetallic phosphide (NiFeP) nanoflower array on a self-standing assembled MXene nanosheet film (denoted as NiFeP@MXene) as a structurally integrated electrode for overall water splitting. The NiFeP@MXene film with 3D hierarchical nanoflower structures can be directly used as an electrode without traditional polymer binders, which significantly reduces the contact resistance and facilitates the electron transfer at the interface. Meanwhile, an interfacial synergistic coupling is created between the highly conductive MXene film and the bimetallic phosphides, which is favorable for the catalytic activity. Moreover, the addition of Fe improves the intrinsic activity and simultaneously facilitates the formation of 3D flower-like structures with more active sites. Thus, the self-standing NiFeP@MXene electrode demonstrates an excellent bifunctional catalytic activity in the alkaline electrolyte with small overpotentials of 240 and 122 mV to drive 10 mA cm–2 current density for the OER and HER, respectively, along with a superior overall water electrolysis performance compared to the commercial precious IrO2∥Pt/C catalyst

Nuclear localization of CDK5RAP3 was important for the suppression of p14ARF promoter activity.

<p>(<b>a</b>) <i>S</i>chematic diagram of CDK5RAP3 mutants (<b>b</b>) Western blotting showing the expression levels of CDK5RAP3 mutants overexpressed in HepG2. Protein lysates from reporter assay were used for Western blotting probed with anti-Myc antibody. (<b>c</b>) <i>D</i>ual luciferase reporter was performed by co-transfection of CDK5RAP3 mutants with p14^ARF-luc reporter in HepG2. Results were mean of three independent experiments, with promoter activity of vector control set as 100%. *, <i>P</i><0.05 and **, <i>P</i><0.005 compared with vector control, Student’s <i>t</i>-test. (<b>d</b>) Confocal images of wild type (WT) and the indicated deletion mutants of Myc-CDK5RAP3.</p

Suppression of endogenous expression of p14^ARF by CDK5RAP3.

<p>(<b>a</b>) The <i>p14^ARF</i> and <i>CDK5RAP3</i> mRNA expression in stable CDK5RAP3 knockdown SMMC-7721 stable clones was determined by Quantitative real-time PCR (qPCR). Data was analyzed by comparative Ct method. Band intensity was analyzed using AlphaEasePC software and normalized with <i>β-actin</i>. Results were mean of three independent experiments. *, <i>P</i><0.005, Student’s <i>t</i>-test. (b) Similar to (a), the CDK5RAP3 stable expressing HepG2 clones (CDK5RAP3#1 and #2), vector control and parental cells were used for qPCR assay. Results were mean of three independent experiments. *<i>P</i><0.04 and **<i>P</i><0.02 compared with vector control, Student’s <i>t</i>-test. (c) The CDK5RAP3 expression construct and p14^ARF luciferase reporter, pGL3-p14^ARF were co-transfected into SMMC-7721 cells for dual-luciferase reporter assay. Results represent mean ±SD for triplicate wells. *, <i>P</i><0.05 compared with vector control, Student’s <i>t</i>-test. (d) Similar to (c), luciferase reporters carrying truncation mutants of the p14^ARF promoter, CDK5RAP3 expression construct (0.3 µg) and vector (0.3 µg) were used for dual-luciferase reporter assay. Results represent mean ±SD for triplicate wells. *, <i>P</i><0.02 compared with vector control, Student’s <i>t</i>-test. (e) CDK5RAP3 bound <i>p14^ARF</i> promoter by performing chromatin immunoprecipitation (ChIP) analysis on CDK5RAP3 stable overexpression clone #2 HepG2 cells (1×10⁷). Input (IN) and no antibody control (No Ab) were included. Error bars: mean ±SD.</p