Single Ru Sites on Covalent Organic Framework-Coated Carbon Nanotubes for Highly Efficient Electrocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) with precisely controllable structures and highly ordered porosity possess great potential as electrocatalysts for hydrogen evolution reaction (HER). However, the catalytic performance of pristine COFs is limited by the poor active sites and low electron transfer. Herein, to address these issues, the conductive carbon nanotubes (CNTs) are coated by a defined structure RuBpy(H2 O)(OH)Cl2 in bipyridine-based COF (TpBpy). And this composite with single site Ru incorporated can be used as HER electrocatalyst in alkaline conditions. A series of crucial issues are carefully discussed through experiments and density functional theory (DFT) calculations, such as the coordination structure of the atomically dispersion Ru ions, the catalytic mechanism of the embedded catalytic site, and the effect of COF and CNTs on the electrocatalytic properties. According to DFT calculations, the embedded single sites Ru act as catalytic sites for H2 generation. Benefitting from increasing the catalyst conductivity and the charge transfer, the as-prepared c-CNT-0.68@TpBpy-Ru shows an excellent HER overpotential of 112 mV at 10 mA cm-2 under alkaline conditions as well as an excellent durability up to 12 h, which is superior to that of most of the reported COFs electrocatalysts in alkaline solution.

Self-Assembly Strategy for Constructing Porous Boron and Nitrogen Co-Doped Carbon as an Efficient ORR Electrocatalyst toward Zinc-Air Battery.

Carbon nanomaterials doped with N and B could activate nearby carbon atoms to promote charge polarization through the synergistic coupling effect between N and B atoms, thus facilitating adsorption of O2 and weakening O-O bond to enhance oxygen reduction reaction. Herein, a simple and controllable self-assembly strategy is applied to synthesize porous B, N co-doped carbon-based catalysts (BCN-P), which employs the macrocyclic molecule cucurbit[7]uril (CB7) as nitrogen source, and 3D aromatic-like closo-[B12H12]2- as boron source. In addition, polystyrene microspheres are added to help introduce porous structure to expose more active sites. Benefitting from porous structures and the synergistic coupling effect between N and B atoms, BCN-P has a high onset potential (Eonset=0.846 V) and half-wave potential (E1/2=0.74 V) in alkaline media. The zinc-air battery assembled with BCN-P shows high operating voltage (1.42 V), peak power density (128.7 mW cm-2) and stable charge/discharge cycles, which is even comparable with Pt/C.

Porous g-C3N4 with defects for the efficient dye photodegradation under visible light.

Porous graphitic carbon nitride (p-C3N4) was fabricated via simple pyrolyzing treatment of graphitic carbon nitride (g-C3N4). The defects could be introduced into the structure of g-C3N4 by breakage of some bonds, which was beneficial for the generation of electron-hole pairs and inhibiting their recombination. Compared with g-C3N4, p-C3N4 showed a narrow band gap to promote the utilization of visible light. Furthermore, the porous structure also increased the specific surface area to maximize the exposure of active sites and promote mass transfer during photodegradation. As a result, the as-reported p-C3N4 exhibited considerably higher degradation efficiency for Rhodamine B (RhB) and Methyl Orange (MO) than that of the original g-C3N4. Moreover, the photocatalyst showed high durability and stability in recycling experiments.

Using a novel adsorbent macrocyclic compound cucurbit[8]uril for Pb2+ removal from aqueous solution.

In this study, cucurbit[8]uril (CB[8]) was utilized as a kind of new adsorbent to remove Pb2+ ions from aqueous solution. With the solution pH increased from 2 to 6, the removal efficiency of adsorption increased from 55.6% to 74.5%correspondingly. The uptake of Pb2+ increased rapidly in the initial 30min, and then the adsorption rate became slower. The Pseudo-second order model could be used to interpret the adsorption kinetics satisfactorily; and the rate determining step in Pb2+ adsorption onto CB[8] was the external mass transfer step. Equilibrium isotherm study reveals that the Langmuir model gave a better fitting result than Freundlich model. The maximum adsorption capacity calculated by the Langmuir model was 152.67mg/g for 298K, 149.70mg/g for 313K and 136.42mg/g for 323K, respectively. The adsorption is a spontaneous process of exothermic nature. The effect of the adsorbent dosage and the influences of solution pH and co-existing cations were also investigated. The CB[8] was synthesized and characterized by 1H NMR, IR, ESI-MS spectra, SEM-EDAX, Zeta-potential and BET-analysis. The adsorption mechanism was due to the coordination between CB[8] molecule and Pb2+ ions.

Strong metal-support interactions for high sintering resistance of Ru-based catalysts toward the HER and ORR.

B, N co-doped carbon-supported small-sized Ru nanoparticles (RuBCN) were constructed by a facile ion exchange strategy using closo-[B12H12]2- and Ru(bpy)32+ as the precursors. Benefitting from strong metal-support interactions caused by the synergistic coupling effect of co-dopants B and N, RuBCN exhibits improved sintering resistance and the Ru nanoparticles are stabilized at sub-3 nm at 900 °C. Besides, introducing B doping further increases the electron deficiency of Ru in RuBCN, which could weaken the interaction between Ru and Had species or O2 adsorption. As a result, it exhibits impressive HER (η10 = 20 mV) and ORR (E1/2 = 0.76 V) catalytic performances, as well as outstanding stability, which are much higher than those of the single dopant counterpart.

Chloridobis(dimethyl-glyoximato-κN,N')(ethyl pyridine-3-carboxyl-ate-κN)cobalt(III).

In the title compound, [Co(C(4)H(7)N(2)O(2))(2)Cl(C(8)H(9)NO(2))], which was prepared as a model complex of vitamin B(12), the Co(III) atom, which is linked to four N atoms of the pseudo-macrocyclic (dmgH)(2) ligand (dmgH is dimethyl-glyoximate) in the equatorial plane and one Cl(-) anion and one N atom of ethyl nicotinate in apical positions, displays an approximately octa-hedral coordination. The Co atom is 0.0187 (8) Šout of the mean plane of the four equatorial N atoms. The structure has an O⋯H⋯O bridge, which is very common in cobaloxime derivatives, with O⋯H distances of 1.24 (2) and 1.25 (2) Å.

Chloridobis(dimethyl-glyoximato-κN,N')(ethyl pyridine-4-carboxyl-ate-κN)cobalt(III) chloro-form monosolvate.

The title compound, [Co(C(4)H(7)N(2)O(2))(2)Cl(C(8)H(9)NO(2))]·CHCl(3), was synthesized as a model complex of vitamin B(12). The Co(III) cation displays an approximately octa-hedral coordination environment, being displaced by 0.0240 (15) Šfrom the mean plane of the four N atoms of the equatorial plane. The O-H distances in the dimethyl-glyoximate hy-droxy groups are 0.89 (6) and 1.14 (6) Å; such long O-H bonds are very common in cobaloxime derivatives. Weak classical O-H⋯N and non-classical C-H⋯Cl hydrogen-bonding interactions further consolidate the crystal packing.

Boron-induced activation of Ru nanoparticles anchored on carbon nanotubes for the enhanced pH-independent hydrogen evolution reaction.

As a promising dopant, electron deficient B atom not only tunes the electronic structure of electrocatalysts for improving their intrinsic catalytic activities, but also combines with hydroxy radical as strong adsorption sites for accelerating the water dissociation during the hydrogen evolution reaction (HER). In this paper, we report an electrocatalyst based on boron-modified Ru anchored on carbon nanotubes (B-Ru@CNT) that shows impressive HER activity in acidic and alkaline media. The boron-rich closo-[B12H12]2- borane was selected as a moderately strong reductant for the in situ reduction of a Ru salt, which yielded B-doped Ru nanoparticles. The experimental and theoretical results indicate that the incorporation of B not only weakens the Ru-H bond and downshifts the d-bond centre of Ru from the Fermi level by reducing the electron density at Ru but also accelerates the water dissociation reaction by providing B sites, which strongly adsorb OH* intermediates, and nearby Ru sites, which act as sites for the adsorption of the H* intermediate, thus boosting the HER performance and enhancing the HER kinetics. As a result of the tuning of the electronic structure via B doping, B-Ru@CNT showed excellent HER performance, yielding overpotentials of 17 and 62 mV at a current density of 10 mA cm-2 in alkaline and acidic solutions, respectively. These results indicate that our synthetic method is a promising route to B-doped metallic Ru with enhanced pH-independent HER performance.

Effect of TiO2 as an additive on the sintering performance of Sm-doped CeO2-based electrolyte for solid oxide fuel cells.

In this work, TiO2 was selected as an additive to the Sm0.2Ce0.8O2-δ (SDC) electrolyte and its influence on the electrolyte properties were investigated. The tetrabutyl titanate hydrolysis product was introduced into the SDC samples as a source of TiO2. The lattice contraction of SDC was observed by XRD when the smaller ionic radius Ti4+ (0.605Å) were substituted for Ce4+ (0.97 Å). XRD analysis shows that the doping content of the TiO2 in SDC should be limited to 1 wt% to maintain the single-phase cubic fluorite structure of the SDC and avoid impurity phases. SEM characterizations suggest that the addition of TiO2 significantly promoted the grain growth and the sintering activity, especially when doping with 0.5 wt% of TiO2. The electrochemical measurements reveal that the addition of TiO2 had little effect on the conductivity of SDC samples, which was 0.0306 S cm-1 at 700°C. This study shows that 0.5 wt% TiO2 doping can effectively improve the sintering activity without reducing the SDC performance.

A new strategy for improving the electrochemical performance of perovskite cathodes: pre-calcining the perovskite oxide precursor in a nitrogen atmosphere.

Increasing the concentration of oxygen deficiency in perovskite oxides by suitable cation doping or anion doping can significantly increase the cathode ionic conductivity, thus improving the oxygen reduction reaction activity in solid oxide fuel cells (SOFCs). Herein, pre-calcining the perovskite oxide precursor in N2 atmosphere is a new strategy to further improve the oxygen non-stoichiometry (δ) and electrocatalytic activity of the cathode. The obtained nitrogen-treated Sm0.5Sr0.5CoO3-δ (SSC) powder has higher oxygen non-stoichiometry than the untreated one. The δ value is 0.27 for SSC-400 at 800 °C in air. The obtained nitrogen-treated SSC-400 cathodes calcined at 1000 °C show improved electrochemical performance compared to SSC-air, achieving the polarization resistance (R p) values to be 0.035, 0.078 and 0.214 Ω cm2 at 700 °C, 650 °C and 600 °C. The maximum power density of the cell with the SSC-600 cathode reaches 0.87, 1.16 and 1.24 W cm-2 at 600, 650 and 700 °C, which are more excellent than SSC-air. Pre-calcining the perovskite oxide precursor in N2 at a suitable temperature can remarkably improve the electrochemical capability of the cathode and provide a convenient and useful strategy to alleviate the problem of oxygen deficiency in perovskite oxides.

Ultrasmall Ru Nanoparticles Highly Dispersed on Sulfur-Doped Graphene for HER with High Electrocatalytic Performance.

Nanostructuring and metal-support interactions have been explored as effective methods to improve the electrocatalytic activity in heterogeneous catalysis. In this study, we have fabricated ultrasmall Ru nanoparticles (NPs) dispersed on S-doped graphene (denoted as Ru/S-rGO) by a facile "one-pot" procedure. The experimental results indicated that both the S doping and moderate degree of oxidization of GO can induce the formation and high dispersion of the ultrasmall Ru NPs with larger electrochemically active surface areas for exposing more active sites. Metal-support interaction between S-doped graphene and Ru NPs was observed from the X-ray photoelectron spectroscopy and electronic charge-difference studies. It resulted in the decrease in the electron density of Ru, which facilitated electron release from H2O and H-OH bond breakage. The results of density functional theory calculation confirmed that the S-dopants could reduce the energy barrier for breaking the H-OH bond to accelerate water dissociation during the alkaline hydrogen evolution reaction (HER). At a current density 20 mA cm-2, the lowest overpotential of 14 mV, superior to that of Pt/C in alkaline solution, was observed for Ru/S-rGO-24. The observed lowest value of overpotential was because of the ultrasmall size, high dispersion, and metal-support interaction. This work provides a simple and effective method in designing advanced electrocatalysts for the HER in an alkaline electrolyte.

Orthogonal Supramolecular Assembly Triggered by Inclusion and Exclusion Interactions with Cucurbit[7]uril for Photocatalytic H2 Evolution.

The fabrication of efficient and convenient photocatalytic H2 evolution systems is a fascinating research topic in the field of solar energy conversion. A ternary self-assembled photocatalytic H2 evolution system was fabricated through supramolecular host-guest chemistry. The system consisted of the H2 evolution catalyst [Co(dmgH)2 (4-ppy)2 ]NO3 (1; dmgH2 =dimethylglyoxime, 4-ppy=4-phenylpyridine) and the photosensitizer Eosin Y (EY) assembled with the macrocyclic compound cucurbit[7]uril (CB[7]) to form the 1@CB[7]/EY complex through inclusion and exclusion interactions, respectively. The synchronous self-assembly drives an orthogonal arrangement of the 1@CB[7]/EY system. The inclusion complex 1@CB[7] was successfully characterized by 1 H NMR spectroscopy and single-crystal XRD. The exclusion process of CB[7] with EY was identified by NMR titration and the optimized geometry of the exclusion structure was determined by DFT calculations. The use of CB[7] resulted in a 6-fold increase in turnover number, a 3-fold increase in turnover frequency, and a 3-fold extension of lifetime for photocatalytic H2 evolution as compared with the system in the absence of CB[7]. The improvement of the light-driven H2 evolution activity was ascribed to the ability of CB[7] to link the photosensitizer and catalyst.

Transformation of micelles into supramolecular vesicles triggered by the formation of [4]pseudorotaxanes.

Spontaneous formation of supramolecular vesicles which are triggered by the formation of [4]pseudorotaxane B was demonstrated, whereas both Guest and [2]pseudorotaxane A, the precursors of [4]pseudorotaxane B, only assemble into micelles in DMF/water solution. The remarkable transformation of Guest from micelles to supramolecular vesicles was confirmed through DLS, TEM, and Cryo-TEM experiments. The cumulative release of a model drug, 5-carboxyfluorescein (CF), was used to determine the permeability of the supramolecular vesicles. No leakage of entrapped CF was observed within 48 h by fluorescence measurement, indicating the high stability of supramolecular vesicles. The formation mechanism of supramolecular vesicles self-assembled by [4]pseudorotaxane B was also discussed. In [4]pseudorotaxane B, CB[6] is used to increase the hydrophobic property of site ß, which acts as hydrophobic "tail." Meanwhile, CB[7] plays the role of increasing "head area" of site α, which acts as hydrophilic "head." The synergistic effect of CB[6] and CB[7] induces the formation of supramolecular vesicles. Moreover, the effect of DMF content was investigated by TEM observations. It was found that the [4]pseudorotaxane B can self-assemble into regular supramolecular vesicles when the DMF content is in the range of 50-70%.