Search

Lithium (Li)-O2 batteries have triggered worldwide interest due to their ultrahigh theoretical energy density. However, it is a long shot for the grand-scale applications of Li-O2 battery at current stage owing to its significant polarization, inferior cycling life, and irreversible decomposition of Li2O2. Herein, a facile way of preparing the highly dispersed Co-based nanoparticles encapsulated into porous N-doping carbon polyhedral with the low content of Ru modification (LRu@HDCo-NC) is explored through the pyrolysis of Co/Zn based zeolitic imidazole frameworks (ZIFs) containing Ru-based ligands. Even with the very small amount of Ru introduction (1.8%), LRu@HDCo-NC still exhibits the superior oxygen evolution reaction/oxygen reduction reaction (OER/ORR) performance and also inhibits side reactions in Li-O2 battery because of the abundant pores, plentiful surface N heteroatoms, and highly dispersed metal-based sites which are induced by the volatilization of Zn, and conductive/stable carbon skeleton derived from ZIFs. When applied in Li-O2 batteries, LRu@HDCo-NC cathode delivers a high discharge capacity of 15,973 mAh·g−1 at 200 mA·g−1, good capacity retention at higher rate (12,362 mAh·g−1 at 500 mA·g−1) and outstanding stability for > 300 cycles with low voltage polarization of < 2.3 V under a cut-off capacity of 1,000 mAh·g−1 at 500 mA·g−1. More critically, a series of ex situ and in situ characterization technologies disclose that the LRu@HDCo-NC cathodes can effectively promote the reversible reactions in Li-O2 batteries.

Tuning the structural features that furnish electrochemically active sites with improved kinetic diffusion can provide an alternative way to achieve high performance of electrocatalysis. Here, we report a nano-structure of Ni2P/C(NPC) nano-sheets supported on nickel foam (NF) that is prepared by sequenced nitrogen pyrolysis and gas phosphatization of Ni-MOF nanosheets. Initially, the passivated surface of nickel foam facilitates the oriented growth of Ni-MOF nanosheets, which is crucial for the maintenance of structure stability during the subsequent pyrolysis and phosphatization treatment. As a result, more catalytic active sites are exposed than the non-oriented NPC catalysts and diffusion kinetics is favorable. Consequently, the obtained composite can exhibit excellent hydrogen evolution catalytic activity in an alkaline electrolyte. For hydrogen evolution reaction, a current density of 10 mA cm−2 is provided at an overpotential of 97 mV and its onset overpotential is only 29 mV. Meanwhile, good morphology and catalytic activity can be maintained after 12 h of stability testing. This excellent performance is believed to be the result of NPC nanosheet structure on NF derived from the facet-oriented control of pristine Ni-MOF, enabling excellent reaction kinetics.

Metronidazole(MTZ) is an important antibiotic, which has been widely applied to cure protozoal and bacterial diseases for human beings or animals. Herein, three novel drug supramolecular crystals constructed by MTZ with 2,5-dihydroxy-benzoic acid(2,5-DHBA)(1), 2,6-dihydroxy-benzoic acid(2,6-DHBA)(2) and 3,5-dihydroxy-benzoic acid(3,5-DHBA)(3), respectively, have been discovered. The hydrogen bonds of N—H⋯O(O—H⋯N), C—H⋯O and O—H⋯O play important roles in the 3D supramolecular framework formation for crystals 1–3. Interestingly, due to the vary locations of the substituent groups, the two-dimensional layers in crystals 1 or 2 are constructed via intermolecular hydrogen bonds between MTZ and 2,5-DHBA or 2,6-DHBA, while in crystal 3 water molecules play a significant role except the intermolecular hydrogen bonds between MTZ and 3,5 -DHBA. In addition, five synthons of I R22(8), II R33(9) in crystal 1, III R21(4), IV R22(8) in crystal 2 and V R22(7) in crystal 3 formed through various hydrogen bonds are founded in this work. Systematic studies of syntheses, crystal structures and thermal analysis are reported.

The ingenious design and synthesis of bifunctional electrocatalysts with high activity and robust stability for hydrogen evolution reaction and oxygen evolution reaction (HER and OER) is desirable and challenging. Herein, bimetallic phosphides CoFeP with hollow microspheres structure has been synthesized through a facile gas phosphorization as bifunctional electrocatalyst for overall water splitting. SEM and TEM demonstrate the formation of uniform hollow microspheres of CoFeP. The hollow structure of CoFeP is helpful to increase the exposed actives and the larger contact surface with electrolyte. The bimetallic composites can provide the better intrinsic activity. Compared with single metallic phosphides CoP and FeP, the obvious enhancement of electrocatalytic performances of CoFeP can be observed. The electrochemical results show that the bimetallic CoFeP hollow microspheres only have the lower overpotential of 177 and 350 mV (vs. RHE) to drive a current density of 10 mA cm−2 for HER and OER, respectively. The reasons may be due to the hollow nanostructure and the synergistic effect from bimetallic phosphides. This work provides a facile and effective way to design excellent phosphides electrocatalysts for water splitting based on gas phosphorization of bimetallic oxides precursors.

Pyridyltetrazolium is an advantageous molecular precursor for its abundant coordination sites, which is adequate for the design of novel multi-dimensional structures. Three compounds of P-pyridyltetrazolium with 1,2,3-benzenetricarboxylic acid 1, M-pyridyltetrazolium with 1,2,3-benzenetricarboxylic acid 2, and P-pyridyltetrazolium with 2,3-dihydroxybenzoic acid 3 were synthesized and investigated. Compounds 1 and 2 indicated that the position of the coordination nitrogen atom will affect the structure of the supramolecule. Compound 1 finally formed a three-dimensional network through hydrogen bonds of O–H⋯O and O–H⋯N, whereas compound 2 formed a two-dimensional layered structure and water molecules play an important role in the construction of the two-dimensional layer. In addition to O–H⋯N hydrogen bond interaction, a weak C–H⋯C hydrogen bond also has significant effect on the construction of compound 3. Some main supramolecular synthons observed in three compounds were shown to construct most of these hydrogen bonding networks. The three compounds have been characterized by single crystal X-ray diffraction, 1H nuclear magnetic resonance, infrared spectroscopy and thermogravimetric analysis (TGA). Furthermore, their supramolecular structures are fully analyzed.

Two new metal-organic frameworks {[Ni0.5(DTA)0.5(H2O)]‧H2O}n (1) and [Ni(DTA)]n (2), where H2DTA = 2,5-di(1H-imidazol-1-yl)terephthalic acid, were constructed from the same reaction system at 120 °C and 180 °C, respectively. Different reaction temperatures were found to trigger different assembly processes and final structures. Single-crystal X-ray analyses show that compound 1 exhibits a 2D layered structure, further forming a 3D supramolecular by hydrogen bonding, while compound 2 shows 2-fold interpenetrating 3D framework with PtS topology. Compounds 1–2 have been evaluated as electrode materials for supercapacitors. The results show that compound 1 exhibits better electrochemical performance than 2. It may be ascribed to 2D layered structures facilitating electron transport and sufficient interlayer spaces available for the storage.