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.

Herein, three novel cocrystals of 1-hydroxy-2-naphthoic acid: tetramethylpyrazine, 1-hydroxy-2-naphthoic acid:1,10-phenanthroline, and 1-hydroxy-2-naphthoic acid:1,4-bis(imidazol-1-ylmethyl)benzene (L2) were obtained by crystallization in methanol–water mixed solvent via a slow evaporation method. The cocrystalline products 1−3 were carried out by a range of techniques, including single-crystal X-ray diffraction, Fourier transform–infrared spectroscopy, elemental analysis, and thermogravimetric testing. We analyzed the crystal structures of the cocrystals 1−3 and found that weak interactions C–H···X (X = O or π) were of great importance in the process of self-assembly as well as strong and conventional hydrogen bonds (N–H···O, O–H···N, O–H···O), leading to a stable and diverse multidimensional supramolecular architecture. It is worth noting that a series of ring motifs with different sizes were explored in the crystal structures of the above complexes, such as R22(5), R22(7), R22(8), R23(13), R24(16), R44(16), R44(22), and so on. The classical and robust supramolecular synthon intermolecular bond between acid and pyridine (acid···pyridine) heterosynthon R22(7), commonly found in organic solids containing carboxylic acids with other N-containing heteroaromatics, was further demonstrated to be involved in the construction of the hydrogen-bond networks of cocrystal 1. The thermogravimetric technique used in this study proved that the mass losses of these three cocrystals were closely related to the strength of the hydrogen bonds in the package fraction.

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.

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.