Dongbo Yu

Decorating nanoporous ZIF-67-derived NiCo2O4 shells on a Co3O4 nanowire array core for battery-type electrodes with enhanced energy storage performance

Particle-shaped metal–organic framework-derived metal oxides almost dominate the applications for energy storage. However, they always suffer from agglomeration and terrible internal resistance, which reduce the surface area of active materials, ion diffusion and charge transfer efficiency during the charge–discharge process. Constructing metal–organic framework-derived core–shell nanostructures is a promising route to overcome this obstacle. In this work, a layer of ZIF-67-derived nanoporous NiCo2O4 nanoflakes was perfectly decorated on a Co3O4 nanowire array to build up a core–shell nanowire array architecture. Due to the unique structure that facilitates ion diffusion and charge transfer but without losing the high surface area, the resulting ZIF-67-derived core–shell nanostructure exhibits 3.37 C cm−2 of area capacity at a current density of 4 mA cm−2 as well as good rate capability and durability. In addition, the assembled asymmetric supercapacitor delivers a high specific energy density of 50.6 W h kg−1 at a specific power density of 856 W kg−1. Even at a high power density of 11.1 kW kg−1, the device still has an energy density of 30.2 W h kg−1. The strategy proposed here provides a good way to synthesize metal–organic framework-derived metal oxide nanostructures, and the as-prepared electrodes will be excellent materials for energy storage and other applications.

In situ growth of Co3O4 nanoparticles on α-MnO2 nanotubes: a new hybrid for high-performance supercapacitors

A new MnO2@Co3O4 hybrid with small-sized Co3O4 nanoparticles grown on α-MnO2 nanotubes was prepared from a low concentration precursor solution by a facile two-step hydrothermal synthesis method, and its charge storage properties were investigated by cyclic voltammetry and galvanostatic charge–discharge measurements. Due to their hybrid structure, the well-dispersed Co3O4 nanoparticles not only facilitated the charge and ion transfer, but also hindered the dissolution of Mn species; this type of hybrid maximized the electroactivity of both components. The hybrid exhibited a specific capacitance of 234 F g−1, which was greater than those of pristine α-MnO2 nanotubes and a physical mixture of α-MnO2 nanotubes and Co3O4 nanoparticles at a current density of 200 mA g−1. The hybrid also showed good rate capacity and long-term cycling performance.

Precisely tailoring ZIF-67 nanostructures from cobalt carbonate hydroxide nanowire arrays: toward high-performance battery-type electrodes

The controllable synthesis of metal–organic frameworks with diverse morphologies is highly desirable for many potential applications, but it still remains a big challenge. In this study, we for the first time report a facile and green route to the synthesis of ZIF-67 at room temperature by transformation of water-insoluble cobalt carbonate hydroxide nanowires in the presence of 2-methylimidazole. When cobalt carbonate hydroxide nanowires were grown onto a Ni foam substrate, four different kinds of ZIF-67 nanocrystal morphologies were synthesized. In particular, a ZIF-67-based nanotube array was used as an example for synthesis of a mesoporous Co3O4 nanotube array, which showed greatly enhanced performance as a battery-type electrode in comparison to the directly converted Co3O4 nanowire array from cobalt carbonate hydroxide. Our study provides a new insight into the preparation of metal–organic frameworks with tunable morphologies; in addition, the as-synthesized ZIF-67-based nanostructures are promising materials for other applications.

An ordered ZIF-8-derived layered double hydroxide hollow nanoparticles-nanoflake array for high efficiency energy storage

A facile room-temperature synthesis of ZIF-8 nanoflakes using insoluble inorganic crystal zinc nitrate hydroxide nanoflakes as the Zn source has been demonstrated in this study for the first time. The transformation mechanism is discussed and investigated. It is found that apart from the acid–base affinity between zinc nitrate hydroxide and 2-methylimidazole, the specific layered crystal structure of zinc nitrate hydroxide is also responsible for the transformation kinetics. As a typical proof-of-concept application, the prepared ZIF-8 nanoflake array is subsequently used as a sacrificial template for constructing layered double hydroxides with extraordinary hollow nanoparticles-nanoflake architectures, in which each nanoflake comprises numerous hollow nanoparticles. Due to its unique structure, which facilitates effective ion and charge transfer without compromising the high surface area, the NiCo layered double hydroxide nanoflake array exhibits a very high capacity of 971.4 C g−1 at a current density of 1.9 A g−1, as well as excellent rate capability and durability. Furthermore, an assembled asymmetric supercapacitor integrated with commercial active carbon shows a high specific energy density of 52.1 W h kg−1 and a power density of 16.5 kW kg−1. The strategy proposed here gives significant insight into the synthesis of metal organic frameworks and provides a very important reference for the controllable design of MOF-based structures.

A fast in situ seeding route to the growth of a zeolitic imidazolate framework-8/AAO composite membrane at room temperature

A new zeolitic imidazolate framework-8 (ZIF-8) composite membrane was prepared by a fast in situ seeding method. The commercial anodic aluminum oxide (AAO) membrane was used as the support, which was immersed in the ZIF-8 precursor solution to allow the solution to diffuse into the AAO nanochannels. Ammonium hydroxide was then added to quickly nucleate ZIF-8 nanocrystals in the AAO channels as seeds. After secondary growth at room temperature, the ZIF-8/AAO composite membrane was obtained with ZIF-8 nanocrystals plugged in the AAO nanochannels, and the membrane exhibited high gas separation performance with H2/CO2 and H2/N2 ideal selectivities of 6.38 and 4.19, respectively. For comparison, only a layer of ZIF-8 was formed on the AAO membrane surface by a normal dip-coating method with ammonium hydroxide pre-added in the precursor solution, and the resulting membrane was not dense and continuous.

Cationic metal–organic framework porous membranes with high hydroxide conductivity and alkaline resistance for fuel cells

Hydroxide conductivity and alkaline stability are challenging issues for anion exchange membrane fuel cells (AEMFCs). Here, a novel sandwiched anion exchange membrane (AEM) was prepared from porous bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) entrapped cationic metal–organic frameworks (MOFs) with a polyvinyl alcohol (PVA) coating on the two sides. The porous BPPO matrix prepared by a non-solvent induced phase separation (NIPS) method provides numerous interconnected nanopores and sponge-like walls and enhanced uptake of alkali. The entrapped cationic MOFs can work as OH− conductive channels while the PVA coating can block the crossover of fuels such as methanol. The final membranes can reach an OH− conductivity of 145 mS cm−1 at 80 °C and a methanol permeability of 3.68 × 10−7 cm2 s−1, the performance of which is much higher than that in the existing literature.

A general route to the synthesis of layer-by-layer structured metal organic framework/graphene oxide hybrid films for high-performance supercapacitor electrodes

The synthesis of well-designed metal organic framework-based hybrid structures still remains a very big challenge in recent scientific research. Here, we develop a facile route for preparing metal organic framework/graphene oxide hybrid films with highly ordered layer-by-layer architecture, and water-insoluble inorganic crystals, as excellent metal ion sources, also serve as the spacer materials to form interconnected porous networks and ensure the continuous proceeding of coordination reactions. The obtained hybrids are subsequently used as the precursors for the preparation of the active materials of supercapacitor electrodes. Their derived layered double hydroxide-based and nanoporous carbon-based hybrids could maintain the similar layer-by-layer structure, and they exhibit exceptional energy storage performances including high capacity and rate capability as well as good cycling stability, resulting from the unique structure offering higher surface area and faster ion and charge transfer efficiency. In addition, the assembled asymmetric supercapacitor device delivers an energy density of 50.5 W h kg−1 at a power density of 853.3 W kg−1, and even at a power density of 25.1 kW kg−1, it still achieves a high energy density of 34.8 W h kg−1. Our prepared layer-by-layer metal organic framework-derived materials demonstrate promise for high-performance energy storage application, and the as-prepared functional materials also show great potential in other fields.

Fabrication of cation exchange membrane from polyvinyl alcohol using lignin sulfonic acid: Applications in diffusion dialysis process for alkali recovery

ABSTRACT We report polyvinyl alcohol (PVA)-based hybrid membranes composed of salt of lignin sulfonic acid (LSA) and tetraethyl orthosilicate. The concentration of LSA with respect to PVA varied from 10% to 40%. The hybrid membranes showed water uptake (WU) in the range of 122–210%, ion exchange capacities in the range of 0.32–0.75 mmol g−1, dialysis coefficient (UOH) from 0.0068 to 0.0119 m h−1, and selectivity (S) from 15 to 26. The hybrid membranes also showed thermal and mechanical stability.

Highly conductive and stabilized side-chain-type anion exchange membranes: ideal alternatives for alkaline fuel cell applications

Side-chain-type (SC) anion exchange membranes (AEMs) with pendant quaternary ammonium (QA) groups anchored onto the backbones via a six-carbon spacer demonstrate superior alkaline resistance. Yet, conventional SC AEMs have QA functionalized side chains randomly spread on the backbone, resulting in insufficient QA aggregation. Herein, we attempted to enhance the QA collection of SC AEMs by gathering the alkyl chains terminated by QA groups along the backbone or the grafting chain on the molecular level to gain dense or long SC configurations (termed as D-SC and L-SC). Coarse-grained molecular dynamics (CGMD) simulations reveal that the D-SC and L-SC architectures are much more beneficial for promoting the formation of desired long-range OH− transport channels compared with SC architectures, thereby leading to strikingly increased OH− conductivity. In particular, the D-SC AEM (IEC = 2.41 mmol g−1) with a limited water uptake of 30.4% shows quite a high hydroxide conductivity of 0.058 S cm−1 at 30 °C. The H2–O2 alkaline anion exchange membrane fuel cell using D-SC as ionomers gives rise to an exceptional peak power density of 683 mW cm−2 at 80 °C. Long-term alkaline aging measurements indicate that the D-SC and L-SC AEMs still preserve the advantages of typical SC AEMs in the aspect of alkaline tolerance. We thus believe that the molecular design opinions reported here can be appreciated as versatile strategies in the development of highly conductive and alkaline stabilized AEMs for electrochemical associated applications.

MOF-74 derived porous hybrid metal oxide hollow nanowires for high-performance electrochemical energy storage

Metal–organic framework-derived materials have attracted much attention due to their great potential for applications in energy storage and conversion. Herein, we report a rational design and organic solvent-free synthesis of MOF-74 and derived hybrid metal oxide nanowires with hollow structure. The evolution process and mechanism of MOF-74 have been investigated by adjusting solvent compositions and Ni/Co ratios. Different phases of metal oxide nanowires can be tailored after calcinations, enabling the systematic investigation of the effect of different metal species counts on the electrochemical properties of hybrid metal oxide nanomaterials. Results indicate that the hybrid metal oxides exhibit obvious advantages compared with monometallic oxides of Co3O4 and NiO, and NiO/NiCo2O4 (1 : 1) with two mixed phases of NiCo2O4 and NiO exhibits a superior specific capacity of 732.0C g−1 at a current density of 1 A g−1 among three different hybrid metal oxides. Furthermore, an assembled asymmetric supercapacitor device achieves a high specific energy density of 46.9 W h kg−1 at a specific power density of 425.3 W kg−1 with excellent cycling performance. The as-prepared materials will be competitive and promising candidates for electrochemical energy storage and other applications.