Yibo Dou

Hierarchically structured layered-double-hydroxide@zeolitic-imidazolate-framework derivatives for high-performance electrochemical energy storage

CoAl-based layered-double-hydroxide@zeolitic-imidazolate-framework-67 (LDH@ZIF-67) was fabricated via a hydrothermal synthesis of LDH film on Ni substrate followed by the in situ growth of ZIF-67. Its derivatives, MMO@Co3O4, spinelle@C and LDH@CoS with hierarchical structures were obtained by the subsequent oxidation, carbonization and sulfurization of LDH@ZIF-67, respectively, which exhibit distinct specific capacitances of 692, 781 and 1205 F g−1 at a discharge current density of 1 A g−1. Interestingly, these derivatives retained hierarchical structures with large surface area, which ensures that the majority of exposed active species can participate in the charge–discharge process and thus effectively contribute to total capacitances. The synergistic effect from fast electronic transfer reduces reversible ion accumulation at the interface, which imparts LDH@ZIF-67 derivatives improved electrochemical activities, in contrast to conventional bulk MOF derivatives. In addition, it was found that the combination of the remarkable electrical conductivity of sulfides (compared with their oxide counterparts) and the strong electronic coupling between LDH and CoS can facilitate fast electron transfer. As a result, LDH@CoS exhibits an excellent specific energy of 44.5 W h kg−1 at a current density of 20 A g−1, as well as good capacitance retention of 88.5% after 2000 cycles. This work thus demonstrates a feasible strategy for the design and fabrication of LDH@MOF derived composites as SCs components, which is applicable in constructing other novel electrode materials with hierarchical structures for applications in energy storage systems.

Visible-light responsive MOF encapsulation of noble-metal-sensitized semiconductors for high-performance photoelectrochemical water splitting

A strategy that visible-light responsive zeolitic-imidazolate-framework-67 (ZIF-67) encapsulates noble-metal sensitized semiconductors, ZnO@M (M = Au, Pt, and Ag) to fabricate composite catalysts for photoelectrochemical (PEC) water splitting is proposed. The obtained ZnO@M@ZIF-67 catalysts have good catalytic performance, particularly, the ZnO@Au@ZIF-67 exhibits quite improved photoconversion efficiency and photocurrent density, superior to most of the reported photoelectrode catalysts. This can be attributed to the wider solar spectra harvesting capability originating from visible-light responsive ZIF-67 and UV-light active ZnO. Simultaneously, their integration enables interfacial electrons in the ZIF-67 shell to easily transfer to the ZnO@Au core, providing good electron–hole separation. In addition, the porous ZIF-67 as a protective shell ensures structural robustness, while maintaining fast ion or gas bubble diffusion through its pores, accounting for stable and excellent PEC performance.

Functionalized Base-Stable Metal–Organic Frameworks for Selective CO2 Adsorption and Proton Conduction

Metal-organic frameworks (MOFs) have shown great potential for application in various fields, including CO2 capture and proton conduction. For promoting their practical applications, both optimization of a given property and enhancement of chemical stability are crucial. In this work, three base-stable isostructural MOFs, [Ni8 (OH)4 (H2 O)2 (BDP-X)6 ] (Ni-BDP-X; H2 BDP=1,4-bis(4-pyrazolyl)benzene, X=CHO, CN, COOH) with different functional groups, are designed, synthesized, and used in CO2 capture and proton conduction experiments. They possess face-centered cubic topological structures with functional nanoscale cavities. Importantly, these MOFs are fairly stable to maintain their structures in boiling water and 4 M sodium hydroxide solution at room temperature. Functionalization endows them with tunable properties. In gas adsorption studies, these MOFs exhibit selective adsorption of CO2 over CH4 and N2 , and in particular the introduction of COOH groups provides the highest selectivity. In addition, the COOH-functionalized Ni-BDP exhibits a high proton conductivity of 2.22×10-3  S cm-1 at 80 °C and approximately 97 % relative humidity.