Metal–organic frameworks (MOFs) are of great interest as potential electrochemically active materials. However, few studies have been conducted into understanding whether control of the shape and components of MOFs can optimize their electrochemical performances due to the rational realization of their shapes. Component control of MOFs remains a significant challenge. Herein, we demonstrate a solvothermal method to realize nanostructure engineering of 2D nanoflake MOFs. The hollow structures with Ni/Co- and Ni-MOF (denoted as Ni/Co-MOF nanoflakes and Ni-MOF nanoflakes) were assembled for their electrochemical performance optimizations in supercapacitors and in the oxygen reduction reaction (ORR). As a result, the Ni/Co-MOF nanoflakes exhibited remarkably enhanced performance with a specific capacitance of 530.4 F g−1 at 0.5 A g−1 in 1 M LiOH aqueous solution, much higher than that of Ni-MOF (306.8 F g−1) and ZIF-67 (168.3 F g−1), a good rate capability, and a robust cycling performance with no capacity fading after 2000 cycles. Ni/Co-MOF nanoflakes also showed improved electrocatalytic performance for the ORR compared to Ni-MOF and ZIF-67. The present work highlights the significant role of tuning 2D nanoflake ensembles of Ni/Co-MOF in accelerating electron and charge transportation for optimizing energy storage and conversion devices.
Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-017-0144-6) contains supplementary material, which is available to authorized users.
Terahertz (THz) absorption spectroscopy is a powerful tool for molecular label-free fingerprinting, but it faces a formidable hurdle in enhancing the broadband spectral signals in trace-amount analysis. In this paper, we propose a sensing method based on the geometry scanning of metal metasurfaces with spoof surface polarization sharp resonances by numerical simulation. This scheme shows a significant absorption enhancement factor of about 200 times in an ultra-wide terahertz band to enable the explicit identification of various analytes, such as a trace-amount thin lactose film samples. The proposed method provides a new, to the best of our knowledge, choice for the enhancement of wide terahertz absorption spectra, and paves the way for the detection of trace-amount chemical, organic, or biomedical materials in the terahertz regime.
We propose a terahertz surface plasmon resonance sensor based on dielectric metagrating coupling to the spoof surface plasmon (SSP) mode on periodically grooved metal films. The well-designed silicon metagrating converts the normal incident to the necessary angle in the dielectric substrate exciting SSP with the transmission coupling between couplers and SSP metasurfaces. Using an all-dielectric metagrating as an external coupler, the tightly confined SSP mode can be excited within a small resonant cavity, causing the strong light–matter interaction. The proposed SSP dielectric meta-couplers will pave new routes for ultra-thin and compact sensing devices. The dielectric substrate thickness, the air gap distance between the substrate and the metal groove array, and metal groove gaps have remarkable influences on the characteristics of SSP sensing. The SSP sensing by metagrating coupling with the resonance frequency around 0.404 THz provides a high sensitivity of up to 335 GHz/RIU and a detection limit less than 0.0001 RIU with a frequency resolution of 33.5 MHz. Dielectric metagrating coupling SSP provides enormous potential for constructing ultra-sensitive and compact SSP sensors in the terahertz frequency region.
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