Research Fellow, National University of Singapore
Rational design of functional materials from metal organic framework
In recent years, Metal Organic Frameworks (MOFs) and their derivatives have received considerable attention due to their unique structures and wide applications in catalysis, sensors as well as energy storage and conversion. However, most of the previous studies on MOF-based/derived materials were focused on particle-like structures, and there are few reports on one-dimensional (1D) or two-dimensional (2D) structured MOFs. In addition the electrode materials were prepared in powdered forms with polymer binder and carbon additives, which can hardly meet the application requirement for flexible and wearable devices. Thus it will be very promising to develop novel structured MOFs on flexible support for high-performance flexible energy storage and electrocatalysis.
In the present work, a novel hollowed NiCo2O4 nanobox arrays have been rational designed on flexible carbon cloth substrate from a 2D cobalt MOF precursor. The resulted hollow and porous structure can be directly used as a flexible electrode for both supercapacitor and oxygen evolution reaction catalyst. Due to the unique hollow and porous structure which can provide rich reaction sites and short ion diffusion length, and the direct electrical and mechanical contact with the conductive support, the unique NiCo2O4 nanobox arrays demonstrated high robust mechanical flexibility and outstanding electrochemical performance in both supercapacitor and oxygen evolution reaction tests.
Abstract: Based on a new “one for two” strategy, a single two-dimensional (2D) metal–organic framework (MOF) precursor has been transformed into both electrodes (i.e., a Co3O4 cathode and a N-doped carbon anode) for a flexible asymmetric supercapacitor. The device demonstrated not only highly robust mechanical flexibility but also outstanding electrochemical performance. The “one for two” concept can significantly ease the fabrication process and has great potential to be extended to other functional materials for different applications.
Pub.: 17 Jan '17, Pinned: 27 Jul '17
Abstract: This study reports the design and fabrication of ultrathin MoS2 nanosheets@metal organic framework-derived N-doped carbon nanowall array hybrids on flexible carbon cloth (CC@CN@MoS2) as a free-standing anode for high-performance sodium ion batteries. When evaluated as an anode for sodium ion battery, the as-fabricated CC@CN@MoS2 electrode exhibits a high capacity (653.9 mA h g−1 of the second cycle and 619.2 mA h g−1 after 100 cycles at 200 mA g−1), excellent rate capability, and long cycling life stability (265 mA h g−1 at 1 A g−1 after 1000 cycles). The excellent electrochemical performance can be attributed to the unique 2D hybrid structures, in which the ultrathin MoS2 nanosheets with expanded interlayers can provide shortened ion diffusion paths and favorable Na+ insertion/extraction space, and the porous N-doped carbon nanowall arrays on flexible carbon cloth are able to improve the conductivity and maintain the structural integrity. Moreover, the N-doping-induced defects also make them favorable for the effective storage of sodium ions, which enables the enhanced capacity and rate performance of MoS2.
Pub.: 07 Jul '17, Pinned: 27 Jul '17
Abstract: Aqueous Ni/Fe batteries have great potential as flexible energy storage devices, owing to their low cost, low toxicity, high safety, and high energy density. However, the poor cycling stability has limited the widely expected application of Ni/Fe batteries, while the use of heavy metal substrates cannot meet the basic requirement for flexible devices. In this work, a flexible type of solid‐state Ni/Fe batteries with high energy and power densities is rationally developed using needle‐like Fe3O4 and flake‐like NiO directly grown on carbon cloth/carbon nanofiber (CC–CF) matrix as the anode and cathode, respectively. The hierarchical CC–CF substrate with high electric conductivity and good flexibility serves as an ideal support for guest active materials of nanocrystalline Fe3O4 and NiO, which can effectively buffer the volume change giving rise to good cycling ability. By utilizing a gel electrolyte, a robust and mechanically flexible quasi‐solid‐state Ni/Fe full cell can be assembled. It demonstrates optimal electrochemical performance, such as high energy density (5.2 mWh cm−3 and 94.5 Wh Kg−1), high power density (0.64 W cm−3 and 11.8 KW Kg−1), together with excellent cycling ability. This work provides an example of solid‐state alkaline battery with high electrochemical performance and mechanical flexibility, holding great potential for future flexible electronic devices.
Pub.: 18 Jul '16, Pinned: 27 Jul '17
Abstract: Metal-organic frameworks (MOFs) are promising porous precursors for the construction of various functional materials for high-performance electrochemical energy storage and conversion. Herein, a facile two-step solution method to rational design of a novel electrode of hollow NiCo2O4 nanowall arrays on flexible carbon cloth substrate is reported. Uniform 2D cobalt-based wall-like MOFs are first synthesized via a solution reaction, and then the 2D solid nanowall arrays are converted into hollow and porous NiCo2O4 nanostructures through an ion-exchange and etching process with an additional annealing treatment. The as-obtained NiCo2O4 nanostructure arrays can provide rich reaction sites and short ion diffusion path. When evaluated as a flexible electrode material for supercapacitor, the as-fabricated NiCo2O4 nanowall electrode shows remarkable electrochemical performance with excellent rate capability and long cycle life. In addition, the hollow NiCo2O4 nanowall electrode exhibits promising electrocatalytic activity for oxygen evolution reaction. This work provides an example of rational design of hollow nanostructured metal oxide arrays with high electrochemical performance and mechanical flexibility, holding great potential for future flexible multifunctional electronic devices.
Pub.: 25 Jan '17, Pinned: 27 Jul '17