Daniel H. C. Chua

National University of Singapore, Tumasik, Singapore

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Publications (99)216.83 Total impact

  • Yong Liu, Xingtao Xu, Ting Lu, Zhuo Sun, Daniel H. C. Chua, Likun Pan
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    ABSTRACT: A nitrogen-doped electrospun reduced graphene oxide–carbon nanofiber composite (NG–CNF) was fabricated via electrospinning by adding graphite oxide into a precursor solution and subsequent thermal treatment under an ammonia atmosphere. The morphology, structure and electrochemical performance of the composite were characterized by scanning electron microscopy, nitrogen adsorption–desorption, cyclic voltammetry and electrochemical impedance spectroscopy, and their capacitive and electrosorption performances in NaCl solution were studied. The NG–CNF composite electrode shows excellent specific capacitance (337.85 F g−1) and electrosorption capacity (3.91 mg g−1), much higher than those of pure carbon nanofibers (171.28 F g−1 and 3.13 mg g−1) and the reduced graphene oxide–carbon nanofiber composite (264.32 F g−1 and 3.60 mg g−1). The enhanced performance of the NG–CNF is ascribed to the nitrogen doping and the formation of an effective “plane-to-line” conducting network in the composite, which facilitates the electron transfer and ion transport as well as increases the specific surface area.
    RSC Advances 04/2015; 5(43). DOI:10.1039/C5RA00620A · 3.71 Impact Factor
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    ABSTRACT: Nitrogen-doped porous carbon spheres (NPCSs) were prepared through a fast microwave-assisted approach using sucrose as the precursor in a microwave system and subsequent thermal treatment in ammonia atmosphere at different temperatures. The morphology, structure and electrochemical performance of the NPCSs were characterized by scanning electron microscopy, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy, and their electrosorption performance in NaCl solution was studied. The results show that NPCSs treated at 1000 °C exhibit an extremely high electrosorption capacity of 14.91 m g g−1 when the initial NaCl concentration is 1000 mg l−1, which shows great improvement compared with their undoped counterpart. The nitrogen doping is suggested to be a very effective method to improve the electrosorption performance, and the NPCSs should be a very promising candidate as electrode material for CDI application.
    Electrochimica Acta 03/2015; 158:403-409. DOI:10.1016/j.electacta.2015.01.179 · 4.09 Impact Factor
  • Yong Liu, Likun Pan, Xingtao Xu, Ting Lu, Zhuo Sun, daniel h. c. chua
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    ABSTRACT: Carbon nanorods (CNRs) were fabricated from natural based nanocrystalline cellulose through simple thermal treatment at 800, 1000 and 1200 °C. The morphology, structure and electrochemical performance of CNRs were characterized by atomic force microscopy, Raman spectroscopy, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy. Their electrosorption performance in NaCl solution was studied. The results show that CNRs treated at 1200 °C exhibit the highest specific capacitance of 264.19 F g-1 and electrosorption capacity of 15.12 mg g-1 with the initial NaCl concentration is 500 mg l-1, due to their high specific surface area and low charge transfer resistance.
    10/2014; DOI:10.1039/C4TA04578E
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    ABSTRACT: Molybdenum sulfide has recently attracted much attention due to its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 oC. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo5+ and S22- species in the MoSx, especially with S22- serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mLg-1cm-2h-1 (286 mmolg-1cm-2h-1) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy.
    ACS Applied Materials & Interfaces 09/2014; DOI:10.1021/am5039592 · 5.90 Impact Factor
  • Aditya P. Murawala, Tamie A.J. Loh, Daniel H.C. Chua
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    ABSTRACT: We report the fabrication of a three-dimensional forest of highly crystalline two-dimensional (2D) molybdenum disulfide (MoS2) nano-petals encapsulating vertically aligned carbon nanotubes (CNT) in a core-shell configuration. Growth was conducted via magnetron sputtering at room temperature and it was found that the nano-petal morphology was formed only when a critical threshold in sputter deposition time was reached. Below this threshold, an amorphous tubular structure composed of mainly molybdenum oxides dominates instead. The presence of the MoS2 nano-petals was shown to impart photoluminescence to the CNTs, in addition to significantly enhancing their electron emission properties, where the turn-on field was lowered from 2.50 Vμm−1 for pristine CNTs to 0.80 Vμm−1 for MoS2-CNT heterostructures fabricated at 30 min sputter deposition time. Photoluminescence was detected at wavelengths of approximately 684 nm and 615 nm, with the band at 684 nm gradually blue-shifting as sputter time was increased. These results demonstrate that it is possible to synthesize 2D MoS2 layers without the need for chemical routes and high growth temperatures.
    Journal of Applied Physics 09/2014; 116(11):114305-114305-8. DOI:10.1063/1.4895834 · 2.19 Impact Factor
  • Tamie A J Loh, Daniel H C Chua
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    ABSTRACT: Pulsed laser deposition (PLD) on metal substrates has recently been discovered to present an alternative method for producing highly crystalline few-layer MoS2. However, not every metal behaves in the same manner during film growth, and hence, it is crucial that the ability of various metals to produce crystalline MoS2 be thoroughly investigated. In this work, MoS2 was deposited on metal substrates, Al, Ag, Ni, and Cu, using a pulsed laser. Highly crystalline few-layer MoS2 was successfully grown on Ag, but is absent in Al, Ni, and Cu under specific growth conditions. This discrepancy was attributed to either excessively strong or insufficient adlayer-substrate interactions. In the case of Al, the effects of the strong interface interactions can be offset by increasing the amount of source atoms supplied, thereby producing semicrystalline few-layer MoS2. The results show that despite PLD being a physical vapor deposition technique, both physical and chemical processes play an important role in MoS2 growth on metal substrates.
    ACS Applied Materials & Interfaces 09/2014; 6(18). DOI:10.1021/am503719b · 5.90 Impact Factor
  • Tamie A.J. Loh, Daniel H. C. Chua
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    ABSTRACT: Precise control of the thickness of few-layer molybdenum disulphide (MoS2) is still a challenge for commonly utilized physical exfoliation and chemical synthesis methods. Herein, we report the successful fabrication of highly crystalline few-layer MoS2 on silver substrates by pulse laser deposition at the relatively low temperature of 500 degrees C. The growth process is facilitated by the in situ formation of nearly lattice-matching Ag2S on the silver surface. The number of layers is easily controlled by selection of appropriate laser energy and deposition time. This synthetic approach is straightforward and easily adapted to other transition metal dichalcogenides to create heterostructures with alternating layers.
    Chemical Physics Letters 08/2014; 610. DOI:10.1016/j.cplett.2014.07.041 · 1.99 Impact Factor
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    ABSTRACT: Graphene has been known for its superior electronic properties ever since its discovery in 2004. The high aspect ratio and ballistic transport properties exhibited by this one-dimensional material are especially useful for electron emission applications. However, they are typically grown horizontally and excess efforts, such as the use of transfer techniques, is required to orientate them before effective electron emission from the graphene edges can occur. These transfer techniques have been shown to lead to additional defects to the as-grown graphene structure, thereby degrading its properties. Here, we present an approach to directly fabricate graphene onto metal nano-sized spindt tips (or nanocones) using the solid-state transformation of carbon deposited from a pulsed laser system at low temperature. Besides providing a layer of chemical and mechanical protection for the metal nanocones, the graphene-on-metal nanocones gave enhanced emission properties compared to bare metal nanocones. This was due to the reduction of effective field emission tunneling barrier, which was a result of graphene-metal charge transfer interactions. Controlling the metal nanocones density was also an important factor in determining the field emission performance, as electron screening from neighboring cones should be minimized.
    Advanced Materials Interfaces 08/2014; 1(5). DOI:10.1002/admi.201300147
  • Canadian Journal of Physics 07/2014; 92(7/8):667-670. DOI:10.1139/cjp-2013-0648 · 0.93 Impact Factor
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    ABSTRACT: Nitrogen-doped carbon microspheres (NCSs) were fabricated via a simple, fast and energy-saving microwave-assisted method followed by thermal treatment under an ammonia atmosphere. NCSs thermally treated at different temperatures were investigated as anode materials for lithium ion batteries (LIBs). The results show that NCSs treated at 900 °C exhibit a maximum reversible capacity of 816 mA h g(-1) at a current density of 50 mA g(-1) and preserve a capacity of 660 mA h g(-1) after 50 cycles, and even at a high current density of 1000 mA g(-1), a capacity of 255 mA h g(-1) is maintained. The excellent electrochemical performance of NCSs is due to their porous structure and nitrogen-doping. The present NCSs should be promising low-cost anode materials with a high capacity and good cycle stability for LIBs.
    Dalton Transactions 06/2014; 43(40). DOI:10.1039/c4dt01223b · 4.10 Impact Factor
  • Yong Liu, Likun Pan, Xingtao Xu, Ting Lu, Zhuo Sun, Daniel H.C. Chua
    Electrochimica Acta 06/2014; 130:619-624. DOI:10.1016/j.electacta.2014.03.086 · 4.09 Impact Factor
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    ABSTRACT: We report the direct growth of a unique all-carbon hierarchical graphene-carbon nanotube (G-CNT) hybrid structure on Toray carbon paper using chemical vapor deposition methods. Morphological characterization shows that the graphene is directly grafted onto the CNT scaffold. The hybrid possesses an ultra-high density of exposed graphene edges while retaining the porous structure of CNT scaffold. Using the G-CNT hybrid in the magnetron sputtering electrocatalyst preparation technique, an integrated, polytetrafluoroethylene binder-free cathode (Pt/G-CNT) with an ultra-low Pt loading of 0.04 mg cm−2 is obtained. This cathode shows superior polarization performance compared to a commercial carbon black-supported Pt catalyst (Pt/VXC72) reference.
    03/2014; 3(6-6):F37-F40. DOI:10.1149/2.009406eel
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    ABSTRACT: Carbon aerogels (CAs) electrodes with reduced graphene oxide (RGO) additive were fabricated and used as electrosorption electrodes. The capacitive deionization (CDI) performance of the CAs electrodes with different proportions of RGO was investigated. The results show that the CAs electrodes with RGO additive exhibit better electrosorption performance compared with pure CAs electrodes and an electrode with acetylene black additive, indicating that RGO can serve as a flexible bridge to form a “plane-to-point” (RGO-to-CAs) conducting network, which can improve the electron transfer within the CAs electrode. The CAs electrode with 15 wt% RGO was further used in membrane capacitive deionization which integrates ion-exchange membranes with CDI and an extremely high desalination efficiency of 98% was obtained.
    03/2014; 1(3). DOI:10.1039/C3QI00102D
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    ABSTRACT: A simple and scalable electrospinning process followed by thermal treatment was used to fabricate carbon nanofibers (CFs). The as-prepared CFs were investigated as anode materials for sodium ion batteries (SIBs). Remarkably, due to their weakly ordered turbostratic structure and a large interlayer spacing between graphene sheets, the CFs exhibit a dominant adsorption/insertion sodium storage mechanism that shows high reversibility. As a result, the CFs show excellent electrochemical performance, especially cycle stability (97.7% capacity retention ratio over 200 cycles). Reversible capacities of 233 and 82 mA h g−1 are obtained for the CFs at a current density of 0.05 A g−1 and even a high current density of 2 A g−1, respectively. The excellent cycle performance, high capacity and good rate capability make the CFs promising candidates for practical SIBs.
    02/2014; 2(12). DOI:10.1039/C3TA14806H
  • T. A. J. Loh, D. H. C. Chua
    01/2014; 3(4):M11-M17. DOI:10.1149/2.005404jss
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    ABSTRACT: A fast microwave-assisted approach was developed to fabricate carbon microspheres (CSs) using sucrose as the precursor in a microwave system. After thermal treatment at 300, 500, 700 and 1000 °C, the CSs were used as anode materials for sodium ion batteries (SIBs). The results show that CSs treated at 500 °C exhibit a maximum capacity of 183 mA h g−1 at a current density of 30 mA g−1 after 50 cycles, and even at a high current density of 1000 mA g−1 a capacity of 83 mA h g−1 is maintained. The high capacity, good cycling stability and excellent rate performance of CSs, due to their unique spherical structure, make them a promising candidate for anode materials for SIBs.
    12/2013; 2(5). DOI:10.1039/C3TA14037G
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    ABSTRACT: Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized.
    Sensors 10/2013; 13(10):13744-78. DOI:10.3390/s131013744 · 2.05 Impact Factor
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    ABSTRACT: A mille-feuille structured amorphous selenium (a-Se)-arsenic selenide (As2Se3) multi-layered thin film and a mixed amorphous Se-As2Se3 film is compared from a durability perspective and photo-electric perspective. The former is durable to incident laser induced degradation after numerous laser scans and does not crystallise till 105 degrees of annealing, both of which are improved properties from the mixed evaporated film. In terms of photo-electric properties, the ratio between the photocurrent and the dark current improved whereas the increase of the dark current was higher than that of As2Se3 due to the unique current path developed within the mille-feuille structure. Implementing this structure into various amorphous semiconductors may open up a new possibility towards structure-sensitive amorphous photoconductors.
    Journal of Non-Crystalline Solids 10/2013; 378:96-100. DOI:10.1016/j.jnoncrysol.2013.06.022 · 1.72 Impact Factor
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    ABSTRACT: In recent years, energy security and climate change have emerged as the topmost global concern. The quest for viable renewable energy technologies has been on the rise. Proton Exchange Membrane Fuel Cells (PEMFCs) are identified as one of the most promising candidates for direct applications in transportation and portable applications. However, the commercialisation of PEMFCs is currently hindered by unsolved issues of which one is the insufficient durability, partly due to carbon support corrosion during PEMFC operations. In this work, we report the use of a Graphene nanoflakes-Carbon nanotubes (GNFs-CNTs) hybrid material as an alternative catalyst support for PEMFCs. GNFs-CNTs were grown directly onto carbon paper, using radio frequency plasma enhanced chemical vapour deposition. Scanning electron microscopy (SEM) showed that GNFs-CNTs hybrid was composed mainly of GNFs densely grafted onto CNTs. The morphology of the as-grown GNFs-CNTs hybrid possessed numerous exposed graphene edges while retaining the porous morphology of CNTs with an average diameter of 100 nm. The GNFs-CNTs hybrid was both used as the catalyst support and micro-porous layer. Platinum catalyst was directly sputtered onto the surface. The accelerated degradation test (ADT) was measured on single cell 5 cm 2 membrane electrode assembly with cathode is the working electrode. ADT was performed by oxidation potential cycling between 0.6 V (for 40 s) and 1.4 V (for 20 s) for 100 cycles. The results showed a significant improvement in the electrochemical stability of the GNFs-CNTs supported Pt catalyst over commercially available Pt/Vulcan XC72 catalyst.
    246th National Meeting of the American-Chemical-Society (ACS), Indianapolis, IN; 09/2013
  • physica status solidi (RRL) - Rapid Research Letters 07/2013; 7(7):n/a-n/a. DOI:10.1002/pssr.201370438 · 2.34 Impact Factor

Publication Stats

554 Citations
216.83 Total Impact Points


  • 2009–2014
    • National University of Singapore
      • Department of Materials Science and Engineering
      Tumasik, Singapore
  • 2007
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Tumasik, Singapore
  • 2002–2004
    • University of Cambridge
      • Department of Engineering
      Cambridge, England, United Kingdom