Chunhui Chen - Academia.edu (original) (raw)
Papers by Chunhui Chen
Integrated on-chip energy storage is increasingly important in the fields of internet of things, ... more Integrated on-chip energy storage is increasingly important in the fields of internet of things, energy harvesting, sensing, and wearables; capacitors being ideal for devices requiring higher powers or many thousands of cycles. This work demonstrates electrochemical capacitors fabricated using an electrolyte and porous silicon nanostructures with very high surface-to-volume ratios. Nanopore morphologies and passivation coatings for maximizing energy and power densities of porous-silicon based electrochemical capacitors are studied. Stability is achieved through atomic layer deposition (ALD) titanium nitride or chemical vapor deposition (CVD) carbon coatings. The use of silicon processing methods creates the potential for on-chip energy storage.
Ni-Fe-Al alloys were made by powder metallurgy from mixing the elementary powder Ni, Fe and Al wi... more Ni-Fe-Al alloys were made by powder metallurgy from mixing the elementary powder Ni, Fe and Al with the mole ratio of 56.552׃5.81׃ by three different methods, i.e. balling mill elementary powder Ni, Fe, Al (300 r/min, 12 h); mixing elementary powder Ni, Fe, Al; mixing 50% elementary powder and 50% prealloyed powder. The alloys were sintered at 1 280 for 2 h after shapi ℃ ng them under 500 MPa. The sintered NiFe 18.5 Al 25 alloys were studied by density test, tensile strength measurement, X-ray diffractometry (XRD) and fracture observation. The results show that the alloy fabricated by 50% prealloyed powder and 50% elementary powder has the best property, the density is 6.61 g/cm 3 (relative density is 94.8%) and the tensile strength of sintered alloy is 868 MPa, which indicates that the prealloyed powder added into the elementary powder can control the sintering process, improve the alloy's sintered density, and enhance the mechanical properties of the alloy.
Scanning electron microscopy and X-ray diffraction analysis were used to study microstructure and... more Scanning electron microscopy and X-ray diffraction analysis were used to study microstructure and mechanical properties of PM Ni 56 Fe 19 Al 25 alloy. The results indicate that as sintered specimen is (bzc) dual phase structure, and its density is 6?54 g cm 23 (the relative density is 94?0%), tensile strength is 771 MPa and the total strain is 4?3%. As quenched specimen presents a large superelasticity with the maximum recovery strain of 4?5%, and its tensile strength is 850 MPa and the total strain is 9?2%. The fracture modes of Ni 56 Fe 19 Al 25 alloy is transgranular, intergranular and tough mixed type.
Journal of Power Sources, 2012
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
RARE METAL MATERIALS AND ENGINEERING
ABSTRACT
ECS Transactions, 2014
The rapid development of miniaturized electronic devices has led to a growing need for rechargeab... more The rapid development of miniaturized electronic devices has led to a growing need for rechargeable micro-power sources with high performances. Miniaturized micro-supercapacitors have great potential to replace batteries and electrolytic capacitors in different types of applications. Carbon microelectromechanical systems (C-MEMS) technique, in which patterned photoresist is pyrolyzed in an inert environment at a high temperature is a powerful approach to fabricate high aspect ratio carbon microelectrode arrays, which could be a promising platform for various micro-power applications. To further improve the electrochemical properties of the carbon microelectrodes, different nanomaterials could be integrated by electrostatic spray deposition (ESD). This review provides an overview of our research at FIU on micro-supercapacitors with different structural designs and active materials. 10.1149/06107.0055ecst ©The Electrochemical Society ECS Transactions, 61 (7) 55-64 (2014) 55 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.105.154.21 Downloaded on 2014-08-06 to IP
Energy Harvesting and Storage: Materials, Devices, and Applications VI, 2015
ABSTRACT
ECS Transactions, 2014
ABSTRACT Energy storage systems such as Li-ion batteries and supercapacitors are extremely import... more ABSTRACT Energy storage systems such as Li-ion batteries and supercapacitors are extremely important in today’s society, and have been widely used as the energy and power sources for portable electronics, electrical vehicles and hybrid electrical vehicles. A lot of research has focused on improving their performance; however, many crucial challenges need to be addressed to obtain high performance electrode materials for further applications. Recently, the electrostatic spray deposition (ESD) technique has attracted great interest to satisfy the goals. Due to its many advantages, the ESD technique shows promising prospects compared to other conventional deposition techniques. In this paper, our recent research outcomes related to the ESD derived anodes for Li-ion batteries and other applications is summarized and discussed.
MRS Proceedings, 2011
ABSTRACT
Yusoff/Graphene-based Energy Devices, 2015
ABSTRACT Graphene, the one-atom-thick sheet of sp2-hybridized carbon atoms, ever since its advent... more ABSTRACT Graphene, the one-atom-thick sheet of sp2-hybridized carbon atoms, ever since its advent in the scientific world, has enjoyed a star status. Owing to its unique structure, graphene is known to have extraordinary physical and chemical properties, such as very high electrical conductivity, exceptionally high surface area, and phenomenal mechanical strength. All these properties make graphene particularly attractive for its application in electrochemical capacitors (ECs), also known as supercapacitors. This chapter focuses on the fundamentals of a capacitor; different types of electrochemical capacitors, including electrochemical double-layer capacitors, pseudocapacitors, asymmetric or “hybrid” capacitors; and the applicability of graphene to each of these supercapacitor classes. One section of this chapter is dedicated to the emerging field of microsupercapacitors and the application of graphene as a material for microsupercapacitors. The chapter concludes with a summary and an outlook for further improvements to the currently existing works.
Nanoscale, 2015
Two-dimensional graphene is a promising candidate material for use in high-performance enzymatic ... more Two-dimensional graphene is a promising candidate material for use in high-performance enzymatic biofuel cells (EBFCs). In this work, graphene/enzyme has been integrated onto three-dimensional (3D) micropillar arrays in order to obtain efficient enzyme immobilisation and enhanced enzyme loading and facilitate direct electron transfer. The fabrication process of this system combines top-down carbon microelectromechanical systems (C-MEMS) to fabricate the 3D micropillar array platform and bottom-up electrophoretic deposition (EPD) to deposit the graphene/enzyme onto the electrode surface. The amperometric response of the graphene-based bioelectrode exhibited excellent electrochemical activity, which indicated the successful co-deposition of graphene with the enzymes. The developed 3D graphene/enzyme network-based EBFC generated a maximum power density of 136.3 μW cm(-2) at 0.59 V, which is almost seven times the maximum power density of the bare 3D carbon micropillar array-based EBFC.
Nanomaterials, 2013
Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (... more Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (ESD) technique, and tested as anode materials for Li-ion batteries. The electrochemical performance of the as-deposited TG composites were compared to heat-treated TG composites along with pure tin-oxide films. The heat-treated composites exhibited superior specific capacity and energy density than both the as-deposited TG composites and tin oxide samples. At the 70th cycle, the specific capacities of the as-deposited and post heat-treated samples were 534 and 737 mA·h/g, respectively, and the corresponding energy densities of the as-deposited and heat-treated composites were 1240 and 1760 W·h/kg, respectively. This improvement in the electrochemical performance of the TG composite anodes as compared to the pure tin oxide samples is attributed to the synergy between tin oxide and graphene, which increases the electrical conductivity of tin oxide and helps alleviate volumetric changes in tin-oxide during cycling.
Journal of The Electrochemical Society, 2011
Porous Si prepared by the magnesiothermic reaction was used as anode material for lithium ion bat... more Porous Si prepared by the magnesiothermic reaction was used as anode material for lithium ion batteries. The synthesis conditions were investigated to obtain high purity of silicon phase. The structures of porous Si were characterized by TEM, Raman and N 2 adsorption-desorption. The electrochemical performance was tested by cyclic voltammetry (CV) and discharge-charge measurement. The porous Si exhibits larger storage capacity and improved cyclability compared to commercial Si powders. The enhanced capacity and cyclability are attributed to the loose mesoporous structure of porous Si, which can accommodate large volume change in the lithiation/delithiation process.
Improving the energy capacity of spinel Li4Ti5O12 (LTO) is very important to utilize it as a high... more Improving the energy capacity of spinel Li4Ti5O12 (LTO) is very important to utilize it as a high-performance Li-ion battery (LIB) electrode. In this work, LTO/Si composites with different weight ratios were prepared and tested as anodes. The anodic and cathodic peaks from both LTO and silicon were apparent in the composites, indicating that each component was active upon Li + insertion and extraction. The composites with higher Si contents (LTO:Si = 35:35) exhibited superior specific capacity (1004 mAh·g −1 ) at lower current densities (0.22 A·g −1 ) but the capacity deteriorated at higher current densities. On the other hand, the electrodes with moderate Si contents (LTO:Si = 50:20) were able to deliver stable capacity (100 mAh·g −1 ) with good cycling performance, even at a very high current density of 7 A·g −1 . The improvement in specific capacity and rate performance was a direct result of the synergy between LTO and Si; the former can alleviate the stresses from volumetric changes in Si upon cycling, while Si can add to the capacity of the composite. Therefore, it has been demonstrated that the addition of Si and concentration optimization is an easy yet an effective way to produce high performance LTO-based electrodes for lithium-ion batteries.
Carbon nanofibers (CNFs) were synthesized by electrospinning followed by thermal treatments. Acti... more Carbon nanofibers (CNFs) were synthesized by electrospinning followed by thermal treatments. Activated CNFs (ACNFs) with a surface area of 167.9 m 2 g −1 were obtained from KOH chemical activation. Both CNFs and ACNFs were tested as electrode materials for Li-ion batteries. The ACNFs electrode exhibited enhanced electrochemical performance compared to CNFs electrode, owing to its higher surface area and porous structure. A reversible capacity of 512 mAh g −1 was retained at the 100 th cycle for a current density of 100 mA g −1 . Moreover, even at very high current densities of the order of 1000 mA g −1 the ACNF electrode still maintained a reversible capacity of 265 mAh g −1 . These results demonstrate the potential application of ACNFs as electrode material for Li-ion batteries.
Integrated on-chip energy storage is increasingly important in the fields of internet of things, ... more Integrated on-chip energy storage is increasingly important in the fields of internet of things, energy harvesting, sensing, and wearables; capacitors being ideal for devices requiring higher powers or many thousands of cycles. This work demonstrates electrochemical capacitors fabricated using an electrolyte and porous silicon nanostructures with very high surface-to-volume ratios. Nanopore morphologies and passivation coatings for maximizing energy and power densities of porous-silicon based electrochemical capacitors are studied. Stability is achieved through atomic layer deposition (ALD) titanium nitride or chemical vapor deposition (CVD) carbon coatings. The use of silicon processing methods creates the potential for on-chip energy storage.
Ni-Fe-Al alloys were made by powder metallurgy from mixing the elementary powder Ni, Fe and Al wi... more Ni-Fe-Al alloys were made by powder metallurgy from mixing the elementary powder Ni, Fe and Al with the mole ratio of 56.552׃5.81׃ by three different methods, i.e. balling mill elementary powder Ni, Fe, Al (300 r/min, 12 h); mixing elementary powder Ni, Fe, Al; mixing 50% elementary powder and 50% prealloyed powder. The alloys were sintered at 1 280 for 2 h after shapi ℃ ng them under 500 MPa. The sintered NiFe 18.5 Al 25 alloys were studied by density test, tensile strength measurement, X-ray diffractometry (XRD) and fracture observation. The results show that the alloy fabricated by 50% prealloyed powder and 50% elementary powder has the best property, the density is 6.61 g/cm 3 (relative density is 94.8%) and the tensile strength of sintered alloy is 868 MPa, which indicates that the prealloyed powder added into the elementary powder can control the sintering process, improve the alloy's sintered density, and enhance the mechanical properties of the alloy.
Scanning electron microscopy and X-ray diffraction analysis were used to study microstructure and... more Scanning electron microscopy and X-ray diffraction analysis were used to study microstructure and mechanical properties of PM Ni 56 Fe 19 Al 25 alloy. The results indicate that as sintered specimen is (bzc) dual phase structure, and its density is 6?54 g cm 23 (the relative density is 94?0%), tensile strength is 771 MPa and the total strain is 4?3%. As quenched specimen presents a large superelasticity with the maximum recovery strain of 4?5%, and its tensile strength is 850 MPa and the total strain is 9?2%. The fracture modes of Ni 56 Fe 19 Al 25 alloy is transgranular, intergranular and tough mixed type.
Journal of Power Sources, 2012
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
RARE METAL MATERIALS AND ENGINEERING
ABSTRACT
ECS Transactions, 2014
The rapid development of miniaturized electronic devices has led to a growing need for rechargeab... more The rapid development of miniaturized electronic devices has led to a growing need for rechargeable micro-power sources with high performances. Miniaturized micro-supercapacitors have great potential to replace batteries and electrolytic capacitors in different types of applications. Carbon microelectromechanical systems (C-MEMS) technique, in which patterned photoresist is pyrolyzed in an inert environment at a high temperature is a powerful approach to fabricate high aspect ratio carbon microelectrode arrays, which could be a promising platform for various micro-power applications. To further improve the electrochemical properties of the carbon microelectrodes, different nanomaterials could be integrated by electrostatic spray deposition (ESD). This review provides an overview of our research at FIU on micro-supercapacitors with different structural designs and active materials. 10.1149/06107.0055ecst ©The Electrochemical Society ECS Transactions, 61 (7) 55-64 (2014) 55 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.105.154.21 Downloaded on 2014-08-06 to IP
Energy Harvesting and Storage: Materials, Devices, and Applications VI, 2015
ABSTRACT
ECS Transactions, 2014
ABSTRACT Energy storage systems such as Li-ion batteries and supercapacitors are extremely import... more ABSTRACT Energy storage systems such as Li-ion batteries and supercapacitors are extremely important in today’s society, and have been widely used as the energy and power sources for portable electronics, electrical vehicles and hybrid electrical vehicles. A lot of research has focused on improving their performance; however, many crucial challenges need to be addressed to obtain high performance electrode materials for further applications. Recently, the electrostatic spray deposition (ESD) technique has attracted great interest to satisfy the goals. Due to its many advantages, the ESD technique shows promising prospects compared to other conventional deposition techniques. In this paper, our recent research outcomes related to the ESD derived anodes for Li-ion batteries and other applications is summarized and discussed.
MRS Proceedings, 2011
ABSTRACT
Yusoff/Graphene-based Energy Devices, 2015
ABSTRACT Graphene, the one-atom-thick sheet of sp2-hybridized carbon atoms, ever since its advent... more ABSTRACT Graphene, the one-atom-thick sheet of sp2-hybridized carbon atoms, ever since its advent in the scientific world, has enjoyed a star status. Owing to its unique structure, graphene is known to have extraordinary physical and chemical properties, such as very high electrical conductivity, exceptionally high surface area, and phenomenal mechanical strength. All these properties make graphene particularly attractive for its application in electrochemical capacitors (ECs), also known as supercapacitors. This chapter focuses on the fundamentals of a capacitor; different types of electrochemical capacitors, including electrochemical double-layer capacitors, pseudocapacitors, asymmetric or “hybrid” capacitors; and the applicability of graphene to each of these supercapacitor classes. One section of this chapter is dedicated to the emerging field of microsupercapacitors and the application of graphene as a material for microsupercapacitors. The chapter concludes with a summary and an outlook for further improvements to the currently existing works.
Nanoscale, 2015
Two-dimensional graphene is a promising candidate material for use in high-performance enzymatic ... more Two-dimensional graphene is a promising candidate material for use in high-performance enzymatic biofuel cells (EBFCs). In this work, graphene/enzyme has been integrated onto three-dimensional (3D) micropillar arrays in order to obtain efficient enzyme immobilisation and enhanced enzyme loading and facilitate direct electron transfer. The fabrication process of this system combines top-down carbon microelectromechanical systems (C-MEMS) to fabricate the 3D micropillar array platform and bottom-up electrophoretic deposition (EPD) to deposit the graphene/enzyme onto the electrode surface. The amperometric response of the graphene-based bioelectrode exhibited excellent electrochemical activity, which indicated the successful co-deposition of graphene with the enzymes. The developed 3D graphene/enzyme network-based EBFC generated a maximum power density of 136.3 μW cm(-2) at 0.59 V, which is almost seven times the maximum power density of the bare 3D carbon micropillar array-based EBFC.
Nanomaterials, 2013
Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (... more Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (ESD) technique, and tested as anode materials for Li-ion batteries. The electrochemical performance of the as-deposited TG composites were compared to heat-treated TG composites along with pure tin-oxide films. The heat-treated composites exhibited superior specific capacity and energy density than both the as-deposited TG composites and tin oxide samples. At the 70th cycle, the specific capacities of the as-deposited and post heat-treated samples were 534 and 737 mA·h/g, respectively, and the corresponding energy densities of the as-deposited and heat-treated composites were 1240 and 1760 W·h/kg, respectively. This improvement in the electrochemical performance of the TG composite anodes as compared to the pure tin oxide samples is attributed to the synergy between tin oxide and graphene, which increases the electrical conductivity of tin oxide and helps alleviate volumetric changes in tin-oxide during cycling.
Journal of The Electrochemical Society, 2011
Porous Si prepared by the magnesiothermic reaction was used as anode material for lithium ion bat... more Porous Si prepared by the magnesiothermic reaction was used as anode material for lithium ion batteries. The synthesis conditions were investigated to obtain high purity of silicon phase. The structures of porous Si were characterized by TEM, Raman and N 2 adsorption-desorption. The electrochemical performance was tested by cyclic voltammetry (CV) and discharge-charge measurement. The porous Si exhibits larger storage capacity and improved cyclability compared to commercial Si powders. The enhanced capacity and cyclability are attributed to the loose mesoporous structure of porous Si, which can accommodate large volume change in the lithiation/delithiation process.
Improving the energy capacity of spinel Li4Ti5O12 (LTO) is very important to utilize it as a high... more Improving the energy capacity of spinel Li4Ti5O12 (LTO) is very important to utilize it as a high-performance Li-ion battery (LIB) electrode. In this work, LTO/Si composites with different weight ratios were prepared and tested as anodes. The anodic and cathodic peaks from both LTO and silicon were apparent in the composites, indicating that each component was active upon Li + insertion and extraction. The composites with higher Si contents (LTO:Si = 35:35) exhibited superior specific capacity (1004 mAh·g −1 ) at lower current densities (0.22 A·g −1 ) but the capacity deteriorated at higher current densities. On the other hand, the electrodes with moderate Si contents (LTO:Si = 50:20) were able to deliver stable capacity (100 mAh·g −1 ) with good cycling performance, even at a very high current density of 7 A·g −1 . The improvement in specific capacity and rate performance was a direct result of the synergy between LTO and Si; the former can alleviate the stresses from volumetric changes in Si upon cycling, while Si can add to the capacity of the composite. Therefore, it has been demonstrated that the addition of Si and concentration optimization is an easy yet an effective way to produce high performance LTO-based electrodes for lithium-ion batteries.
Carbon nanofibers (CNFs) were synthesized by electrospinning followed by thermal treatments. Acti... more Carbon nanofibers (CNFs) were synthesized by electrospinning followed by thermal treatments. Activated CNFs (ACNFs) with a surface area of 167.9 m 2 g −1 were obtained from KOH chemical activation. Both CNFs and ACNFs were tested as electrode materials for Li-ion batteries. The ACNFs electrode exhibited enhanced electrochemical performance compared to CNFs electrode, owing to its higher surface area and porous structure. A reversible capacity of 512 mAh g −1 was retained at the 100 th cycle for a current density of 100 mA g −1 . Moreover, even at very high current densities of the order of 1000 mA g −1 the ACNF electrode still maintained a reversible capacity of 265 mAh g −1 . These results demonstrate the potential application of ACNFs as electrode material for Li-ion batteries.