Carbon nanofibers decorated with FeO<i> _x </i> nanoparticles as a flexible electrode material for symmetric supercapacitors

Samuel, Edmund,Joshi, Bhavana,Jo, Hong Seok,Kim, Yong Il,An, Seongpil,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. Elsevier 2017 Chemical Engineering Journal Vol. No.

<P><B>Abstract</B></P> <P>We have produced flexible, freestanding, and light weight mats of FeO<I> <SUB>x</SUB> </I>-decorated carbon nanofibers (CNFs) and demonstrated their use in supercapacitors with high energy and power density and excellent long term capacitance retention. Highly flexible carbon-iron oxide nanofibers were synthesized by electrospinning a solution of polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and iron acetylacetonate (FeAcAc), followed by annealing to carbonize the PAN, pyrolyze the PMMA to produce pores, and convert FeAcAc to FeO nanoparticles. The morphology of the FeO<I> <SUB>x</SUB> </I>/CNF composite was determined by scanning and transmission electron microscopies, which showed that the embedded FeO<I> <SUB>x</SUB> </I> nanoparticles were well distributed in the CNF electrode. We employed cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy to evaluate the electrochemical performance of symmetric supercapacitors prepared from the FeO<I> <SUB>x</SUB> </I>/CNF composite. The supercapacitors exhibited high specific capacitance (427F·g<SUP>−1</SUP> at 10mV·s<SUP>−1</SUP> and 436F·g<SUP>−1</SUP> at 1A·g<SUP>−1</SUP> in the optimal case) and good stability, retaining 89% of their initial capacitance after 5000 cycles at a current density of 1A·g<SUP>−1</SUP>. The optimal device achieved an energy density of 167Wh·kg<SUP>−1</SUP> at a power density of 0.75kW·kg<SUP>−1</SUP>, and an energy density of 66Wh·kg<SUP>−1</SUP> at a power density of 7.5kW·kg<SUP>−1</SUP>. These combinations of energy and power densities can meet the needs of many emerging supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly flexible FeO<SUB>x</SUB>-carbon nanocomposite nanofibers were fabricated. </LI> <LI> Freestanding FeO<I> <SUB>x</SUB> </I>-CNF showed excellent retention (89%) after 5000 cycles at 1A·g<SUP>−1</SUP>. </LI> <LI> A FeO<SUB>x</SUB>/CNF-based supercapacitor provides 436F·g<SUP>−1</SUP> of capacitance at 1A·g<SUP>−1</SUP>. </LI> <LI> Excellent uniform decoration of CNF with FeO<SUB>x</SUB> was demonstrated. </LI> </UL> </P>

Flexible and freestanding core-shell SnO_<i>x</i>/carbon nanofiber mats for high-performance supercapacitors

Samuel, Edmund,Joshi, Bhavana,Jo, Hong Seok,Kim, Yong Il,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.728 No.-

<P><B>Abstract</B></P> <P>We demonstrate the fabrication of core-shell SnO<SUB> <I>x</I> </SUB>/carbon nanofiber (CNF) composite mats via single-nozzle one-step electrospinning for use as flexible freestanding electrodes in supercapacitors. The freestanding and flexible nature of the composites is essential for their use in lightweight, portable, and foldable electronic devices and eliminates the need for a separate current collector. We fully characterized the structural and morphological properties of the SnO<SUB> <I>x</I> </SUB>/CNF mats and optimized the SnO<SUB> <I>x</I> </SUB> to CNF precursor ratio. The optimized SnO<SUB> <I>x</I> </SUB>/CNF-based symmetric supercapacitor exhibited a capacitance of 289 F·g<SUP>−1</SUP> at a scan rate of 10 mV·s<SUP>−1</SUP>. Moreover, it retained more than 88% of its initial capacitance after 5000 cycles, highlighting the long-term stability of supercapacitors based on these SnO<SUB> <I>x</I> </SUB>/CNF mats.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A core-shell-structured SnO<SUB>x</SUB>/CNF composite mat electrodes were synthesized by single-nozzle-electrospinning. </LI> <LI> The core-shell composite is highly flexible and freestanding. </LI> <LI> Capacitors using these electrodes had specific capacitance of up to 289 F·g<SUP>−1</SUP> at a scan rate of 10 mV·s<SUP>−1</SUP>. </LI> <LI> Specific capacitance at a current density of 100 mA·g<SUP>−1</SUP> reached 273 F·g<SUP>−1</SUP>. </LI> </UL> </P>

Decoration of MnO Nanocrystals on Flexible Freestanding Carbon Nanofibers for Lithium Ion Battery Anodes

Samuel, Edmund,Jo, Hong Seok,Joshi, Bhavana,An, Seongpil,Park, Hyun Goo,Il Kim, Yong,Yoon, Woo Young,Yoon, Sam S. Elsevier 2017 ELECTROCHIMICA ACTA Vol.231 No.-

<P><B>Abstract</B></P> <P>We demonstrate the fabrication of freestanding and flexible MnO-decorated carbon nanofiber (CNF) composites as lithium-ion battery anode materials. They showed an initial capacity of 1131mAh·g<SUP>−1</SUP> and a retention capacity of 923mAh·g<SUP>−1</SUP> after 90 charge-discharge cycles under a current rate of 123mA·g<SUP>−1</SUP>. Decoration of MnO nanocrystals on the CNFs enhanced the lithium storage capacity of the composites. The optimal concentration of MnO was identified by varying its weight percentage from 0 to 7%. When the concentration was increased, more reaction sites for lithium ions were formed, which in turn increased the overall specific capacity. The intensity of the <I>D</I> band in the Raman spectra of the decorated CNFs was higher than that of the <I>G</I> band, indicating the enhanced diffusion of lithium ions. The plateau region of the discharge curve observed in the cases of higher MnO concentrations indicated the active reduction of MnO; consequently, a higher reversible capacity was achieved. These flexible and freestanding MnO-CNF nanocomposites can be used in lightweight, portable, and flexible batteries.</P>

Supersonic cold spraying of titania nanoparticles on reduced graphene oxide for lithium ion battery anodes

Samuel, Edmund,Lee, Jong-Gun,Joshi, Bhavana,Kim, Tae-Gun,Kim, Min-woo,Seong, Il Won,Yoon, Woo Young,Yoon, Sam S. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.715 No.-

<P><B>Abstract</B></P> <P>Titania (TiO<SUB>2</SUB>) nanoparticles were uniformly distributed on and are well attached to reduced graphene oxide (rGO) by supersonic cold spraying. The process facilitated rapid production of lithium ion battery (LIB) anodes. Integration of TiO<SUB>2</SUB> with rGO not only enhanced the conductivity of the anode, but also prevented agglomeration of the titania nanoparticles, which facilitated uniform distribution of the nanoparticles and thus consistently reduced the electron diffusion length. Integration of rGO with TiO<SUB>2</SUB> widened the characteristic voltage range of the resulting rGO-TiO<SUB>2</SUB> composite (0.01–3 V) relative to that of pure TiO<SUB>2</SUB>, which enhanced the capacity during the lithiation process. Therefore, the LIB cell exhibited superior performance with long cycle durations even under high current rate. The optimal weight ratio of rGO to TiO<SUB>2</SUB> was found to be 1:1, which produced a retention capacity of 203 mA h g<SUP>−1</SUP> at <I>N</I> = 300 cycle under a current rate of 1 C = 336 mA g<SUP>−1</SUP>. Rapid production of rGO/TiO<SUB>2</SUB> nanocomposites via supersonic cold spraying may facilitate commercialization of high-quality LIB cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Uniform rGO-TiO<SUB>2</SUB> films were fabricated as LIB anode via rapid supersonic spraying. </LI> <LI> The optimized concentrations of rGO and TiO<SUB>2</SUB> presented to get higher capacity. </LI> <LI> Very high retention capacity of 203 mA h g<SUP>−1</SUP> is obtained at 1 C at 300th cycle. </LI> <LI> Excellent rate capability performance exhibited through synergy of rGO and TiO<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

High-performance supercapacitors using flexible and freestanding MnO_x/carbamide carbon nanofibers

Samuel, Edmund,Jo, Hong Seok,Joshi, Bhavana,Park, Hyun Goo,Kim, Yong Il,An, Seongpil,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.423 No.-

<P><B>Abstract</B></P> <P>We demonstrate the fabrication of a MnO<I> <SUB>x</SUB> </I>/carbamide carbon nanofiber (CCNF) composite consisting of MnO particles embedded in CCNFs as a highly flexible and freestanding electrode material for supercapacitors. A sacrificial polymer component, polymethylmethacrylate, included in the precursor solution, pyrolyzes during heating, resulting in pores in the fibers, some of which are filled by the MnO nanocrystals. Carbamide is added to control the size of the MnO<I> <SUB>x</SUB> </I> particles as well as to increase the carbon content of the composite and hence its conductivity. The X-ray diffraction and Raman spectra of the composite show that the MnO particles formed have low crystallinity. Transmission electron microscopy confirms that the MnO particles are distributed very uniformly over the CCNFs. Symmetric supercapacitors constructed using electrodes of this composite exhibit specific capacitances of 498F∙g<SUP>−1</SUP> at a scan rate of 10mV∙s<SUP>−1</SUP> and 271F∙g<SUP>−1</SUP> at a current density of 1A∙g<SUP>−1</SUP>. They also exhibit excellent long-term cycling performance, retaining 93% of their initial capacity after 5000 cycles of galvanostatic charging/discharging.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We successfully fabricated a novel flexible MnO/CCNF composite. </LI> <LI> Flexible MnO/CCNF showed excellent retention (93%) after 5000 cycles at 1Ag<SUP>−1</SUP>. </LI> <LI> MnO/CCNF composite demonstrated specific capacitance of 498Fg<SUP>−1</SUP> at a scan rate of 10mVs<SUP>−1</SUP>. </LI> <LI> Dynamic MnO particle formation controlled by using carbamide. </LI> </UL> </P>

Electrosprayed graphene decorated with ZnO nanoparticles for supercapacitors

Samuel, Edmund,Londhe, Priyanka U.,Joshi, Bhavana,Kim, Min-Woo,Kim, Karam,Swihart, Mark T.,Chaure, Nandu B.,Yoon, Sam S. Elsevier 2018 Journal of alloys and compounds Vol.741 No.-

<P><B>Abstract</B></P> <P>A binder-free nanocomposite consisting of ZnO nanoparticles (NPs) grown directly on graphene sheets by electrospraying was fabricated for use as an electrode material in supercapacitors. The optimal concentrations of graphene and ZnO NPs were determined from the capacitive characteristics of the composite. Scanning electron microscopy confirmed that the ZnO NPs grew in a uniformly distributed manner on the graphene sheets and that they exhibited negligible agglomeration. Further, X-ray diffraction analysis confirmed that ZnO growth was preferentially oriented along (100) plane in the ZnO/graphene composite. A symmetric supercapacitor fabricated using this composite exhibited an energy density of 67 mWh·cm<SUP>−3</SUP> and power density of 6000 mW·cm<SUP>−3</SUP>. The composite also showed good long-term cycling performance, retaining 90% of its capacitance after 1000 galvanostatic charge/discharge cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO/graphene electrodes for supercapacitor applications have been fabricated using electrospraying. </LI> <LI> A symmetric supercapacitor exhibited an energy density of 67 mWh·cm-3 and power density of 6000 mW·cm<SUP>−3</SUP>. </LI> <LI> The composite retained 90% of its capacitance after 1000 galvanostatic charge and discharge cycles. </LI> <LI> The graphene sheets prevented agglomeration of the ZnO nanoparticles. </LI> </UL> </P>

Hierarchical zeolitic imidazolate framework-derived manganese-doped zinc oxide decorated carbon nanofiber electrodes for high performance flexible supercapacitors

Samuel, Edmund,Joshi, Bhavana,Kim, Min-Woo,Kim, Yong-Il,Swihart, Mark T.,Yoon, Sam S. Elsevier 2019 Chemical Engineering Journal Vol.371 No.-

<P><B>Abstract</B></P> <P>We demonstrate freestanding, flexible, and cost-effective supercapacitor electrodes comprising carbon nanofibers (CNFs) decorated with metal oxide framework (MOF)-derived manganese-doped zinc oxide (Mn@ZnO). Nanoparticles of manganese-doped zeolitic imidazolate framework (ZIF-8) were grown directly on electrospun polyacrylonitrile nanofibers by a simple solution-phase synthesis. Carbonization of these composite fibers produced high surface area dodecahedral Mn@ZnO on core CNFs that provide fast electron-transfer pathways. The synergy between Mn@ZnO (active sites for Faradaic reactions) and the highly electrically conductive carbon nanofiber improves the performance of the supercapacitor electrode. The Mn@ZnO/CNF electrodes exhibit a high specific capacitance of 501 F·g<SUP>−1</SUP> and retain >92% of their initial capacitance after 10,000 cycles. The optimized Mn@ZnO/CNF electrodes deliver impressive energy densities of 72.1 W·h·kg<SUP>−1</SUP> and 33.3 W·h·kg<SUP>−1</SUP> at power densities of 500 W·kg<SUP>−1</SUP> and 5000 W·kg<SUP>−1</SUP>, respectively. This electrochemical performance demonstrates that the Mn@ZnO/CNF nanostructured composite is a robust electrode material for long-lifetime high-rate energy storage/delivery devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrospun nanofiber mats are surface-decorated with Mn-doped ZIF-8 nanoparticles. </LI> <LI> Freestanding flexible Mn@ZnO/CNF is demonstrated as a promising supercapacitor electrode. </LI> <LI> Enhanced capacitance of 501 F·g<SUP>−1</SUP> and 92% capacitance retention after 10,000 cycles are obtained. </LI> </UL> </P>

Hierarchically designed ZIF-8-derived Ni@ZnO/carbon nanofiber freestanding composite for stable Li storage

Joshi, Bhavana,Samuel, Edmund,Il Kim, Yong,Kim, Min-Woo,Jo, Hong Seok,Swihart, Mark T.,Yoon, Woo Young,Yoon, Sam S. Elsevier 2018 Chemical engineering journal Vol.351 No.-

<P><B>Abstract</B></P> <P>We present a uniform rhombohedral Ni@ZnO bimetallic oxide host over carbon nanofibers (CNF) as an anode material for Li-ion batteries. Ni@ZnO was produced by annealing a Ni@zeolitic imidazolate framework (ZIF-8) hierarchically decorated over CNFs. The rationally-designed freestanding composite exhibited promising stability in electrochemical performance. A first reversible capacity of 1051 mA·h·g<SUP>−1</SUP> was measured at a current density of 100 mA·g<SUP>−1</SUP>, and 88% of this capacity was retained after 100 cycles. We attribute this high capacity retention to the hierarchical structure of the Ni@ZnO-enwrapped carbon framework encapsulating the conductive CNFs, as demonstrated by scanning and transmission electron microscopy. The composite electrode also showed a high specific capacity of ∼497 mA·h·g<SUP>−1</SUP> in high-rate testing at 1000 mA·g<SUP>−1</SUP>, because the cage-like framework of the material allowed rapid charge transfer and Li-ion diffusion in the anode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Carbon enwrapped with bimetallic Ni@ZnO was decorated on carbon nanofibers via chemical surface treatment. </LI> <LI> The composite electrode showed highly stable electrochemical performance during long-term cycling. </LI> <LI> The superior performance is attributed to synergy of Ni@ZnO (high capacity) and carbon (stability). </LI> </UL> </P>

Hierarchical ZIF-67 of dodecahedral structure on binder-free carbon nanofiber for flexible supercapacitors

Ashwin Khadka,Edmund Samuel,김용일,Chanwoo Park,이해석,Sam S. Yoon 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.118 No.-

Binder-free, highly flexible carbon nanofibers decorated with ZIF-67 dodecahedral structures are synthesizedvia electrospinning and impregnation for use in supercapacitor applications. Because cobalt ionsfrom ZIF-67 are highly attracted to carbon rings and the oxygen functional groups of polyvinylpyrrolidone(PVP), the concentration of PVP is varied to tune the morphology of ZIF-67. Accordingly, morphologytuning via PVP inclusion enhances the electron transfer within the ZIF-67-derived CoOx dodecahedralstructure. Parametric studies are conducted to investigate the effect of PVP concentration on the electrochemicalperformance of carbon nanofibers decorated with ZIF-67. The optimal sample yields a capacitanceof 444 mFcm2 at a current rate of 5 mAcm2. The corresponding capacitance retention is 94 %after 30,000 cycles with a potential window of 1 V. Furthermore, the energy density increases by262.7 % when the potential window is increased from 1 to 1.5 V. These results confirm the long-term stabilityand outstanding energy-storage capabilities of the fabricated supercapacitor electrodes.

Supersonically spray-coated zinc ferrite/graphitic-carbon nitride composite as a stable high-capacity anode material for lithium-ion batteries

Joshi, Bhavana,Samuel, Edmund,Kim, Tae-Gun,Park, Chan-Woo,Kim, Yong-Il,Swihart, Mark T.,Yoon, Woo Young,Yoon, Sam S. Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.768 No.-

<P><B>Abstract</B></P> <P>This manuscript reports the preparation, characterization, and testing of stable high-capacity lithium-ion battery anodes based on graphitic carbon nitride (g-CN) nanosheets hosting ZnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles (ZFCN). The ZFCN is prepared by a one-pot thermal process, then supersonic cold spraying is used to rapidly deposit films with a lamellar morphology that allows enhanced capacity retention by preventing particle agglomeration. The presence of g-CN nanosheets minimizes degradation of ZnFe<SUB>2</SUB>O<SUB>4</SUB> by providing a buffering space during the lithiation/delithiation process. The ZFCN composite anodes exhibit first reversible capacities of 1550 mAh·g<SUP>−1</SUP> at 50 mA·g<SUP>−1</SUP> and up to 934 mAh·g<SUP>−1</SUP> at 1000 mA·g<SUP>−1</SUP> after 20 cycles. The superior electrochemical performance and capacity retention (88% after 160 cycles at 100 mA·g<SUP>−1</SUP> relative to the first reversible capacity) are attributed to highly reversible alloying/conversion mechanisms. The combination of high performance and stability with the use of low-cost earth-abundant elements and scalable processing approaches gives this ZFCN composite immense potential for use as a stable high-performance anode material for lithium-ion batteries.</P> <P> <UL> <LI> ZnFe<SUB>2</SUB>O<SUB>4</SUB>/g-C<SUB>3</SUB>N<SUB>4</SUB> films were fabricated as LIB anode via rapid supersonic spraying. </LI> <LI> Lamellar morphology prevented particle agglomeration ensuing enhanced capacity retention. </LI> <LI> High capacity retention of 93% is observed at 100 mA·g<SUP>-1</SUP> after 70th cycle. </LI> <LI> The ZFCN composite shows high capacity of 934 mAh·g<SUP>-1</SUP> at 1000 mA·g<SUP>-1</SUP> current rate. </LI> </UL> </P>