Browsing by Author "Chang, Jeng-Kuei"

Now showing 1 - 20 of 42

A functionalized membrane for lithium-oxygen batteries to suppress the shuttle effect of redox mediators
(2019-06-21)
Chen, Zi-Fang
;
Lin, Xiaodong
;
Xia, Hui
;
Hong, Yuhao
;
Liu, Xiaoyu
Redox mediators (RMs) are widely applied in lithium-oxygen (Li-O-2) batteries since they offer an alternative way to avoid the direct electrochemical oxidization of Li2O2 during charging, and thus greatly reduce the charge overpotential. Unfortunately, the defenseless Li-metal anode is severely corroded by the oxidized RMs shuttled from the cathode side, resulting in the low utilization of RMs and poor cycling stability. Herein, a functionalized double-guaranteed NPG membrane with electrostatic repulsion and steric hindrance characteristics is proposed to suppress the shuttle effect of LiI RM. Benefiting from the interaction between the O atoms in PEO and the sulfonic acid groups in Nafion and the two-dimensional skeleton structure of graphene, Nafion, PEO and graphene can couple with each other, forming a large network barrier with multi-functional properties. As expected, the LiI-based Li-O-2 batteries with the NPG membrane exhibited a smooth, iodine-free Li anode surface after many cycles and delivered an ultrahigh discharge capacity of similar to 26 917 mA h g(-1) at a current density of 200 mA g(-1) and ultralong cycle life (472 cycles) at 500 mA g(-1) with a cutoff capacity of 500 mA h g(-1), which are far better than that of the bare batteries.
A Holey Graphene Additive for Boosting Performance of Electric Double-Layer Supercapacitors
(2020-04-01)
Huang, Jun-Bin
;
Patra, Jagabandhu
;
Lin, Ming-Hsien
;
Ger, Ming-Der
;
Liu, Yih-Ming
We demonstrate a facile and effective method, which is low-cost and easy to scale up, to fabricate holey graphene nanosheets (HGNSs) via ultrafast heating during synthesis. Various heating temperatures are used to modify the material properties of HGNSs. First, we use HGNSs as the electrode active materials for electric double-layer capacitors (EDLCs). A synthesis temperature of 900 degrees C seems to be optimal, i.e., the conductivity and adhesion of HGNSs reach a compromise. The gravimetric capacitance of this HGNS sample (namely HGNS-900) is 56 Fg(-1). However, the volumetric capacitance is low, which hinders its practical application. Secondly, we incorporate activated carbon (AC) into HGNS-900 to make a composite EDLC material. The effect of the AC:HGNS-900 ratio on the capacitance, high-rate performance, and cycling stability are systematically investigated. With a proper amount of HGNS-900, both the electrode gravimetric and volumetric capacitances at high rate charging/discharging are clearly higher than those of plain AC electrodes. The AC/HGNS-900 composite is a promising electrode material for nonaqueous EDLC applications.
A Lithium-Ion Rechargeable Full Cell Using the Flower-like Na3V2(PO4)(3)@C Cathode and Li4Ti5O12 Anode
(2020-05-18)
Akhtar, Mainul
;
Pradhan, Sunil Kumar
;
Chang, Jeng-Kuei
;
Majumder, Subhasish Basu
;
材料科學與工程學系
In the present work, we have demonstrated that nanopetal-assembled hierarchical carbon-coated Na3V2(PO4)(3) (nNVP@C) microflowers, synthesized via a microwave-assisted hydrothermal route, play an important role for yielding superior electrochemical characteristics of a Li4Ti5O12 (LTO)//nNVP@C full cell. Thus, the full cell yields superior power density with decent discharge capacity after extended cycling and good rate performance. The nanosize petals help Li+ to diffuse faster in NVP particles, and the inner mesoporous morphology of microflowers allows the electrolyte to easily penetrate into the embedded NVP@C nanocrystals. Furthermore, the homogeneous carbon coating provides an elastic buffer to mitigate the strain developed during Na+ extraction and subsequent Li+ insertion and extraction. The LTO//nNVP@C full cell is claimed to be suitable for power applications, where relatively thinner electrodes would be flooded with a sufficient amount of the lithium salt-containing organic electrolyte. To improve the cycleability characteristics, one requires to match carefully the Li+ activity in the organic electrolyte with electrode capacity. This would ensure stoichiometric lithium-ion insertion in the LTO electrode together with predominant lithium-ion insertion in the nNVP@C cathode.
A Novel Moisture-Insensitive and Low-Corrosivity Ionic Liquid Electrolyte for Rechargeable Aluminum Batteries
(1970-01-01)
Li, Chi
;
Patra, Jagabandhu
;
Li, Ju
;
Rath, Purna Chandra
;
Lin, Ming-Hsien
Rechargeable aluminum batteries (RABs) are extensively developed due to their cost-effectiveness, eco-friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture-sensitive and corrosive. To address these problems, a 4-ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4-ethylpyridine molar ratio on the electrode charge-discharge properties are systematically examined. A maximum graphite capacity of 95 mAh g(-1) is obtained at 25 mA g(-1). After 1000 charge-discharge cycles, approximate to 85% of the initial capacity can be retained. In situ synchrotron X-ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon-fiber paper electrodes are confirmed in the 4-ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N-2-filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications.
A polyoxometalate-based polymer electrolyte with an improved electrode interface and ion conductivity for high-safety all-solid-state batteries
(2019-07-14)
Yuan, Xiangfei
;
Sun, Cui
;
Duan, Jia-Ning
;
Fan, Jingmin
;
Yuan, Ruming
Solid electrolytes have been considered as some of the most promising candidates for next generation lithium-based batteries because they eliminate the potential safety hazards of liquid organic electrolytes and further increase the energy density of batteries. However, inherent defects such as low conductivity and poor interface compatibility with electrodes critically hinder their extensive application. Polyoxometalate Li-7[V15O36(CO3)] (LVC) can dissociate Li+ in electrolyte and possesses a high diffusion coefficient, which constitute a pathway for Li+ transmission. Herein, a polyoxometalate-based polymer electrolyte (PPE) with an improved electrode interface and ion conductivity for high-safety all-solid-state batteries has been designed and synthesized to further enhance their electrochemistry behaviour. Compared with the routine PEO18LiTFSI electrolyte, the ionic conductivity was enhanced. Meanwhile, LVC can improve the interface compatibility between the electrode and electrolyte significantly, which promotes reaction kinetics and suppresses lithium dendrites against Li metal. When employed in LiFePO4|Li batteries, the specific discharge capacity after 180 cycles reached 148 mA h g(-1) with a high coulombic efficiency of around 99.9% at 0.5C. According to the result of ARC, LiFePO4|C batteries with PPEs are endowed with superior safety as the onset temperature of the self-heating process reaches up to 181.4 degrees C and the thermal runaway process does not occur within the range of 360 degrees C, indicating the potential of the PPE for high-safety all-solid-state batteries.
A Water-Soluble NaCMC/NaPAA Binder for Exceptional Improvement of Sodium-Ion Batteries with an SnO2-Ordered Mesoporous Carbon Anode
(2018-11-23)
Patra, Jagabandhu
;
Rath, Purna Chandra
;
Li, Chi
;
Kao, Hsien-Ming
;
Wang, Fu-Ming
SnO2@CMK-8 composite, a highly promising anode for Na-ion batteries (NIBs), was incorporated with polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to optimize the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA led to the formation of an effective protective film on the electrode. This coating layer not only increased the charge-discharge Coulombic efficiency, suppressing the accumulation of solid-electrolyte interphases, but also kept the SnO2 nanoparticles in the CMK-8 matrix, preventing the agglomeration and removal of oxide upon cycling. The adhesion strength and stability towards the electrolyte of the binders were evaluated. In addition, the charge-transfer resistance and apparent Na+ diffusion of the SnO2@CMK-8 electrodes with various binders were examined and post-mortem analyses were conducted. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mAh g(-1) were obtained at charge-discharge rates of 20 and 2000 mA g(-1), respectively. After 300 cycles, 90 % capacity retention was achieved. The thermal reactivity of the sodiated electrodes was studied by using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are discussed.
Amino-functionalization on graphene oxide sheets using an atomic layer amidation technique
(2020-01-14)
Gu, Siyong
;
Hsieh, Chien-Te
;
Mallick, Bikash Chandra
;
Gandomi, Yasser Ashraf
;
Chang, Jeng-Kuei
Nitrogen functionalization on graphene sheets has solely been demonstrated with a stepwise amidation implementation within the literature. The present work proposes an atomic layer amidation (ALN) technique to linearly adjust the surface amidation level on the carbon nanostructures. The ALN cycling protocol proposed in this work consists of an ammonia pulse, nitrogen pulse, and pumping at 100 and 150 degrees C. Both surface amidation and oxidation levels were linearly controlled by the ALN cycle number. The ALN technique was demonstrated as a self-limiting process capable of step-by-step N-functionalizing graphene oxide (GO) sheets on the atomic scale. The amidation reaction rates were ca. 0.023 (100 degrees C) and 0.028 atomic percent (at%) cycle(-1) (150 degrees C), and the apparent activation energy was determined to be 14.3 kJ mol(-1) (= 0.148 eV atom(-1)) from the Arrhenius equation. The amidation mechanism for forming the "chemical N" and "lattice N" at an atomic level was also proposed. Linearly controlling the optical band-gap with the ALN cycle number was suggested as a robust method for tuning the oxidation as well as the amidation level on the GO sheets. In this sense, nitrogen functionalization can be utilized for engineering any desirable properties within the graphene sheets.
Applications of Copolymers Consisting of 2,6-di(9H-carbazol-9-yl)pyridine and 3,6-di(2-thienyl)carbazole Units as Electrodes in Electrochromic Devices
(2019-04-02)
Kuo, Chung-Wen
;
Chang, Jui-Cheng
;
Huang, Yu-Ting
;
Chang, Jeng-Kuei
;
Lee, Li-Ting
A series of carbazole-based polymers (PdCz, P(dCz2-co-dTC1), P(dCz2-co-dTC2), P(dCz1-co-dTC2), and PdTC) were deposited on indium tin oxide (ITO) conductive electrodes using electrochemical polymerization. The as-prepared P(dCz2-co-dTC2) displayed a high T (57.0%) and multichromic behaviors ranging from yellowish green, greenish gray, gray to purplish gray in different redox states. Five organic electrochromic devices (ECDs) were built using dCz- and dTC-containing homopolymers and copolymers as anodic materials, and poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProdot-Me-2) as the cathodic material. The P(dCz2-co-dTC2)/PProdot-Me-2 ECD presented remarkable electrochromic behaviors from the bleached to colored states. Moreover, P(dCz2-co-dTC2)/PProdot-Me-2 ECD displayed a high optical contrast (T, 45.8%), short switching time (ca. 0.3 s), high coloration efficiency (528.8 cm(2) C-1) at 580 nm, and high redox cycling stability.
Atomic layer oxidation on graphene sheets for tuning their oxidation levels, electrical conductivities, and band gaps
(2018-09-07)
Gu, Siyong
;
Hsieh, Chien-Te
;
Lin, Tzu-Wei
;
Yuan, Chun-Yao
;
Gandomi, Yasser Ashraf
Graphene sheets that can exhibit electrical conducting and semiconducting properties are highly desirable and have potential applications in fiber communications, photodetectors, solar cells, semiconductors, and broadband modulators. However, there is currently no efficient method that is able to tune the band gap of graphene sheets. This work adopts an efficient atomic layer oxidation (ALO) technique to cyclically increase the oxidation level of graphene sheets, thus, tuning their electrical conductance, band-gap structure, and photoluminescence (PL) response. The O/C atomic ratio as an increasing function of the ALO cycle number reflects two linear regions: 0.23% per cm(2) per cycle (0-15 cycles) and 0.054% per cm(2) per cycle (15-100 cycles). The excellent correlation coefficients reveal that the ALO process follows a self-limiting route to step-by-step oxidize graphene layers. The interlayer distance of ALO-graphene sheets shows an obvious increase after the ALO treatment, proved by X-ray diffraction. As analyzed by X-ray photon spectroscopy, the hydroxyl or epoxy group acts as a major contributor to the interlayer spacing distance and oxidation extent in the initial ALO stage, as compared to carbonyl and carboxyl groups. The ALO mechanism, based on Langmuir-Hinshelwood and Eley-Rideal models, is proposed to clarify the formation of oxygen functionalities and structural transformation from pristine graphene sheets to oxidized ones during the ALO cycle. With a tunable oxidation level, the electrical resistivity, semiconductor character, and PL response of ALO-graphene samples can be systematically controlled for desired applications. The ALO approach is capable of offering a straightforward route to tune the oxidation level of graphene sheets or other carbons.
Carbonaceous Anodes Derived from Sugarcane Bagasse for Sodium-Ion Batteries
(2019-05-21)
Rath, Purna Chandra
;
Patra, Jagabandhu
;
Huang, Hao-Tzu
;
Bresser, Dominic
;
Wu, Tzi-Yi
To realize the sustainability of Na-ion batteries (NIBs) for large-scale energy storage applications, a resource-abundant and cost-effective anode material is required. In this study, sugarcane bagasse (SB), one of the most abundant types of biowaste, is chosen as the carbon precursor to produce a hard carbon (HC) anode for NIBs. SB has a great balance of cellulose, hemicellulose, and lignin, which prevents full graphitization of the pyrolyzed carbon but ensures a sufficiently ordered carbon structure for Na+ transport. Compared with HC derived from waste apples, which are pectin-rich and have less cellulose than SB, SB-derived HC (SB-HC) has fewer defects and a lower oxygen content. SB-HC thus has a higher first-cycle sodiation/desodiation coulombic efficiency and better cycling stability. In addition, SB-HC has a unique flake-like morphology, which can shorten the Na+ diffusion length, and higher electronic conductivity (owing to more sp(2)-hybridized carbon), resulting in superior high-rate charge-discharge performance to apple-derived HC. The effects of pyrolysis temperature on the material characteristics and electrochemical properties, evaluated by using chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy, are systematically investigated for both kinds of HC.
Composition Modulation of Ionic Liquid Hybrid Electrolyte for 5 V Lithium-Ion Batteries
(2019-11-13)
Wu, Chia-Jung
;
Rath, Puma Chandra
;
Patra, Jagabandhu
;
Bresser, Dominic
;
Passerini, Stefano
Electrolyte is a key component in high-voltage lithium-ion batteries (LIBs). Bis(trifluoromethanesulfonyl)imide-based ionic liquid (IL)/organic carbonate hybrid electrolytes have been a research focus owing to their excellent balance of safety and ionic conductivity. Nevertheless, corrosion of Al current collectors at high potentials usually happens for this kind of electrolyte. In this study, this long-standing problem is solved via the modulation of the IL/carbonate ratio and LiPF6 concentration in the hybrid electrolyte. The proposed electrolyte suppresses Al dissolution and electrolyte oxidation at 5 V (vs Li+/Li) and thus allows for ideal lithiation/delithiation performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode even at 55 degrees C. The underlying mechanism is examined in this work. Excellent cycling stability (97% capacity retention) for an LNMO cathode after 300 cycles is achieved. This electrolyte shows good wettability toward a polyethylene separator and low flammability. In addition, satisfactory compatibility with both graphite and Si-based anodes is confirmed. The proposed electrolyte design strategies have great potential for applications in high-voltage LIBs.
Effects of TiO2 and SDC addition on the properties of YSZ electrolyte
(2019-11-12)
Shen, Chin-Tien
;
Lee, Kan-Rong
;
Hsieh, Yu-Pin
;
Lee, Sheng-Wei
;
Chang, Jeng-Kuei
In this study, we investigate the effects of adding titanium dioxide (TiO2) and samarium doped cerium oxide (SDC) on the properties of yttrium-stabilized zirconia (YSZ) electrolyte. The microstructure, mechanical, and electrochemical properties of the electrolyte are investigated. The performance in CO2 electrolysis is measured by supplying carbon dioxide to Ni-YSZ electrode and nitrogen to LSM electrode. Results show that TiO2 and SDC addition can reduce the sintering temperature and increase grain size. The ionic conductivity is 0.123 S cm(-1) at 1000 degrees C. In addition, the thermal expansion coefficient at 1000 degrees C is 8.25 x 10(-6)K(-1). The current density of the cell is 439 mA cm(-2) at 1.3 V and 1000 degrees C in solid oxide electrolysis cell. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Fabrication of anode-supported thin BCZY electrolyte protonic fuel cells using NiO sintering aid
(2019-09-03)
Lee, Kan-Rong
;
Tseng, Chung-Jen
;
Jang, Shian-Ching
;
Lin, Jing-Chie
;
Wang, Kuan-Wen
A thin and fully dense BaCe0.6Zr0.2Y0.2O3-delta(BCZY) electrolyte for the use of anode-supported protonic fuel cells has been successfully prepared by spin coating using NiO sintering aid. The effects of NiO addition on the electrolyte microstructures and fuel cell performances are also investigated. An appropriate NiO addition has a significant positive contribution to the densification and grain growth of thin BCZY electrolytes. However, too much NiO addition gives rise to NiO aggregation in BCZY electrolyte and deteriorates the cell performance. The enhanced sintering mechanism can be mainly attributed to the oxygen vacancies generated from the NiO decomposition and bulk diffusion of Ni into BCZY perovskites. The fuel cell with a BCZY-3%NiO electrolyte exhibits the highest maximum power density of similar to 106.6 mW/cm(2) at 800 degrees C among all fuel cells in this study. The electrochemical impedance characteristics of thin BCZY electrolyte fuel cells are further discussed under open circuit conditions. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Facile synthesis of core-shell structured Si@graphene balls as a high-performance anode for lithium-ion batteries
(2020-05-07)
Jamaluddin, Anif
;
Umesh, Bharath
;
Chen, Fuming
;
Chang, Jeng-Kuei
;
Su, Ching-Yuan
Encapsulating silicon (Si) nanoparticles with graphene nanosheets in a microspherical structure is proposed to increase electrical conductivity and solve stability issues when using Si as an anode material in lithium-ion batteries (LIBs). Currently the main strategies to produce high-quality Si-graphene (Si@Gra) electrodes are (1) chemical vapor deposition (CVD) of graphene grown in situ on Si by hydrocarbon precursors and (2) encapsulating Si with a graphene oxide followed by postannealing. However, both methods require a high-temperature and are costly and time-consuming procedures, which hinders their mass scalability and practical utilization. Herein, we report a Si@Gra composite with a ball-like structure that is assembled by a facile spray drying process without a postannealing treatment. The graphene sheets are synthesized by an electrochemical exfoliation method from natural graphite. The resulting Si@Gra composite exhibits a unique core-shell structure, from which the ball-like morphology and the number of graphene layers in the Si@Gra composites are found to affect both the electric conductivity and ionic conductivity. The Si@Gra composites are found to increase the capacity of the anode and provide excellent cycling stability, which is attributed to the high electrical conductivity and mechanical flexibility of the layered graphene; additionally, a void space in the core-shelled ball structure inside the Si@Gra compensates for the Si volume expansion. As a result, the Si@few-layer graphene ball anode exhibits a high initial discharge capacity of 2882.3 mA h g(-1) and a high initial coulombic efficiency of 86.9% at 0.2 A g(-1). The combination of few-layer graphene sheets and the spray drying process can effectively be applied for large-scale production of core-shell structured Si@Gra composites as promising anode materials for use in high-performance LIBs.
Fluorescence of functionalized graphene quantum dots prepared from infrared-assisted pyrolysis of citric acid and urea
(2020-01-01)
Gu, Siyong
;
Hsieh, Chien-Te
;
Yuan, Chun-Yao
;
Gandomi, Yasser Ashraf
;
Chang, Jeng-Kuei
This paper reports an efficient fabrication of N-doped graphene quantum dots (GQDs) showing controllable chemical and fluorescence (FL) properties through infrared carbonization (IRC) of citric acid and urea. The GQDs prefer to form an equilibrium shapes of circle with an average particle size ranged from 5 to 10 nm. The N/C atomic ratio in GQDs can be precisely tailored in a range from 21.6 to 49.6 at.% by simply controlling the weight ratio of citric acid to urea. With increasing the urea content, the GQDs not only contain N-doped graphene but also incorporate with crystalline cyanuric acid, forming a binary crystallinity. The quantum yield of 22.2% is achieved by N-doped GQDs, prepared from the IRC synthesis of chemical precursor at the citric acid/urea at 3:1. Excessive N and cyanuric acid can lead to FL quenching, red shift and wide spectral distribution. The design of GQDs possesses a multiple chromophoric band-gap structure, originated from the presence of cyanuric acid, defect-related emissive traps, and functional group distributions. This work offers an effective and inspiring approach to engineering both chemical compositions and unique crystalline structures of GQDs, and will therefore facilitate their fundamental research and applications to optical, sensing, energy and biological fields.
Ga-doped lithium lanthanum zirconium oxide electrolyte for solid-state Li batteries
(2020-09-01)
Mishra, Mrinalini
;
Hsu, Che-Wei
;
Rath, Purna Chandra
;
Patra, Jagabandhu
;
Lai, Hong-Zheng
Cubic-phase Li7La3Zr2O12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al-and Ga-doped LLZO can transform to a cubic-phase garnet at 900 degrees C. After 1200 degrees C sintering, a Li2ZrO3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900-1200 degrees C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(tri-fluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications. (c) 2020 Elsevier Ltd. All rights reserved.
Germanium-assisted growth of titanium dioxide nanowires for enhanced photocatalytic and electron emission performance
(2020-11-15)
Chen, Chih-Yen
;
Lin, Tzu-Chien
;
Chuang, Wen-Shuo
;
Chang, Jeng-Kuei
;
Lee, Sheng-Wei
In this study, free-standing and well-aligned titanium dioxide (TiO2) nanowires were grown on a Ti foil by precisely controlling the growth temperature and the thickness of the Ge catalyst layer. The catalyst layer played an important role in activating the surface of the Ti foil, facilitating the growth of TiO2 nanowires on it in a chemical vapor deposition furnace system. The structure of the TiO2 nanowires was investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The photocatalytic experiment results showed that the optimum Ge catalyst layer thickness significantly improved the rhodamine B (RhB) degradation efficiency of the nanowires. The TiO2 nanowires grown using a 40-nm-thick Ge layer could degrade 74% of RhB after 5 h of ultraviolet irradiation. In addition, the TiO2 nanowires exhibited excellent electron field emission performance as compared to the TiO2 nanocrystals grown without the Ge catalyst layer. The results suggested that TiO2 nanowires grown using a Ge catalyst layer are promising materials for next-generation electronic emitters and photocatalytic systems.
High energy density of all-screen-printable solid-state microsupercapacitors integrated by graphene/CNTs as hierarchical electrodes
(2019-05-28)
Chih, Jui-Kung
;
Jamaluddin, Anif
;
Chen, Fuming
;
Chang, Jeng-Kuei
;
Su, Ching-Yuan
Microsupercapacitors (MSCs) are alternative power sources that have the potential to fulfill the increasing demand for wearable and on-chip electronics as they are small and lightweight, and show extremely high charge-discharge rates and power densities, and have high flexibility. However, the critical challenge of recent MSCs is the limitation of low energy density and complicated fabrication processes that are high cost and time-consuming. Here, we reported an all-screen-printable method for fabricating all-solid (including electrolytes) and flexible MSCs by rationally designed composite electrodes with electrochemically exfoliated graphene (ECG) and long single-walled carbon nanotubes (CNTs). This method demonstrated to be a facile and scalable route to fabricate and assemble MSCs in a cost-effective manner and with high throughput. As a result, the resulting MSC devices exhibit an areal capacitance of 7.7 mF cm(-2) and volumetric capacitance of 77.3 F cm(-3), with an excellent cyclic stability of >99% after 15000 cycles; this can be attributed to the creation of a high diffusion path and the promotion of ion transport capability. The cell exhibits energy and power densities of 10.7 mW h cm(-3) and 3.17 W cm(-3), respectively. Moreover, there was negligible degradation in capacitance when subjected to bending deformation with radius reduced to 0.5 mm, indicating excellent mechanical flexibility and operation stability. Further, the output voltage and current can be rationally designed by multiple connections of MSC devices in series and parallel to fulfill the demands of various applications. This study provides a scalable and cost-effective method to produce solid-state MSCs with high energy density, which paves the way for their applications in potential wearable devices.
High Power Na3V2(PO4)(3)@C/AC Bi-material Cathodes for Hybrid Battery-Capacitor Energy Storage Devices
(2020-01-08)
Akhtar, Mainul
;
Chang, Jeng-Kuei
;
Majumder, S. B.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have reported the synthesis and electrochemical characteristics of carbon-coated sodium vanadium phosphate/activated carbon (NVP@C/AC) bi-material electrodes. We have reported that bi-material type NVP@C/AC cathodes offer superior rate performance as compared to either NVP@C or AC electrodes. Through a detailed impedance spectroscopy analyses, we demonstrated that the synergic effect observed in the bi-material electrodes correlates well with the lowering of their charge transfer resistances (R-CT) and the increase of Li(+)diffusion coefficient (DLi+) with the increase of activated carbon content from 0 to 0.60 weight fraction. Through a detailed cyclic voltammogram analyses we have delineated the faradaic and capacitive contribution towards the overall capacities of the bi-material electrodes at various rate conditions. For both these bi-materials, irrespective of the AC content and rate, capacitive contribution dominates the overall capacity. NVP@C/AC40 yields discharge capacities of 67 and 40 mAh g(-1)with capacity retention of more than 93% and 67% after 500 cycles measured at 50 and 1000 mA g(-1), respectively. These bi-materials are demonstrated to be excellent material candidates for high power density lithium titanium oxide (LTO)//NVP@C/AC hybrid battery-capacitor (bat-cap) energy storage devices.
High reversible Li plating and stripping by in-situ construction a multifunctional lithium-pinned array
(2020-06-01)
Xu, Pan
;
Lin, Xiaodong
;
Hu, Xinyu
;
Cui, Xueyang
;
Fan, Xiaoxiang
Lithium metal is the most promising anode candidate because of its ultrahigh theoretical specific capacity. Unfortunately, its high reactivity, uncontrolled dendrites, "dead lithium" formation, and infinite volume expansion hinder its commercial application. Herein, by in-situ constructing a multifunctional lithium-pinned array (m-LPA) endowed with functions of lithiophilicity, zoning effect and riveting effect on a surfacely phosphorized three-dimensional (3D) copper foam, a high reversible Li plating/stripping electrochemistry can be achieved. Benefiting from the m-LPA, lithium can uniformly plate/strip both on the surface and in the inner space of the 3D skeletons with improved morphology. Consequently, a high Coulombic efficiency (similar to 98.41%) could be achieved at 1 mA cm(-2) with 1 mA h cm(-2) for over 600 cycles (1200 h). Moreover, at a higher current density of 10 mA cm(-2) with 0.5 mA h cm(-2), a symmetric cell with m-LPA@Li electrode could still stably cycle for 900 cycles. Finally, a full cell coupled with LiFePO4 cathode displayed excellent rate performance with a lower overpotential. The conception and strategy of m-LPA, which were first proposed here, are a promising way to realize large-scale application of Li anode.