| 1. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Cellulose-derived carbon nanofibers/graphene composite electrodes for powerful compact supercapacitors
- 2017
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 7:73, s. 45968-45977
-
Journal article (peer-reviewed)abstract
- Herein, we demonstrate a unique supercapacitor composite electrode material that is originated from a sustainable cellulosic precursor via simultaneous one-step carbonization/reduction of cellulose/graphene oxide mats at 800 degrees C. The resulting freestanding material consists of mechanically stable carbon nanofibrous (CNF, fiber diameter 50-500 nm) scaffolds tightly intertwined with highly conductive reduced graphene oxide (rGO) sheets with a thickness of 1-3 nm. The material is mesoporous and has electrical conductivity of 49 S cm(-1), attributed to the well-interconnected graphene layers. The electrochemical evaluation of the CNF/graphene composite electrodes in a supercapacitor device shows very promising volumetric values of capacitance, energy and power density (up to 46 F cm(-3), 1.46 W h L-1 and 1.09 kW L-1, respectively). Moreover, the composite electrodes retain an impressive 97% of the initial capacitance over 4000 cycles. With these superior properties, the produced composite electrodes should be the "looked-for" components in compact supercapacitors used for increasingly popular portable electronics and hybrid vehicles.
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| 2. |
- Haque, Mohammad Mazharul, 1984
(author)
-
Electrolyte evaluation and engineering for the performance enhancement of electrochemical capacitors
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- As a consequence of a fast-paced technological evolution along with the acknowledgment of utilizing clean and renewable energy resources over fossil fuels, the importance of energy storage devices is widely recognized. The electrochemical capacitor (EC), commonly known as a supercapacitor or ultracapacitor, is an energy storage device that is already being used in portable consumer electronics, electrification of transportation, and grid-level applications. High power density and long cycle life are the two most prominent properties of ECs, thanks to the electrostatic nature of their charge storage mechanism. These properties are well utilized in a system where ECs are used as a backup power-boosting device to rechargeable batteries. By providing the peak power required, they eventually prolong the battery lifetime. However, the relatively low energy density of ECs compared to rechargeable batteries limits their application as a standalone device. In addition, low operating voltage, adverse self-discharge rate, severe leakage current, elevated temperature incompatibility are some of the crucial issues that are preventing the widespread application of ECs. Besides a general discussion about ECs, the main objective of this thesis is to identify and address the above-mentioned critical challenges, and to propose and demonstrate corresponding solutions. Firstly, it is revealed that utilizing a redox-active KBr electrolyte can enhance both operating voltage and capacitance, and hence increases energy density without sacrificing power density or cycle life. Secondly, an evaluation of elevated temperature influence on the capacitive performance of ECs containing ionic liquid (IL) electrolyte demonstrates a high working temperature beyond 120 °C. Thirdly, a systematic investigation of ECs containing IL at elevated temperatures shows a significant increase of the self-discharge rate with temperature and pinpoints the underlying mechanisms; at lower initial voltages the self-discharge rate is dominated by diffusion of electrolyte ions rather than charge redistribution. Fourthly, the addition of a small amount of liquid crystals (LC) in neutral electrolyte shows a reduction of self-discharge and leakage current due to slower diffusion of ions in the device, which is proposed to originate from the anisotropic properties of LC. Finally, by utilizing the thermocapacitive effect, a thermal charging of ECs containing IL is demonstrated, where a high voltage of more than 900 mV could be recovered when two devices in series are exposed to a 60 °C temperature environment.
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| 3. |
- Haque, Mohammad Mazharul, 1984, et al.
(author)
-
Exploiting low-grade waste heat to produce electricity through supercapacitor containing carbon electrodes and ionic liquid electrolytes
- 2022
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 403
-
Journal article (peer-reviewed)abstract
- Low-grade thermal energy harvesting presents great challenges to traditional thermoelectric systems based on the Seebeck effect, the thermogalvanic effect, and the Soret effect due to fixed temperature gradient and low voltage output. In this study, we report an ionic thermoelectric system, essentially a supercapacitor (SC) containing an ionic liquid (IL) electrolyte and activated carbon electrodes, which works on the thermocapacitive effect and does not require any fixed temperature gradient, rather it works in a homogeneously changing temperature. A systematic investigation is carried out on SCs containing two different ILs, 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl), EMIm TFSI, and 1-Ethyl-3-methylimidazolium acetate, EMIm OAc. A high voltage output of 176 mV is achieved for EMIm TFSI containing SC by exposing just to 60 °C environment. Moreover, a large voltage of 502 mV is recovered from the SC upon subjecting to heat after one electrical charge/discharge cycle. A system containing two SCs in series demonstrates a significant voltage of 947 mV. The observed performance difference between the two ILs is rationalized in terms of the extent of asymmetry in the interfaces of the electrical double layer that essentially originates from different diffusivity of individual ions. The mechanism can be applied to a plethora of ILs to exploit low-grade heat to store electricity without a fixed temperature gradient, opening up the possibility to merge different scientific communities and enrich this rising research field.
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| 4. |
- Haque, Mohammad Mazharul, 1984, et al.
(author)
-
Identification of self-discharge mechanisms of ionic liquid electrolyte based supercapacitor under high-temperature operation
- 2021
-
In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 485
-
Journal article (peer-reviewed)abstract
- Ionic liquids (ILs) are promising electrolytes for supercapacitors (SCs) aimed for high-temperature applications, where increased ionic conductivity results in superior capacitive performance compared to room temperature (RT) performance. However, an increased temperature also accelerates the self-discharge rate that adversely affects energy retention and restricts the usage of SCs in standalone applications. In this study, a detailed electrochemical investigation on the self-discharge behaviour of carbon-based SCs containing an IL, 1-Ethyl-3-methylimidazolium acetate (EMIM Ac), has been carried out in the temperature range RT - 60 °C, and the underlying self-discharge mechanisms are identified. The results reveal that at a high voltage of 1.5 V, the self-discharge is characterized by a combination of charge redistribution and diffusion at both RT and 60 °C. At 60 °C, the diffusion-controlled mechanism dominates at lower voltages over the charge redistribution effect, while at RT both mechanisms contribute to a similar extent. The observed difference in the self-discharge mechanism between RT and 60 °C is explained in terms of a decreased RC time constant (τRC) at elevated temperature, and the same conclusions are potentially applicable to other IL-containing SCs as well.
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| 5. |
- Haque, Mohammad Mazharul, 1984, et al.
(author)
-
Ionic liquid electrolyte for supercapacitor with high temperature compatibility
- 2017
-
In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1
-
Conference paper (peer-reviewed)abstract
- This work describes the electrochemical investigation of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate (EMIM Ac) and 1-butyl-3-methylimidazolium chloride (BMIM Cl), as electrolytes in supercapacitors (SC). A comprehensive study on high temperature (HT) endurance that is required for system integration in microelectronics has also been carried out. It has been found that EMIM Ac containing SC performs better than a BMIM Cl containing SC, and HT treatment improves the capacitive performance.
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| 6. |
- Haque, Mohammad Mazharul, 1984, et al.
(author)
-
Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive
- 2020
-
In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 453
-
Journal article (peer-reviewed)abstract
- Self-discharge is being recognized as one of the main obstacles to implementing the supercapacitor (SC) in standalone self-powered systems. Strategies for addressing this issue include the modification of electrodes, electrolytes, separators, and diverse device configurations. However, an improved self-discharge behavior is often achieved with a large compromise on other prominent figures of merit such as capacitance, energy density, or cycle life of the device. In this work, a thorough comparative electrochemical investigation of SCs containing a neutral aqueous electrolyte, 1 M Li2SO4, and with a liquid crystal (LC) additive, 2% 4-n-pentyl-4′-cyanobiphenyl (5CB) in 1 M Li2SO4, has been carried out at different states of charge. The results demonstrate that the device containing the LC additive 5CB exhibits a reduced self-discharge and leakage current without compromising the capacitive performance at different nominal voltages compared to the behavior of the device without 5CB. We suggest an explanation of the difference of the self-discharge behavior between the devices through tunability of the effective conductivity of the electrolyte composite upon applied voltages. As a result, in an open circuit condition, the device containing LC shows a slower diffusion of ions that facilitates a decreased self-discharge and leakage current.
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| 7. |
- Haque, Mohammad Mazharul, 1984, et al.
(author)
-
Thermal influence on the electrochemical behavior of a supercapacitor containing an ionic liquid electrolyte
- 2018
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In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 263, s. 249-260
-
Journal article (peer-reviewed)abstract
- Emerging demands on heat-durable electronics have accelerated the need for high temperature supercapacitors as well as for understanding the influence of elevated temperatures on the capacitive behavior. In this work, we present a comprehensive study of the thermal influence on a supercapacitor containing 1-ethyl-3-methylimidazolium acetate (EMIM Ac) electrolyte and activated carbon (AC) electrodes. The performance variation as a function of temperature in a range from 21 °C to 150 °C reveals that a high specific capacitance of 142 F g−1 can be achieved at 150 °C at a current density of 2 A g−1 with a rate capability of 87% at 15 A g−1 (relative to 2 A g−1). At 150 °C, equivalent series resistance (ESR) is only 0.37 Ω cm2, which is a result of improved ionic conductivity of the electrolyte at elevated temperature. The ESR value of 2.5 Ω cm2 at room temperature reflects a good compatibility between EMIM Ac and AC. In addition, a capacitance retention of more than 95% (in the end of 1000 cycles) is maintained up to120 °C followed by 85% at 150 °C. These results confirm EMIM Ac as a suitable candidate for carbon-based high temperature supercapacitors, and the observations regarding the thermal influence on performance metrics e.g. usable operation voltage could be applicable to other energy storage devices.
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| 8. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Capacitive effects of nitrogen doping on cellulose-derived carbon nanofibers
- 2015
-
In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584. ; 160, s. 59-65
-
Journal article (peer-reviewed)abstract
- Carbons with valuable electrochemical characteristics are among the most convenient electrode materials used for energy storage. At the moment, their production is mostly reliant on unsustainable fossil fuels. A preferential sustainable production of enhanced carbonaceous electrodes can be achieved with more extensive utilization of abundant renewable resources instead of fossils. In this study, nitrogen-doped carbon nanofibers (CNFs) were synthesized from cellulose, the most abundant renewable resource, via consecutive steps of cellulose acetate electrospinning, subsequent deacetylation to cellulose, impregnation with nitrogen-containing additive (ammonium chloride), and carbonization. Results of material characterization showed that the carbonization of functionalized cellulose samples led to formation of CNFs doped with 4–5.6 at.% of nitrogen. In comparison with pristine CNFs N-doped samples had a slightly lower specific surface area, but higher conductivity and hydrophilicity. Moreover, electrochemical measurements indicated that the enhanced N-doped materials had about 2.5 times higher specific capacitance which was increasing throughout 1000 charge–discharge cycles. These results suggest that nitrogen doping method used in this study has a positive pseudocapacitive effect on the electrochemical performance of carbonized cellulose materials.
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| 9. |
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| 10. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Carbon nanotubes/nanofibers composites from cellulose for supercapacitors
- 2014
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In: 16th European Conference on Composite Materials, ECCM 2014; Seville; Spain; 22 June 2014 through 26 June 2014.
-
Conference paper (peer-reviewed)abstract
- Cellulose-based carbon nanofibers (CNFs) with high mechanical strength and electrochemical stability were nitrogen-doped and functionalized with carbon nanotubes (CNTs) via two different methods. The diameter of incorporated CNTs was in the range of 1-20 nm. The doping with nitrogen atoms and incorporation of CNTs into the CNFs improved conductivity, while CNTs also increased surface area of the produced material. As a result, the composite materials with capacitance values up to 241 F/g were obtained.
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| 11. |
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| 12. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Hierarchical cellulose- derived CNF/CNT composites for electrostatic energy storage
- 2016
-
In: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 1361-6439 .- 0960-1317. ; 26:12, s. 124001-
-
Journal article (peer-reviewed)abstract
- Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g(-1) at 5 mV s(-1)), energy and power density (10.28 W h kg(-1) and 1.99 kW kg(-1), respectively, at 1 A g(-1)) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.
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| 13. |
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| 14. |
- Kuzmenko, Volodymyr, 1987, et al.
(author)
-
Sustainable carbon nanofibers/nanotubes composites from cellulose as electrodes for supercapacitors
- 2015
-
In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 90:2, s. 1490-1496
-
Journal article (peer-reviewed)abstract
- Supercapacitors are efficient energy storage devices with long lifetime and safe service. Their effectiveness,to a big extent, is dependent on electrode materials used for accumulation of energy in form ofelectrostatic charges. Over the last decades, variety of carbonaceous electrode materials has been used insupercapacitors. Mostly the production of such electrodes is still oriented on unsustainable fossil fuels asprecursors instead of sustainable renewable resources. In this study, freestanding carbonaceous electrodematerials for supercapacitors were derived from cellulose, the most abundant renewable resource. Theywere synthesized via carbonization of fibrillar cellulose impregnated with CNTs (carbon nanotubes). Theensuing composite materials consisted of a CNF (carbon nanofiber) scaffold (fiber diameter in the rangeof 50-250 nm) covered with layers of CNTs (tube diameter in the range of 1-20 nm). Moreover, thesecomposites were tested as electrode materials for supercapacitors. Incorporation of the CNTs into theCNFs improved electrical conductivity and also increased the surface area of the produced compositematerials, which led to high specific capacitance values (up to 241 F/g), cyclic stability, and powerdensity of these materials in electrochemical measurements. These results suggest that cellulose-derivedoriginal CNF/CNT composites are sustainable and efficient carbonaceous electrodes for supercapacitors.
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| 15. |
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| 16. |
- Li, Qi, 1990, et al.
(author)
-
Explanation of anomalous rate capability enhancement by manganese oxide incorporation in carbon nanofiber electrodes for electrochemical capacitors
- 2020
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 340
-
Journal article (peer-reviewed)abstract
- Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, characteristics which most battery technologies lack. Making composites out of carbon and pseudocapacitive materials is a popular strategy directed on narrowing the gap in energy density with regard to batteries. Usually, the incorporation of pseudocapacitive materials leads to a decrease in power performance compared to a pure carbon matrix, due to inferior electrical conductivity. This work, however, presents significant improvement in rate capability demonstrated by a composite electrode containing carbon nanofibers (NCNF) and manganese oxides (MnO2). The NCNF/MnO2 is prepared with a common method through the reaction with permanganate. The material has excellent performance metrics, especially a 78.2% rate capability (capacitance retention at 15 A g−1 relative to 0.5 A g−1), more than 10 times that for the NCNF carbon matrix. The exceptional enhancement can be explained by the development of micropores and surface area of NCNF, thus alleviating the “pore starvation” issue, and surface functional groups variation that enhances capacitive performance. This work highlights the importance of paying attention to the modification of carbon substrate when investigating carbon composite electrodes e.g. carbon/MnO2 networks.
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| 17. |
- Li, Qi, 1990, et al.
(author)
-
Finger Number and Device Performance: A Case Study of Reduced Graphene Oxide Microsupercapacitors
- 2021
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In: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Journal article (peer-reviewed)abstract
- Microsupercapacitors (MSCs) are recognized as suitable energy storage devices for the internet of things (IoTs) applications. Herein is described the work conducted to assess the areal energy and power densities of MSCs with 2, 10, 20, and 40 interdigital finger electrodes on a fixed device footprint area (the finger interspacing is fixed at 40 μm, and the finger width and length are allowed to vary to fit the footprint area). The MSCs are based on reduced graphene oxide (rGO) materials and fabricated with a spin-coating and etch method. The performance evaluation indicates a strong dependency of areal capacitance and energy density on the number of fingers, and the maximum (impedance match) power density is also influenced to a relatively large extent, whereas the average power density is not sensitive to the configuration parameters in the present evaluation settings (scan rate 20–200 mV s−1 and current density of 100 μA cm−2). For the rGO-based devices, the equivalent distributed resistance may play an important role in determining the device resistance and power-related performance.
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| 18. |
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| 19. |
- Li, Qi, 1990, et al.
(author)
-
Graphite paper / carbon nanotube composite: A potential supercapacitor electrode for powering microsystem technology
- 2017
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1
-
Conference paper (peer-reviewed)abstract
- This work describes fabrication of a flexible supercapacitor electrode. The fabrication starts with graphite paper (GP). Carbon nanotubes (CNTs) are then grown directly to the carbon surface by chemical vapor deposition (CVD), forming a heterogeneous structure of GP/CNT. The integration of CNT enhances capacitive performance while maintaining the flexibility of GP, thus making GP/CNT a promising supercapacitor electrode material for potentially powering microsystem technology.
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| 20. |
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| 21. |
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| 22. |
- Li, Qi, 1990, et al.
(author)
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Redox enhanced energy storage in an aqueous high-voltage electrochemical capacitor with a potassium bromide electrolyte
- 2017
-
In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 348, s. 219-228
-
Journal article (peer-reviewed)abstract
- This paper reports a detailed electrochemical investigation of a symmetric carbon-carbon electrochemical device with a potassium bromide (KBr) electrolyte. Below 1.6 V, KBr gives electrochemical double layer behavior. At higher voltages the Br-/Br-3 redox reaction comes into effect and enhances the energy storage. The redox-enhanced device has a high energy density, excellent stability, as well as high coulombic and energy efficiencies even at 1.9 V. More importantly, the redox contribution can be “triggered” by pre-cycling at 1.9 V, and remains beneficial after switching to 1.6 V. The triggering operation leads to a 22% increase in stored energy with negligible sacrifice of power. The intriguing behavior is accompanied by a series of complex variations including the shifts of electrode potential limits and the shift of potential of zero voltage. The electro-oxidation of the positive electrode and kinetics of the Br-/Br-3 electrode reactions are proposed to be the main causes for the triggering phenomenon. These findings provide means to improve the design and operation of devices that contain bromine, or other redox species with a comparably high electrode potential.
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| 23. |
- Rajendra Babu Kalai Arasi, Azega, 1995, et al.
(author)
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Durable Activated Carbon Electrodes with a Green Binder
- 2022
-
In: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2
-
Journal article (peer-reviewed)abstract
- Herein, the fabrication and electrochemical performance of thick (180−280 μm) activated carbon (AC) electrodes with carbonized lignin-derived carbon fiber (LCF) inclusions are reported. Efforts are taken in fabricating robust free-standing electrodes from an environmentally friendly binder, microfibrillated cellulose (MFC), considering the biologically hazardous nature of other commonly used binders like polytetrafluoroethylene (PTFE), n-methyl-2-pyrrolidone (NMP), and polyvinylidene fluoride (PVDF). Generally, electrodes composed of MFC binder are prone to cracking upon drying, especially with higher mass loadings, which leads to nonflexibility and poor device stability. The LCF inclusions into the AC electrode with MFC binders not only increase flexibility but also contribute to better conductivity in the electrodes. The LCFs act as an intermediate layer among AC particles and serve as conductive pathways, facilitating exposure of more active surfaces to the electrolyte. A thick electrode with high mass loading of 10 mg cm−2 is achieved. The results show that by incorporating 2 wt% LCF to the AC material, the best device with 5 mg cm−2 delivers a specific capacitance of 97 F g−1, while the specific capacitance of the reference AC device without LCF is 85 F g−1.
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| 24. |
- Rajendra Babu Kalai Arasi, Azega, 1995, et al.
(author)
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Effect of plasma treatment on electrochemical performance of lignin-based carbon fibers
- 2023
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In: Journal of Electroanalytical Chemistry. - 1572-6657. ; 946
-
Journal article (peer-reviewed)abstract
- The abundant and renewable nature of lignin obtained from wood renders it as a sustainable carbon resource for energy storage applications. However, their environmentally unfavorable processing conditions and limited energy storage performance prohibit the use of lignin-based carbon materials' use as supercapacitor electrodes. The material's properties require advancement to overcome the limitation of low specific capacitances. In this study, we report on the impact on the electrochemical performance of inherently hydrophobic lignin-based carbon fibers (LCF) by subjecting them to a mild plasma treatment. The electrode’s capacitance was thus increased by 20%, with better rate capability and energy-power performance (11 Wh/kg and 0.8 kW/kg) in the KOH electrolyte. The quantified improvements were attributed to the capacitive functional groups, and enhanced surface wettability, which increased ion accessibility to active surface area improving charge-transfer ability to the surface with more additional functional groups. Remarkably, the selected plasma conditions introduced mostly desirable functional groups that limited any parasitic faradaic reactions prone to affect the device's long-term cycling stability and self-discharge characteristics. Furthermore, the impact of different inherent and introduced oxygen surface functional groups, including COO−, COH, CO, and CO, on the capacitive performance of these fibers at different device conditions (such as cycling and electrochemical activation) was investigated in different aqueous electrolytes. To ensure environmental favorability, the electrospinning of lignin fibers was conducted using a high molecular fraction of lignin without the inclusion of any fossil-based co-spinning polymers.
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| 25. |
- Smith, Anderson David, 1985, et al.
(author)
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Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks : Present and Future Development
- 2019
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In: Sensors. - : MDPI AG. - 1424-8220. ; 19:19
-
Journal article (peer-reviewed)abstract
- There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering.
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| 26. |
- Smith, Anderson David, 1985, et al.
(author)
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Toward CMOS compatible wafer-scale fabrication of carbon-based microsupercapacitors for IoT
- 2018
-
In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1052:1
-
Conference paper (peer-reviewed)abstract
- This work presents a wafer-scale method of microsupercapacitor (MSC) fabrication. Deposition of the electrode precursor, i.e. graphene oxide, is accomplished through spin-coating which allows for potential application in CMOS compatible processes for future integrated on-chip energy storage systems. Our MSCs have an areal capacitance of 0.4 mF/cm2at 10 μA, which is a very promising result. Further, the MSC has good rate capability as its capacitance decreases by only 0.03 mF/cm2when the current increases to 50 μA. The MSCs have a maximum energy density of 0.04 μWh/cm2and a maximum power density as high as 96 μW/cm2. Additionally, the wafer-scale process demonstrates industrial viability.
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| 27. |
- Vyas, Agin, 1992, et al.
(author)
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Comparison of Thermally Grown Carbon Nanofiber-Based and Reduced Graphene Oxide-Based CMOS-Compatible Microsupercapacitors
- 2021
-
In: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Journal article (peer-reviewed)abstract
- Microsupercapacitors as miniature energy storage devices require complementary metal-oxide-semiconductor (CMOS) compatible techniques for electrode deposition to be integrated in wireless sensor network sensor systems. Among several processing techniques, chemical vapor deposition (CVD) and spin coating, present in CMOS manufacturing facilities, are the two most viable processes for electrode growth and deposition, respectively. To make an argument for choosing either of these techniques to fabricate MSCs utilizable for an on-chip power supply, we need a comparative assessment of their electrochemical performance. Herein, the evaluation of MSCs with CVD-grown carbon nanofiber (CNF)-based and spin-coated reduced graphene oxide (rGO)-based electrodes is reported. The devices are compared for their capacitance, energy and power density, charge retention, characteristic frequencies, and ease of fabrication over a large sweep of scan rates, current densities, and frequencies. The rGO-based MSCs demonstrate 112 mu F cm(-2) at 100 mV s(-1) and a power density of 12.8 mW cm(-2). The CNF-based MSCs show 269.7 mu F cm(-2) and 30.8 mW cm(-2). CVD-grown CNF outperforms spin-coated rGO in capacitive storage at low frequencies, whereas the latter is better in terms of charge retention and high-frequency capacitance response.
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| 28. |
- Vyas, Agin, 1992, et al.
(author)
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Enhanced Electrode Deposition for On-Chip Integrated Micro-Supercapacitors by Controlled Surface Roughening
- 2020
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 5219-5228
-
Journal article (peer-reviewed)abstract
- On-chip micro-supercapacitors (MSCs), integrated with energy harvesters, hold substantial promise for developing self-powered wireless sensor systems. However, MSCs have conventionally been manufactured through techniques incompatible with semiconductor fabrication technology, the most significant bottleneck being the electrode deposition technique. Utilization of spin-coating for electrode deposition has shown potential to deliver several complementary metal-oxide-semiconductor (CMOS)-compatible MSCs on a silicon substrate. Yet, their limited electrochemical performance and yield over the substrate have remained challenges obstructing their subsequent integration. We report a facile surface roughening technique for improving the wafer yield and the electrochemical performance of CMOS-compatible MSCs, specifically for reduced graphene oxide as an electrode material. A 4 nm iron layer is deposited and annealed on the wafer substrate to increase the roughness of the surface. In comparison to standard nonroughened MSCs, the increase in surface roughness leads to a 78% increased electrode thickness, 21% improvement in mass retention, 57% improvement in the uniformity of the spin-coated electrodes, and a high yield of 87% working devices on a 2″ silicon substrate. Furthermore, these improvements directly translate to higher capacitive performance with enhanced rate capability, energy, and power density. This technique brings us one step closer to fully integrable CMOS-compatible MSCs in self-powered systems for on-chip wireless sensor electronics. ©
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| 29. |
- Vyas, Agin, 1992, et al.
(author)
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Investigation of palladium current collectors for vertical graphene-based microsupercapacitors
- 2019
-
In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1319:1
-
Conference paper (peer-reviewed)abstract
- As microsystems are reduced in size and become integrated in the Internet of Things (IoT), they require an adequate power supply which can be integrated at the same size scale. Microsupercapacitors (MSCs), if coupled with on-chip harvesters, can offer solutions for a self-sustaining, on-chip power supply. However, the implementation of reliable MSC wafer-scale production compatible with CMOS technology remains a challenge. Palladium (Pd) is known as a CMOS compatible metal and, in this paper, we investigate the use of Pd as a contact material for vertical graphene (VG) electrodes in wafer-scale MSC fabrication. We show that a Ti diffusion barrier is required to prevent short-circuiting for the successful employment of Pd contacts. The fabricated MSCs demonstrate a capacitance of 1.3 μF/cm2 with an energy density of 0.42 μJ/cm2. Thus, utilization of a Ti diffusion barrier with a CMOS compatible Pd metal electrode is a step towards integrating MSCs in semiconductor microsystems.
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| 30. |
- Vyas, Agin, 1992, et al.
(author)
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Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors
- 2022
-
In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:4, s. 4221-4231
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Journal article (peer-reviewed)abstract
- Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF/cm^2 at 20 mV/s^1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF/cm^2 at 20 mV/s^1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.
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| 31. |
- Vyas, Agin, 1992, et al.
(author)
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Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes
- 2019
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In: MRS Advances. - : Springer Science and Business Media LLC. - 2059-8521. ; 4:23, s. 1335-1340
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Conference paper (peer-reviewed)abstract
- Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things' sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO 2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
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