Sustainable AC/AC hybrid electrochemical capacitors in aqueous electrolyte approaching the performance of organic systems (original) (raw)
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Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes
Journal of the Electrochemical Society, 2015
Strategies are presented to enhance operating potential and cycle life of AC/AC capacitors using salt aqueous electrolytes. Li 2 SO 4 (pH = 6.5) allows 99% efficiency to be exhibited at 1.6 V cell potential with low self-discharge, while in BeSO 4 (pH = 2.1) efficiency is low (81%). Li 2 SO 4 performs better due to high di-hydrogen over-potential at the negative electrode and related pH increase in AC porosity. When stainless steel current collectors are used in Li 2 SO 4 , the cell resistance suddenly increases after 12 hours floating at 1.6 V, due to corrosion of the positive collector. With nickel negative and stainless steel positive collectors, the electrode potentials are shifted by −105 mV at cell potential of 1.6 V, allowing stable cell parameters (capacitance, resistance) and reduction of corrosion products formation on positive steel collector after 120 hours floating. Phenanthrenequinone was grafted on activated carbon to get an additional faradaic contribution in buffer solutions (pH = 4.0 or 7.2). The three-electrode cell CVs show that the redox peaks of the phenanthrenequinone graft shift toward negative values when pH increases from 4 to 7.2. The grafted carbon displays a capacitance value of 194 F g −1 at pH = 4.0 as compared to 82 F g −1 for the as-received carbon.
Asymmetric electrochemical capacitors—Stretching the limits of aqueous electrolytes
MRS Bulletin, 2011
Electrochemical capacitors (ECs, also commonly denoted as "supercapacitors" or "ultracapacitors") represent an emerging class of energy-storage devices whose particular performance characteristics fi ll the gap on the energy versus power spectrum between the high specifi c power provided by conventional capacitors and the high specifi c energy provided by batteries (see Figure 1). 1-4 Electrochemical capacitors are distinguished from their solid-state electrostatic capacitor counterparts by storing charge at electrochemical interfaces, where the effective capacitances are orders of magnitude greater than those obtained by storing charge in an electric fi eld imposed across a conventional dielectric. The enhanced specifi c energy of ECs comes with some tradeoff in specifi c power because of the
ABSTRACT: We report a new electrochemical capacitor with an aqueous KIKOH electrolyte that exhibits a higher specific energy and power than the stateof- the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx −/I− couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx −/I− redox couple for the positive electrode, which pins the positive electrode potential to be 0.4−0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach −1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3 − ions (+5) from I− (−1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between −20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14 000 cycles.
An Artificial Interface for High Cell Voltage Aqueous-Based Electrochemical Capacitors
Journal of The Electrochemical Society, 2021
Aqueous electrolytes are very effective for supercapacitor applications but their narrow electrochemical potential window (∼1 V) and associated limited energy currently limits their use. Here, we demonstrate a new strategy to enlarge the potential window by designing an artificial interface (ai). An effective ai was achieved via a mixture of siloxanes doped with an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI). Indeed, the as-deposited ai on the carbon-based electrode hinders the electron charge transfer but not the ionic charge transfer, making the ai ionic conductive. As a result, a cell voltage of about 1.8 V was obtained in aqueous electrolyte-EMI HSO4 1 mol l−1 in water. Used as a membrane, the ai was found to be ionically specific to EMI+; the proton transference number being close to zero. These results show the strategy of developing an ai at the electrode/electrolyte interface could represent a new path for aqueous-based carbon-carbo...
High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte
We report a new electrochemical capacitor with an aqueous KIKOH electrolyte that exhibits a higher specific energy and power than the stateof- the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx −/I− couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx −/I− redox couple for the positive electrode, which pins the positive electrode potential to be 0.4−0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach −1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3 − ions (+5) from I− (−1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between −20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14 000 cycles.
Principles and applications of electrochemical capacitors
Electrochimica Acta, 2000
Electrochemical capacitors (EC) also called 'supercapacitors' or 'ultracapacitors' store the energy in the electric field of the electrochemical double-layer. Use of high surface-area electrodes result in extremely large capacitance. Single cell voltage of ECs is typically limited to 1-3 V depending on the electrolyte used. Small electrochemical capacitors for low-voltage electronic applications have been commercially available for many years. Different applications demanding large ECs with high voltage and improved energy and power density are under discussion. Fundamental principles, performance, characteristics, present and future applications of electrochemical capacitors are presented in this communication.
Scientific reports, 2017
Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg(-1). The cycle life test proves that HyLIC exhi...
A double-redox aqueous capacitor with high energy output
The paper puts forward the concept of a double-redox electrochemical capacitor operating in an aqueous electrolyte. The redox activity of sulphur from insoluble Bi 2 S 3 nanocrystals embedded in the negative electrode material (up to 10 wt%) operating in 1 mol L −1 Li 2 SO 4 electrolyte is demonstrated. It is also shown that the performance is significantly boosted using MPA (3-mercaptopropionic acid) as a ligand attached to the surface of the nanocrystals, which allows for more efficient use of Bi 2 S 3 redox active species. This redox activity is combined with the reactions of iodides, which occur at the opposite electrode with 1 mol L −1 NaI. This enables the formation of a discharge voltage plateau that effectively boosts the capacitance (275 F g −1), and thus specific energy of the device owing to the relatively high cell voltage of 1.5 V. This performance is possible due to the advantageous electrode mass ratio (m − : m + = 2 : 1), which helps to balance the charge. The rate capability test of the device demonstrates its capacitance retention of 73% at 10 A g −1 of the discharge current. The different states of the redox species ensure their operation at separate electrodes in an immiscible manner without a shuttling effect. The specific interactions of the redox active species with carbon electrodes are supported by operando Raman spectroscopy.
ACS Applied Materials & Interfaces, 2020
Electrolyte solutions and electrode active materials, as core components of energy storage devices, have a great impact on the overall performance. Currently, supercapacitors suffer from the drawbacks of low energy density and poor cyclic stability in typical alkaline aqueous electrolytes. Herein, the ultrathin Co 3 O 4 anode material is synthesized by a facile electrodeposition, followed by post-heat treatment process. It is found that the decomposition of active materials induces reduction of energy density and specific capacitance during electrochemical testing. Therefore, a new strategy of pre-adding Co 2+ cations to achieve the dissolution equilibrium of cobalt in active materials is proposed, which can improve the cyclic lifetime of electrode materials and broaden the operation window of electrochemical devices. Co 2+ and Li + embedded in carbon electrode during charging can enhance H + desorption energy barrier, further hampering the critical step of bulk water electrolysis. More importantly, the highly reversible chemical conversion mechanism between Co 3 O 4 and protons is demonstrated to be the fact that a large amount of quantum dots and second-order flaky CoO layers were in-situ formed in the electrochemical reaction process, which is firstly discovered and reported in neutral solutions. The as-assembled device achieves a high operation voltage (2.2 V), excellent cycling stability (capacitance retention of 168 % after 10000 cycles) and ultrahigh energy density (99 W h kg-1 at a power density of 1100 W kg-1). The as-prepared electrolytes and highly active electrode materials will open up new opportunities for aqueous supercapacitors with high safety, high voltage, high energy density and long-lifespan.
Supercapacitors are evolving into an important component in energy storage technology with the capability for storing and discharging energy very quickly and effectively. State-of-the-art supercapacitors feature activated carbon electrodes impregnated with a non-aqueous electrolyte (typically acetonitrile) that operate at voltages between 2.2–2.7 V. Unfortunately, activated carbons have low specific capaci-tance (100–120 F g −1) in organic electrolytes which severely limits the energy density of supercapacitors. In addition, organic solvents are often flammable leading to safety and environmental concerns. Aqueous electrolytes, on the other hand, are safer, cheaper and have higher ionic conductivity, promising higher capacitance electrodes. However, the low voltage window enforced by the low decomposition voltage of water around 1.23 V is a major challenge. Here, we demonstrate symmetric supercapacitors operating at an ultrahigh voltage of 1.8 V that can provide specific electrode capacitances up to 716 F g −1 , which is higher than traditional activated carbon electrodes. This is possible through designing both the electrode and electrolyte to work synergistically towards improving not only the capacitance of the electrodes, but also the voltage and cycling stability of the supercapacitor. We also demonstrate by using a simple laser technique the possibility of fabricating micro-supercapacitors with great potential for miniaturized electronics. This work provides an effective strategy for designing and fabricating aqueous supercapacitors that hold promise for a sustainable energy future.