Neutral Aqueous Electrolyte Research Articles

Supercapacitor electrode based on few-layer h-BNNSs/rGO composite for wide-temperature-range operation with robust stable cycling performance

Currently, developing supercapacitors with robust cycle stability and suitability for wide-temperature-range operations is still a huge challenge. In the present work, few-layer hexagonal boron nitride nanosheets (h-BNNSs) with a thickness of 2–4 atomic layers were fabricated via vacuum freeze-drying and nitridation. Then, the h-BNNSs/reduced graphene oxide (rGO) composite were further prepared using a hydrothermal method. Due to the combination of two two-dimensional (2D) van der Waals-bonded materials, the as-prepared h-BNNSs/rGO electrode exhibited robustness to wide-temperature-range operations from −10 to 50°C. When the electrodes worked in a neutral aqueous electrolyte (1 M Na2SO4), they showed a great stable cycling performance with almost 107% reservation of the initial capacitance at 0°C and 111% at 50°C for 5000 charge—discharge cycles.

Cation intercalated one-dimensional manganese hydroxide nanorods and hierarchical mesoporous activated carbon nanosheets with ultrahigh capacitance retention asymmetric supercapacitors

We have reported the electrochemical performance of K+ ion doped Mn(OH)4 and MnO2 nanorods as a positive electrode and a highly porous activated carbon nanosheet (AC) made from Prosopis Juliflora as negative electrode asymmetric supercapacitor (ASC) with high rate capability and capacity retention. The cation K+ doped Mn(OH)4 and MnO2 nanorods with large tunnel sizes allow the electrolyte to penetrate through a well-defined pathway and hence benefits from the intercalation pseudocapacitance and surface redox reactions. As a result, they exhibit good electrochemical performance in neutral aqueous electrolytes. More specifically, the K+-Mn(OH)4 nanorods exhibit higher capacitance values than K+-MnO2 nanorods due to the homogenous distribution of 1D nanorods and optimum amount of OH bonds. The fabricated K+-Mn(OH)4 symmetric electrochemical Pseudocapacitor shows very high energy density of 10.11 Wh/kg and high-power density of 51.04 W/kg over the range of 1.0 V in aqueous electrolyte. The energy density of AC||K+-Mn(OH)4 ASC is improved significantly compared to those of symmetric supercapacitors. The fabricated ASC exhibits a wide working voltage window (1.6 V), high power (143.37 W/kg) and energy densities (41.38 Wh/kg) at 0.2 A g−1, and excellent cycling behavior with 107.3% capacitance retention after 6000 cycles at 2 A g−1 indicating the promising practical applications in electrochemical supercapacitors.

“Green” Catalyst for the Oxygen Reduction Reaction in Metal-Air Systems with Aqueous Electrolyte

Thermally treated caffeine doped active carbon (Caffeine-Norit) is studied as a catalyst for the oxygen reduction reaction (ORR) with application in metal-air systems with neutral aqueous electrolytes. Catalytic activity is characterized by polarization curves and Tafel plots and the results are compared with 5% Platinum (5% Pt-Norit) and 4% Silver (4% Ag-Norit) catalysts. The Tafel slopes of all three catalysts are equal, the activity of Ag-Norit being somewhat lower then both Caffeine-Norit and Pt-Norit. The polarization curves are also comparable, especially in the low current density region. The increase of overpotential for the Caffeine-Norit at current density higher than 50 mA cm−2 is due to accumulation of H2O2 in the catalyst layer. This was demonstrated by a simple method for detection of peroxides in neutral electrolytes based on indigo carmine indicator. The discharge curves of Caffeine-Norit in 4 M NaCl electrolyte at 10 mA cm−2 display a plateau at potential of −320 mV vs Ag/AgCl (1.23 V vs MA8M magnesium alloy).

Electrodeposited manganese oxide supercapacitor microelectrodes with enhanced performance in neutral aqueous electrolyte

1.6–4 μm thick microelectrodes of manganese oxide MnO2 were produced by electrolytic deposition on nickel nanowires Ninw previously electrodeposited on Anodized Aluminium Oxide (AAO). MnO2/Ninw electrodes prepared under optimized pressure, obtained by application of a torque of 0.2–1.5 N m between the electrolytic cell blocks, show significant electrochemical capacities without addition of conductive additive or binder and can compete with current microsupercapacitor electrodes. Thus, MnO2/Ninw microelectrodes provide a large and reproducible capacitance of 51.8 mF cm−2 (per MnO2 electrode surface) at a scan rate of 200 mV s−1 in a three-electrode configuration in neutral aqueous 0.5 M Na2SO4. Time constant for the electrochemical process is in the 1.4–2.0 s range, which compares quite well with other microelectrodes. After 3400 cycles, two-electrode devices containing activated carbon negative electrode provide a capacity of 12.76 mF cm−2 and an energy density of 4.17 μWh·cm−2 per total surface area of both electrodes at a cycling rate of 0.05 A g−1 per MnO2 electrode mass which turns into a power density of 3.75 μW cm−2 per total surface of an electrode. Ragone plot shows a high energy density of 5.4 Wh·kg−1 (2.14 μWh·cm−2) for a power exceeding 0.7 kWh·kg−1 (0.31 mW cm−2). These results are, overall, significantly higher than those found in the literature for symmetrical or asymmetric devices based on manganese oxide (with or without carbonaceous materials), and even comparable with some 3D microdevices.

A Rechargeable Aqueous Lithium Ion Battery with High Rate Capability Based on Metallic Cadmium and LiCoO2

An aqueous rechargeable lithium ion battery with metallic cadmium as the negative electrode, LiCoO2 nanoparticles as the positive electrode, and a neutral aqueous electrolyte solution of 0.5 M Li2SO4 and 10 mM Cd(Ac)2 is reported. It has good electrochemical performance. The calculated energy density based on the practically available capacity of the two electrodes is 72 W h kg–1; this is comparable to that of Ni–Cd batteries. The positive mercury electrode of the Weston cell is replaced by a LiCoO2 electrode, the negative cadmium amalgam by a plain cadmium metal electrode. Mercury is completely avoided. Compared with Ni–Cd batteries an alkaline electrolyte solution is not needed making the system more environment-friendly.

Nile Blue Functionalized Graphene Aerogel as a Pseudocapacitive Negative Electrode Material across the Full pH Range.

The pursuit of new negative electrode materials for redox supercapacitors with a high capacitance, boosted energy, and high rate capability is still a tremendous challenge. Herein, we report a Nile Blue conjugated graphene aerogel (NB-GA) as a negative electrode material with excellent pseudocapacitive performance (with specific capacitance of up to 483 F g-1 at 1 A g-1) in all acidic, neutral, and alkaline aqueous electrolytes. The contribution from capacitive charge storage represents 93.4% of the total charge, surpassing the best pseudocapacitors known. To assess the feasibility of NB-GA as a negative electrode material across the full pH range, we fabricated three devices, namely, a symmetric NB-GA||NB-GA device in an acidic (1.0 M H2SO4) electrolyte, an NB-GA||MnO2 device in a pH-neutral (1.0 M Na2SO4) electrolyte, and an NB-GA||LDH (LDH = Ni-Co-Fe layered double hydroxide) device in an alkaline (1.0 M KOH) electrolyte. The NB-GA||NB-GA device exhibits a maximum specific energy of 22.1 Wh kg-1 and a specific power of up to 8.1 kW kg-1; the NB-GA||MnO2 device displays a maximum specific energy of 55.5 Wh kg-1 and a specific power of up to 14.9 kW kg-1, and the NB-GA||LDH device shows a maximum specific energy of 108.5 Wh kg-1 and a specific power of up to 25.1 kW kg-1. All the devices maintain excellent stability over 5000 charge-discharge cycles. The outstanding pseudocapacitive performances of the NB-GA nanocomposites render them a highly promising negative electrode material across the entire pH range.

Wool roving textured reduced graphene oxide-HoVO4-ZnO nanocomposite for photocatalytic and supercapacitor performance

Reduced graphene oxide-HoVO4-ZnO nanocomposite was prepared via simple hydrothermal method and characterized by X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive Spectroscopy (EDX), High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Photoelectron Spectroscopy (XPS), FT-Raman, UV–Visible Diffuse Reflectance Spectroscopy (DRS), Electrochemical impedance spectroscopy and Cyclic Voltammogram(CV). The XRD pattern confirmed the formation of hexagonal wurtzite structure of ZnO and monoclinic scheelite structure of HoVO4. FE-SEM images depicted the Wool roving textured reduced Graphene Oxide-HoVO4-ZnO catalyst. As prepared rGO-HoVO4-ZnO exhibits highest photodegradation efficiency achieving at 97.2% and 98% for ibuprofen (IBF)and ciprofloxacin (CIP) respectively in 60 min under UV light illumination. Superoxide radicals (O•-2) play an important role in the decomposition of IBF and CIP. Prepared catalysts were found to be stable and reusable even after six consecutive cycles without loss of catalyst. Also Besides, the electrochemical efficiency and galvanostatic charge-discharge of the rGO-HoVO4-ZnO and HoVO4-ZnO composites electrode materials were evaluated by cyclic voltammetry. rGO-HoVO4-ZnO composite showed higher specific capacitance of 322 Fg-1, compared to HoVO4-ZnO (252 Fg-1) in neutral aqueous electrolyte. The enhancement of specific capacitance of the composite electrode is mainly due to the interconnected conductive network as well as synergism of rGO. The experimental results reveal that rGO-HoVO4-ZnO material is an efficient electrode material for high-performance supercapacitors.

Hierarchical porous carbon foam supported on carbon cloth as high-performance anodes for aqueous supercapacitors

Carbon anodes have been widely utilized for the fabrication of high-performance asymmetric supercapacitors. However, they generally suffer from unsatisfactory energy density due to low specific capacitance arising from inferior conductivity and insufficient ionic diffusion rate. Here a surface modification method is conducted after the annealing of ZIF-67 precursor to produce hydrophilic, porous and heteroatom-doped carbon foam. On top of enhanced area capacitance, widened voltage window of −1.3–0 V (vs saturated calomel electrode) can be achieved through electrochemical reduction to suppress the hydrogen evolution reaction. The optimized reduced porous carbon foam on carbon cloth exhibits a maximum area capacitance of 1049 mF/cm2 at an applied current density of 12 mA/cm2 with excellent capacitance retention of 98.4% after 6000 charge-discharge cycles at 15 mA/cm2. By well pairing with hierarchical MnO2/CC cathode, a 2.3 V asymmetric supercapacitor in neutral aqueous Na2SO4 electrolyte is assembled, which delivers an exceptional energy density of up to 10.07 mWh/cm3. The procedure in this paper for carbonaceous material to simultaneously achieve considerable capacitance and enlarged voltage window can open up a wider prospect toward design of anodes for high-performance aqueous supercapacitor.

Fabrication and electrochemical properties of well-dispersed molybdenum oxide nanoparticles into nitrogen-doped ordered mesoporous carbons for supercapacitors

Environment-friendly supercapacitors demand the high-performance electrode materials working with neutral aqueous electrolyte. In this work, the nitrogen-doped ordered mesoporous carbons (NOMCs) have been synthesized and subsequently modified with molybdenum oxide nanoparticles (NPs) by a self-developed temperature controlled impregnation method. The prepared hybrids possess ordered mesoporous structure, high specific surface area (600–1000 m2 g−1), favorable pore size (∼4 nm) and well-dispersed uniform molybdenum oxide NPs. The results demonstrate that the nano-sized molybdenum oxides encapsulated in the ordered mesoporous channels exhibit significant electrochemical activity with an enhanced specific capacitance up to 410 F g−1, which can be attributed to the nanosize effects from the nanopore confinement and efficient surface area of molybdenum oxide NPs under well dispersion. The hybrids exhibit quasi-rectangular CV curves within the enlarged potential window compared with the pristine NOMCs together with pairs of redox peaks owing to the multi-valance changes of molybdenum corresponding to the Faradaic reactions. Thus, the synthesized hybrids demonstrate not only the synergistic contribution of electrical double-layer capacitance and pseudocapacitance but also superior cycling stability in aqueous neutral electrolyte.

Investigating the large potential window of NiCo2O4 supercapacitors in neutral aqueous electrolyte

The enhancement of potential window can be identified as one of the effective pathways to boost the energy density of supercapacitors to break the limitation of practical applications. NiCo2O4 nanosheet networks grown on carbon cloth are prepared via a facile cathodic electrodeposition process with a post-annealing procedure. A neutral electrolyte of mixing 2 M LiSO4 and 0.1 M CoSO4 is employed to enlarge the potential window of the as-prepared NiCo2O4/CC electrode to 0–1.2 V (vs SCE), while the corresponding potential window in alkaline electrolyte is merely 0–0.5 V. Moreover, the NiCo2O4/CC electrode shows an excellent cycling stability of maintaining 129.7% after 10,000 cycles in neutral electrolyte. The quantitative CV kinetic analysis is carried out to explore the charge storage mechanism, manifesting that capacitive contribution is estimated as high as 64.7–81.8% at the sweep rate of 3–10 mV s−1. Results demonstrate that this neutral electrolyte can greatly boost the electrochemical characteristics of the NiCo2O4 electrode and also provide the possibility of achieving better characteristics in the field of energy storage when applied in other battery-type materials.

Metal-organic-framework-derived hollow polyhedrons of prussian blue analogues for high power grid-scale energy storage

Prussian blue and its analogues are recognized as a class of attractive materials for stationary energy storage on the electrical grid. Challenges are still existed to meet the rigid requirements of high power and long cycle life. In this work, we develop a universal metal-organic-framework templating strategy for fabricating hollow polyhedrons of prussian blue analogues with tailored composition and shape. Hollow dodecahedrons of cobalt hexacyanoferrate (CoHCF) are investigated as a proof-of-concept material, which shows high surface area and mesoporous characteristics. The CoHCF hollow dodecahedrons exhibit large Na + storage capacity in neutral aqueous electrolytes and particularly, superhigh rate capability owing to rapid ion diffusion rate and short carrier transport distances. By coupling with a low-cost carbon anode, hybrid Na-ion cells are constructed to deliver moderate specific energy (32.7–50 Wh kg−1), a high specific power of 30 kW kg−1, and superior 3000-cycling durability. The excellent electrochemical properties make the present aqueous Na-ion hybrid devices to be a promising alternative to lead-acid batteries for high power grid-scale energy storage.

(Invited) Investigation of Ba0,5Sr0,5CoxFe1-XO3-Δ As Pseudocapacitive Electrode for Aqueous Electrochemical Capacitor

Supercapacitors are attractive electrochemical energy storage devices for high power applications. However, volumetric energy density is the main limitation for their integration in such applications as terrestrial transport systems. The use of high density pseudocapacitive oxides as electrode material could lead to a volumetric energy density improvement. With this aim, materials from Ba0,5Sr0,5CoxFe1-xO3-δ family, so called BSCFs, have been studied. Several compositions have been prepared and evaluated as positive electrode materials in aqueous neutral electrolyte. Volumetric capacitances have shown to be greater than those of activated carbons, already used in commercialized supercapacitors. Their electrochemical properties are strongly related to the cobalt to iron ratio, to the charging rate, to the electrolyte composition, and other key parameters. The study of the charge storage mechanism occuring in these materials has been investigated thanks to in situ X-Ray absorption spectroscopy and operando X-Ray diffraction performed at SOLEIL (France) and SPring-8 (Japan) synchrotron facilities respectively. Devices coupling BSCF based positive electrode with activated carbon or FeWO4 based negative electrode have demonstrated the added value of such materials to improve the volumetric energy density of supercapacitors.

A Recoverable Carbon/Zn Hybrid-Ion Supercapacitor with High Rate Charge Storage, Improved Rate Capability and Superior Gravimetric Power Density Using a Mixed Mono/Multivalent Electrolyte

Carbon aqueous symmetric supercapacitors are attractive supercapacitor devices owing to the low-cost and high conductivity of porous carbons. However, the limited capacitive charge storage process in carbon symmetric capacitors still leads to low energy density even when the cell voltage is extended up to 2.0 V in neutral aqueous electrolytes. Meanwhile, a carbon/metal ion capacitor such as sodium (Na), lithium (Li), Potassium (K) and much recently, zinc (Zn) can easily achieve high energy density from the synergistic contribution of double layer and mono/multivalent faradaic charge storage. Taking Zn-based devices as an example, the zinc anode presents the advantages of the large theoretical capacity of Zn, low redox potential, excellent stability and lower cost in comparison with Na and Li. The major emphasis on Zn-ion hybrid supercapacitor research has been on the energy density. However, compared with a carbon symmetric supercapacitor, the zinc stripping/de-stripping reaction occurring at the zinc may increase the overall equivalent series resistance leading to lower gravimetric power density. Since the study of these devices is still in its infancy, it is highly necessary to devise an effective strategy to enhance the gravimetric power density as well. Herein, we successfully report a recoverable activated zinc ion hybrid supercapacitor with enhanced high rate charge storage, improved rate capability and gravimetric power density by utilizing a mixed mono/multivalent electrolyte. A facilely activated carbon fiber clothes with a large specific surface area (615 m2 g-1), rich microporosity and superhydrophilicity serves as the positive electrode, whiles zinc foil serves as anode. At first, a zinc-ion HSC is fabricated using conventional 1 M ZnSO4 electrolyte, and the device exhibits a high voltage drop of 1.21 V at 50 mA cm-2, which would definitely affect the rate capability and maximum gravimetric power density of the device. This voltage drop is almost halved to 0.68 V at 50 mA cm-2 as well as the equivalent series resistance is significantly reduced, using the mono/multivalent aqueous electrolyte. This translates into charge storage at the high current density of 50 mA cm-2, a rate capability of 55 % compared to 38 % in the conventional ZnSO4 electrolyte and a maximum gravimetric energy density of 130.2 kW kg-1, compared to 73.62 kW kg-1 in the conventional ZnSO4 electrolyte. Using ex-situ SEM, XRD and cyclic voltammetry characterizations, we fully confirm that the 1 M Na2SO4 inhibits the formation of ZnO/Zn4SO4(OH)6•5H2O dendrites and serves as the preferential adsorption electrolyte at high rates in the carbon positive electrode. In terms of energy density, the fabricated Zn-ion HSC achieves a maximum energy density of 81.4 Wh kg-1, far exceeding fabricated carbon symmetric capacitors as well as stable cycling performances up to 10000 cycles with ~ 99 % coulombic efficiencies. Finally, we believe our work will draw research attention into developing high-energy, high-rate and high-power aqueous Zn-ion supercapacitors through electrolyte modification.

Scalable fabrication of printed Zn//MnO2 planar micro-batteries with high volumetric energy density and exceptional safety.

The rapid development of printed and microscale electronics imminently requires compatible micro-batteries (MBs) with high performance, applicable scalability, and exceptional safety, but faces great challenges from the ever-reported stacked geometry. Herein the first printed planar prototype of aqueous-based, high-safety Zn//MnO2 MBs, with outstanding performance, aesthetic diversity, flexibility and modularization, is demonstrated, based on interdigital patterns of Zn ink as anode and MnO2 ink as cathode, with high-conducting graphene ink as a metal-free current collector, fabricated by an industrially scalable screen-printing technique. The planar separator-free Zn//MnO2 MBs, tested in neutral aqueous electrolyte, deliver a high volumetric capacity of 19.3 mAh/cm3 (corresponding to 393 mAh/g) at 7.5 mA/cm3, and notable volumetric energy density of 17.3 mWh/cm3, outperforming lithium thin-film batteries (≤10 mWh/cm3). Furthermore, our Zn//MnO2 MBs present long-term cyclability having a high capacity retention of 83.9% after 1300 cycles at 5 C, which is superior to stacked Zn//MnO2 batteries previously reported. Also, Zn//MnO2 planar MBs exhibit exceptional flexibility without observable capacity decay under serious deformation, and remarkably serial and parallel integration of constructing bipolar cells with high voltage and capacity output. Therefore, low-cost, environmentally benign Zn//MnO2 MBs with in-plane geometry possess huge potential as high-energy, safe, scalable and flexible microscale power sources for direction integration with printed electronics.

A Crosslinked Soybean Protein Isolate Gel Polymer Electrolyte Based on Neutral Aqueous Electrolyte for a High-Energy-Density Supercapacitor.

A crosslinked membrane based on renewable, degradable and environmentally friendly soybean protein isolate was formed by solution casting method. A series of gel polymer electrolytes were prepared with the crosslinked membranes saturated with 1 mol·L−1 Li2SO4. The solid-state electric double-layer capacitors were fabricated with the prepared gel polymer electrolytes and activated carbon electrodes. The optimized solid-state supercapacitor delivered a single electrode specific capacitance of 115.17 F·g−1 at a current density of 1.0 A·g−1, which was higher than the supercapacitor assembled with the commercial separator in 1 mol·L−1 Li2SO4. The solid-state supercapacitor exhibited an outstanding cycling stability, indicating that the gel polymer electrolyte based on the crosslinked soybean protein isolate membrane could be a promising separator for a solid-state supercapacitor.

Nickel doped cobalt - hollow nanoparticles as an efficient electrocatalyst for hydrogen evolution from neutral water

The development of efficient electrocatalyst based on earth-abundant elements for hydrogen generation under simple conditions is highly desired, but still a serious challenge. Herein, we report a simple synthesis of Ni doped Co hollow nanoparticles (CoNiHNP) through an easy ultrasonic-assisted chemical reduction method in the presence of non-metal (B and P) and metal (W) as an additive. The addition of low valency non-metals (B and P) and non-3d high valency metals like tungsten (W) improve the near-optimal adsorption energy for hydrogen evolution reaction (HER). The CoNiHNP requires a 41 mV overpotential to drive a 10 mA cm−2 current density for HER in 1.0 M potassium phosphate buffer solution (pH = 7). Remarkably, the CoNiHNP achieves a 400 mA cm−2 current density at a low overpotential of 417 mV in neutral pH aqueous electrolyte. Moreover, the CoNiHNP shows better performance during long-term electrolysis as compared to Pt/C. To the best of our knowledge, the CoNiHNP is the most stable, active and efficient non-noble metal electrocatalyst for hydrogen generation from a neutral solution.

Nitrogen-coordinated single Fe sites for efficient electrocatalytic N2 fixation in neutral media

Electrocatalytic nitrogen reduction reaction (NRR) for NH3 generation under ambient conditions presents a promising alternative to the conventional Haber–Bosch process. Here, we report a Fe single-atom catalyst for ambient electrochemical NH3 synthesis. This catalyst achieves high Faradaic efficiency (18.6 ± 0.8%) and NH3 yield rate (62.9 ± 2.7 μg h−1 mgcat.−1) in neutral aqueous electrolyte at room temperature and −0.4 V versus reversible hydrogen electrode. Furthermore, this catalyst exhibits a negligible activity decay during electrolysis for 24 h. X-ray absorption fine structure analyses and theoretical calculations reveal that atomically dispersed single Fe species are stabilized by N in Fe–N4 configuration, which is favorable for N2 activation. This work opens new opportunities for developing advanced single atomic site catalysts for NH3 synthesis via NRR.

Low Temperature Performance of MnOx@Carbon Nanofoam-Based Ecs with Neutral pH-Based Aqueous Electrolytes

Electrochemical capacitors (ECs) comprising high-surface-area carbon electrodes and nonaqueous electrolytes offer many attractive performance attributes including long cycle life and the ability to operate at low temperatures (–40⁰C), yet their energy density is ultimately limited by reliance on the double-layer charge-storage mechanism. Asymmetric EC configurations that include pseudocapacitive materials (e.g., transition metal oxides) offer the opportunity to increase energy density while also using safer and cheaper aqueous electrolytes. We have shown that with the appropriate electrode structure and electrolyte additives, the additional charge stored via pseudocapacitance is delivered at EC-like rates over 1000 cycles with minimal capacitance fade. To further prove the practical feasibility of such aqueous-electrolyte ECs, we turned our attention to low-temperature performance, focusing on aqueous electrolyte compositions containing lithium or sodium cations and sulfate or nitrate anions. We characterized pertinent bulk properties (e.g., freezing point and ionic conductivity) of down-selected electrolytes and found that the anion dominates the freezing point, with sulfate-based electrolytes having a freezing point of –45oC, while nitrate-based electrolytes have a freezing point of –35oC. The ionic conductivities ranged from 63 to 136 mS cm-1 at 20oC, conductive enough to support high-rate operation. To assess the impact of temperature on performance as a function of electrolyte composition, we fabricated symmetric pouch cells comprised of MnOx@carbon nanofoam electrodes, evaluating the resulting devices via cyclic voltammetry and electrochemical impedance spectroscopy over a wide temperature range (25⁰C to –45⁰C). All ECs exhibited a gradual decrease in capacitance as the temperature decreased; however, capacitance was recovered upon warming to 25°C for all electrolyte compositions. We found that ECs with Li2SO4-based electrolytes (neat or mixed composition) were operational at temperatures as low as –35°C, revealing that these electrolytes are competitive with the nonaqueous electrolytes used in conventional double layer capacitors.

Highly Reversible Reactions in Neutral Aqueous Zinc Battery Systems

Along with the rapid development of renewable energy storage such as wind and solar, the large-scale energy storage technologies are highly desired. Among different energy storage solutions, the rechargeable aqueous Zn-MnO2 batteries are very promising due to their low cost, high environmental benignity and high energy, potentially two times high of the lead-acid batteries. However, the widely investigated rechargeable alkaline Zn-MnO2 batteries suffer from limited depth of discharge (DOD), Zn anode passivation and dendrite, and limited cycle life. In this talk, we will introduce the use of mild aqueous-based electrolytes to address the above issues based on the greatly improved rechargeability of both MnO2 cathode and Zn anode in such systems.[1,2] We will also discuss our recent understanding on how to realize and maintain the highly reversible reactions for both zinc metal and cathodes by optimizing the electrolyte and electrode structures in optimal neutral aqueous electrolyte systems to realize the long-term cycling stability for their future practical applications in large-scale energy storage.

Highly stable nickel-aluminum alloy current collectors and highly defective multi-walled carbon nanotubes active material for neutral aqueous-based electrochemical capacitors

Neutral aqueous electrolytes are known to promote corrosion of carbon coated aluminum current collectors used in electrochemical capacitors, limiting their applications on energy storage devices. Alternatively to the standard electrode manufacturing recipe, we have grown multi-walled carbon nanotubes as the active material on modified aluminum foils to avoid the corrosion of the latter in neutral aqueous solutions. Therefore, the purpose of the present study is the fabrication of a binary alloy that is resistant to corrosion in neutral aqueous solutions. In this sense, we modified standard aluminum foil current collectors by coating them with a thin nickel layer, which was converted on nickel-aluminum alloy (NixAl, x = 1 & x = 3) during the first heating steps of nanotubes growth on the current collector. This novel aluminum modified current collector is electrically conductive and very resistant to corrosion, which allows applying aluminum-based current collectors on aqueous-based electrochemical capacitors devices. To better investigate the electrochemical performance of carbon-based electrodes in aqueous filled coin cell devices, we performed several electrochemical studies using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Our results show specific electrode capacitance is up to ∼60 F g−1. After 85,000 (re)charge/discharge cycles, the cell operating on 0–1.5 V voltage range, indicate very long lifespan with no significant loss of specific capacitance and energy density. These results are unexpected for aluminum current collectors on supercapacitor or batteries. On the Ragone plot, our aqueous-based electrochemical capacitor is on supercapacitors region with fairly high power and energy densities.