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Multiwalled carbon nanotubes (MWCNTs) were longitudinally split to be unzipped by a facile chemical oxidative etching. Transmission electron microscope images and Raman spectra confirmed that most of MWCNTs were opened and some were transformed to multi-layered graphene nanoribbons. Scanning electron microscope images showed that unzipped carbon nanotubes (UCNTs) were interwined each other to form a tridimensional porous film. The N2 adsorption/desorption analysis showed that the UCNTs had larger specific surface area and more mesopores compared to MWCNTs. The galvanostatic charge-discharge experiments showed that the reversible capacity of UCNTs were up to 765mAhg−1 at 0.1Ag−1 and kept 635mAhg−1 at various current densities. The reversible capacity remained stable around 420 and 330mAhg−1 at current rates of 0.6and 1Ag−1 with coulombic efficiency above 99% over 300 cycles.
The surface of LiFePO4/C cathode material is coated with nano-sized Sn via a simple electroless deposition (ED) process, and the effects of the Sn-coating on the electrochemical performances of LiFePO4/C are investigated systematically by the charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiFePO4/C, the Sn-coated LiFePO4/C exhibits higher capacity, better cyclability and higher rate capability in a wide operation temperature range. An analysis of the electrochemical measurements reveals that Sn-coated LiFePO4/C has good electric contact among particles, much lower charge-transfer resistances and higher lithium diffusion rate, especially at low temperature. In addition, the Sn-coating layer protects the active materials from chemical attack by HF and thus suppresses the dissolution of Fe from LiFePO4 in the LiPF6 based electrolyte.
The nickel–manganese compounds were synthesized by redox reactions in aqueous solutions using potassium permanganate as an oxidizing agent at ambient temperature. Also, a layered Li–Ni–Mn–O system was synthesized by using a nickel–manganese compound as precursor for electrode materials. X-ray diffraction patterns of the lithiated Li1.296Ni0.056Mn0.648O2 sample were indexed to a layered structure based on hexagonal α-NaFeO2 (space group: R-3m, 166) with signs of monoclinic-related peaks indicating the existence of monoclinic Li2MnO3 phase. The lithiated Li1.296Ni0.056Mn0.648O2 electrode provides the initial discharge capacity of 108mAhg−1 and the maximum discharge capacity of 192mAhg−1 between 2.0 and 4.8V versus Li/Li+ at 0.2mAcm−2.
To reduce greenhouse gas emissions, the electricity sector is going through two main transitions. First, the electric grid is integrating variable renewable generation, such as wind and solar. Second, demands are changing as heating systems are shifting from gas-based to high efficiency electric heat pumps. This paper provides a comparative analysis of future energy scenarios with distributed technology options including (1) wind and solar generation; (2) heat pumps for heating and cooling; and (3) battery and thermal storage in representative residential blocks in four cities, including New York City, New York; Minneapolis, Minnesota; Tallahassee, Florida; and Fort Collins, Colorado. These cities are located in three climate regions with different weather patterns which result in different demand profiles and different local renewable resources. Future energy demand scenarios with 100% penetration of air source or ground source heat pumps for heating and cooling are estimated for the four residential city blocks. Under a future scenario with all electric demand with air source heat pumps and high renewable energy penetration, this study finds that (1) the optimal wind and solar generation mix varies with location and amount of storage and (2) battery storage is more cost effective than thermal storage, ground source heat pumps, and overbuilt renewable generation.
Two bis(ethylenedioxythiophene)naphthalene monomers 1,4-bis(2-(3,4-ethylenedioxythiophene))-naphthalene (M1) and 2,6-bis(2-(3,4-ethylenedioxythiophene))-naphthalene (M2) were synthesized, and corresponding polymer poly(1,4-bis(2-(3,4-ethylenedioxythiophene))-naphthalene) (P1) and poly(2,6-bis(2-(3,4-ethylenedioxythiophene))-naphthalene) (P2) were electrochemically synthesized and characterized. Characterizations of the resulting polymers were performed by cyclic voltammetry, UV–vis spectroscopy and scanning electron microscopy. The oxidation potential of monomer M2 was lower than that of the M1, and the conjugation lengths of both the M2 and P2 were longer than the corresponding M1 and P1, respectively. Spectroelectrochemical analysis revealed that both the polymer films had good electrochromic properties and exhibited multi-electrochromic behaviors. Besides, the corresponding devices P1/Poly(3,4-ethylenedioxythiophene) (PEDOT) device and P2/PEDOT device showed satisfactory optical contrast (ΔT%), fast response time and excellent cyclic voltammetry stability. The electrochromic properties of two EDOT-naphthalene-EDOT style polymers are dependent on the position of substitution.
Lithium metal batteries (LMBs) have been considered as one of the highly attractive candidates for next-generation energy-storage devices. Ether electrolytes are compatible with lithium metal anode, however, they are excluded from being used in 4 V class batteries due to their limited oxidative stability, which highly limits the specific energy density of batteries. Herein, we demonstrate a facile and effective strategy to stabilize ether-based electrolyte with high voltage cathode LiCoO2 (LCO). The LCO is modified by Li1.5Al0.5Ge1.5(PO4)3 (LAGP) via ball milling and sintering, accompanied with salts passivation during cycling, attaining a capacity retention of 80.7% over 500 cycles with a charge cut-off voltage of 4.3 V. This study offers a viable method to improve the stability between ether-based electrolytes and high voltage cathode, and open up new possibilities for practical application in high performance lithium batteries.
Novel nitrogen and sulfur dual-doped graphene sheets are synthesized via carbonization of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT) functionalized graphene oxides. Here, PDMcT, polymerized by the commercially available 2,5-dimercapto-1,3,4-thiadiazole (DMcT) monomer is chosen as the nitrogen and sulfur precursor, which plays a key role in the formation of nitrogen and sulfur dual-doped graphene. When evaluated as anode materials for lithium ion batteries, the nitrogen and sulfur dual-doped graphene sheets show high initial specific capacity of 1428.8mAhg−1, excellent cycling stability over 5000 cycles, and good rate capability (107mAhg−1 even at a current density of 10Ag−1), which can be attributed to the unique structure and dual-heteroatom doping.
Climate control applications in the form of heating and cooling account for a significant portion of energy consumption in buildings and transportation. Consequently, improved efficiency of climate control systems can significantly reduce the energy consumption and greenhouse gas emissions. In particular, by leveraging intermittent or continuous sources of waste heat and solar energy, thermally-driven energy storage systems for climate control can play a crucial role. We demonstrate the concept of a thermophysical battery, which operates by storing thermal energy and subsequently releasing it to provide heating and cooling on demand. Taking advantage of the adsorption-desorption and evaporation-condensation mechanisms, the thermophysical battery can be a high-power density and rechargeable energy storage system. We investigated the thermophysical battery in detail to identify critical parameters governing its overall performance. A detailed computational analysis was used to predict its cyclic performance when exposed to different operating conditions and thermodynamic cycles. In addition, an experimental test bed was constructed using a contemporary adsorptive material, NaX-zeolite, to demonstrate this concept and deliver average heating and cooling powers of 900W and 650W, respectively. The maximum power densities and specific powers observed were 103W/l and 65W/kg for heating, and 78W/l and 49W/kg for cooling, respectively, making the thermophysical battery competitive with the state-of-the-art climate control systems that provide relatively lower power densities. Additionally, with further opportunities for development and innovation, especially in synthesizing novel adsorptive materials, the thermophysical battery can achieve significantly higher power densities. With its ability to function using thermal energy input while being compact and lightweight, the thermophysical battery offers an option to address the energy challenges associated with the rising demand for climate control.
A series of Li-ion cells containing LiNi1/3Co1/3Mn1/3O2 and artificial graphite as the active materials, have been stored at various temperatures from 0 to 70°C. The 3-electrode impedance study shows that both the solid electrolyte interphase (SEI) film resistance and charge-transfer resistance of the negative electrode first decrease and then increase during storage at 70°C, while both resistances for the positive electrode increase under this condition. The reversible capacity loss of the 3-electrode cell, which is possibly attributed to dissolution of SEI film, accounts for over half of the total capacity loss after 5 weeks of storage. Gases generated from the swelling aged cell at 60°C are mainly attributed to the reduction of the electrolyte on the negative electrode. A further study on the side-reaction has been done on graphite electrodes and separators, indicating that SEI films may be rearranged and reformed on negative electrodes, and that some pores on the positive electrode side of separator are blocked due to the oxidation of electrolyte, resulting in poor Li-ion transfer and rise of the ohmic resistance during storage at elevated temperature. However, at 0°C, this side-reaction is impeded.
A series of Ni0.6CoxMn0.4-x(OH)2 hydroxide precursors with x=0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 are prepared by co–precipitation method from sulfate solutions using NaOH and NH4OH as precipitation and complexing agents. Then, well–ordered layered LiNi0.6CoxMn0.4-xO2 are synthesized by sintering the mixture of as–prepared precursors and LiOH·H2O at 820°C for 12h in flowing oxygen. Their structural and electrochemical properties are investigated using X–ray diffraction(XRD), scanning electron microscope(SEM), X–ray photoelectron spectroscopy(XPS), charge–discharge test, Cyclic voltammetry(C–V) and electrochemical impedance spectroscopy (EIS). The increase of the Co content in LiNi0.6CoxMn0.4−xO2 leads to the decrease of the tap–density of the powders, the increase of discharge capacity and the deterioration of cycling performance. It also leads to the enhancement of the ratio Ni3+/Ni2+ in LiNi0.6CoxMn0.4−xO2, confirmed by the XPS analysis. The results show that the sample with x=0.2 has the highest tap–density, delivers an initial discharge capacity of 172.3 mAh g−1 at 1C rate between 2.8 and 4.3V, more than 94.1% of that is retained after 100 cycles, and also with excellent rate capability and high-temperature performance.
Mechanical durability and the triboelectric property of the friction layer are crucial for obtaining stable high power output from triboelectric nanogenerators (TENGs). Here, we introduce butylated melamine formaldehyde (BMF) as a promising triboelectric material because of both its mechanical durability and its highly positive triboelectric property. These unique characteristics originate from its functional group, which contains hydrogen atoms. Kelvin probe force microscopy measurements and density functional theory calculations confirm that BMF is triboelectrically more positive than are pristine MF and methylated MF. In addition, the Young's modulus, calculated by molecular dynamics simulations, of BMF is six times higher than that of polytetrafluoroethylene (PTFE). Additionally, BMF has demonstrated a lower wear rate than PTFE in an abrasion test with Cu as the counter friction material. Because of the superior mechanical and triboelectric characteristics, the root-mean-square output of a rotation-type BMF based TENG [210 V and 125 μA (24 mA m−2)] is higher than that of the one with PTFE [90 V and 31 μA (5.9 mA m−2)] and remained stable over extended operation of 27000 cycles. BMF thus offers an opportunity for fabricating high-performance TENGs with applications in self-powered smart systems.
The architecture of a control system can be designed vertically with the distinction between functional levels. We adopt this layered approach for the design and implementation of a network-based control and monitoring application. In this paper we present the design and implementation of a network-based management application for controlling and monitoring the input and output data of remote equipment aiming at performance macro-observation, alarm detection, handling operation failures, installation security, access control, collection and recording of statistical data and provisioning of reports. The main services provided to the user and operating over the public internet and/or mobile network include control, monitoring, notification, reporting and data export. Our proposed system consists of a front-end for field (site-level) control and monitoring as well as a service back-end which undertakes to collect, store and manage data from all remote installations. Hierarchical data acquisition methodology and performance macro-observation are according to the IEC 61724 standard. We have successfully used our control and monitoring application for integrated facility management of photovoltaic plant installations; nevertheless it can be easily migrated to other renewable energy generation installations and remote automation applications in general.
The unitized regenerative fuel cell (URFC) is a promising electrochemical device for intermittent renewable energy storage in chemical bonds. However, widespread application has been hindered due to low round-trip efficiencies (RTEs) and disappointing durability, in particular at high rates. Here, we break through that barrier by demonstrating highly efficient, flexible, and stable URFCs via hierarchical design of the multiscale catalyst-layer structures. A more porous and less tortuous Pt and Ir catalyst layer is realized using a doctor blade fabrication method that significantly improves URFC performance. We demonstrate RTEs of 56% and 53% under constant-electrode and constant-gas mode, respectively, while operating at 1000 mA cm−2, and significantly, a RTE of 45% at 2000 mA cm−2, achievements that were previously viewed as unfeasible under the onerous demands of URFC operation. At the same time we demonstrate URFCs under both constant-electrode and constant-gas mode operated continuously for over 500 h with negligible degradation. These results demonstrate the viability of applying URFCs for long-term energy storage at previously unattainable efficiencies and cast new light on electrode design and optimization of URFCs.
The nitrogen dissociation and plasma parameters during radio frequency sputtering of lithium phosphorus oxynitride thin films in nitrogen gas are investigated by mass appearance spectrometry, electrostatic probes and optical emission spectroscopy, and the results are correlated with electrochemical properties and microstructure of the films. Low pressure and moderate power are associated with lower plasma density, higher electron temperature, higher plasma potential and larger diffusion length for sputtered particles. This combination of parameters favors the presence of more atomic nitrogen, a fact that correlates with a higher ionic conductivity. Despite of lower plasma density the film grows faster at lower pressure where the higher plasma potential, translated into higher energy for impinging ions on the substrate, resulted in a compact and smooth film structure. Higher pressures showed much less nitrogen dissociation and lower ion energy with thinner films, less ionic conductivity and poor film structure with large roughness.
Herein, the novel binary tungsten-molybdenum oxides (W0.4Mo0.6O3) nanoneedle arrays have been prepared by a facile one-step hydrothermal method without adding any surfactant. The as-prepared W0.4Mo0.6O3 nanoneedle arrays can provide abundant exposed reaction active sites and utilize expedite transport channel to facilitate the diffusion of electrolyte ion. Thus, as an electrode for supercapacitor, it exhibits a high specific capacity of 115.7 mAh g−1 at the current density of 1 A g−1 and good rate performance. To achieve the high energy density of supercapacitor, an asymmetric supercapacitor is fabricated by using the W0.4Mo0.6O3 nanoneedle arrays as the negative electrode and the polygni multiflori caulis-based honeycomb-like carbon (PMCHC) as the positive electrode, which possesses a high output voltage of 1.5 V and an energy density of 20.2 Wh kg−1 at a high power density of 750.6 W kg−1, as well as good cycling stability. Such facile synthesis strategy and outstanding electrochemical behaviors imply that the binary metal oxides nanoneedle arrays is a promising electrode material for energy-storage system.
Proton exchange membrane fuel cell offers higher energy density than the existing battery technologies for high-energy applications, and it is a promising power source for various industries including aerospace vehicles. We have been developing and testing a non-external humidified fuel cell system for high-altitude balloons, which require simple, light, and easy-to-operate power systems. This system consists of three major subsystems—a fuel cell stack, a reactant supply subsystem, and an electrical control subsystem. Ground performance testing in a vacuum chamber simulating the high-altitude vacuum condition was performed before the flight. Then, a demonstration flight of the fuel cell system was launched using a large balloon for verifying its performance under practical high-altitude conditions. Cell voltage variations synchronized with oxygen pressure spikes were observed that were probably caused by condensed product water plugging the flow passages of the back pressure regulator. Flight results indicated that the fuel cell system operated better when water was expelled as vapor, rather than in the liquid form. In addition, a back pressure regulator should be installed to avoid the accumulation of water droplets for realizing a stable performance.
MoO3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials were synthesized via using co-precipitation method and wet coating process, and their crystal structure and particle morphology were analyzed and observed by XRD, SEM and TEM. The electrochemical properties of these materials were investigated and analyzed by using charge-discharge tests and electrochemical impedance spectroscopy. The results showed that the surface coating on Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode was composed of α-MoO3 and Li2MoO4, and the electrochemical properties were improved after coated with MoO3 thin films. The initial coulombic efficiencies increased from 71.2% to 79.3% when the MoO3 content increased to 5wt.%. Particularly, the 3wt.% MoO3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 showed the highest capacity retention of 90.8% after 100 cycles, and possessed the excellent rate discharge performance. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetric results demonstrated that the layered MoO3 coating could restrain the increment of the charge transfer resistance and stabilize the active material structure during cyclic process.
Microreactor technology is a promising approach in harnessing the high energy density of hydrocarbons and is being used to produce hydrogen-rich gases by reforming of methanol and other liquid hydrocarbons. However, on-demand H2 generation for miniature proton exchange membrane fuel cell (PEMFC) systems has been a bottleneck problem, which has limited the development and demonstration of the PEMFC for high-performance portable power. A number of crucial challenges exist for the realization of practical portable fuel processors. Among these, the management of heat in a compact format is perhaps the most crucial challenge for portable fuel processors. In this study, a silicon microreactor-based catalytic methanol steam reforming reactor was designed, fabricated, and demonstrated in the context of complete thermal integration to understand this critical issue and develop a knowledge base required to rationally design and integrate the microchemical components of a fuel processor. Detailed thermal and reaction experiments were carried out to demonstrate the potential of microreactor-based on-demand H2 generation. Based on thermal characterization experiments, the heat loss mechanisms and effective convective heat coefficients from the planar microreactor structure were determined and suggestions were made for scale up and implementation of packaging schemes to reduce different modes of heat losses.
In this work hybrid materials composed of electroactive polymer poly(3,4-ethylenedioxythiophene) (pEDOT) and metal hexacyanoferrates (Mehcf) (Me=Fe, Co, Ni) were tested in ethylene carbonate (EC):propylene carbonate (PC) electrolytes containing 0.5M KPF6 or 0.5M LiPF6 salts. The hybrid materials pEDOT/Mehcf were examined by using: cyclic voltammetry (CVA), potentiometry and impedance spectroscopy (IS). The materials pEDOT/Mehcf exhibit electrode activity, good stability and high electrical capacity in tested nonaqueous electrolytes and they are considered to be suitable active materials for supercapacitors or for positive electrode of secondary cell with lithium and potassium salts. Contrary to the solid Prussian Blue “PB” analogues, hybrid pEDOT/Cohcf electrodes work with good efficiency in contact with nonaqueous electrolyte containing lithium salts.
Lithium sulfur battery is deemed to one of the most hopefully useable and cost-effective options beyond traditional lithium ion batteries. Nevertheless, the intermediates shuttle effect and the instability of the lithium metal anode are still the significance of barriers to the actual application of lithium sulfur battery. In this work, zirconium oxynitrate (ZrO(NO3)2), which delivers good thermal stability and little hygroscopicity, is proposed as a dual functional electrolyte additive to ameliorate the electrochemical performance of lithium sulfur batteries. For one thing, the ZrO2+ cations possess a strong affinity to sulfur, which can catalyze the conversion of dissolved polysulfides to S8. For another, ZrO(NO3)2 is negatively charged in the ether electrolyte because of the coordination ability of ZrO2+. It displays a strong repulsion to polysulfides which would effectively trap the dissolved polysulfides and prevent the polysulfides from diffusing into the electrolyte phase. Additionally, NO3 − anions can be reduced and form a stable passivation film on Li-metal anode, which is beneficial to decrease the reacting activity of Li-metal anode upon polysulfides and stabilizing the surface topography of the Li-metal anode. Ultimately, the ZrO(NO3)2 electrolyte additive observably enhances the discharge capacity and cycle stability of Lithium sulfur battery.