Fast Reversible Reaction Research Articles

Amorphous AlPO4 Layer Coating Vacuum Thermal Reduced SiOx with Fine Silicon Grains to Enhance the Anode Stability.

Micrometer-sized silicon monoxide (SiO) is regarded as a high-capacity anode material with great potential for lithium ion batteries (LIBs). However, the problems of low initial Coulombic efficiency (ICE), poor electrical conductivity, and large volume change of SiO inevitably impede further application. Herein, the vacuum thermal reduced SiOx with amorphous AlPO4 and carbon double-coating layers is used as the ideal anode material in LIBs. The vacuum thermal reduction at low temperature forms fine silicon grains in the internal particles and maintains the external integrity of SiOx particles, contributing to mitigation of the stress intensification and the subsequent design of multifunctional coating. Meanwhile, the innovative introduction of the multifunctional amorphous AlPO4 layer not only improves the ion/electron conduction properties to ensure the fast reversible reaction but also provides a robust protective layer with stable physicochemical characteristics and inhibits the volume expansion effect. The sample of SiOx anode shows an ICE up to 87.6% and a stable cycling of 200 cycles at 1 A g-1 with an initial specific capacity of 1775.8 mAh g-1. In addition, the assembled pouch battery of 1.8 Ah can also ensure a cycling life of over 150 cycles, demonstrating a promising prospect of this optimized micrometer-sized SiOx anode material for industrial applications.

CuMnO2 nanosheets for high performance aqueous Zn-ion batteries

Zinc-ion batteries based on aqueous electrolytes have great advantages over organic ones. Here, CuMnO2 nanosheets with a thickness of about 10 nm have been prepared by a hydrothermal method assisted by nitrilotriacetic acid. Benefiting from its layered structure and unique two-dimensional (2D) nanosheets, the as-prepared CuMnO2 nanosheets are a good host for fast zinc ion transport, high capacity, and reversible electrochemical reactions, as well as excellent cycling stability. Specifically, a zinc storage capacity of 299.1 mAh g−1 at 0.2 A g−1 and stable cycling (189.9 mAh g−1 after 300 cycles), fast diffusion kinetics of Zn-ions (1.52 × 10−13 cm2 s−1), and good rate capabilities (78 mAh g−1 even at 2.0 A g−1) are achieved. This work suggests a potential candidate cathode for zinc-ion batteries.

Mobile Efficient Diagnostics of Infectious Diseases via On-Chip RT-qPCR: MEDIC-PCR.

The COVID-19 outbreak has caused public and global health crises. However, the lack of on-site fast, reliable, sensitive, and low-cost reverse transcription polymerase chain reaction (RT-PCR) testing limits early detection, timely isolation, and epidemic prevention and control. Here, the authors report a rapid mobile efficient diagnostics of infectious diseases via on-chip -RT-quantitative PCR (RT-qPCR): MEDIC-PCR. First, the authors use a roll-to-roll printing process to accomplish low-cost carbon-black-based disposable PCR chips that enable rapid LED-induced photothermal PCR cycles. The MEDIC-PCR can perform RT (3min), and PCR (9min) steps. Further, the cohort of 89 COVID-19 and 103 non-COVID-19 patients testing is completed by the MEDIC-PCR to show excellent diagnostic accuracy of 97%, sensitivity of 94%, and specificity of 98%. This MEDIC-PCR can contribute to the preventive global health in the face of a future pandemic.

Electrochemical properties modulation of Zinc oxide nanoparticles

The influence of zinc salts precursors (nitrate, acetate, chloride) on the electroactivity of the synthesised Zinc oxide nanoparticles (ZnONPs) was investigated using Glassy carbon ZnONPs modified electrode (ZnONPs films). The precipitation synthesised ZnONPs ‘s optical, morphological, size and Structural properties were assessed by usual spectroscopical technique. The XRD data confirmed synthesis of The ZnONPs which were predominately Zincite except for the nitrate product (zincite, ZHNH). All the NPs were of smaller size with the highest diameter size of 0.25 μM and lowest 0.066 μM for nitrate and chloride NPs respectively. All had good electroactivity, with rate constants (ks) above 1 × 10−2 indicating fast reversible reactions, values ranged from 0.6152 to 0.7515 for Zn(NO3) and Zn(CH3COO)2 respectively. Excellent opto-electric properties were observed with the nitrate product that had the highest band gaps (∼3.7 eV), DPV current(,7.57 × 10−7 A) ΔEp, diffusion coefficient (De) (3.120 × 10−1(cm2/s (Ariyanta et al., 2022) [5]) and rate constant (0.62 S-1). In addition it had the lowest resistance as indicated by the Rs value (1.13 kΩ) below the bare electrode value lowest Rct (444.77 kΩ) and CPE (3.00 × 10−6 F). For fabrication of sensors and batteries where low resistance and conductivity are essential, ZnONPs using Nitrate is ideal.

Bilateral growth of monoclinic WO3 and 2D Ti3C2Tx on 3D free-standing hollow graphene foam for all-solid-state supercapacitor

• Hollow graphene foam was successfully prepared by TA-CVD method. • m -WO 3 /Ti 3 C 2 T X /HGF-7 electrode was fabricated by UPED and drop-casting methods. • The electrode exhibited a specific capacitance of 573F g −1 with 93.3% cycling stability. • An ASC device showed 27.2 Wh kg −1 energy density at power density of 752 W kg −1 . • The ASC device endured superior cycling stability of 93% over 10,000 GCD cycles. The free-standing three dimensional (3D) hollow graphene foam (HGF) decorated nanostructured pseudocapacitive materials could offer a large active surface area and a extreme conductive porous 3D network for fast reversible charge transfer reactions in the supercapacitor. Herein, the 3D HGF was prepared by a template assisted-chemical vapor deposition (TA-CVD) method and the monoclinic WO 3 ( m- WO 3 ) interconnected nanoparticles as well as 2D Ti 3 C 2 T x sheets were bilaterally loaded on the inner and outer sides of HGF by a simple unipolar electrodeposition (UPED) method and a drop casting method, respectively. The obtained 3D free-standing m- WO 3 /Ti 3 C 2 T X /HGF electrode exhibited an excellent specific capacitance of 573F g −1 at 5 mV s −1 with outstanding rate performance and 93.3% cycling stability over 5000 cycles, which can be attributed to the metal-like conductivity and reversible redox reactions of hydrophilic 2D Ti 3 C 2 T x . The asymmetric solid-state supercapacitor (ASC) illustrated a 2-fold wider potential of 1.4 V in an acidic electrolyte when compared with the MXene-based symmetric supercapacitor. It displayed an excellent specific capacitance of 145.2F g −1 (111.3 mF cm −2 ) at 5 mV s −1 , an ultra-high energy density of 27.2 Wh kg −1 (20.83 μWh cm −2 ) at a power density of 752 W kg −1 along with 93% cycling stability over 10,000 cycles. Therefore, such a m- WO 3 /Ti 3 C 2 T x /HGF electrode should be promising for the fabrication of advanced supercapacitors.

Coaxial Cable‐Like Carbon Nanotubes‐Based Active Fibers for Highly Capacitive and Stable Supercapacitor

AbstractPolyoxometalate (POM) as one pseudocapacitive material could efficiently boost the capacitance of carbon materials. However, POM hydrolysis is a key obstacle in utilizing POM for supercapacitors, causing reduced cycling stability. Here, coaxial cable‐like carbon nanotubes(CNTs)‐based active fibers are synthesized for highly capacitive and stable supercapacitors. The POM layer of PMo12O403− (PMo) is physically protected from the hydrolysis by the external polyaniline (PANI) layer. The optimal CNT/PMo/PANI fibers show a highly specific capacitance of 825 F g−1 at 5 A g−1 and excellent cycling stability (≈85% retention at 6000th cycle). However, the control structure of CNT/PANI/PMo only deliver 486 F g−1 at 5 A g−1 and 64% capacitance retention achieved after 500 cycles. The significant improvements of CNT/PMo/PANI can be attributed to the synergistic effect of CNTs, PMo, and PANI. CNTs serve as a 1D charge transport expressway and anchor through poly(diallyldimethylammonium chloride) linkers. PMo clusters and PANI serve as the main active centers for fast reversible redox reactions, contributing pseudocapacitance. PANI serves as a shield layer for maintaining the integrity of PMo clusters and thus ensure good stability.

Boosting the supercapacitor performance of polyaniline nanofibers through sulfonic acid assisted oligomer assembly during seeding polymerization process

Polyaniline (PANI), thanks to low cost, easy synthesis, fast reversible Faradic reaction and especially theoretical charge storage capability, has been extensively studied in the field of energy conversion and storage. However, its development as electrode material in supercapacitor is still be restricted by the need of high–yield production of PANI with robust electrochemical performance. Herein, inspired by the seeding polymerization, and tunable conductivity and solubility with organic acid, one–pot bulk synthesis of PANI nanofibers in fully aqueous solution was realized with the aid of aniline oligomer and sulfonic acid. During the seeding polymerization process, four kinds of sulfonic acids with different functional groups and sizes including 5–sulfosalicylic acid (SSA), p–toluenesulfonic acid (pTSA), p–aminobenzenesulfonic acid (pASA) and camphorsulfonic acid (CSA) were introduced to efficiently control the assembly behavior of oligomers to form PANI nanofibers, meanwhile provide better electrical and electrochemical properties as well as good dispersion in aqueous solution compared with pure hydrochloric acid (HCl) medium. Benefiting from the bifunctional doping effects of sulfonic acid on the oligomer assembly and nanofiber dispersion, great enhancements on the electrochemical performances of PANI nanofibers can be easily achieved. Especially for CSA, high specific capacitance of 600.7 F g–1 at the current density of 1 A g–1 and good cycling stability with retention of 74% could be manifested, which are over 55% and 11% improvements in contrast to neat HCl medium, respectively. These results suggest that sulfonic acid assisted oligomer assembly is highly effective in combining smaller diameter of PANI nanofiber with superior supercapacitor property, and also provides a new strategy to promote the development of conductive polymers in energy related fields.

MnO2 nanosheets grown on N and P co-doped hollow carbon microspheres for high performance asymmetric supercapacitor

The rapid development of supercapacitors has led to an increasing demand for the exploitation of stable and excellent electroactive electrode materials. Herein, a novel hybrid material of N, P co-doped hollow carbon microspheres (N/P-HCS) and ultrathin MnO2 nanosheets was facilely constructed for the electrode material of supercapacitors through a two-step synthetic strategy including the preparation of N/P-HCS and subsequent growth of MnO2 nanosheets on N/P-HCS. The N/P-HCS@MnO2 hybrid possesses a N/P-HCS core and a porous shell composed of ultrathin MnO2 nanosheets. Moreover, the morphology and content of MnO2 in the hybrid can be controlled by designing the stoichiometric chemical reaction between N/P-HCS and KMnO4. The hybrid electrode exhibits excellent electron transport, fast electrolyte ions diffusion, rapid and reversible Faradaic reaction, and good rate performance. Additionally, a green asymmetric supercapacitor was manufactured using typical hybrid N/P-HCS@MnO2-30 as positive electrode and N/P-HCS as negative electrode, which displayed a high energy density of 32.21 Wh kg−1 at a power density of 449.8 W kg−1 and excellent cycling stability (capacitance retention of 94.5% after 3000 cycles). These results show that the N/P-HCS@MnO2 might be an attractive electrode material for practical application in advanced supercapacitor.

Aluminum phosphate as a bifunctional additive for improved cycling stability of Li-S batteries

We demonstrate a facile way to alleviate lithium polysulfide shuttle effect by using aluminum phosphate (AlPO4) as a bifunctional additive in lithium-sulfur (Li-S) batteries. AlPO4 microparticles are synthesized via sol-gel and subsequent calcination process. The effects of AlPO4 on adsorption of lithium polysulfide as well as the performance of Li-S cell are investigated. The Li-S cell containing AlPO4 1.0 wt% retains 76% of the initial capacity after 100 cycles at 0.2 C and it retains 453 mAh∙g−1 at 1.0 C. Using ex-situ X-ray photoelectron spectroscopy and infra-red analysis, it is found that lithium polysulide is chemically adsorbed on AlPO4 through Lewis acid-base interaction with the PO groups in (PO4)3-. The improvement in cycling stability is attributed to the strong interaction between AlPO4 and lithium polysulfides. The adsorbed lithium polysulfides are converted to thiosulfates/polythionates, preventing the dissolution of the lithium polysulfides into the electrolyte and migration to the anode. Various electrochemical measurements including electrochemical impedance spectroscopy and cyclic voltammetry demonstrate that AlPO4 lowers the interfacial resistance and helps fast reversible conversion reaction of sulfur to lithium polysulfides, which enables fast charge/discharge. These results suggest that use of AlPO4 is a convenient and effective way to improve the performance of Li-S batteries.

Quaternary transition metal molybdate (Mn 0.25Ni0.25Co0.25Fe0.25MoO4) design to improve the kinetics of the redox reaction in supercapacitors

In this work, we report on a new Mn0.25Ni0.25Co0.25Fe0.25MoO4 (denoted as MNCFMo) material synthesized by a one-step hydrothermal method and studied the electrochemical performance of this quaternary molybdate as a pseudocapacitive material. The exact formation of the structure was confirmed with the aid of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) which reveal a pure crystal structure and nanorods-like morphology with the expected elemental composition. At current density of 2 A/g, MNCFMo exhibited promising electrochemical performance with calculated specific capacitance up to 1097 F/g compared to 897 F/g for Mn0.33Ni0.33Co0.33MoO4 (denoted as MNCMo) and could maintain a high capacitance of 413.6 F/g even at 40 A/g signifying an excellent rate material, which are ascribed to the additional fast reversible reaction offered by iron (Fe) insertion. Remarkably, the energy density could reach up to 38.1 Wh/kg at power density of 322.8 W/kg. Moreover, this material delivers a superior cycling stability with approximately 20% capacity loss after 5000 cycles at 10 A/g. Electrochemical impedance spectroscopy results reveal low solution resistance (Rs) of 0.307 Ω and charge transfer resistance (Rct) of 12.40 Ω respectively. These profound outputs are attributed to the cumulative redox effects from Mn, Ni, Co and Fe implying a high consideration for MNCFMo as an electrode in advanced supercapacitor application.

Effect of Free Fatty Acid Pretreatment to Yield, Composition and Activation Energy in Chemical Synthesis of Fatty Acid Methyl Ester

Transesterification of waste cooking oil (WCO) for fatty acid methyl ester synthesis using calcium oxide (CaO) as a catalyst with absence and presence of free fatty acid (FFA) pretreatment (untreated and pretreated) prior to reaction have been investigated. The preliminary study was started from theoretical stoichiometric amount molar ratio of methanol to oil. This preliminary experiment showed that indeed, in transesterification with the chemical catalyst the molar ratio of methanol to oil should be exceeding the theoretical stoichiometric molar ratio, due to the fast reversible reaction. The highest FAME content of 81% was achieved at a temperature of 75 °C with pretreated FFA. The composition of methyl ester with pretreated FFA was affected by temperature, where increasing temperature leads to increasing of methyl oleate as major methyl ester in the product. The relation of temperature dependence was further studied by Arrhenius law correlation. It is shown that activation energy was affected by pretreatment of fatty acid. The activation energy (Ea) of transesterification with untreated and pretreated free fatty acid were found as ± 16 kJ/mol and ± 68 kJ/mol, respectively. Unlike untreated FFA, the Ea of transesterification with pretreated FFA was within the range of activation energy for transesterification for the base catalyst. This study showed that methyl ester synthesis was best obtained when FFA was pretreated prior to transesterification. In addition, WCO is a potential feedstock for biodiesel production since it is biodegradable, economic, environmentally friendly and abundantly available.

Aqueous Al-Ion Supercapacitor with V2O5 Mesoporous Carbon Electrodes.

A high-performance, low-cost, aqueous Al-ion supercapacitor was fabricated based on nanostructured V2O5 impregnated mesoporous carbon microspheres (MCM/V2O5) electrodes and Al2(SO4)3 electrolyte for efficient energy storage. MCM/V2O5 composites exhibit high dispersion of nanostructured V2O5 in a mesoporous carbon matrix, beneficial to fast reversible redox reactions with a short diffusion path. The corresponding capacitor illustrates the distinguishable redox behavior, most likely due to the Al3+ intercalation/deintercalation leading to the reduction/oxidation of V5+/V4+. It delivers a high-energy density of 18.0 Wh kg-1 at 147 W kg-1 and a long cycling lifespan with over 88% capacitance retention over 10 000 cycles. The competitive performance can be ascribed to the integration of the electric double layer capacitance provided from MCM with pseudocapacitance contributed by nanostructured V2O5. This work offers the possibilities of high-performance aqueous capacitors based on trivalent Al-ion as guest species, providing new directions for future development of supercapacitors.

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo 2 O 4 electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo 2 O 4 /Ni@NF) shows the superior specific capacity of 1142 C g −1 at 1 A g −1 with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g −1 . These values are about 3.7 times higher than that of the electrode (NiCo 2 O 4 @NF) without a seed layer, which shows the specific capacity of 305 C g −1 @1 A g −1 with cycle stability of 84% even at a lower current density of 1 A g −1 . The enhanced performance of the NiCo 2 O 4 /Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo 2 O 4 /Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe 2 O 3 nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo 2 O 4 /Ni20@NF//rGO-Fe 2 O 3 @NF asymmetric solid state device delivers an areal capacitance of 446 mF cm −2 with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm −2 (at 3.58 kW cm −2 ) and power density of 14.88 kW cm −2 (at 31.41 Wh cm −2 ).

Faster Ion Switching NiCo2O4 Nanoparticle Electrode-Based Supercapacitor Device with High Performances and Long Cycling Stability

Although nanostructured NiCo2O4 is the most appealing and studied electrode material by far as it is cheap, nontoxic, and efficient for supercapacitor application, it still lacks suitable device application comprising a wide voltage window and high operating current density, high specific energy and power, and absolute stability. Here, we report a successful application of our NiCo2O4 nanoparticles (NPs) in a highly efficient electrochemical supercapacitor device, which is brought to reality because of the NPs’ fast ion intercalation/extraction and fast reversible Faradaic surface reactions. The as-synthesized spinel NiCo2O4 NPs are 65 nm in average diameter, have 59 m2/g of surface area, and 0.44 cm3/g of pore volume. Charge storage capability and reliability of the material as an active electrode have been demonstrated in terms of a conventional three-electrode method and in a coin-cell device. Specific capacity values of 150.56 to 41.66 mAh·g–1 (1084 to 300 Fg–1 in terms of capacitance) have been reali...

Cytotoxicity of local anesthetics on rabbit adipose-derived mesenchymal stem cells during early chondrogenic differentiation.

Local anesthetics (LAs) are commonly used to provide peri-operative pain control in the peripheral joints. In the field of regenerative medicine, adipose-derived mesenchymal stem cells (ADMSCs) are gaining attention as a cellular source for repair and regeneration in degenerative diseases. However, previous studies have demonstrated that the commonly used drugs lidocaine, ropivacaine, bupivacaine and mepivacaine may be toxic to human chondrocytes, which has raised concerns over whether they exert similar negative effects on ADMSCs during early chondrogenic differentiation. In the present in vitro study, the cytotoxicity of different LAs to ADMSCs was determined during early chondrogenic differentiation. At concentrations similar to those after physiological dilution once injected into the degenerative tissues, LAs (1% lidocaine, 0.5% bupivacaine, 0.5% ropivacaine or 2% mepivacaine) and PBS (control group) were incubated with rabbit ADMSCs (rADMSCs) for 60 min. Following further culture for 3 or 7 days, the cell viability, apoptosis and morphological alterations of chondrogenic differentiation were measured by determining the mitochondrial activity, by flow cytometric analysis, Safranine Fast Green double staining and reverse transcription-quantitative polymerase chain reaction of chondrogenesis-associated genes. The results indicated that the mitochondrial activity in rADMSC was decreased and the apoptotic rate was increased, following treatment with LAs (P<0.05). Lidocaine (1%) was less cytotoxic to rADMSCs during early chondrogenesis compared with other LAs. The expression levels of chondrogenesis-associated markers, including collagen I, collagen III and sex-determining region Y box 9 were all decreased at day 3 following exposure to LAs compared with the control group (P<0.05). The expression levels of these chondrogenesis-associated genes began to increase on day 7 following exposure but remained lower compared with the control group (P<0.05). Of note, 2% mepivacaine and 1% lidocaine exhibited a less pronounced negative effect on chondrogenesis-associated gene expression compared with other LAs. Therefore, the present study concluded that LAs are cytotoxic to rADMSCs during early chondrogenesis. Attention should be paid to the different types of LA selected in conjunction with ADMSC injection therapy.

A review on the heterostructure nanomaterials for supercapacitor application

The typical physical and chemical properties lead the nanomaterials to breakthrough in the field of energy storage especially, supercapacitor applications. The optimization of electrical conductivity, structural flexibility, band gap and charge carrier mobility are the key point to solve the issues in the electrochemical charge storage mechanism of supercapacitor. The semiconducting heterostructured nanomaterials are the best choice to store energy by near-surface ion adsorption along with additional contribution from fast reversible faradic reactions. The creation of active sites and defects in the grain boundary of the heterostructure materials results in multiple redox activity, superior ionic conductivity and short diffusion path. Therefore, sufficient researches enrooted to the doped and nano heterostructure electrode materials needs to be performed in order to exploit the high power and energy storage applications. This article reviews current trends in the synthesis of heterostructure electrode through hybridization of different electrochemical double layer capacitance (EDLC) and pseudocapacitive materials. This article also emphasize on the effect of doping on the electrode possessing both EDLC as well as the pseudocapacitance. In addition, the advantages of superlattice structure for the superior electrochemical properties are also discussed.

Reduced graphene oxide-modified Ni-Co phosphate nanosheet self-assembled microplates as high-performance electrode materials for supercapacitors

It is demonstrated that the incorporation of reduced graphene oxide (rGO) and pseudocapacitance materials often offer an effective strategy toward fast reversible redox reactions while remaining their high pseudocapacitance. In this work, a type of rGO-modified Ni-Co phosphates (Ni(Co)NH4PO4@rGO) microplates were fabricated for supercapacitors electrodes via a one-step hydrothermal method. SEM and TEM tests indicated that the obtained microplates are comprised of well-aligned crystalline Ni(Co)NH4PO4 nanosheets. Moreover, the rGO-modified microplates exhibit a high specific capacitance of 1020 F g−1 at 1 A g−1, which is 16.3% enhanced compared to that of the untreated Ni(Co)NH4PO4) ones (877 F g−1). While the rate capacitor can reach to 92%. Furthermore, it is observed that after 700-cycles, the specific capacitance can increase to their maximum value of 1451 F g−1 at current density of 10 A g−1, and can still remain 1275 F g−1 after 5000 cycles, showing a high cycling stability. The Ni(Co)NH4PO4 showed the same tendency but the low values. These excellent electrochemical performances could be due to rGO modification and self-assembled well-aligned nanosheets. This type of structures cannot only facilitate the transfer electrons, but also offer high electrochemical activity sites and short transport path length for electrolyte ions.

Pseudocapacitive behavior of the Fe2O3 anode and its contribution to high reversible capacity in lithium ion batteries.

Pseudocapacitance, which is the storage of charge based on continuous and fast reversible redox reactions at the surface of electrode materials, is commonly observed for electrodes in lithium ion batteries, especially for transition metal oxide anodes. In this report, bare Fe2O3 of granular morphology (∼30 nm in diameter) with high purity and decent crystallinity as well as recommendable electrochemical performances is fabricated hydrothermally and employed as the subject to clarify pseudocapacitive behavior in transition metal oxide anodes. Electrochemical technologies such as galvanostatic charging/discharging, differential capacity analysis (dQ/dV) and the power law relationship (i = aνb), which can distinguish pseudocapacitive behaviors of an electrode reaction were employed to analyze the electrodes. Reversible capacities of ∼120 mA h g-1 (0.117 F cm-2) for Fe2O3 were found within particular electrochemical windows (2.3-3.0 V, 0.3-0.8 V for discharging and 2.2-3.0 V, 0.3-1.3 V for charging). A new direction of optimizing the capacities, rate and cycling performances for lithium ion batteries is pointed out with connections between the pseudocapacitive behavior and morphologies of surfaces as well as structures of the electrodes.

Amorphous Ni-C nanoparticles with high electric conductivity and high specific capacitance for rechargeable charge storage

High electrical conductivity is a crucial factor for improving the electrochemical performance of energy storage materials. In the work, amorphous Ni-C nanoparticles with high electric conductivity are fabricated by mechanical alloying and are used as a novel cathode for supercapacitors. It is shown that the amorphous Ni-C retains a high specific capacitance and remarkable cycling stability after the electrode is activated by chronopotentiometry at 0.5 A g−1, and even more gratifyingly, the rate capability of the material is superior to that of other Ni based materials due to its high electrical conductivity, which is convenient for fast electron transfer in active material and fast reversible Faradic reaction characteristics. Finally, an asymmetric supercapacitor based on Ni-C as the positive electrode and activated carbon as the negative electrode could be cycled reversibly at a high working potential of 0–1.6 V and delivered a high energy density of 39.8 Wh kg−1. These results confirm the significance and tremendous potential of amorphous Ni-C materials for the development of high-performance energy supply systems.

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.