Applications In Energy Storage Devices Research Articles

Development of ternary nanocomposite based on ferrocenyl-modified graphene quantum dots for high-performance energy storage applications

Graphene quantum dots were synthesized in a simple one-step procedure using citric acid as starting material. 4-Ferrocenylbutanol as a battery-type electrode material was further used to modify the surface of graphene quantum dots based on hydrogen bonding and π-π interactions. Finally, the nanocomposites with different compositions were synthesized using different amounts of CNT and Fe3O4. Their electrochemical performance shows the properties of the final nanocomposite for practical application in supercapacitors. The final nanocomposite exhibits ideal battery-type capacity, including high capacity of 258 mAh g−1 at 2.5 A g−1, excellent cycle life (89.2 %), and high energy and power density of 75 Wh kg−1 and 6000 W kg−1 (in two electrode system), respectively. The results show superior electrochemical performance and improved ion transfer rate between the electrode/electrolyte surface. The superiority of the final nanocomposite indicates its special properties for potential applications in energy storage devices.

Green synthesis of zero‐dimensional carbon nanostructures in energy storage applications—A review

AbstractOver the past decade, carbon quantum dots (CQDs) and graphene quantum dots (GQDs) have emerged as the supreme category of zero‐dimensional (0D) carbonaceous nanostructures having potential applications in energy storage and optoelectronics devices. These zero‐dimensional carbon nanostructures have captivated excellent consideration and have ascended as a substitute to traditional metal‐based semiconductor QDs due to their intriguing estates like excellent photoluminescence, quantum yield, scalability, tuneable emission, biocompatibility, chemical inertness, and excellent hydrophilicity. These unique properties of zero‐dimensional carbon materials have inspired researchers to employ them in bioimaging, optoelectronic, catalytic, and energy storage applications. The last couple of years have perceived an incredible rise in the green synthetic strategies of carbon‐based QDs and their applications and this review familiarizes the reader with the current and significant progress in the synthesis of carbon‐based QDs/GQDs from various natural precursors with their quantum yields as well as intriguing applications in diverse fields. In addition, this communication not only delivers critical perceptions toward the development in the field of advanced energy devices but also highlights the advancements of these nanosized carbonaceous materials in the energy storage devices such as in supercapacitors and batteries. Also, it focuses on the broad scope of carbon nanomaterials and nanotechnology towards cutting‐edge research and expansion in the arena of energy storage applications of carbon‐based QDs.

Hollow heterogeneous CuSe@MnSe for high-performance printed flexible supercapacitor

High-performance electrode materials are of great significance to realize the practical application of energy storage devices. One proficient approach to achieving high-performance electrode materials is through the design of nanostructure and heterostructure. Herein, a high-performance printed hybrid supercapacitor is fabricated by using a nanostructured CuSe@MnSe composite. The α-MnSe nanoparticles are successfully loaded onto the hollow cubic CuSe through ingenious design, which not only maintained high conductivity but also reduced the issue of volume expansion during the energy storage process. The CuSe@MnSe composite possesses a high capacity (635.32 C g−1) and over 7000 cycles of stability (91.62% capacity retention). The as-printed flexible hybrid supercapacitor exhibits a high capacitance of 164.9 mF cm−2 while exhibiting outstanding energy density (58 μWh cm−2) (19.54 Wh kg−1) and power density (0.8 mW cm−2) (266 W kg−1) when operating at high voltage of 1.6 V. It can fulfill the bending resistance requirements of wearable electrical devices (93% capacitance retention after repeated bending 1000 times). Effective electrode design shows great development potential for printed energy storage devices in wearable electronics, which offers a good way for material inspiration and synthesis.

Supercapacitance performance of novel core/shell poly(m-toluidine)/(Co-Ni) nanoplatelets/nanoneedles nanocomposite

Poly(m-toluidine) (PmT) is a promising polymer material for many applications due to its high electrical conductivity, stability, and ease of synthesis. This work uses PmT/(Co-Ni) nanoplatelets/nanoneedles core/shell composite as an electrode for designing a high-performance supercapacitor. Firstly, nanoneedles of basic Co-Ni compounds composed of cobalt nickel oxide [CNO; Co1.29Ni1.71O4] and cobalt carbonate hydroxide hydrate [CCHH; Co(CO3)0.5(OH)0·.11H2O] were prepared via hydrothermal process. Then, the poly(m-toluidin) [PmT; C7H9N] nanoplatelets were grown on the (Co-Ni) nanoneedles by the in-situ oxidation polymerization method. The elemental composition, crystal structure, and morphology of the PmT/(Co-Ni) electrode were characterized by physicochemical characterization techniques. The supercapacitance performance of the PmT/(Co-Ni) electrode was measured by using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy in HCl solution. The results show that the specific capacitance of the PmT/(Co-Ni) electrode was measured at a current density of 0.6 A/g reaching 308F/g. while the values of specific power density and specific energy are 720 W/kg and 15.4 W h/kg, respectively. Moreover, the PmT/(Co-Ni) electrode exhibits long-term stability and retained about 98% of its starting capacitance value after thousand cycles. The remarkable electrochemical execution recorded could be ascribed to unique nanoplatelets/nanoneedles architectures and conductive PmT polymer. These encouraging results refer to good performance and high stability of the PmT/(Co-Ni) electrode for potential application in energy storage devices.

Improvement of fatigue endurance through modulating strain response in BaTiO3–Ca3Ti2O7 composite ceramics

Ferroelectric ceramics are highly desired for applications in energy storage devices due to their fast charge-discharge capability. However, electric field-driven gradual degradation of ferroelectric polarization (i.e., fatigue) inevitably results in a decrease in energy efficiency and energy storage density. Therefore, improving fatigue endurance is one challenge for their practical applications in energy storage devices. Here, we provide a strategy to modulate the strain response to the external electric field, and thus, increase the fatigue endurance by employing hybrid improper ferroelectricc Ca3Ti2O7 ceramic that exhibits a negative piezoelectric effect. We synthesized [Formula: see text] BaTiO[Formula: see text] Ca3Ti2O7 (BT-xCT) ceramics, in which the strain response of ceramics to the electric field gradually decreases with the increasing proportion of Ca3Ti2O7. For BT-0.3CT ceramic, the energy density storage efficiency is improved to 74.95% which is much higher than that of BT-0.1CT (48.07%). The strain response to the external electric field of BT-0.3CT is substantially lowered and almost reaches zero, leading to excellent fatigue endurance ability. This research work paves a route for designing ferroelectric ceramics with smaller strain response and enhanced fatigue endurance ability, which is expected to benefit a wide range of applications of ferroelectric ceramics in various electric capacitors and electric storage devices.

Engineering hierarchical honeycomb-wall-like MgP4O11/CoP nanosheets as advanced binder-less electrode for supercapacitors

Herein, Mg/Co(OH)F precursors were constructed by a hydrothermal method using secondary water and anhydrous ethanol in a volume ratio of 3:2 as solvents, followed by sodium hypophosphite and high temperature to yield stable MgP4O11/CoP (MPO/CP) composite electrode materials. The optimized MPO/CP nano-walls exhibited more outstanding energy storage performance compared with the single MgCo2O4/MgO oxide (MCO/MO). Specifically, the fabricated MPO/CP electrodes displayed paramount specific capacitance (1870 Fg−1 formed at 1 Ag−1), high rate retention (72.2% specific capacitance maintained when the current density was ramped up from 1 to 15 Ag−1), and exceptional cycling stability (93% after 6000 charge and discharge cycles). These boosted results are ascribed to the formation of multistage honeycomb-walled MPO/CP nanosheets with optimized crossover and multivalency, which promotes MPO/CP with faster transport channels and more reactive sites. Moreover, the P element can reasonably modulate the electronic structure, reduce the internal resistance of ion or electron transport, as well as give full play to the synergistic effect, which can enhance the electrochemical function. Meanwhile, the constructed MPO/CP//AC asymmetric supercapacitor achieves an energy density of 34.3 Wh kg−1 at a power density of 707.2 W kg−1. An encouraging stability of 86.2% was obtained after 8000 cycles at 10 A g−1. Thereby, the proposed novel MPO/CP electrode material with modified electrochemical properties was developed as a prospective candidate for application in energy storage devices.

Protonated chitosan nanostructures for enhancing ionic conductivity of solid-state electrolytes

Solid polymer electrolytes (SPEs) have aroused widespread attention for their high flexibility and good interface contact with electrode. However, the low ionic conductivity severely hinders their application in energy storage devices. Herein, a novel protonated nanostructure was synthesized through the reaction between PEO and Chitosan (Chi) and applied as fillers to form PEO/Chi composite solid-state electrolytes (PCCSEs). The fillers, which achieve nanization by the reaction with PEO, plays an important role in promoting the property of transporting Li+, due to the protonated amino (–NH3+) improving the dissociation of LiTFSI and the nanoscale size with high dispersity. Various characterizations and density functional theory (DFT) calculations were applied to reveal the enhanced Li+ transport mechanism in PCCSE. Owing to the unique design, PCCSE exhibits excellent ionic conductivity at room temperature (1.02 × 10−4 S cm−1) and the Li||SSEs||Li symmetric cells and LFP||SSEs||Li batteries with PCCSE show great cycling stability. This strategy of taking full use of the cations in protonated Chi provides effective design guidance for promoting the Li+ transport in polymer-based electrolytes.

One-Pot Hydrothermal Synthesis of SnMnS Nanosheets for Dielectric Energy Storage Applications

Recently, dielectric materials with high energy storage capacity, low loss, and good temperature stability are highly desired for the rapidly growing field of power electronics. In the current work, we have investigated the change in electrical, optical, and dielectric properties by varying the concentration of compositional elements Sn and Mn. We have prepared the Sn1–xMnxS (0.1, 0.3, 0.5, 0.7, and 0.9) matrix by using the simple single-step hydrothermal method. The samples show that the reflectance percentage increased with the increase of the Mn amount in the composition. The samples exhibit narrow band gap values, which further increase with the Mn content. The band gap value increases from 0.43 to 0.56 eV. The structural analysis shows that the prepared samples are polycrystalline in nature, having SnS and MnS phases. Furthermore, the crystallite sizes increase with an increase in Mn addition, whereas dislocation density and strain decrease simultaneously. The refractive index is calculated from optical band gap values by using the Dimitrov and Sakka equation. The morphological study reveals the uniformity in size and shape of the prepared composition throughout the sample. The presence of compositional elements Sn, Mn, and S is confirmed by EDX analysis. The electrical study reveals that the sample shows good electrical properties, which increase with the Mn contents. The dielectric behavior as a function of frequency and temperature was investigated, and the parameters like dielectric constant, AC conductivity, impedance spectroscopy, and electric modulus were deeply analyzed. All the above optical, electrical, and dielectric properties of the SnMnS matrix have potential use in the field of electronic and energy storage device applications.

Study of the photoluminescence, optical, thermal, and electrical parameters of the Cs/PVP blend/zinc oxide nanorods films for energy storage devices

In this research, well-crystallized zinc oxide nanorods (ZnO NRs) were produced via a solid-state synthesis. Then, employing the casting method, doped chitosan/polyvinyl pyrrolidone (Cs/PVP) blended polymers with different concentrations of ZnO NRs were created. The wurtzite structure of ZnO was determined using XRD. The sample became increasingly amorphous up to a content of 1.5 wt% ZnO NRs, as shown by the XRD examination. TEM measurements of the ZnO nanorods show that their lengths range from 200 to 300 nm and their diameters are between 40 and 80 nm. FTIR analysis has been used to study the relationship between the polymer blend and ZnO NRs. The absorbance, transmittance, and reflectance spectra obtained from the diffused reflectance technique were utilized to study optical characteristics. With the addition of ZnO NRs to the polymer matrix, the optical band-gap narrows while the Urbach energy (tail bandwidth), extinction coefficient, refractive index, and optical conductivity increase. A photoemission peak at about 470 nm was visible in the PL spectra of films made of polymer nanocomposites. At normal temperature, polymer nanocomposites containing 1.5 wt% ZnO NRs had a greater ionic conductivity of 4.2 × 10−5 Scm−1. Studies on electric modulus and dielectric permittivity have also been conducted in order to comprehend the conductivity relaxation and charge storage characteristics. The Cs/PVP-ZnO nanocomposite is more suitable for use in thin-film solar cell applications and energy storage device applications because the decrease in band gap energy and values of the PL were typically accompanied by an increase in the dielectric and conductivity.

Biomass derived porous carbon incorporated nickel oxide hybrid electrode as supercapacitor electrodes for energy storage device applications

Biomass derived porous carbon incorporated nickel oxide hybrid electrode as supercapacitor electrodes for energy storage device applications

Heteroatom-Driven Coordination Fields Altering Single Cerium Atom Sites for Efficient Oxygen Reduction Reaction.

For current single-atom catalysts (SACs), modulating the coordination environments of rare-earth (RE) single atoms with complex electronic orbital and flexible chemical states is still limited. Herein, cerium (Ce) SAs supported on a P, S, and N co-doped hollow carbon substrate (Ce SAs/PSNC) for the oxygen reduction reaction (ORR) are reported. The as-prepared Ce SAs/PSNC possesses a half-wave potential of 0.90V, a turnover frequency value of 52.2s-1 at 0.85V, and excellent stability for the ORR, which exceeds the commercial Pt/C and most recent SACs. Ce SAs/PSNC-based liquid zinc-air batteries (ZABs) exhibit a high and stable open-circuit voltage of 1.49V and a maximum power density of 212mWcm-2 . As the catalyst of the air cathode, it also displays remarkable performance in flexible electronic devices. Theoretical calculations reveal that the introduction of S and P sites induces significant electronic modulations to the Ce SA active sites. The P and S dopings promote the electroactivity of Ce SAs and improve the overall site-to-site electron transfer within the Ce SAs/PSNC. This work offers a unique perspective for modulating RE-based SACs in a complex coordination environment toward superior electrocatalysis and broad applications in energy conversion and storage devices.

Combining functionalized CNT film with CuS microflowers through hyperbranched polymers for a flexible and appliable rechargeable Mg battery

The flexibility and high tolerance for mechanical deformation of batteries under operation is a critical aspect of flexible energy storage devices. In this paper, a large-area CNT film (CF) is prepared via chemical vapor deposition (CVD) method and then functionalized with hyperbranched polymers (HP) using the thiol-ene click reaction. CuS microflowers are in-situ grown on the flexible CNTs, where HP significantly enhances interfacial compatibility and greatly enhances the combination of CuS nanosheets with CNTs substrate. The modification strategy effectively promotes Mg2+ conversion reaction of CuS and greatly enhances the stability of the flexible electrode. The as-prepared flexible CuS/CF-HP cathode delivers a high magnesium storage capacity of 178 mAh g−1 at 50 mA g−1 and a good rate performance of 94 mAh g−1 at 2 A g−1, with a high Mg2+ diffusion coefficient of about ∼10−12 cm2 s−1 and a capacity retention rate of 79.2% after 200 cycles at 200 mA g−1. Furthermore, a practical flexible thin-film rechargeable Mg battery device based on the CuS/CF-HP cathode and Mg powder/CF anode was fabricated in a sealed polydimethylsiloxane package. The flexible full battery provides an outstanding power output as well as remarkable mechanical durability, demonstrating its potential applications for flexible energy storage devices.

Facile synthesis of 2D acid-etched g-C3N4 nanosheets with 1D ZnO nanorods as a promising electrode material for supercapacitor

A low-cost, non-toxic nanocomposite of two-dimensional (2D) nanosheets of acid-etched graphitic carbon nitride (TGCN) and one-dimensional (1D) nanorods of zinc oxide (ZnO NRs) is prepared using one-step calcination method. The average size and diameter of ZnO nanorods in TGCN/ZnO (T-ZnO) nanocomposite is reduced to 0.5 and 0.73 times than pristine ZnO NRs, respectively. After the acid-etching process, the size of the T-ZnO nanocomposite is further reduced which enhanced its specific surface area to 16.82 m2/g as compared to pristine ZnO NRs (3.56 m2/g). T-ZnO NRs shows a specific capacitance of 398.47 F/g using 0.5 M H2SO4 which is higher as compared to T-ZnO NRs using 0.5 M Na2SO4 (278.16 F/g) and 6 M KOH (106.10 F/g). Using Electrochemical impedance spectroscopy, diffusion coefficient (D) value 1.85 × 10−11 is obtained for T-ZnO NRs (0.5 M H2SO4). T-ZnO NRs also exhibits a higher specific capacitance of 311.80 F/g at 1 A/g using 0.5 M H2SO4. The nanocomposite shows superior energy density of 97.43 Wh/kg at 750 W/kg of power density. The superior capacitance retention (>95 %) and stable coulombic efficiency (>80 %) of T-ZnO NRs enables the nanocomposite for practical applications in energy storage devices. The electric double layer (EDL) and pseudocapacitive (PC) contribution of 6.04 % and 93.96 % to the total specific capacitance of T-ZnO NRs is evaluated using Trasatti method. The capacitive and diffusion-controlled contribution is also investigated for T-ZnO NRs using Dunn's method. The practical aspect of a supercapacitor using leakage current and self-discharge is also tested for the T-ZnO NRs. T-ZnO NRs is a promising energy storage material to fill the gap in the ongoing energy crisis.

Free-standing SnNb2O6@CSN film as flexible anode for high performance sodium-ion batteries

Free-standing electrodes are promising candidates for flexible rechargeable batteries, toward the application of flexible energy storage devices, due to their merits of additive-free, lightweight, and high energy density. Herein, we report a free-standing SnNb2O6@CSN flexible film with SnNb2O6 encapsulated in 3D carbon skeleton nanofibers by electrospinning and carbonization processes as flexible anode for sodium-ion batteries (SIBs). The 3D carbon skeleton nanofibers serve as ion/electron transport pathway to improve the electrochemical reaction kinetics and meanwhile alleviate the volume changes of SnNb2O6 during charge-discharge processes. The as-constructed half-cell (SnNb2O6@CSN‖Na) exhibits excellent cycling stability of 99.2 mAh/g at 0.5 A/g after 950 cycles (coulombic efficiency of ∼100%) and a high rate performance of 108.6 mAh/g at 10 A/g. In addition, the pouch cell can light up the LEDs at different bending angles (0°, 90°, 180°). This research shows a promising anode material for flexible energy storage electronics.

Rational designed Cu-MOF@1D carbon nanofibers as free-standing and flexible electrode for robust electrochemical energy storage

The present study reported the performance of free-standing carbon nanofibers decorated with copper-metal-organic frameworks (Cu-MOFs). A green electrospinning technique was utilized to obtain nanofiber sheets that were carbonized and activated to produce activated carbon nanofiber sheets (ACNFs). These ACNFs consist of inherent oxygen functionalities of the lignin that can aid the growth of MOF structure on it in a single step, which motivated us to do this work. Cu-MOF particles were in-situ grown over the surface of ACNFs using a hydrothermal-assisted technique. The developed materials were characterized using FESEM, Raman Spectroscopy and BET analysis in order to identify morphological, porosity, and surface area transformations. Along with these, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Charge-Discharge (GCD) studies were performed to compare the electrochemical performance of the Cu-MOF, ACNF, and Cu-MOF@ACNF as electrode materials for supercapacitors. Among three electrodes, the Cu-MOF@ACNF sheet reveals a higher specific capacitance of 303.2 F/g compared to ACNF (203.3 F/g) and Cu-MOF (68.2 F/g) at the same current density of 1 A/g. Based on the higher performance of Cu-MOF@ACNF two types of symmetrical devices, i.e., aqueous (using electrolyte-impregnated filter paper) and solid-state devices (using a polymeric gel electrolyte), were fabricated. The all-solid-state supercapacitor device was found to feature high flexibility, stand-alone characteristics, and excellent performance as an electrode with a working potential window of 0–2.0 V. The device demonstrates a high energy density of 78.71 Wh/kg and a power density of 1050.0 W/kg, along with high coulombic efficiency (99.8 %) after 10,000 cycles. The achieved performance is superior to many published reports, revealing that the developed composite materials hold prospect for applications in green and high-performance flexible energy storage devices.

Niobium doped triazine based covalent organic frameworks for supercapacitor applications

Covalent organic frameworks (COFs) are gaining high importance in energy storage systems due to their uniform porosity and versatile functionality. The present work deals with the fabrication of triazine-based COF through Schiff base formation. The method involves the polycondensation reaction between melamine and terephthalaldehyde. In addition, the COF was also decorated with Niobium to generate Nb@COF. The morphological, elemental mapping, X-ray photoelectron spectroscopy, C13 NMR results show the effective doping of Nb to the COF and provide insights into the nature of bond formation. The obtained experimental XRD results are in good agreement with Materials Studio simulated results. COF and Nb@COF have been used for supercapacitor applications in a three-electrode system. Enhanced specific capacitance was observed in Nb@COF (367 F g−1) compared to pure COF (244 F g−1) at a scan rate of 2 mV s−1. The superior electrochemical performance in Nb@COF could be due to the increased porosity and interlayer spacing. COF and Nb@COF exhibited good stability towards charge and discharge and managed to retain 82 and 89 % specific capacitance, respectively even at 5000 cycles. COF and Nb@COF were assembled in a coin cell and fabricated an asymmetric supercapacitor device as negative and positive electrodes, respectively. The results obtained were satisfactory and shows a specific capacitance of 87 F g−1 at a scan rate of 2 mV s−1.The good stability, specific capacitance and reliability of Nb@COF indicate its potential application in energy storage devices.

Low-temperature Griffiths phase in chemically synthesized CoMn2O4 spinel oxide

Mixed transition metals and their oxides have gained a myriad of research interests because of their wide applications in electronics, magnetism, and electrochemical energy storage and conversion devices. In this study, we have synthesized CoMn2O4 spinel oxide through the auto-combustion method. At room temperature, the x-ray diffraction technique confirms the tetragonal crystal structure and phase purity. The Fourier transform infrared spectroscopy investigated that the oxide and hydroxyl groups are the major active sites. The absorption bands around 544 cm−1 and 638 cm−1 correspond to the atomic vibration of Co-O and Mn-O in octahedral and tetrahedral sites, respectively. The bandgap confirmed from the UV-Vis spectrum is 1.3 eV, indicating that synthesized sample is near-infrared light active material. The scanning electron microscopy shows that the average particle size of CoMn2O4 is 161 ± 26 nm. X-ray photoelectron spectra suggest a mixed spinel structure comprised of Co and Mn cations. The magnetic investigations revealed that the CoMn2O4 exhibits a ferrimagnetic response. However, the emergence of large exchange bias is observed well above the transition temperature of ∼172 K due to the Griffiths phase. It is proposed that the appearance of Griffiths phase arises due to the presence of antiferromagnetic impurities, which become active at low temperature.

Modification and development in the microstructure of PVA/CMC-GO/Fe3O4 nanocomposites films as an application in energy storage devices and magnetic electronics industry

We used casting method to create nanocomposites films from carboxymethylcellulose (CMC)/polyvinyl alcohol (PVA) and GO/Fe3O4 as nanofiller. Various analyses such as structural, vibrational, optical, conductivity, dielectric and magnetic studies reveal promising properties of the prepared polymer nanocomposites (PNCs) films. The amorphous phase of the polymer blend increased with increasing GO/Fe3O4 concentration up to samples containing 0.05%GO/1%Fe3O4 nanofiller, according to X-ray diffraction. The complexation of the nanofiller with the polymer blend's –OH, –COO, CO, and –CH groups through a coordinate bond/hydrogen bond was confirmed by Fourier-transform infrared analysis. While the Urbach energy showed a trend in the opposite direction, the optical bandgap gradually turned red as the nanofiller concentration increased. The interaction of GO/Fe3O4 ions with the CMC/PVA matrix is attributed to the changes in optical properties of CMC/PVA. The Jonscher's power law (JPL) is observed in all samples' ac conductivity spectra. To comprehend the charge storage competences, research of dielectric permittivity was also conducted. A study of dielectric permittivity was also conducted to comprehend the charge storage competences. While AC conductivity increases with frequency, dielectric characteristics decrease with frequency. With the addition of nanofiller, AC conductivity and dielectric characteristics increase. For 0.05%GO/1%Fe3O4 nanofiller loaded sample, the highest AC conductivity and dielectric constant were attained. The results of vibrating sample magnetometer (VSM) revealed that synthesized nanocomposite films exhibit superparamagnetic features. The unique features of CMC/PVA-GO/Fe3O4 films enable their employment in a variety of industries, including magnetic electronics, energy storage devices, and optoelectronics.

Cooperation between Dual Metal Atoms and Nanoclusters Enhances Activity and Stability for Oxygen Reduction and Evolution

We have achieved the synthesis of dual-metal single atoms and atomic clusters that co-anchor on a highly graphitic carbon support. The catalyst comprises Ni4 (and Fe4) nanoclusters located adjacent to the corresponding NiN4 (and FeN4) single-atom sites, which is verified by systematic X-ray absorption characterization and density functional theory calculations. A distinct cooperation between Fe4 (Ni4) nanoclusters and the corresponding FeN4 (NiN4) atomic sites optimizes the adsorption energy of reaction intermediates and reduces the energy barrier of the potential-determining steps. This catalyst exhibits enhanced oxygen reduction and evolution activity and long-cycle stability compared to counterparts without nanoclusters and commercial Pt/C. The fabricated Zn-air batteries deliver a high power density and long-term cyclability, demonstrating their prospects in energy storage device applications.

Adaptive overcurrent protection scheme for distribution networks with connection of mobile energy storage devices

The increasing penetration of renewable energy sources in distribution networks has caused great challenges to the reliable operation of the conventional overcurrent protection schemes. In particularly, serious underreach and overreach problems of protection scope may occur under the ever growing application of mobile energy storage (MES) devices. To improve the adaptability to the connection of MES devices under distribution networks, this paper proposes an adaptive overcurrent protection scheme, which can avoid the unfavorable effects caused by infeed currents and out flowing currents. Firstly, the effects of MES device on the protection scope of the overcurrent protection strategy are investigated, considering the charging, discharging, and backup operation modes of MES device. Secondly, to adapt to the different operation modes, the equivalent impedance of MES device is calculated, and then it is introduced to determine the adaptive settings of fast current protection and time-critical fast current protection. Finally, the constructed adaptive overcurrent protection scheme can adapt to varied fault conditions, including different operation modes and output power of MES device, connection locations, fault locations, and fault types. Large amounts of simulation results show that the proposed adaptive overcurrent method can overcome the underreach and overreach problems of protection scope, demonstrating its good application prospects.