Power Density Research Articles

Zinc cobaltite embedded in binary metal-organic frameworks using a direct binder-free electrode fabrication approach for efficient energy storage devices and monosodium glutamate detection

There is an imperative need to develop high performance electrode for advance energy storage devices. This work represents the successful synthesis of zinc cobaltite (ZnCo2O4), nickel cobalt metal organic framework, and their composite (ZnCo2O4@NiCo-MOF). The materials are synthesized by using both hydrothermal and sonication techniques. The ZnCo2O4 offers eco-friendly and diffusion regulated properties, while NiCo-MOF provides large specific surface area and tunable pore structure. The ZnCo2O4@NiCo-MOF provide superior electrochemical performance compared to ZnCo2O4 and NiCo-MOF in a three electrode setup. The ZnCo2O4@NiCo-MOF provides a specific capacity of 984 C/g at 1.5 A/g. The ZnCo2O4@NiCo-MOF is also utilized in two electrode setup with activated carbon. The ZnCo2O4@NiCo-MOF//AC device demonstrates the energy density of 92.4 Wh/kg and a power density of 930 W/kg. Additionally, the real time application of ZnCo2O4@NiCo-MOF electrode is also tested in the detection of monosodium glutamate in food. This study highlights the importance of ZnCo2O4@NiCo-MOF electrode materials for future storage and detection devices.

Modulating intramolecular charge transfer via π-d conjugative effect in coordination polymers toward photo-thermo-electric conversion

The prospect of harnessing sunlight to generate cost-effective heat and electricity presents a captivating opportunity to address water scarcity and electricity shortages. Photothermal materials with a broad absorption spectrum are indispensable for effectively harnessing solar energy and converting it into heat/electricity. Herein, we developed an intramolecular charge transfer strategy via conjugated effect to regulate solar absorption and photothermal conversion ability of M-DABDT (M = Fe/Co/Ni/Cu/Zn, DABDT = 2,5-diaminobenzene-1,4-dithiol), overcoming a common limitation of narrow absorption and low photothermal efficiency in traditional metal-organic assemblies. The density functional theory calculations reveal that altering transition metal ions induces the structural torsion of organic linkers, resulting in a significant change in dihedral angle from 89.96° to 2.57°. The structural change significantly facilitates the charge transfer and electron relaxation, ultimately promoting the conversion of light to heat. Under one sun irradiation, the maximum temperature of Fe-DABDT can reach approximately 92.5 ℃. More significantly, the integration of M-DABDT CPs and thermoelectric devices under normal solar irradiation results in an extraordinary open circuit voltage (238 mV) and maximum power density (364.5 μW m−2), processing a peak output voltage density of 76.9 V m−2 at 11:00 a.m. in the presence of outdoor sunlight. This strategy presents an avenue for developing metal-organic solar absorbers for photo-thermo-electric conversion systems.

1D Textile Yarn Battery with MoS2@Si Anode and NCM Cathode

AbstractWearable electronics are surging for various applications ranging from critical functions like personal health monitoring to communication and entertainment. To power these electronic devices, advanced high‐performing textile‐based batteries are reckoned. In this work, a 1D textile yarn battery is designed using silicon (Si) nanoparticles wrapped in molybdenum disulfide (MoS2) as an anode and layered Ni‐rich material Li[Ni0.8Co0.1Mn0.1]O2 (NCM) as a cathode. The anode materials design is selected to ensure the use of Si due to its high specific capacity but suppressing its known issue of volume expansion by layered MoS2 nanosheets and, at the same time, MoS2 providing channels for lithium‐ion (Li‐ion) transport during electrochemical cycles. The NCM cathode, on the other hand, is adopted as it has higher energy density and improved cycle life. The full yarn battery (FYB) delivered an excellent electrochemical performance (areal capacity of 3.13 mAh cm−2, power density of 421 mW cm−3, and energy density of 78.9 mWh cm−3) with a capacity retention of 86% at 0.1 C and coulombic efficiency of 91.3%. This work pointed out a new way to design and fabricate textile‐based batteries with high‐performance materials using simple, cost‐effective, and scalable approaches targeting to be used as energy sources for future wearable electronics.

Co/CoOx–N–C bifunctional nanocatalyst derived from carbothermally optimized graphene networks with in-situ formed zeolitic imidazolate framework for high performance zinc-air batteries

Rechargeable zinc-air batteries are underpinned by high-performance and durable bifunctional oxygen electrocatalysts. Among the platinum-group metals (PGMs)-free catalysts, the redox-active cobalt-nitrogen-carbon (Co/CoOx–N–C) based materials are promising, however require further structural improvements. This work utilises extremely porous graphene networks (EGO) of hierarchical porosity to in-situ grow ZIF-67 nanocrystals extensively and homogeneously within the porous structure. A simple carbonization of nanoZIF-67@EGO not only generates finely dispersed redox capable Co/CoOx–N–C active sites with the help of residual oxygen functional groups of EGO, but also produces 2-3 dimensional hierarchical porous and conducting structure, readily facilitating high electrochemical surface area. This characteristic structure synergistically contributes to rapid charge and mass transfer rates along with high activity and stability for both ORR and OER. Here, it is worth mentioning that to produce equivalent catalyst material involving different graphitic or template supports requires prolonged and multi-step synthesis routes. The optimized catalyst delivers low potential difference of 0.86 V for bifucntional activity by offering superb ORR half-wave potential of 0.83 V vs RHE and limiting current density of 5.85 mA cm−2 in 0.1 M KOH electrolyte. Zinc-air battery exhibits peak power density of ∼175 mW cm−2 and specific capacity of ∼767 mAh g−1, along with durable cycling round trip efficiency of >63 % (correspond to low voltage gap of ∼0.74 V). These characteristics are better than numerous M–N–C based catalysts reported in the literature. This new strategy holds a great potential to boost the development of diverse MOFs and carbon-based electrocatalysts for a wide range of energy storage and conversion technologies.

Self-sulfur doped mesoporous novel carbon electrodes derived from poly-anthraquinone sulfide for high-performance supercapacitors! A comparative study

Carbon materials are suitable electrode candidates in supercapacitors (SCs) because of their availability, well-defined microstructures, and ultrahigh surface areas. Herein, a universal chemical activation method was utilized to obtain activated carbon (C-KOH) from poly-anthraquinone sulfide (PAQS) at 850 °C and reduced activated carbon (C-KOH-H) from C-KOH via a mild hydrogen reduction process at low temperature. The electrochemical performances of the PAQS derived activated carbon electrodes were investigated by assembling electric double-layer capacitors (EDLCs). Electrodes fabricated from C-KOH and C-KOH-H showed 174 and 182.3 F g−1 specific capacitances at 0.5 A g−1 current density, respectively. Whereas their energy densities were 44 and 46 Wh kg−1 at 350 and 423 W kg−1 power densities, respectively. SCs assembled from C-KOH-H showed excellent rate performance, that retained 140 F g−1 even at high current density (20 A g−1), while the one assembled with C-KOH stored 54 F g−1. Furthermore, the C-KOH-H electrode retained 98 % of the initial capacitance at 1 A g−1 over 20,000 continuous cycles. The experimental results revealed that C-KOH-H showed the best electrochemical performance in SCs, which is attributed to the presence of less sulfur and oxygen than C-KOH after the mild reduction. These results prove that PAQS show excellent activation with KOH to produce well-organized porous activated carbons having high specific surface areas, which can be utilized as high-performance electrode materials in SCs.

A dead-time compensation method for motor drive inverters based on nonlinear observer

Silicon carbide (SiC) inverters and interior permanent magnet synchronous motors (IPMSMs) are widely employed in electric vehicles (EVs) due to their superior efficiency and high power density. However, the harmonics generated by the high switching frequency and the dead-time effect in SiC inverters present a significant challenge. The time-varying nature of on–off delays and conduction voltage drops in power devices makes it difficult to establish a precise nonlinear model for inverters, thus limiting the effectiveness of traditional dead-time compensation methods. This paper introduces a dead-time compensation approach for voltage source inverters (VSIs) that leverages a nonlinear observer, thereby circumventing the need for a complex inverter model while enhancing compensation accuracy. The method determines the three-phase stator current polarity of the IPMSM by deriving the relationship between the current vector angle and the rotor position angle. Along with duty cycle variations computed by the PI controller, the inverter’s nonlinearity is adaptively compensated. Simulation and experimental results indicate that the proposed method outperforms the traditional method based on the error voltage model, effectively reducing the total harmonic distortion (THD) of the phase current.

Effect of processing parameters on the properties of carbon paper as a free-standing supercapacitor electrode

As newly emerging energy storage devices, supercapacitors are being investigated thoroughly by researchers. Free-standing electrode is one of the major research focuses in this area, which not only avoids the use of resistive binders but also simplifies device assembly. The study describes the synthesis and study of carbon fiber-based carbon carbon composite paper (heat treated to different temperatures) as a free-standing supercapacitor electrode. Due to the inert nature of carbon paper, it was activated to create defect sites and to increase the specific surface area. Electrochemical studies suggested that activated carbon paper heat treated to 750°C (ACP-750) exhibited the highest areal capacitance of 11.4 F/cm2 (422.2 F/g) at the current density 2.5 mA/cm2 (0.09 A/g), probably due to the generation of larger number of defect sites (as depicted by XRD and RAMAN studies). ACP-750 electrode was used to fabricate the solid-state symmetric supercapacitor device that exhibited an energy density 0.77 Wh/cm2 at a power density of 2.34 W/cm2. The electrode was allowed to age (ACPA-750), after which it exhibited enhanced specific capacitance of 16.8 F/cm2 (622.2 F/g) at a current density 2.5 mA/cm2. ACPA-750//ACPA-750 device delivered maximum energy density of 1.66Wh/cm2 at a power density of 3 W/cm2. The device exhibited a coulombic efficiency of 96.1% and capacitance retention of 89% after 10,000 cycles.

Synergistic effect of Fe-Ru alloy and Fe-N-C sites on oxygen reduction reaction

In the pursuit of optimizing Fe-N-C catalysts for the oxygen reduction reaction (ORR), the incorporation of alloy nanoparticles has emerged as a prominent strategy. In this work, we effectively synthesized the FeRu-NC catalyst by anchoring Fe-Ru alloy nanoparticles and FeN4 single atom sites onto carbon nanotubes. The FeRu-NC catalyst exhibits significantly enhanced ORR activity and long-term stability, with a high half-wave potential of 0.89 V (vs. RHE) in alkaline conditions, and the half-wave potential remains nearly unchanged after 5000 cycles. The zinc-air battery (ZAB) assembled with FeRu-NC demonstrates a power density of 169.1 mW cm−2, surpassing that of commercial Pt/C. Density functional theory (DFT) calculations reveal that the synergistic interaction between the Fe–Ru alloy and FeN4 single atoms alters the electronic structure and facilitates charge transfer at the FeN4 sites, thereby modulating the adsorption and desorption of ORR intermediates. This enhancement in catalytic activity for the ORR process underscores the potential of this approach for refining M-N-C catalysts, providing novel insights into their optimization strategies.

Insights of oxygen vacancies engineered structural, morphological, and electrochemical attributes of Cr-doped Co3O4 nanoparticles as redox active battery-type electrodes for hybrid supercapacitors

The global warming issue is spurring the development of renewable energy solutions, where supercapacitors are emerging as promising options for energy storage. Despite advancements in battery-type materials, doping is a practical approach to enhancing electrochemical performance. In this study, using the solution combustion method, we synthesized spinel Co3O4 nanoparticles doped with chromium (Cr) at 2.5 % and 5 % concentrations. The addition of Cr significantly modifies the structural, morphological, surface, and electrochemical properties of Co3O4 nanoparticles. Raman and X-ray photoelectron spectroscopy confirm that this doping method effectively regulates the oxygen vacancy defect level. Moreover, Cr dopants and oxygen vacancies modify electronic states, facilitating more accessible contact to active sites, improving electrical conductivity and more intricate redox chemistry. Notably, the 2.5 % Cr-doped Co3O4 configuration demonstrates substantially enhanced specific capacity (334.64 C g−1/92.95 mAh g−1 at 1 A g−1) and rate performance (59 %), surpassing those of 5 % Cr-doped Co3O4 and undoped Co3O4. Furthermore, the as-fabricated 2.5 % Cr-doped Co3O4//activated carbon (AC) hybrid supercapacitor (HSC) device exhibits a noteworthy energy density of 42.5 Wh kg−1 at 1295.73 W kg−1, withstanding 33.54 Wh kg−1 even at a power density of 5720.46 W kg−1. The HSC device showcases outstanding cyclic performance with 100 % capacity retention after 5000 cycles. Therefore, our work offers a viable way to improve the efficiency of hybrid supercapacitors by providing essential insights into the design of defect-engineered battery-type electrode materials.

A novel membrane-based absorber for sorption heat transformers: A comparative experimental study of a thin-film absorbent and salt-impregnated adsorbents

The present study proposes a novel membrane-based sorber bed with stationary solution film for oscillatory sorption heat transformers. A custom-built gravimetric large pressure jump setup is used to experimentally compare the performance of the novel membrane-based sorber bed with a Lithium Bromide/Silica gel solid composite sorbent synthesized using the salt-impregnation method. It is shown that the current membrane-based sorber bed provides up to about four times the specific cooling power and more than twice the cooling power density of solid sorbents, demonstrating the capability of the present sorber bed as a promising alternative to solid sorbents. The specific cooling power, cooling power density, and energy storage density of about 2.8 kW/kg, 470 kW/m3, and 269 MJ/m3 are experimentally obtained, respectively. According to experimental results, it is observed that the film thickness plays a significant role in sorption dynamics, while the effect of membrane mass transfer resistance on sorption dynamics is less than 10%. In addition, the present membrane-based sorber bed is analytically modeled, and the results are validated with present experimental data. The present analytical model is also used to investigate the effects of design parameters on the performance metrics.

Plasma-assisted surface modification of MXene/carbon nanofiber electrodes for electrochemical energy storage

Inferior ion diffusion and relatively low electrochemically active sites of MXene-based electrodes make them becoming a major challenge to develop advanced electrode. Surface modification of electrodes using non-thermal plasma is a great way to suppress these challenges through providing more space for energy storage and facilitating the diffusion of electrolyte ions. Herein, the effect of nitrogen and oxygen plasma treatments on MXene/carbon nanofiber electrode is reported to enhance the electrochemical performance. In this work, Ti3C2Tx MXene/CNF composites were fabricated using a hybrid needleless electrospinning/plasma method for the electrochemical energy storage. Surface modification of the composites was performed by a DBD plasma reactor under N2 and O2 gases at low-pressure glow discharge as a two-step plasma treatment process. The results revealed that total pore volume and the surface area of the plasma-treated Ti3C2Tx/CNF composite increased considerably due to the N2 and O2 plasma treatments. It was found that the electrochemical active surface area of the N2/O2-plasma-treated Ti3C2Tx/CNF electrode enhanced by approximately two times compared to the non-treated one, leading to the specific capacitance of 162 F/g at 1 A g−1 in a 2 M KOH electrolyte. The increase in electrochemical activity arises from separate doping of N2 and O2 plasma, which not only improves the pore structure and wettability, but also modifies the electrical conductivity and capacitance of the electrode. The N2/O2-plasma-treated Ti3C2Tx/CNF electrode achieved excellent cycling stability with 124 % capacitance retention after 10,000 cycles, while the capacitance retention of the pure N2 and O2-plasma-treated Ti3C2Tx/CNF electrodes as well as the non-treated one were 111 %, 105 % and 98 %, respectively. Additionally, an asymmetric supercapacitor N2/O2-plasma-treated Ti3C2Tx/CNF//AC based on the N2/O2-plasma-treated Ti3C2Tx/CNF as a positive electrode and activated carbon (AC) as a negative electrode was successfully constructed, which demonstrated an energy density of 26.3 Wh kg−1 with a power density of 750 W kg−1 at the current density of 1 A g−1 with excellent capacitance retention (102 %) after 5000 cycles. This work provides a highly efficient method for the surface modification of MXene-based electrodes through non-thermal plasma treatment.

Exploring the potential of metal tailored imine based covalent organic framework for asymmetric supercapacitor applications

Currently, a fascinating area of research involves the development of stable and efficient materials for energy storage systems. The current work describes the synthesis of imine linked covalent organic framework (COF) using 4,4′,4′',4′''-(ethene-1,1,2,2-tetrayl) tetraaniline and terephthalaldehyde (TAT-COF) as precursors through solvothermal method. In addition, cobalt has been integrated to the imine linkage of TAT-COF to generate CO@TAT-COF. The X-ray diffraction study reveals the formation of ordered and crystalline TAT-COF with eclipsed (AA) stacking configuration. Morphological characterization indicated the accumulation of metal species over stick like structured TAT-COF. Energy-dispersive X-ray (EDX) and Fourier Transform Infrared Spectroscopy results shows the successive intercalation of Co to the TAT-COF matrix. TAT-COF and Co@TAT-COF were examined towards electrochemical performance for supercapacitor applications. A two fold higher specific capacitance (Csp) was obtained in Co@TAT-COF (637 F/g) compared to TAT-COF (315 F/g) at 5 mV/s scan rate. The Co@TAT-COF showed an energy density (ED) of 58 Wh/kg at a power density of (PD) of 1500 W/kg. Enhanced electrochemical performance in Co@TAT-COF could be attributed to the structural confinement, conductivity, enhanced interlayer spacing and porosity. Co@TAT-COF has been used as positive electrode to fabricate an asymmetric device (ASD) in using Swagelok cell. The Csp of the fabricated ASD was found to be 95 F/g at 2 mV/s scan rate. ASD showed good stability with 73 % retention of Csp over 5000 charge/discharge cycles. The obtained results indicate the suitability of the engineered COFs towards energy storage devices.

Pt/C protection by Fe-N-C via Fenton reaction for direct methanol fuel cells operated under high concentrated methanol with high performance

In this paper, a hierarchical cathode catalytic layer (CCL) composed of Pt/C and Fe-N-C was proposed to mitigate severe methanol crossover in direct methanol fuel cells (DMFCs). Several validation experiments and electrochemical analysis were conducted to reveal that the reactive oxygen species (ROS) produced by Fe-N-C via Fenton reaction in an incomplete four-electron transfer in oxygen reduction reaction (ORR) can be utilized to oxidize methanol nearby Pt/C efficiently, thus protecting ORR active sites from poisoning in concentrated methanol solution. Based on this strategy, the optimized DMFC outputs a high peak power density of 22.5 mWcm−2 at 10 M methanol, which is among the highest performance achieved merely by CCL design. Additionally, the reaction of ROS with methanol is confirmed to protect the Fe-N-C CCL from the potential attack of ROS, leading to a great stability of the DMFC. This work is of great practical significance for the design of DMFCs with high specific energy density and good stability for portable application.

A voltage-decoupled Zn-Br2 flow battery for large-scale energy storage

The flow battery represents a highly promising energy storage technology for the large-scale utilization of environmentally friendly renewable energy sources. However, the increasing discharge power of rechargeable battery results in a higher charge voltage due to its coupling relationship in charge-discharge processes, intensifying the burden of renewable energy power systems. Herein, we proposed a voltage-decoupled Na+-conducting Zn-Br2 flow battery (Ud-Na-ZBFB). Within a pH-regulation strategy, both neutral Zn/Zn2+ and alkaline Zn/Zn(OH)42− negative redox couples are integrated into one device, so as to increase discharge voltage a 0.5 V theoretical increase while remains a low charge voltage. The proof-of-concept Ud-Na-ZBFB demonstrates an unprecedented voltage characteristic, achieving a discharge voltage of up to 2.18 V while maintaining a remarkably low charge voltage of 1.78 V at a current density of 20 mA cm−2. Benefiting from the high discharge voltage, the peak power density of Ud-Na-ZBFB reaches 580 mW cm−2, nearly twice higher than the traditional ZBFB. Besides, the Ud-Na-ZBFB cycling operates for 45 h with excellent stability and resilience. With the “cycle-to-stage” operational mode, battery state of Ud-Na-ZBFB can be completely recovered after a long-term operation stage with several cycles, which electrolyte utilization efficiency of one stage is up to 41 %. This work offers a brand-new utilization pattern for high-power rechargeable battery that possesses a great potential in energy storage application scenes.

Enhancing the electrochemical performance of a nickel molybdenum nitride for an energy storage device using cobalt nitride and phosphorus doping

Compared to traditional energy storage devices, hybrid solid-state supercapacitors have gained a lot of attention because of their exceptional power, energy density and outstanding cyclic stability. Transition metal nitrides are eminent candidates with high-performance electrochemical properties for energy storage devices. In this work, a high-performance CoN/NiMoN interface with P-doping was prepared by a simple feasible strategy for the positive electrode of a supercapacitor. The electrochemical performance in a 2 M KOH electrolyte revealed a specific capacity of 2070C·g−1 at a 5 A·g−1, which is exceptional compared to recently reported literature. Encapsulating NiMoN with CoN and its P-doping, resulting in a three-dimensional structure with desirable textural properties and easy permeation of electrolyte, enhances the electrochemical performances prepared electrode. Further, a hybrid solid-state supercapacitor was prepared with P-CoN/NiMoN (positive) and activated carbon (negative) as a electrodes. The prepared P-CoN/NiMoN//activated carbon supercapacitor showed an operating potential window of 1.7 V with an admirable specific capacity of 573.99C·g−1, for 135.5 Wh·kg−1 energy and 850 W·kg−1 power density at a 1 A·g−1. The results provide a feasible strategy to prepare and modify the electrochemical properties of NiMoN by CoN encapsulation and P-doping. The method gives insights for the preparation of other transition metal nitrides for high-density energy storage without much change in the power density.

Hollow-structured and nano-flower shaped high entropy layer double hydroxide for superiority specific capacitance and rate capability of supercapacitor

High entropy hydroxide as electrode materials has been widely studied in the field of supercapacitors, but due to the limited active site and poor conductivity, it usually shows poor specific capacity and magnification performance, which seriously limit its development in the field of supercapacitors. In this work, a hollow-structured and nano-flower shaped high entropy layer double hydroxide was synthesized by the double template method combined with nano-etching to achieve superiority specific capacitance and rate capability of supercapacitor. The experimental and theoretical results indicate that the specific capacitance of this novel electrode material is as high as 1820.1 F·g−1. In particular, after the current density was increased by 40 times, the specific capacitance can reach 1140.2 F·g−1, and its electrochemical performance is higher than most of high entropy electrode materials reported so far. More importantly, the S-HE-LDH//AC HSC was constructed with the material as the electrode. It has an energy density of 74.2 Wh·kg−1 at 475 W·kg−1 power density. After 5000 cycles, the specific capacitance of the HSC device can still maintain 90.8 % of its initial value. These results indicate that the electrochemical properties of LDHs can be effectively improved by the combination of microstructure adjustment and electronic structure optimization.

Wet-chemical synthesized TiN-CuO nanocomposite: Advancing supercapacitor technology with high energy and power density

Modern-era energy crises have arisen as a result of industry's quick expansion. There must be a proliferation of autonomous, renewable-energy-powered, high-capacity storage systems. The high specific capacitance (Cs) is a result of the Electric Double Layered Capacitors (EDLC's) stellar cathode characteristics. The remarkable conductivity and storage capacity of transition metal nitride-based oxides (TMOs) have made them an attractive option for use as cathode materials in SC devices. The present study successfully synthesized the TiN-CuO composite for electrode material by employing the straightforward wet-chemical method. But the fact that the TiN-CuO combination is crystalline suggests it could be used as an electrode in SCs. The electrochemical performance of the TiN-CuO electrode was also highlighted by its excellent Cs of 843.5 F g−1. Furthermore, the TiN-CuO‖MnO2-KOH electrode displays a power density (Pd) of 17595 W/kg and an energy density (Ed) of 44.88 Wh kg−1. In addition, the TiN-CuO‖MnO2-KOH electrode has shown remarkable cyclic stability of 97.3 % up to 10,000 cycles, at 10 A g−1. The electrochemical characteristics of fabricated TiN-CuO electrode material are superior to those of pure materials, rendering it an attractive candidate for use in energy storage devices such as SCs.

Optimal power density estimation in Sub-Saharan Africa regions based on Weibull distribution parameters

The production of wind energy requires knowledge of certain wind speeds and directions. Several tools are used for this purpose to characterize the wind power, including the Weibull distribution function with two parameters, shape factor k, and the scale factor c. In this paper six methods Graphical Method (GP), Empirical Method of Justus (EMJ), Empirical Method of Lysen (EML), Energy Pattern Factor (EPF), Maximum Likelihood (ML), and Moroccan Method (MMa) are used to estimate Weibull distribution parameters to evaluate the wind potential an its power density. Twelve sites in West African sub-region such as Abuja, Accra Kotoka, Bamako Senou, Conakry Gbessia, Cotonou Cadjehoun, Kano Mallam Aminu, Lagos Ikeja, Lome Tokoin, Niamey, Niamtougou, Ouagadougou, Tambacounda were selected as case studies. For each selected site, hourly wind speed data collected at 10 m height for the twelve years from January 2011 to December 2023 are used. The evaluations of each method were carried out every month and statistical criteria to provide a more complete analysis. The results show that the EPF, EMJ, EML, and ML provide highly desirable better performance while the GP and MMa showed poor performance for all stations. For all sites, the EPF was recognized as the most appropriate method except for the Lagos site where the EMJ ranks first on the others. The methods that ranked second after EPF varied among the sites.

Excellent energy storage performance of Nd-modified lead-free AgNbO3 ceramics via triple collaborative optimization

Lead-free Dielectric capacitors that possess high power density as well as swift charging/discharging speed are in tremendous requirement in pulse/high power fields, but the lower recovery energy density and efficiency restrict their applications. Herein, via triple collaborative optimization, we designed Nd-modified AgNbO3 antiferroelectric ceramics with excellent energy storage performance. First, Nd3+ ions are smaller than Ag+ ions, which effectively inhibits cation displacements and the tilting of oxygen octahedra, leading to an optimized phase composition, the suppressed ferroelectricity and enhanced antiferroelectricity. Second, the valence of Nd3+ ions are higher than that of Ag+ ions, which help to lower the content of oxygen vacancies. Third, the random substitution of Nd3+, extrinsic ions, cause the chemical disorder, thus dwindling the grain size. Both of the latter could boost the breakdown field. Eventually, the synchronously boosted energy density of 7.16 J/cm3 and efficiency of 72 %, together with excellent frequency stability, temperature tolerance, ultrafast charging/discharging time of 45 ns and superhigh power density of 354.2 MW/cm3, are achieved in Ag0.91Nd0.03NbO3. All these merits manifest Nd- AgNbO3 as a promising candidate for lead-free high-power energy storage devices. Our work brings forward a good reference for developing the capabilities of antiferroelectric capacitors.

Ta-ions doping impact on structural modifications and bandgap tuning of NiCo2O4 hexagonal nanosheets for high rated pseudocapacitor electrodes

Getting higher activity, lower cost and especially better stability at the same time is still one of the biggest problems in the supercapacitors research. Morphology tailoring and crystal imperfections induce d due to doping based defects in ternary transition metal oxides at the nano-scale level is crucial for enhancing the performance of supercapacitors. This research investigates of the utilization of Ta-doped NiCo2O4 (Ta-NCO) hexagonal nano-sheets for supercapacitor electrodes. The structural and morphological study of pristine and Ta-doped samples has been determined using XRD, SEM, TEM and HRTEM. The enhanced inherent conductivity and diffusion at the interface are also confirmed using electrochemical measurements study. The NCO-5 material exhibits a notable enhancement in capacitance and cycling retention. The NCO-5 electrode demonstrates a high specific capacitance (Cs) of 2445.7 F/g at 1 A/g. The pseudocapacitive behavior by power law (b = 0.67) and an increase in capacitive contribution with the scan rate reaching a value of 47.2 % at 100 mV/s by Dunn method exhibits it suitability of pseudocapacitors. The low Rct value signifies it improved capacitive performance as deduced from EIS measurements. Crucially, it maintains around 95.3 % of its capacitance after undergoing 10,000 GCD cycles. The high specific capacitance, remarkable capacitive characteristics and high stability of NCO-5 make it an excellent contestant for supercapacitor applications. The fabricated asymmetric supercapacitor (NCO-5//AC) shows exceptional energy density (ED) of 96.35 Wh/kg with power density (PD) of 825.03 W/kg.