Pseudocapacitive Performance Research Articles

Unraveling the Ionic Storage Mechanism of Flexible Nitrogen-Doped MXene Films for High-Performance Aqueous Hybrid Supercapacitors.

2D MXene nanomaterials have excellent potential for application in novel electrochemical energy storage technologies such as supercapacitors and batteries, but the existing pure MXene is difficult to meet the practical needs. Although the electrochemical properties of modified MXene have been improved, the unclear ion storage mechanism still hinders the development of MXene-based electrode materials. Herein, the study develops flexible self-supported nitrogen-doped Ti3C2 (Py-Ti3C2) films by the highly mobile, high nitrogen content, oxygen-free pyridine-assisted solvothermal method, and then deeply investigates the energy storage mechanism of hybrid supercapacitors in four aqueous electrolytes (H2SO4, Li2SO4, Na2SO4, and MgSO4). The experimental results suggest that the Py-Ti3C2 film electrode exhibits a pseudocapacitance-dominated energy storage mechanism. Particularly, the specific capacity of the Py-Ti3C2 in 1M H2SO4 (506 F g-1 at 0.1 A g-1) is 4-5 times higher than other electrolytes (≈110 F g-1), which could be attributed to the substantially higher ionic diffusion coefficient of H+ than those of Li+, Na+, Mg2+ with small ionic size, high ionic conductivity, and fast pseudocapacitance response. Theoretical analysis further confirms that Py-Ti3C2 has strengthened conductivity and electrical double-layer capacitance performance. Meanwhile, it has lower free energy for protonation and deprotonation of functional groups, which gives excellent pseudocapacitance performance.

Designing of a High Performance NiMgPO4/CNT Electrode Material for a Battery-Supercapacitor Hybrid Device

Improved pseudo-capacitance performance can be obtained by phosphates and transition-metal oxides by achieving oxidation states that boost redox (reduction-oxidation) processes. In this work, the nickel magnesium phosphate (NiMgPO4) is synthesized using the hydrothermal method, Additional, carbon nanotubes (CNTs) are blended with NiMgPO4. To build the supercapattery device (NiMgPO4@CNT//AC) and evaluate its electrochemical characteristics, we used NiMgPO4@CNT as the anode & activated carbon as cathode. We also used X-ray diffraction, scanning electron micrscopy, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy techniques to analyze the crystal structure, surface area, and elemental composition. The nanocomposite NiMgPO4@CNT demonstrated a high specific capacity of 1243 C g−1 or 2071.66 F g−1 in a three-electrode system, which was much more than that of the separate reference materials. The supercapattery device shows a specific capacity of 251 C g−1, energy density of 44.5 Wh kg−1 and power density of 1030 W kg−1 is observed. The hybrid electrode exhibited a capacity retention of 85% after 5000 cycles and a columbic efficiency of 91% during the stability measurement. These findings emphasize NiMgPO4@CNT’s potential as an electrode composite material that holds promise for high-performance supercapattery device building.

Nanorod-based smart windows with solid-gel electrolyte: An integrated electrochromic and pseudocapacitive technology for energy-saving and conversion

We fabricated two emerging nanorod-based smart windows with WO3 and NiO nanorods grown on the ITO/glass and ITO/muscovite mica (MM) substrates, respectively. The WO3/ITO/glass and WO3/ITO/MM substrates are excellent working electrodes, while the NiO/ITO/glass and NiO/ITO/MM substrates are exceptional counter electrodes. The nanorod-based WO3/Li+(s)/NiO@glass smart window consists of a WO3/ITO/glass working electrode, a NiO/ITO/glass counter electrode, and a solid-gel LiClO4 electrolyte (labeled as Li+(s)), respectively. The other nanorod-based WO3/Li+(s)/NiO@MM is comprised of a WO3/ITO/MM working electrode, a NiO/ITO/MM counter electrode, and a solid-gel LiClO4 electrolyte, respectively. Both the nanorod-based WO3/Li+(s)/NiO@glass and WO3/Li+(s)/NiO@MM smart windows have brilliant dual-band (red and near-infrared lights) electrochromic behaviors, such as large transmittance differences (ΔT), fast response times (bleaching time, tb, and coloration time, tc) at red (680nm) and near infrared (1000nm) lights and great electrochromic retention (4,000 cycles), and outstanding pseudocapacitive performances like good specific capacitances of ~18.4F/g and ~7.6F/g, intensive power densities of ~1779W/kg and ~2100W/kg with corresponding energy densities of ~5.4Wh/kg and ~2.2Wh/kg, enormous pseudocapacitive retention (10,000 cycles), and so on. Therefore, the brilliant dual-band electrochromic behaviors and outstanding pseudocapacitive performances make the nanorod-based WO3/Li+(s)/NiO@glass and WO3/Li+(s)/NiO@MM smart windows tremendous for use in multifunctional energy-saving-conversion devices.

Superior cycle stability and enhanced pseudocapacitive performance of NiAl-LDH decorated carbon cloth for supercapacitor application

Pseudocapacitors, particularly using layered double hydroxides as cathode material, offers high-power capability and increased energy density, making them popular choices for energy storage devices. This study presents a unique porous structure featuring nickel aluminium layered double hydroxide (NiAl-LDH) deposited onto activated carbon cloth (CC) via a single-step electrochemical process. The NiAl-LDH@CC composite demonstrates exceptional pseudocapacitive capabilities with a specific capacitance of 5893.8 mF cm−2 at a current density of 0.7 mA cm−2 calculated from galvanostatic charge–discharge (GCD) responses. An asymmetric supercapacitor (ASC) is constructed using activated carbon cloth (CC) as anode and NiAl-LDH@CC as cathode. The as-built ASC device, with an operational voltage of 1.6 V, achieves a substantial specific capacitance of 310 mF cm−2 at a current density of 0.2 mA cm−2, along with a high energy density ∼51.67 μWh cm−2 and a power density ∼913.84 μW cm−2. An outstanding cycle stability is also observed with a retention rate of 90 % after 10000 continuous GCD cycles.

Charge storage mechanism and pseudocapacitance performance of NiO and Ce-doped NiO synthesized via modified combustion technique

Supercapacitors, as promising energy storage devices, have gained significant attention due to their ability to deliver high power and efficient charge storage mechanisms. In this work, we report the synthesis and electrochemical characterization of pristine NiO and Ni1-xCexO (x = 0.01, 0.02, 0.03) nanoparticles using a single-step auto ignition combustion method. Preliminary investigations indicate that Ni1-xCexO (x = 0.02) nanoparticles (2 % Ce doping) exhibit superior specific capacitance compared to other compositions. Therefore, we focused on structural, morphological, and vibrational studies on pristine and 2 % Ce-doped NiO. XPS and BET techniques were explored to assess the electronic state and porosity of the samples. Subsequent electrochemical performance evaluations included Cyclic Voltammetry (CV) at various scan rates, Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopic (EIS) techniques. From CV at a scan rate of 5 mVs−1, specific capacitance values of 419 Fg-1 and 604 Fg-1 were obtained for pristine and 2 % Ce-doped NiO, respectively. GCD studies revealed a specific capacitance of 381 Fg-1 for 2 % Ce-doped NiO at a current density of 1 Ag-1 and demonstrated capacitance retention of 95.1 % over 3000 GCD cycles for a current density of 4 Ag-1. The symmetric two-electrode supercapacitor cell demonstrates exceptional electrochemical performance, exhibiting a high specific capacitance of 122 Fg-1, an impressive energy density of 8.17 WhKg−1, a power density of 700 WKg-1 at 1 Ag-1, and a remarkable 88 % capacitance retention after 5000 GCD cycles. DFT calculations suggest that Ce doping significantly alters pristine NiO's electronic and structural features due to lattice strain. Our work highlights the enhanced electrochemical performance of 2 % Ce-doped NiO and its potential as a good-quality supercapacitor material.

Enhanced removal of lead ions from wastewaters by electrochemical adsorption using nitrogen-doped Ti3C2Tx MXene

As a two-dimensional material containing transition metal carbides and nitrides, MXene is often used in capacitive deionization for its excellent hydrophilic and pseudocapacitive properties. Nitrogen doping is widely used to improve the adsorption properties of certain materials. However, the effect of nitrogen doping on the electrochemical adsorption properties of MXene remains unclear. In this work, nitrogen-doped Ti3C2Tx MXene was synthesized using a simple hydrothermal method to achieve highly selective and efficient removal of Pb(II) at a constant cell voltage. The concentration of Pb(II) decreased from 4.95 to 0.02 mg L−1 in a 100 mg L−1 NaCl supporting electrolyte after electrosorption. The removal efficiency of Pb(II) reached 99.5%, whereas it was only 15.2% for Na+. The introduction of nitrogen functional groups increased the electrical conductivity and layer spacing of MXene, thereby improving the pseudocapacitive adsorption performance in the presence of Pb(II). The complexation function of the Ti-OH group on nitrogen-doped Ti3C2Tx surface increased and contributed to the selective adsorption of Pb(II). The removal efficiency of Pb(II) increased with increasing solution pH and cell voltage, reaching the maximum value at pH 5.0 and 1.5 V, respectively. The effect of supporting electrolyte type on the removal of Pb(II) was negligible. In addition, the removal efficiency for mixed heavy metal ion solutions, including Cu(II), Ni(II), and Pb(II), exceeded 79.0%. It exhibited the highest removal efficiency for Pb(II) at 97.9%. After five cycles of electrochemical adsorption–desorption, the nitrogen-doped Ti3C2Tx maintained a stable Pb(II) removal efficiency of 97.0%. This work provides a promising material for the electrochemical removal of low-concentration heavy metal ions from wastewaters.

Hydrothermal preparation of cotton-based rGO/N-doped porous carbon as electrode materials of supercapacitors

Porous carbon electrode materials are commonly used in supercapacitors due to their inexpensive raw materials, simple processing, and low pollution, aligning with the vision for green energy storage. Consequently, there is a current trend to discover porous carbon electrode materials with superior electrochemical properties. To enhance the pore volume ratio and electrochemical performance of porous carbon materials, this study proposes a hydrothermal method to pretreat the raw materials, facilitating the doping of nitrogen from urea. Moreover, graphene is introduced for its excellent conductivity, which can further improve the electrochemical properties of the material. We found a new one-step reduction Graphene Oxide (rGO)and the doping of nitrogen (N) elements were optimized by hydrothermal method, the wettability and pseudo-capacitance performance of the material are improved, and HTPC-700 shows a very excellent specific capacitance, its specific capacitance reaches 600 F g−1 at a current density of 0.5 A g−1, and it even reaches 260 F g−1 at a current density of 1 A g−1. Meanwhile the power density and energy density are respectively 74 W h kg−1 and 280 W kg−1. It also exhibits a remarkable capacitance retention rate of over 98.7 % after 5000 cycles at a current density of 1 A g−1. Additionally, it demonstrates a rich ant nest-like pore structure and good specific surface area of 2427 m2/g, and a large pore volume of 1.09 cm3/g after carbonization and KOH activation. This study offers a novel doping method and provides a unique perspective for the development of porous carbon electrodes.

MoS2@Ti3C2Tx Heterostructure: A new negative electrode material for Li-Ion hybrid supercapacitors

Lithium-ion hybrid supercapacitors (LHSCs) demonstrate promising electrochemical performance, including long cyclic stability and a high-power density. However, their limited energy density has restricted the development towards commercialization. In this work, a novel heterostructure (HS) has been introduced based on molybdenum disulfide (MoS2) nanosheets (NSs) anchored on the surface of exfoliated layers of titanium carbide (Ti3C2Tx) MXenes. The prepared negative electrode material named as MoS2@Ti3C2Tx–HS holds substantial promise for advancing LHSCs to enhance energy density. The MoS2@Ti3C2Tx–HS demonstrates outstanding pseudocapacitive performance in a three-electrode system by achieving a capacitance of 1022.7 F g−1 at 1 A g−1. It exhibited a stable cyclic life (5,000 cycles) and retained 97.02 % of its initial capacitance. Theoretical calculations based on density functional theory (DFT) show impressive results to support the experimental work. The calculated density of states (DOS), band structures, adsorption energies (Eads), and diffusion energy demonstrate that MoS2@Ti3C2Tx–HS possesses excellent electronic and adsorption properties. The fabricated MoS2@Ti3C2Tx–HS//CP–LHSCs device shows a high capacitance of 153.75 F g−1 at 2 A g−1, with stable cyclic life (94.5 %) over 10,000 cycles. Furthermore, it shows a notable high energy density of 54.7 Wh kg−1 at a power density of 1,601.3 W kg−1. The prepared MoS2@Ti3C2Tx–HS electrode, with its synergistic combination, stands out as an auspicious material, showing remarkable electrochemical performance and paving the way for LHSCs.

Carbon Nanotubes Connecting and Encapsulating MoS2-Doped SnO2 Nanoparticles as an Excellent Lithium Storage Performance Anode Material.

Doping and carbon encapsulation modifications have been proven to be effective methods for enhancing the lithium storage performance of batteries. The hydrothermal method and ball milling are commonly used methods for material synthesis. In this study, a composite anode material rich in carbon nanotubes (CNTs) conductive tubular network connection and encapsulation of SnO2-MoS2@CNTs (SMC) was synthesized by combining these two methods. In this highly conductive network, nano-SnO2 particles are uniformly dispersed and embedded in MoS2 with a layered structure, and the obtained SnO2-MoS2 composite material is tightly connected and encapsulated by the tubular network of CNTs. It is worth noting that the incorporation of layered MoS2 not only effectively anchors the SnO2 nanoparticles, but also provides a broader space for lithium-ion movement due to the larger interlayer spacing. The conductive network of CNTs shortens the diffusion path of electrons and Li+ and provides more diffusion channels. The reversible capacity of the SnO2-MoS2@CNTs nanocomposite material remains at 1069.3 mA h g-1 after 320 cycles at 0.2 A g-1, and it exhibits excellent long-term cycling stability, maintaining 904.5 mA h g-1 after 1000 cycles at 1.0 A g-1. The composite material demonstrates excellent pseudocapacitive contribution rate performance, with a contribution rate of 87% at 2.0 mV s-1. The results indicate that SnO2-MoS2@CNTs has excellent electrochemical lithium storage performance and is a promising anode material for lithium-ion batteries.

A novel benzoquinone‐azo linked polymer‐based active electrode material for high‐performance symmetric pseudocapacitors

AbstractPseudocapacitors (PSCs) have attracted researcher's attention due to their potential electrochemical performance as the power source for electronic devices. However, to maintain the high electrochemical properties of pseudocapacitive materials becomes critical. Therefore, the active electrode materials design and synthesis is a challenging task. To tackle these problems, herein, we rationally designed new polymer based on benzoquinone with azo linker. The polymer AZO‐BQ‐P was synthesized and tested for their energy storage applications in combination with graphite foil (GF). In three‐electrode supercapacitor (SC) device, the AZO‐BQ‐P/GF electrode exhibits excellent specific capacitance (Csp) of about 306.27 F g−1 at 0.5 A g−1 current density and higher cycling stability. The pseudocapacitive performance of SC cells result from synergistic effect of AZO‐BQ‐P and GF and due to faster electrolyte ion diffusion and increased availability at electrode/electrolyte interfaces. Furthermore, AZO‐BQ‐P/GF electrode was employed to fabricate two‐electrode AZO‐BQ‐P/GF//AZO‐BQ‐P/GF symmetric SC device. The optimal SSC device shows a Csp reaching 200 F g−1 at 0.5 A g−1, which is an impressive value. Also, it exhibits remarkable cycling stability with 86.18% Csp retention after 5000 galvanostatic charging–discharging (GCD) cycles at 3 A g−1. The SSC device applying AZO‐BQ‐P/GF electrode delivers an excellent energy density (ED) of 25.00 Wh kg−1 at 900.00 W kg−1 power density (PD). Thus, the novel polymer design offers efficient electrode materials to enhance the pseudocapacitive electrochemical performance of the SSC device. This concept can be extended for fabricating other electrochemical systems and accelerate its applications for modern electronic devices.

Boosting supercapacitive performance of pristine covalent organic frameworks via phenolic hydroxyl groups: A two‐in‐one strategy

Two-dimensional covalent organic frameworks (COFs) are ideal electrode materials for electrochemical energy storage devices due to their unique structures and properties, and the accessibility and utilization efficiency of the redox-active sites within COFs are critical determinants of their pseudocapacitive performance. Via introducing meticulously designed phenolic hydroxyl (Ar-OH) groups with hydrogen-bond forming ability onto the imine COF skeletons, DHBD-Sb-COF exhibited improved hydrophilicity and crystallinity than the parent BD-Sb-COF, the redox-active sites (SbPh3 moieties) in COF electrodes could thus be highly accessed by aqueous electrolyte with a high active-site utilization of 93%. DHBD-Sb-COF//AC provided an excellent supercapacitive performance with an energy density of 78 Wh Kg−1 at the power density of 2553 W Kg−1 and super cycling stability, exceeding most of the previously reported pristine COF electrode-based supercapacitors. The “two-in-one” strategy of introducing hydroxyl groups onto imine COF skeletons to enhance both hydrophilicity and crystallinity provides a new avenue to improve the electrochemical performance of COF-based electrodes for high-performance supercapacitors.

Pseudocapacitive Storage in Molybdenum Oxynitride Nanostructures Reactively Sputtered on Stainless-Steel Mesh Towards an All-Solid-State Flexible Supercapacitor

Exploiting pseudocapacitance in rationally engineered nanomaterials offers greater energy storage capacities at faster rates. The present research reports a high-performance Molybdenum Oxynitride (MoON) nanostructured material deposited directly over stainless-steel mesh (SSM) via reactive magnetron sputtering technique for flexible symmetric supercapacitor (FSSC) application. The MoON/SSM flexible electrode manifests remarkable Na+-ion pseudocapacitive kinetics, delivering exceptional ~881.83 F.g-1 capacitance, thanks to the synergistically coupled interfaces and junctions between nanostructures of Mo2N, MoO2, and MoO3 co-existing phases, resulting in enhanced specific surface area, increased electroactive sites, improved ionic and electronic conductivity. Employing 3D Bode plots, b-value, and Dunn’s analysis, a comprehensive insight into the charge-storage mechanism has been presented, revealing the superiority of surface-controlled capacitive and pseudocapacitive kinetics. Utilizing PVA-Na2SO4 gel electrolyte, the assembled all-solid-state FSSC (MoON/SSM||MoON/SSM) exhibits impressive cell capacitance of 30.7 mF.cm-2 (438.59 F.g-1) at 0.125 mA.cm-2. Moreover, the FSSC device outputs superior energy density of 4.26 μWh.cm-2 (60.92 Wh.kg-1) and high power density of 2.5 mW.cm-2 (35.71 kW.kg-1). The device manifests remarkable flexibility and excellent electrochemical cyclability of ~91.94% over 10,000 continuous charge-discharge cycles. These intriguing pseudocapacitive performances combined with lightweight, cost-effective, industry-feasible, and environmentally sustainable attributes make the present MoON-based FSSC a potential candidate for energy-storage applications in flexible electronics. Figure 1

Electrodeposition of CoSx-graphene nanoplatelets on Ni(OH)2 nanosheets for improving the pseudocapacitance performance

In the present work, binder-free CoSx–graphene nanoplatelets porous structures were coated on Ni(OH)2 nanosheets using a one-step electrodeposition process. The graphene was produced from the electroreduction of CO2∗ intermediates during the electrodeposition of CoSx. The surface morphology and interfacial bonding states of CoSx–graphene@Ni(OH)2 were sensitive to the deposition time and Co–to–thiourea molar ratio (Mr). The interface reconstruction between CoSx–graphene NCs and Ni(OH)2 nanosheets improved the pseudocapacitance performance, which was investigated at different Mr and varying deposition times. Raman spectra verified the presence of graphene and CoSx mixed phases in all heterostructure electrodes, where CoS2 was dominant at Mr = 0.2. An XPS analysis indicated the evolution of various interfacial bonding states (CO, CO, CoONi, and SO) between Ni(OH)2 nanosheets and CoSx-graphene nanoplatelets, revealing the improvement in the interfacial synergy and concentration of electroactive sites. The hybrid CoSx-graphene@Ni(OH)2 NCs at Mr = 0.2 exhibited the highest capacitance of 2116 F∙g−1 at 2 mV∙s−1 and 1618 F∙g−1 at 1 A∙g−1 compared with bare Ni(OH)2, which achieved 1212 F∙g−1 at 2 mV∙s−1 and 882.88 F∙g−1 at 1 A∙g−1, and other NCs. Bare Ni(OH)2 nanosheets retained only capacitance retention of 25 % after 2000 cycles, which improved to 70 % in all CoSx-graphene@Ni(OH)2 nanoplatelets.

Chemical reduction-induced defect-rich bismuth oxide-reduced graphene oxide anode for high-performance supercapacitors

We prepare bismuth oxide-reduced graphene oxide (Bi2O3-rGO) composite anode using a one-step chemical precipitation/reduction method. Under a reducing atmosphere, oxygen atoms on the surface of Bi2O3 are gradually removed and neighboring oxygen atoms migrate to the surface, leaving oxygen vacancies. Defective Bi2O3 enhances the number of active sites, providing additional pseudocapacitive performance. The transition metal oxide-based Bi2O3 acts as an anode, providing capacitive performance that far exceeds that of conventional carbon materials. Moreover, the introduction of rGO forms a conductive network for Bi2O3, improving capacitive contribution and ion diffusion capabilities for the electrode. The Bi2O3-rGO-100 (GO added at 100 mg) exhibits a high specific capacitance of 1053F/g at 1 A/g, significantly higher than that of Bi2O3 (866F/g). The Bi2O3-rGO-100 anode and Ni3Co2-rGO cathode are assembled into a battery-type supercapacitor. The coin-cell device achieves an energy density of 88.2 Wh kg−1 at a power density of 850 W kg−1. The Ni3Co2-rGO//Bi2O3-rGO-100 pouch-cell device demonstrates an extremely low Rct of 0.77 Ω. At a power density of 850 W kg−1, the energy density reaches 118.5 Wh kg−1, and remains 67.4 Wh kg−1 at 8500 W kg−1.

One single-atom Mn doping strategy enabling two functions of oxygen reduction reaction and pseudocapacitive performance

Single-atom metal species as highly effective active sites are crucial for enhancing energy storage and conversion properties. However, achieving the simultaneous construction of single-atom sites and the regulation of matrix structures to enable their application in both energy storage and conversion remains a challenge. Here, we have successfully developed unique MnN2C2 active sites, atomically dispersed on N-doped mesoporous graphitic carbon sheets (MnSAs/NMC). This is accomplished through the strategic utilization of MnCl2 salt, which serves dual roles of a pore-forming agent and a template. The MnSAs/NMC catalyst demonstrates compelling electrocatalytic activity for the oxygen reduction reaction (ORR), with an impressive half-wave potential (E1/2 = 0.90 V), alongside superior capacitance reaching 444 F g-1 at 0.5 A g-1 for supercapacitors. Crucially, both experimental and theoretical simulations validate that the single-atom dispersed MnN2C2 optimizes the adsorption energy of reactants and intermediates in the ORR process and pseudocapacitive behavior, leading to excellent ORR activity and capacitive performance. Interestingly, MnSAs/NMC-based Zn-air batteries exhibit concurrently high-power density derived from capacitive property and high energy density enhanced by ORR process. This study presents a novel preparation method for single-atom catalysts, which paves the way for the commercial application of super energy storage and conversion devices.

On the Electrochemical Activation of Nanoporous Reduced Graphene Oxide Electrodes Studied by In Situ/Operando Electrochemical Techniques

AbstractDue to the difficult access of the electrolyte into the nanoconfined space of nanoporous reduced graphene oxide (rGO) electrodes, achieving the optimal electrochemical performance of these devices becomes a challenge. In this work, the dynamics of interfacial‐governed phenomena are investigated during a voltage‐controlled electrochemical activation of nanoporous rGO electrodes that leads to an enhanced electrochemical performance in terms of areal capacitance and electrochemical impedance. In situ/operando characterization techniques are used to reveal the dynamics of the irreversible material changes introduced during the activation process, including ionic diffusion and water confinement within the nanopores, along with the reduction of oxygenated groups and the decrease of the rGO interlayer distance. Furthermore, operando techniques are used to uncover the origin of the complex polarization‐dependent dynamic response of rGO electrodes. The study reveals that the reversible protonation/deprotonation of remaining functional groups and the cation electro‐adsorption/desorption process in the graphene basal plane govern the pseudocapacitive performance of nanoporous rGO electrodes. This work brings new understanding of the complex interplay between surface chemistry, ion confinement, and desolvation processes occurring during electrochemical cycling in nanoporous rGO electrodes, offering new insights for designing high‐performing electrodes based on nanoporous rGO.

Synthesis of Flower-like Crystal Nickel–Cobalt Sulfide and Its Supercapacitor Performance

In order to improve the pseudocapacitance performance of metal sulfide electrode materials and obtain supercapacitor energy storage devices with excellent electrochemical reversibility and long-term cycle stability, the synthesis of flower-shaped crystal nickel–cobalt sulfide and its supercapacitor performance were studied. NiCo2S4 flower-shaped crystal nickel–cobalt sulfide was prepared by the hydrothermal method with nickel foam as the raw material, and electrode materials were added to prepare supercapacitor electrodes for testing of the supercapacitor performance. The physical properties of flower-shaped crystal nickel–cobalt sulfide were tested by a scanning electron microscope and transmission electron microscope, and the voltammetric cycle and constant current charge and discharge of supercapacitor electrodes prepared from this sulfide were analyzed through experiments. The experimental results showed that the flower crystal microstructure had a positive effect on the electrochemical properties. The capacitance value was always high at different current densities, and the capacity was as high as 3867.8 A/g at pH 12. After 2000 voltage–charge–discharge cycle tests, the petal-like sulfide capacity still had a retention rate of 90.57, the flower crystal nickel–cobalt sulfide still showed an excellent supercapacitor performance and the specific capacity was still high, which demonstrates that this sulfide has excellent cyclic stability and durability in electrochemical applications.

Enhanced asymmetric supercapacitor performance via facile construction of Cu-MOF@Co(OH)2 heterostructure

Integrating metal-organic frameworks (MOFs) with transition hydroxides has the potential to enhance the inadequate electronic conductivity and address the slow diffusion of MOF materials in electrochemical applications. Herein, we synthesized a 2D Cu-MOF and successfully prepared a Cu-MOF@Co(OH)2 heterostructure using a one-step hydrothermal method on a Co(OH)2/NF (nickel foam) substrate. The hybrid Cu-MOF@Co(OH)2 material exhibits high electrochemical reactivity, resulting in enhanced pseudocapacitor performance, with a specific capacitance of 2039.8 mF cm−2 at a current density of 1.0 mA cm−2. In addition, an asymmetric two-electrode cell was constructed using Cu-MOF@Co(OH)2/NF and activated carbon (AC)/NF, exhibiting a specific capacitance of 444.5 mF cm−2 at a current density of 1.0 mA cm−2, and demonstrating decent cycling durability with 90.1 % retention after 2000 cycles.

Enhanced pseudocapacitance performance of conductive polymer in the presence of synthesized mesoporous MnO2@Zeolite-Y

In the current study, mesoporous MnO2@Zeolite-Y (MOZ) was synthesized using the ultrasonic method. Then, MOZ was utilized to enhance the electrochemical behavior of poly ortho-aminophenol (POAP) conducting polymer. The POAP/MnO2@Zeolite-Y (MOZ/POAP) composite was synthesized by electropolymerization over the zeolite-modified working electrode surface. To investigate and compare the electrochemical behavior of the synthesized materials, two electrodes of MOZ and MOZ/POAP were designed. Subsequently, the electrochemical characteristics of the two mentioned electroactive compounds were evaluated by galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests in a three-electrode setup. The comparison of the results revealed that the MOZ/POAP electrode had a more significant performance and recorded a specific capacitance (Cs) of 422 F g−1 at 1 A g−1 and cyclic stability of 97.2 % over 10,000 cycles. After verifying this electrode's remarkable efficacy, a symmetric supercapacitor of MOZ/POAP was designed and analyzed by CV and GCD techniques in a two-electrode system. This electrode revealed a Cs of 184 F g−1 at 1 A g−1, energy density of 12.02 Wh kg−1, power density of 275 W kg−1, and cyclic stability of 95.7 % over 10,000 cycles. This impressive performance was due to the presence of the manganese metal in MOZ and nitrogen and oxygen species of POAP in improving the pseudocapacitance behavior, POAP as a conductive chemical and mesoporous zeolite-Y for enhancing the electrical double-layer behavior of the electrode by providing a medium for electrochemical reactions.

Binder-free, multidentate bonding-induced carbon nano-oligomer assembly for boosting charge transfer and capacitance of energy nanoparticle-based textile pseudocapacitors

Energy storage performance of pseudocapacitors (PCs) critically depends on the integration and distribution of electrochemically active materials and conductive fillers as well as the intrinsic energy storage capacity of active materials. This is particularly challenging for nano-sized pseudocapacitive materials that offer high energy density but suffer from low electrical conductivity. Additionally, conventional electrode fabrication methods often neglect crucial interfacial interactions and electrolyte wettability essential for nanoparticle-based PC electrodes in a 3D structure, which can lead to performance degradation. Here, we present a novel approach to fabricate 3D-structured pseudocapacitor electrodes by directly and sequentially assembling hydrophobic energy nanoparticles (NPs) and hydrophilic carbon nano-oligomers (CNOs) with branched space arms onto 3D textile current collectors, eliminating the need of insulating and hydrophobic organic components. This assembly based on direct interfacial multidentate interactions between MnOx NPs and CNOs ensure a uniform nano-level distribution over the entire metallic textile surface. The resulting positive electrodes (i.e., MnOx NP/CNO-based textiles) exhibit the outstanding areal capacitance of ∼1,725 mF cm−2 at 5.0 mA cm−2. This capacitance can be further increased to ∼3,244 mF cm−2 at 10 mA cm−2 via a multi-stacking method. When paired with negative electrodes (i.e., Fe3O4 NP/CNO-based textiles) fabricated using the same approach, asymmetric full-cell demonstrate remarkable areal energy/power densities that surpass those of conventional pseudocapacitors.