A high-performance asymmetric supercapacitor electrode based on a three-dimensional ZnMoO4/CoO nanohybrid on nickel foam

Interface engineering based NiCoMoO4/Ti3C2Tx MXene heterostructure for high-performance flexible supercapacitors

The advancement of interface engineering has demonstrated remarkable efficacy in overcoming the primary impediment associated with sluggish reaction kinetics in supercapacitor electrodes. In this investigation, we employed a facile co-precipitation method to synthesize NiCoMoO4/MXene heterostructures utilizing Ti3C2Tx MXene nanosheets as carriers. This heterostructure inhibits the restacking of MXene nanosheets and simultaneously enhances the exposure of electrochemically active sites in NiCoMoO4 nanorods, thereby mitigating the reduction in specific capacitance resulting from volumetric fluctuations. The NiCoMoO4/MXene electrode, possessing pseudo-capacitance properties, demonstrates an impressive level of specific capacitance, exceptional performance across various charging rates, and consistent behavior throughout repeated cycles. By optimizing the mass ratio, this electrode achieves a specific capacity of 1900 F/g under a current density of 1 A/g. Even after enduring 10,000 cycles at a significantly higher current density of 5 A/g, it still maintains an impressive retention rate of 94.73 %. Our density functional theory (DFT) calculations indicate that the enhanced electrochemical performance can be attributed to the improved electronic coupling within the NiCoMoO4/MXene heterostructure. The integration of NiCoMoO4/MXene cathode and activated carbon (AC) anode with an alkaline gel electrolyte containing potassium ferricyanide in flexible quasi-solid-state supercapacitors (FSSCs) results in exceptional electrochemical performance and flexibility. These FSSCs demonstrate a maximum energy density of 72.89 Wh kg-1 at a power density of 850 W kg-1, while maintaining an impressive power output of 16,780 W kg-1 with an energy density of 37.28 Wh kg-1. Based on these outstanding properties, it is evident that the NiCoMoO4/MXene heterojunction possesses significant advantages as electrode material for supercapacitors, and the fabricated FSSCs devices pave a new pathway for flexible electronic devices.

Activation-Assisted High-Concentration Phosphorus-Doping to Enhance the Electrochemical Performance of Cobalt Carbonate Hydroxide Hydrate

P-doping into metal oxides has been demonstrated as a valid avenue to ameliorate electrochemical performance because it can tune the electronic structures and increase the active sites for an electrochemical reaction. However, it usually results in a low P-doping concentration via the commonly used gas phosphorization method. In this work, an activation-assisted P-doping strategy was explored to significantly raise the P-doping concentration in cobalt carbonate hydroxide hydrate (CCHH). The activation treatment increased active sites for electrochemical reaction and endowed the sample with a high P content in the subsequent gas phosphorization process, thereby greatly enhancing the conductivity of the sample. Therefore, the final CCHH-A-P electrode exhibited a high capacitance of 6.62 F cm^-2 at 5 mA cm^-2 and good cyclic stability. In addition, the CCHH-A-P//CC ASC with CCHH-A-P as the positive electrode and carbon cloth as the negative electrode provided a high energy density of 0.25 mWh cm^-2 at 4 mW cm^-2 as well as excellent cycling performance with capacitance retention of 91.2% after 20,000 cycles. Our work shows an effective strategy to acquire Co-based materials with high-concentration P-doping that holds great potential in boosting the electrochemical performance of electrode materials via P-doping technology.

Multi-Functional Materials Based on Cu-Doped TiO2 Ceramic Fibers with Enhanced Pseudocapacitive Performances and Their Dielectric Characteristics

In this work, pure TiO2 and Cu (0.5, 1, 2%)-doped TiO2 composites prepared by electrospinning technique followed by calcination at 900 °C, and having high pseudocapacitive and dielectric characteristics were reported. These nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, and dynamic water sorption vapor measurements. The structural characterization of these nanostructures highlighted good crystallinity including only the rutile phase. The electrochemical characteristics were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements, which were performed in a KOH electrolyte solution. Among the Cu-doped TiO2 nanostructures that were prepared, the one containing 0.5% Cu exhibited superior electrochemical properties, including high specific gravimetric capacitance of 1183 F·g-1, specific capacitance of 664 F·g-1, energy density of 45.20 Wh·kg-1, high power density of 723.14 W·kg-1, and capacitance retention of about 94% after 100 cycles. The dielectric investigation shows good dielectric properties for all materials, where the dielectric constant and the dielectric loss decreased with the frequency increase. Thus, all the interconnected studies proved that these new materials show manifold ability and real applicative potential as pseudocapacitors and high-performance dielectrics. Future work and perspectives are anticipated for characterizing electrochemical and dielectric properties for materials including larger amounts of Cu dopant.

Effect of oxygen vacancies on the electronic structure and electrochemical performance of MnMoO4: computational simulation and experimental verification

Porous nanopetals of MnMoO4 with oxygen vacancies (MnMoO4–OV) were synthesized and deliver preferable energy storage performance.

Synthesis and electrochemical performance of an electroactive nitrogen-doping SnO2 nanoarray supported on carbon fiber

An electroactive nitrogen-doping tin dioxide nanorod array (N-SnO2 NRA) is designed as an effective energy-storage electrode material for supercapacitor applications. N-SnO2 supported on a carbon fiber substrate is prepared using SnCl4 as a precursor through hydrolysis, hydrothermal growth, and an NH3-nitriding process. Electroactive N-SnO2 is formed by an N-doping reaction between Sn(OH)4 and NH3, revealing a high nitrogen-doping level of 12.5% in N-SnO2. N-SnO2/carbon fiber reveals a lower ohmic resistance and charge transfer resistance than SnO2/carbon fiber, which is consistent with its higher current response and lower voltage drop in electrochemical measurements. N-SnO2 NRA has an independent nanoarray structure and a small side length of a quadrangular nanorod, contributing to a more accessible interspace, reactive sites, and feasible electrolyte ion diffusion. The N-SnO2/carbon fiber NRA electrode shows higher specific capacitance (105.4 F g−1 at 0.5 A g−1) and rate capacitance retention (45.0% from 0.5 to 5 A g−1) than a SnO2/carbon fiber NRA electrode (58.6 F g−1, 38.4%). Significantly, the cycling capacitance retention after 2000 cycles increases from 78.1% of SnO2/carbon fiber to 98.8% of N-SnO2/carbon fiber, presenting a superior electrochemical cycling stability. The N-SnO2 supercapacitor maintains stable power working at an output voltage of 1.6 V. The specific capacitance decreases from 75.2 to 55.1 F g−1 when the current density increases from 1 to 10 A g−1. The corresponding energy density decreases from 24.23 to 9.81 Wh kg−1, presenting a reasonable rate capability. So, the prepared N-SnO2 nanorod array demonstrates superior capacitance performance for energy-storage applications.

Design of a ZnMoO4 porous nanosheet with oxygen vacancies as a better performance electrode material for supercapacitors

A ZnMoO₄ porous nanosheet with oxygen vacancies (ZnMoO₄-OV) was synthesized which delivers a preferable energy storage performance.

Fabrication and charge storage capacitance of PPY/TiO2/PPY jacket nanotube array

A PPY/TiO2/PPY jacket nanotube array was fabricated by coating PPY layer on the external and internal surface of a tube wall-separated TiO2 nanotube array. It shows coaxial triple-walled nanotube structure with two PPY nanotube layers sandwiching one TiO2 nanotube layer. PPY/TiO2/PPY reveals much higher current response than TiO2. The theoretical calculation indicates PPY/TiO2/PPY reveals higher density of states and lower band gap, accordingly presenting higher conductivity and electroactivity, which is consistent with the experimental result of a higher current response. The electroactivity is highly enhanced in H2SO4 rather than Na2SO4 electrolyte due to feasible pronation process of PPY in an acidic solution. PPY/TiO2/PPY could conduct the redox reaction in H2SO4 electrolyte which involves the reversible protonation/deprotonation and HSO4 − doping/dedoping process and accordingly contributes to Faradaic pseudocapacitance. The specific capacitance is highly enhanced from 1.7 mF cm−2 of TiO2 to 123.4 mF cm−2 of PPY/TiO2/PPY at 0.1 mA cm−2 in H2SO4 electrolyte. The capacitance also declines from 123.4 to 31.7 mF cm−2 when the current density increases from 0.1 to 1 mA cm−2, presenting the rate capacitance retention of 26.7% due to the semiconductivity of TiO2. A PPY/TiO2/PPY jacket nanotube with high charge storage capacitance is regarded as a promising supercapacitor electrode material.

One-dimensional zinc-manganate oxide hollow nanostructures with enhanced supercapacitor performance

Hollow electrode materials with structural advantages of large contact interface and sufficient cavity structures are significant for electrochemical energy storage. Herein, ultra-long one-dimensional zinc-manganese oxide (ZnMn₂O₄) hollow nanofibers were successfully prepared by electrospinning at an appropriate temperature (500 °C). The optimal electrode of ZnMn₂O₄ exhibited a larger specific capacitance (1026 F g^-1) as compared to ZnMn₂O₄ powder (125 F g^-1) at a current density of 2 A g^-1 in three-electrode configuration. Moreover, the optimal electrode of the ZnMn₂O₄ hollow nanofibers also possessed long-term cycling stability with a slight upward capacitance (100.8%) after 5000 cycles. Their higher specific capacitance and the outstanding cycle stability may be attributed to the unique 1D hollow nanostructure, which enhanced the charge transfer and improved the diffusion of the electrolyte ions at the surface. Thus, this work designed a high-performance electrode with unique hollow nanostructure that can be applied to the field of energy storage.

Boosting the energy density of supercapacitors by encapsulating a multi-shelled zinc-cobalt-selenide hollow nanosphere cathode and a yolk-double shell cobalt-iron-selenide hollow nanosphere anode in a graphene network

The practical exploration of electrode materials with complex hollow structures is of considerable significance in energy storage applications. Mixed-metal selenides (MMSs) with favorable architectures emerge as new electrode materials for supercapacitor (SC) applications owing to their excellent conductivity. Herein, a facile and effective metal-organic framework (MOF)-derived strategy is introduced to encapsulate multi-shelled zinc-cobalt-selenide hollow nanosphere positive and yolk-double shell cobalt-iron-selenide hollow nanosphere negative electrode materials with controlled shell numbers in a graphene network (denoted as G/MSZCS-HS and G/YDSCFS-HS, respectively) for SC applications. Due to the considerable electrical conductivity and unique structures of both electrodes, the G/MSZCS-HS positive and G/YDSCFS-HS negative electrodes exhibit remarkable capacities (∼376.75 mA h g^-1 and 293.1 mA h g^-1, respectively, at 2 A g^-1), superior rate performances (83.4% and 74%, respectively), and an excellent cyclability (96.8% and 92.9%, respectively). Furthermore, an asymmetric device (G/MSZCS-HS//G/YDSCFS-HS) has been fabricated with the ability to deliver an exceptional energy density (126.3 W h kg^-1 at 902.15 W kg^-1), high robustness of 91.7%, and a reasonable capacity of 140.3 mA h g^-1.

Binder-Free Nickel Oxide Lamellar Layer Anchored CoOx Nanoparticles on Nickel Foam for Supercapacitor Electrodes

To enhance the connection of electroactive materials/current collector and accelerate the transport efficiency of the electrons, a binder-free electrode composed of nickel oxide anchored CoO_x nanoparticles on modified commercial nickel foam (NF) was developed. The nickel oxide layer with lamellar structure which supplied skeleton to load CoO_x electroactive materials directly grew on the NF surface, leading to a tight connection between the current collector and electroactive materials. The fabricated electrode exhibits a specific capacitance of 475 F/g at 1 mA/cm². A high capacitance retention of 96% after 3000 cycles is achieved, attributed to the binding improvement at the current collector/electroactive materials interface. Moreover, an asymmetric supercapacitor with an operating voltage window of 1.4 V was assembled using oxidized NF anchored with cobalt oxide as the cathode and activated stainless steel wire mesh as the anode. The device achieves a maximum energy density of 2.43 Wh/kg and power density of 0.18 kW/kg, respectively. The modified NF substrate conducted by a facile and effective electrolysis process, which also could be applied to deposit other electroactive materials for the energy storage devices.

Boosting the performance of cobalt molybdate nanorods by introducing nanoflake-like cobalt boride to form a heterostructure for aqueous hybrid supercapacitors

Binary transition metal oxides have received extensive attention because of their multiple oxidation states. However, due to the inherent vices of poor electronic/ionic conductivities, their practical performance as supercapacitor material is limited. Herein, a cobalt molybdate/cobalt boride (CoMoO₄/Co-B) composite is constructed with cobalt boride nanoflake-like as a conductive additive in CoMoO₄ nanorods using a facile water bath deposition process and liquid-phase reduction method. The effects of CoMoO₄/Co-B mass ratios on its electrochemical performance are investigated. Remarkably, the CoMoO₄/Co-B composite obtained at a mass ratio of 2:1 shows highly enhanced electrochemical performance relative to those obtained at other ratios and exhibits an optimum specific capacity of 436 F g^-1 at 0.5 A g^-1. This kind of composite could also display great rate capacity (294 F g^-1 at 10 A g^-1) and outstanding long cycle performance (90.5% capacitance retention over 10 000 cycles at 5 A g^-1). Also, the asymmetric supercapacitor device is prepared by using CoMoO₄/Co-B composite as the anode with the active carbon as the cathode. Such a device demonstrates an outstanding energy density of 23.18 Wh kg^-1 and superior long-term stability with 100% initial specific capacity retained after 10,000 cycles. The superior electrochemical properties show that the CoMoO₄/Co-B electrode material has tremendous potential in energy storage equipment applications.

A unique core-shell structured ZnO/NiO heterojunction to improve the performance of supercapacitors produced using a chemical bath deposition approach

The integration of metal oxide composite nanostructures has attracted great attention in supercapacitor (SC) applications. Herein, we fabricated a series of metal oxide composite nanostructures, including ZnO nanowires, NiO nanosheets, ZnO/CuO nanowire arrays, ZnO/FeO nanocrystals, ZnO/NiO nanosheets and ZnO/PbO nanotubes, via a simple and cost-effective chemical bath deposition (CBD) method. The electrochemical properties of the produced SCs were examined by performing cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Of the different metal oxides and metal oxide composites tested, the unique surface morphology of the ZnO/NiO nanosheets most effectively increased the electron transfer rate and electrical conductivity, which resulted in improved energy storage properties. The binder-free ZnO/NiO electrode delivered a high specific capacitance/capacity of 1248 F g-1 (599 mA h g-1) at 8 mA cm-2 and long-term cycling stability over the course of 3000 cycles with a capacity retention of 79%. These results suggested a superiority in performance of the ZnO/NiO nanosheets relative to the nanowires, nanowire arrays, nanocrystals, and nanotubes. Thus, the present work has provided an opportunity to fabricate new metal oxide composite nanostructures with high-performance energy storage devices.

Electrochemical performance of activated carbon fiber with hydrogen bond-induced high sulfur/nitrogen doping

The sulfur/nitrogen co-doped activated carbon fiber (S/N-ACF) is prepared by the thermal treatment of thiourea-bonded hydroxyl-rich carbon fiber, which can bond the decomposition products of thiourea through hydrogen bond interaction to avoid the significant loss of sulfur and nitrogen sources during the thermal treatment process. The sulfur/nitrogen co-doped carbon fiber (S/N-CF) is prepared by the thermal treatment of thiourea-adsorbed carbon fiber. The doping degree of the carbon fiber is improved by reasonable strategy. S/N-ACF shows a higher amount of S/N doping (4.56 at% N and 3.16 at% S) than S/N-CF (1.25 at% N and 0.61 at% S). S/N-ACF with high S/N doping level involves highly active sites to improve the capacitive performance, and high delocalization electron to improve the conductivity and rate capability when compared with the normal S/N co-doped carbon fiber (S/N-CF). Accordingly, the specific capacitance increases from 1196 mF cm⁻² for S/N-CF to 2704 mF cm⁻² for S/N-ACF at 1 mA cm⁻². The all-solid-state flexible S/N-ACF supercapacitor achieves 184.7 μW h cm⁻² at 350 μW cm⁻². The results suggest that S/N-ACF has potential application as a CF-based supercapacitor electrode material.

Sulfur/nitrogen co-doped activated carbon fiber is prepared by thermal treatment of thiourea-bonded hydroxyl-rich carbon fiber, which achieves high doping level and electrochemical performance.

Activation of carbon fiber for enhancing electrochemical performance

Carbon fiber sequentially undergoes thermal activation, electrochemical oxidation activation, electrochemical reduction activation and a secondary thermal activation process to form a highly activated carbon fiber electrode material.