Biosorption-Directed Integration of Hierarchical CoO/C Composite with Nickel Foam for High-performance Supercapacitor

Enhanced electrochemical performance of the cobalt chloride carbonate hydroxide hydrate via micromorphology and phase transformation

Micromorphology and conductivity are two vital factors for the practical capacitance of the electrode materials for supercapacitors. In this work, a novel two-step electrochemical activation method involving a cyclic voltammetry (CV) treatment within 0-0.7 V followed by a CV treatment within -1.2-0 V is explored to induce the micromorphology and phase transformation of the cobalt chloride carbonate hydroxide hydrate (CCCH) nanoneedle arrays. The first-step activation transforms the CCCH to Co(OH)₂ and then the reversible transformation between Co(OH)₂ and CoOOH generates plenty of pores in the sample, thereby increasing the specific capacitance from 0.54 to 1.74 F cm^-2 at the current density of 10 mA cm^-2. The second-step activation inducing the reversible transformation between Co(OH)₂ and Co not only endows the final sample with a nanosheets-assembled fasciculate structure but also decreases the internal resistance via generating Co⁰ in the final sample (CCCH-P75N50). Consequently, the CCCH-P75N50 shows a high specific capacitance of 3.83 F cm^-2 at the current density of 10 mA cm^-2. Besides, the aqueous asymmetric supercapacitor assembled with CCCH-P75N50 and commercial conductive carbon cloth (CC) delivers a high energy density of 2.75 mWh cm^-3 at a power density of 37.5 mW cm^-3. This work provides a novel, facile and promising method to optimize the micromorphology and conductivity of Co-based electrodes.

Construction of hierarchical Co9S8@NiO synergistic microstructure for high-performance asymmetric supercapacitor

Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co₉S₈ structure and NiO nanosheets (Co₉S₈@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co₉S₈@NiO electrode materials exhibit a superior specific capacitance of 1627 F g^-1 at a current density of 1 A g^-1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg^-1 at a power density of 749.8 W Kg^-1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.

Interior and Exterior Decoration of Transition Metal Oxide Through Cu0/Cu+ Co-Doping Strategy for High-Performance Supercapacitor

Although CoO is a promising electrode material for supercapacitors due to its high theoretical capacitance, the practical applications still suffering from inferior electrochemical activity owing to its low electrical conductivity, poor structural stability and inefficient nanostructure. Herein, we report a novel Cu⁰/Cu⁺ co-doped CoO composite with adjustable metallic Cu⁰ and ion Cu⁺ via a facile strategy. Through interior (Cu⁺) and exterior (Cu⁰) decoration of CoO, the electrochemical performance of CoO electrode has been significantly improved due to both the beneficial flower-like nanostructure and the synergetic effect of Cu⁰/Cu⁺ co-doping, which results in a significantly enhanced specific capacitance (695 F g^-1 at 1 A g^-1) and high cyclic stability (93.4% retention over 10,000 cycles) than pristine CoO. Furthermore, this co-doping strategy is also applicable to other transition metal oxide (NiO) with enhanced electrochemical performance. In addition, an asymmetric hybrid supercapacitor was assembled using the Cu⁰/Cu⁺ co-doped CoO electrode and active carbon, which delivers a remarkable maximal energy density (35 Wh kg^-1), exceptional power density (16 kW kg^-1) and ultralong cycle life (91.5% retention over 10,000 cycles). Theoretical calculations further verify that the co-doping of Cu⁰/Cu⁺ can tune the electronic structure of CoO and improve the conductivity and electron transport. This study demonstrates a facile and favorable strategy to enhance the electrochemical performance of transition metal oxide electrode materials.

Electrolyte additive induced fast-charge/slow-discharge process: Potassium ferricyanide and potassium persulfate for CoO-based supercapacitors

The electrolyte additives of potassium ferricyanide and potassium persulfate can ensure that CoO-supercapacitors achieve a fast charge/slow discharge and long cycling stability. The redox couple of Fe(CN)₆^3-/Fe(CN)₆^4- can induce S₂O₈^2- to produce the sulfate radical ( [Formula: see text] ). Strong oxidizing species, including S₂O₈^2-, Fe(CN)₆^3- and [Formula: see text] , can accelerate oxidation of the CoO electrode surface from Co²⁺ to Co³⁺ in the charge process. The additives can achieve a good synergistic effect on accelerating CoO oxidation during the charge process. In a three-electrode cell, a CoO electrode with electrolyte additives achieves a fast-charge and slow-discharge time of 939 s and 1699 s at a current density of 1 A g^-1, respectively. The capacitance retention can be maintained at 84.5% after 10,000 cycles at a current density of 5 A g^-1. As a supercapacitor, the device can achieve a fast-charge and slow-discharge time of 156 s and 191 s at a current density of 1 A g^-1, respectively. The capacitance retention can be maintained at 85.5% after 10,000 cycles at a current density of 5 A 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.

Needle-like CoO nanowire composites with NiO nanosheets on carbon cloth for hybrid flexible supercapacitors and overall water splitting electrodes

A nanoscale core–shell NiO@CoO composite is prepared on flexible carbon cloth for electrodes in supercapacitors and overall water splitting. The needle-like CoO nanowires with NiO nanosheets as the active materials improve the elemental constituents as well as surface area. The NiO@CoO electrode boasts a capacity of 2.87 F cm⁻² (1024.05 F g⁻¹) at 1 A g⁻¹ current density, and even at a large current density of 20 A g⁻¹ the retention ratio is 80.9% after 5000 cycles. The excellent specific capacity with high rate capability can be ascribed to the unique structure which increases the area of the liquid–solid interface and facilitates electron and ion transport, improving the utilization efficiency of active materials. The asymmetric hybrid supercapacitor prepared with the core–shell electrode shows the energy output of 40.3 W h kg⁻¹ at 750 W kg⁻¹ with a better retention (71.7%) of specific capacitance after 15 000 cycles. In addition, linear sweep voltammetry is performed to assess the performance of the electrode in water splitting and the electrode shows excellent activity in the OER as manifested by a Tafel slope of 88.04 mV dec⁻¹. Our results show that the bifunctional structure and design strategy have large potential in energy applications.

A nanoscale core–shell NiO@CoO composite is prepared on flexible carbon cloth for electrodes in supercapacitors and overall water splitting.

An Sn doped 1T–2H MoS2 few-layer structure embedded in N/P co-doped bio-carbon for high performance sodium-ion batteries

A facile route for fabrication of an Sn doped 1T–2H MoS₂ few-layer structure embedded in N/P co-doped bio-carbon is initially developed using natural chlorella as an adsorbent and a nanoreactor.

Facile synthesis of NF/ZnOx and NF/CoOx nanostructures for high performance supercapacitor electrode materials

NF/ZnOx nanocone and NF/CoOx nanoparticle electrode materials were fabricated on a nickel foam surface using a simple chemical bath deposition approach and assessed as an electrode material for high-performance supercapacitors.

Free-standing graphene/bismuth vanadate monolith composite as a binder-free electrode for symmetrical supercapacitors

Preparation of new types of electrode material is of great importance to supercapacitors. Herein, a graphene/bismuth vanadate (GR/BiVO₄) free-standing monolith composite has been prepared via a hydrothermal process. Flexible GR sheets act as a skeleton in the GR/BiVO₄ monolith composites. When used as a binder-free electrode in a three-electrode system, the GR/BiVO₄ composite electrode can provide an impressive specific capacitance of 479 F g⁻¹ in a potential window of −1.1 to 0.7 V vs. SCE at a current density of 5 A g⁻¹. A symmetrical supercapacitor cell which can be reversibly charged–discharged at a cell voltage of 1.6 V has been assembled based on this GR/BiVO₄ monolith composite. The symmetrical capacitor can deliver an energy density of 45.69 W h kg⁻¹ at a power density of 800 W kg⁻¹. Moreover, it ensures rapid energy delivery of 10.75 W h kg⁻¹ with a power density of 40 kW kg⁻¹.

A symmetrical supercapacitor with a high energy density has been assembled based on a free-standing GR/BiVO₄ monolith composite.

Electrostatically Assembled Magnetite Nanoparticles/Graphene Foam as a Binder-Free Anode for Lithium Ion Battery

Lithium ion batteries (LIBs) are promising candidates for energy storage, with the development of novel anode materials. We report the fabrication of Fe₃O₄ nanoparticles/graphene foam via electrostatic assembly and directly utilize it as a binder-free anode for LIBs. Owing to the integrated effect of the well-dispersed Fe₃O₄ nanoparticles and the conductive graphene foam network, such composite exhibited remarkable electrochemical performances. It delivered a large reversible specific capacity reaching to ∼1198 mAh g^-1 at a current density of 100 mA g^-1, a good rate capacity, and an excellent cyclic stability over 400 cycles. This work demonstrated a facile methodology to design and construct high-performance anode materials for LIBs.