CoNiO2/Co3O4 Nanosheets on Boron Doped Diamond for Supercapacitor Electrodes

At a Glance

Metadata	Details
Publication Date	2024-03-05
Journal	Nanomaterials
Authors	Zheng Cui, Tianyi Wang, Ziyi Geng, Linfeng Wan, Yaofeng Liu
Institutions	Jilin University, State Key Laboratory of Superhard Materials
Citations	6
Analysis	Full AI Review Included

Executive Summary

This research details the synthesis and performance of vertically aligned CoNiO₂/Co₃O₄ nanosheet arrays anchored on a Boron Doped Diamond (BDD) substrate, designed for high-performance supercapacitor electrodes.

Novel Architecture: A unique two-dimensional (2D) nanosheet architecture (optimal thickness 20 nm) was fabricated on BDD via a simple one-step electrodeposition method, enhancing ion diffusion and contact area.
Wide Potential Window: The BDD substrate successfully extended the operational voltage window of the single electrode to 1.2 V, significantly higher than typical CoNiO₂ or Co₃O₄ pseudocapacitors (typically < 0.6 V).
High Areal Capacitance: The CoNiO₂/Co₃O₄/BDD electrode achieved a large specific capacitance of 214 mF cm^-2 at 1 mA cm^-2.
Excellent Stability (Single Electrode): The electrode demonstrated robust cycling stability, retaining 85.9% of its initial capacitance after 10,000 cycles.
Asymmetric Supercapacitor (ASC) Performance: When assembled with Activated Carbon (AC), the ASC delivered a maximum energy density of 7.5 W h kg^-1 at a power density of 330.5 W kg^-1.
Exceptional ASC Stability: The ASC maintained 97.4% capacity retention and 90.8% coulombic efficiency after 10,000 cycles in 6 M KOH electrolyte.

Technical Specifications

Parameter	Value	Unit	Context
Single Electrode Areal Capacitance (Max)	214	mF cm^-2	At 1 mA cm^-2 current density
Single Electrode Voltage Window	1.2	V	CoNiO₂/Co₃O₄/BDD in 1 M Na₂SO₄
Single Electrode Cycling Stability	85.9	% retention	After 10,000 cycles
Asymmetric SC Energy Density (Max)	7.5	W h kg^-1	At 330.5 W kg^-1 power density
Asymmetric SC Cycling Stability	97.4	% retention	After 10,000 cycles in 6 M KOH
Optimal Nanosheet Thickness	20	nm	Measured by AFM (2500 s deposition time)
Nanosheet Layer Spacing	94	nm	Measured by TEM
BDD Film Thickness	20	µm	Synthesized by MPCVD
BDD Conductivity	113.63	S cm^-1	Measured by Hall effector
BDD Synthesis Temperature	850	°C	Substrate temperature during MPCVD
BDD Synthesis Power/Pressure	2200 W / 10 kPa	W / kPa	Microwave power / Process pressure
CoNiO₂/Co₃O₄ Annealing Temperature	300	°C	In Argon atmosphere
CoNiO₂ Interplanar Spacing	0.122	nm	HRTEM (222 plane)
Co₃O₄ Interplanar Spacing	0.202	nm	HRTEM (400 plane)

Key Methodologies

The fabrication process involves two main stages: BDD substrate synthesis via MPCVD and electrode material deposition via potentiostatic electrodeposition.

1. Boron Doped Diamond (BDD) Synthesis

Substrate Preparation: Silicon (Si) substrate was polished using nanodiamond particles (5-10 nm) to create micro impact craters, reducing the nucleation barrier.
Deposition Method: Microwave Plasma Chemical Vapor Deposition (MPCVD).
Gas Composition: Methane (CH₄) and Hydrogen (H₂) ratio set at 5% CH₄.
Doping: Trimethyl borate (C₃H₉BO₃) was introduced as the boron source.
Process Parameters: Microwave power of 2200 W, process pressure of 10 kPa, and substrate temperature maintained at 850 °C.
Result: A BDD film of approximately 20 µm thickness was obtained after 12 hours.

2. CoNiO₂/Co₃O₄ Nanosheet Array Synthesis

Electrolyte Preparation: A solution containing Ni(NO₃)₂·6H₂O (0.8 mmol), Co(NO₃)₂·6H₂O (0.8 mmol), and NH₄Cl (8 mmol) in deionized water was used.
Electrodeposition: Performed in a standard three-electrode system (BDD working electrode, Pt counter electrode, Ag/AgCl reference electrode).
Deposition Parameters: Constant voltage of -1.0 V.
Optimal Duration: 2500 seconds was determined to yield the best electrochemical performance (resulting in 20 nm thick nanosheets).
Annealing: The hybrid structure was annealed at 300 °C for 2 hours, using a heating rate of 5 °C min^-1, in an Argon atmosphere to form the final CoNiO₂/Co₃O₄/BDD composite.

3. Asymmetric Supercapacitor (ASC) Assembly

Negative Electrode (AC): Activated carbon (AC), acetylene black (conductive additive), and PVDF binder were mixed in an 8:1:1 weight ratio and coated onto nickel foam.
Electrolyte: 6 M KOH aqueous solution.
Assembly: CoNiO₂/Co₃O₄/BDD served as the positive electrode, and the AC/Ni foam served as the negative electrode, balanced according to charge requirements.

Commercial Applications

The combination of high-performance transition metal oxide nanosheets and the robust, wide-potential-window BDD substrate makes this technology suitable for demanding energy storage applications.

High-Power/Fast-Charging Systems: The high power density (330.5 W kg^-1) and rapid charge/discharge kinetics inherent to supercapacitors are ideal for regenerative braking systems and rapid charging stations for electric vehicles.
Harsh Environment Electronics: BDD is known for its high stability in corrosive media and wide electrochemical window in aqueous solutions, making the electrodes suitable for industrial monitoring or sensing devices operating under extreme pH or temperature conditions.
Grid Stabilization and Peak Shaving: The long cycle life (97.4% retention after 10,000 cycles) and high efficiency are critical for large-scale energy storage systems requiring frequent, rapid cycling.
Miniaturized and Portable Devices: The high areal capacitance (214 mF cm^-2) allows for efficient energy storage in compact footprints, beneficial for advanced portable electronics and wearable technology.
Hybrid Energy Systems: This material is optimized for use in hybrid supercapacitors (supercabatteries), bridging the gap between high-energy batteries and high-power conventional capacitors.

View Original Abstract

Developing novel supercapacitor electrodes with high energy density and good cycle stability has aroused great interest. Herein, the vertically aligned CoNiO2/Co3O4 nanosheet arrays anchored on boron doped diamond (BDD) films are designed and fabricated by a simple one-step electrodeposition method. The CoNiO2/Co3O4/BDD electrode possesses a large specific capacitance (214 mF cm−2) and a long-term capacitance retention (85.9% after 10,000 cycles), which is attributed to the unique two-dimensional nanosheet architecture, high conductivity of CoNiO2/Co3O4 and the wide potential window of diamond. Nanosheet materials with an ultrathin thickness can decrease the diffusion length of ions, increase the contact area with electrolyte, as well as improve active material utilization, which leads to an enhanced electrochemical performance. Additionally, CoNiO2/Co3O4/BDD is fabricated as the positive electrode with activated carbon as the negative electrode, this assembled asymmetric supercapacitor exhibits an energy density of 7.5 W h kg−1 at a power density of 330.5 W kg−1 and capacity retention rate of 97.4% after 10,000 cycles in 6 M KOH. This work would provide insights into the design of advanced electrode materials for high-performance supercapacitors.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano14050474

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