Comparative Study of the Structural Features and Electrochemical Properties of Nitrogen-Containing Multi-Walled Carbon Nanotubes after Ion-Beam Irradiation and Hydrochloric Acid Treatment

At a Glance

Metadata	Details
Publication Date	2021-08-24
Journal	Nanomaterials
Authors	П. М. Корусенко, С. Н. Несов, Anna Iurchenkova, Ekaterina O. Fedorovskaya, В. В. Болотов
Institutions	St Petersburg University, Aalto University
Citations	32
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance Carbon Electrodes

This document analyzes the research on modified Nitrogen-Containing Multi-Walled Carbon Nanotubes (N-MWCNTs) for supercapacitor applications and connects the material requirements to 6CCVD’s advanced MPCVD diamond capabilities, specifically focusing on Boron-Doped Diamond (BDD) for superior electrochemical performance and stability.

Executive Summary

Application Focus: The study investigates structural modification techniques (Hydrochloric Acid treatment and Argon Ion-Beam Irradiation) to enhance the specific capacitance of N-MWCNTs for use in supercapacitors.
Performance Achievement: Specific capacitance was significantly increased from 13 F·g^-1 (as-prepared) up to 27 F·g^-1 (HCl treated) at a scan rate of 5 mV·s^-1 in 1M H₂SO₄ electrolyte.
Mechanism Identified: The enhanced capacitance is primarily attributed to redox pseudocapacitance resulting from electrochemically active pyridinic/pyrrolic nitrogen inclusions and Oxygen-Containing Functional Groups (OCFGs).
Structural Effects: HCl treatment improved crystallinity (L_a increased to 15.05 nm) by removing amorphous carbon, while high-fluence ion irradiation severely damaged the structure (L_a reduced to 5.52 nm) but selectively attached hydroxyl groups (up to 17.2 at.%).
Kinetic Differences: Redox reactions involving OCFGs were found to be fast (surface reactions), dominating at high scan rates, while reactions involving nitrogen inclusions were slower (diffusion-controlled at low scan rates).
Stability: Treated N-MWCNTs demonstrated stable characteristics after cycling in the harsh 1M H₂SO₄ electrolyte, confirming the reversible nature of the redox reactions.
6CCVD Value Proposition: For applications requiring ultimate stability and high redox activity in acidic environments, 6CCVD recommends Boron-Doped Diamond (BDD), which offers superior chemical inertness and a wider potential window compared to conventional carbon materials like MWCNTs.

Technical Specifications

The following hard data points were extracted from the comparative study:

Parameter	Value	Unit	Context
Maximum Specific Capacitance (HCl)	27	F·g^-1	At 5 mV·s^-1 scan rate.
As-Prepared Specific Capacitance	13	F·g^-1	At 5 mV·s^-1 scan rate.
Electrolyte Used	1M Aqueous H₂SO₄	Concentration/Type	Acidic environment for testing.
CV Scan Rate Range	5 to 120	mV·s^-1	Used for kinetic analysis.
Ion Beam Energy (Ar⁺)	5	keV	Used for structural defect induction.
Maximum Ion Fluence	5.5 x 10¹⁶	ion·cm^-2	Resulted in maximum disorder.
Graphene Domain Size (L_a) - As-Prepared	12.73	nm	Calculated from Raman I_D/I_G ratio.
Graphene Domain Size (L_a) - HCl Treated	15.05	nm	Increased crystallinity after acid treatment.
Graphene Domain Size (L_a) - High Fluence	5.52	nm	Significant structural damage post-irradiation.
C-OH Group Concentration (High Fluence)	17.2	at.%	Relative area of C 1s PE spectra component.
EDLC Contribution (HCl Treated)	~70	%	Contribution to total theoretical capacitance (C_Max).
Redox Peak Potential (Pyridinic N, Charge)	507	mV	vs. Ag \| AgCl reference electrode.
Redox Peak Potential (OCFG, Charge)	599	mV	vs. Ag \| AgCl reference electrode.

Key Methodologies

The experimental procedures focused on synthesis, structural modification, and comprehensive electrochemical characterization:

N-MWCNT Synthesis: Catalytic Chemical Vapor Deposition (CCVD) was performed in a flow-through gas-phase reactor. Nickel nanopowder (from NiC₂O₄ decomposition) served as the catalyst on a quartz substrate.
Precursor and Parameters: Acetonitrile was used as the carbon and nitrogen precursor. Synthesis temperature was 800 °C for 1 hour.
Hydrochloric Acid (HCl) Treatment: As-prepared N-MWCNTs (0.25 g) were treated in 50 mL of 15% HCl solution using an ultrasonic water bath for 60 minutes, followed by washing and drying at 80 °C for 12 hours. This process removed amorphous carbon and catalyst particles.
Ion-Beam Irradiation: N-MWCNTs were irradiated using a high-dose ion implanter with a continuous beam of Argon ions (Ar⁺) at an average energy of 5 keV. Fluences ranged from 1 x 10¹⁶ to 5.5 x 10¹⁶ ion·cm^-2.
Electrode Preparation: A mixture of the analyzed material (3-4 mg), ethanol, and a fluoroplastic binder (40% aqueous solution of F4D) was mixed, rolled into a dense black film (~1 cm²), and used as the working electrode.
Electrochemical Testing: Measurements were conducted in a three-electrode cell using a potentiostat/galvanostat. The electrolyte was 1M aqueous H₂SO₄. A platinum foil served as the counter electrode, and Ag | AgCl was the reference electrode.
Characterization: Structural and chemical analysis utilized HRTEM, Raman spectroscopy (514.5 nm laser), XPS (C 1s, N 1s core levels), and NEXAFS (C 1s absorption spectra). Electrochemical analysis included Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS).

6CCVD Solutions & Capabilities

The research demonstrates the critical role of surface chemistry (OCFGs, N-inclusions) and structural integrity in achieving high specific capacitance in carbon-based supercapacitors, particularly in harsh acidic environments (1M H₂SO₄). While MWCNTs offer high surface area, their long-term stability and maximum potential window are limited.

6CCVD’s MPCVD Diamond offers a superior, next-generation solution for high-performance electrochemical devices.

Applicable Materials: The BDD Advantage

To replicate or significantly extend this research into high-stability, high-performance electrochemical storage, 6CCVD recommends:

Heavy Boron-Doped Diamond (BDD): BDD is the ideal material for supercapacitor electrodes, especially in strong acids like H₂SO₄.
- Superior Stability: Unlike MWCNTs, BDD is chemically inert, resisting degradation and structural changes even in highly corrosive electrolytes, ensuring long cycle life far exceeding the stability demonstrated by N-MWCNTs.
- Wide Potential Window: BDD possesses the widest electrochemical potential window of any carbon material, enabling higher energy density storage than conventional carbon electrodes.
- Tunable Conductivity & Redox Activity: 6CCVD can precisely control the boron doping concentration during MPCVD growth, tuning the material from semi-insulating to metallic. This allows optimization of charge transfer kinetics and the introduction of electrochemically active sites, achieving high pseudocapacitance without relying on unstable surface functional groups (OCFGs) or structural defects.

Customization Potential for Electrochemical Research

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Requirement from Paper/Application	6CCVD Customization Capability	Technical Specification
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Electrode Thickness	Precise control over active layer thickness.	SCD/PCD layers from 0.1 µm up to 500 µm.
Substrate Support	Thick, stable diamond substrates for mechanical and thermal management.	Substrates up to 10 mm thick.
Surface Quality	Ultra-smooth surfaces for thin-film deposition or interface studies.	Polishing: Ra < 1 nm (SCD), Ra < 5 nm (Inch-size PCD).
Integrated Contacts	Internal capability for creating low-resistance current collectors.	Custom Metalization: Au, Pt, Pd, Ti, W, Cu.
Material Type	Selection of the optimal carbon phase for the application.	Single Crystal (SCD), Polycrystalline (PCD), Boron-Doped (BDD).

Engineering Support

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View Original Abstract

Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g−1) compared to the as-prepared nanotubes (13 F·g−1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano11092163

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