Boron-doped diamond nanowire array electrode with high mass transfer rates in flow-by operation

At a Glance

Metadata	Details
Publication Date	2018-01-01
Journal	RSC Advances
Authors	Choong-Hyun Lee, Young-Kyun Lim, Eung-Seok Lee, Hyuk-Joo Lee, Hee‐Deung Park
Institutions	Seoul Institute, Korea University
Citations	6
Analysis	Full AI Review Included

6CCVD Technical Documentation: Advanced Boron-Doped Diamond Nanowire Array Electrodes for High-Efficiency Electrochemical Oxidation

Reference: Lee et al., RSC Adv., 2018, 8, 11102-11108. Focus: Enhanced Mass Transport and Energy Efficiency in Flow-By BDD Electrodes.

Executive Summary

This research demonstrates a significant advancement in electrochemical oxidation performance by leveraging microstructured Boron-Doped Diamond (BDD) surfaces, validating a critical market need for custom, high-aspect-ratio diamond electrodes.

Structure-Function Optimization: A highly ordered BDD nanowire (BDDNW) array electrode was fabricated, specifically designed to enhance hydrodynamic flow (flow-by operation), solving a primary limitation of conventional surface-modified BDD electrodes.
Mass Transfer Coefficient ($k$) Doubling: The aligned BDDNW array achieved a mass transfer coefficient of 6.17 x 10⁻⁵ m s⁻¹ at 1 L min⁻¹, nearly double the performance of a randomly structured BDD nanowire electrode (3.26 x 10⁻⁵ m s⁻¹).
Enhanced Energy Efficiency: The aligned BDDNW array reduced specific energy consumption for 80% phenol removal by 43% (8 kWh m⁻³) compared to the random configuration (14 kWh m⁻³), directly addressing the high cost limitation of BDD technology.
Superior Oxidation Kinetics: Bulk electrolysis confirmed the BDDNW array achieved faster phenol and Chemical Oxygen Demand (COD) removal rates, resulting in a 21.2% general current efficiency (GCE).
Fabrication Method: The array was successfully manufactured using soft lithography (PS sphere mask) coupled with Metal-Assisted Chemical Etching (MACE) on p-type Silicon (Si) templates, followed by nanodiamond seeding and Hot-Filament Chemical Vapor Deposition (HFCVD) of BDD.
Commercial Potential: The findings confirm that advanced, carefully controlled diamond surface morphology is the key to scaling BDD from lab sensor applications to energy-efficient industrial wastewater treatment.

Technical Specifications

Parameter	Value	Unit	Context
Target Application	Phenol Oxidation (Wastewater)	N/A	Electrochemical oxidation process
Substrate Type	p-type Si (100)	N/A	Resistivity: 0.005 Ω cm
Electrode Substrate Area	16	cm²	4 cm x 4 cm
Nanowire Length	750	nm	Average BDDNW length
Nanowire Thickness	200	nm	Average BDDNW thickness
Metal Catalyst Thickness	40	nm	Ag film deposited for MACE
Effective Surface Area (Random)	14.11	cm² cm⁻²	Calculated via Chronocoulometry (BDDNW)
Effective Surface Area (Aligned)	11.78	cm² cm⁻²	Calculated via Chronocoulometry (BDDNW Array)
CVD Growth Temperature	800	°C	HFCVD Substrate Temperature
Carbon Source Concentration	1	vol%	CH₄ in H₂
Boron Dopant Concentration	5000	ppm	B₂H₆ in H₂ (Maximum flow used)
Total Gas Flow	100	sccm	HFCVD total flow rate
CVD Pressure	< 10	Torr	Chamber pressure during growth
Hydraulic Flow Rate	1	L min⁻¹	Bulk electrolysis operation
Mass Transfer Coef. (Aligned, k)	6.17 x 10⁻⁵	m s⁻¹	Critical performance metric under flow
Initial Current Efficiency (ICE)	50	%	BDDNW Array at 0.5 A h L⁻¹
Specific Energy (80% Removal)	8	kWh m⁻³	BDDNW Array (Aligned)

Key Methodologies

The highly ordered BDD nanowire array electrode was manufactured via a combination of top-down lithography and bottom-up CVD growth on a Si template:

Si Substrate Preparation: p-type Si wafers (0.005 Ω cm) were cleaned and treated with an HF solution to remove the native oxide layer.
Soft Lithography Masking: Polystyrene (PS) spheres (1 µm initial diameter) were spin-coated to form a highly ordered, hexagonal-packed monolayer across the 4 cm x 4 cm substrate.
Mask Refinement (RIE): Reactive Ion Etching (RIE) was performed at 450 W for 7 min to reduce the PS sphere diameter by 400 nm, controlling the final interspace dimension.
Catalyst Deposition: A 40 nm thick Ag film was thermally evaporated onto the substrate, filling the reduced gaps between the PS spheres.
Mask Removal: The PS mask was ultrasonically removed, leaving a hexagonal array of circular Ag catalyst holes on the Si surface.
Nanowire Etching (MACE): Metal-Assisted Chemical Etching (MACE) was conducted using a solution of DI water, HF, and H₂O₂ to anisotropically etch the exposed Si, creating the highly ordered Silicon Nanowire (SiNW) array.
Diamond Seeding (ESAND): Electrochemical Seeding and Nanodiamond Deposition (ESAND) method was used to densely seed the complex nanotextured Si template with nanodiamond particles (few hundred nanometers size).
BDD Growth (HFCVD/MPCVD): Boron-Doped Diamond (BDD) was deposited using a HFCVD system at 800 °C, using 1 vol% CH₄ in H₂ and B₂H₆ (5000 ppm) as the boron source, resulting in a nanocrystalline BDD film structure.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to transition the advanced nanowire BDD technology demonstrated in this research from the laboratory scale (4 cm x 4 cm) into commercial, high-productivity electrochemical systems. Our capabilities align precisely with the demanding material specifications and customization required for high mass transfer electrodes.

Applicable Materials for Scale-Up

To replicate and extend this high-efficiency electrochemical research, 6CCVD recommends the following specialized materials:

6CCVD Product	Material Specification	Applicable Research Function
Heavy Boron-Doped PCD	Polycrystalline Diamond (PCD) wafer with heavy Boron doping (BDD) optimized for high conductivity. Custom resistivity < 0.005 Ω cm.	Provides the necessary wide potential window and high conductivity required for OER and hydroxyl radical generation essential for oxidation. Ideal for scaling to large surface areas.
Thin Film PCD/SCD	Custom diamond layers from 0.1 µm up to 500 µm thickness.	Enables the exact replication of the high-aspect-ratio nanowire structure (750 nm length, 200 nm thickness) via post-processing or template transfer techniques.
Custom Substrate Wafers	Diamond deposited directly onto customer-supplied p-type Silicon (Si) wafers, or alternatively, high-quality, polished PCD substrates prepared for subsequent lithography.	Facilitates the use of the MACE/lithography techniques described in the paper to ensure high quality starting template material.

Customization Potential

The success of the BDDNW array relies heavily on precise geometry and interface modification, areas where 6CCVD offers unmatched customization:

Large-Area Production: While the paper used 4 cm x 4 cm substrates, 6CCVD routinely produces PCD plates and wafers up to 125mm (5 inches), enabling a massive scale-up for industrial wastewater applications.
Custom Geometric Control: 6CCVD offers laser cutting and patterning services to pre-define electrode shapes or patterns that interface optimally with flow-by reactor designs, supporting advanced microscopic surface design strategies.
Advanced Metalization: The experiment required precise 40 nm Ag catalyst deposition. 6CCVD offers internal, high-quality deposition services for noble metals, including Au, Pt, Pd, Ti, W, and Cu, allowing engineers to test alternative catalyst materials or develop stable, low-resistance ohmic contacts for device integration.
Surface Preparation: Our ability to achieve ultra-low surface roughness (Ra < 5 nm for inch-size PCD) ensures a pristine starting surface for subsequent soft lithography and etching steps, minimizing geometric defects that could impede mass transport efficiency.

Engineering Support

The enhanced performance of the BDDNW array is achieved by carefully balancing effective surface area and hydrodynamic flow dynamics. 6CCVD’s in-house PhD materials science team is available to assist engineers and scientists with material selection, doping concentration optimization, and substrate preparation for similar high-efficiency electrochemical oxidation projects. We ensure that your chosen BDD material is synthesized and processed to maximize the mass transfer coefficient ($k$) for your specific flow-cell application requirements.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We fabricated a boron-doped diamond nanowire (BDDNW) array electrode<italic>via</italic>lithography and metal-assisted chemical etching (MACE) to provide a highly promoted surface area and increased mass transport during the electrochemical oxidation process.

Tech Support

Original Source

DOI: https://doi.org/10.1039/c8ra01005f