Development of Electrochemical Oxygen Demand Measurement Cells Using a Diamond Electrode

At a Glance

Metadata	Details
Publication Date	2016-12-01
Journal	Analytical Sciences
Authors	Takeshi Kondo, Masaki Hoshino, Takeshi Watanabe, Tatsuo Aikawa, Makoto Yuasa
Institutions	Tokyo University of Science, Keio University
Citations	4
Analysis	Full AI Review Included

Technical Documentation and Analysis: High-Efficiency ECOD Measurement Using MPCVD Diamond Electrodes

Executive Summary

This research validates the critical role of optimized Boron-Doped Diamond (BDD) electrodes manufactured by Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) for rapid and precise water quality monitoring.

Core Achievement: Development of optimized electrochemical cells (Type II and Type III) enabling high-speed, low-concentration measurement of Electrochemical Oxygen Demand (ECOD).
Speed and Efficiency: Measurement time was dramatically reduced from 9000 seconds (Type I cell) to a practical range of 140-900 seconds using the Type III design, making ECOD suitable for industrial applications.
Low Detection Limit: The improved cell geometry achieved a measurable ECOD range down to 2 mg-O₂ L^-1, meeting stringent environmental standards (e.g., Japanese effluent regulations).
Mass Transfer Enhancement: The Type III cell optimized mass transfer by utilizing a thin electrolyte layer and exploiting gas bubble evolution (from water decomposition at the highly positive potential) for effective solution mixing, eliminating the need for mechanical stirring.
Absolute Quantification: The BDD methodology provides direct, absolute quantification of organic content through total electrolytic decomposition, requiring no calibration curves or the use of toxic oxidizers (like K₂Cr₂O₇ or KMnO₄).
Material Basis: The success relies entirely on the chemical stability and wide potential window of high-quality, MPCVD-grown BDD working electrodes on conductive silicon substrates.

Technical Specifications

Parameter	Value	Unit	Context
Electrode Material Basis	Boron-Doped Diamond (BDD)	N/A	Prepared by MPCVD on conductive Si wafers
Applied Potential	+2.45	V	Constant potential vs. Ag/AgCl reference electrode
Optimized ECOD Detection Limit	2	mg-O₂ L<sup>-1</sup>	Achieved using the Type III cell design
Model Compound	Potassium Hydrogen Phthalate (KHP)	N/A	Used for organic pollutant modeling
Electrolysis Time (Minimum)	140	s	For 2 mg-O₂ L<sup>-1</sup> KHP using Type III cell
Standard Electrolyte	0.1 M	Na<sub>2</sub>SO<sub>4</sub>	Background support electrolyte
WE Diameter (Type I, III)	10	mm	Working Electrode (WE) dimensions
WE Diameter (Type II)	6	mm	Working Electrode dimensions
Electrolyte Volume (Type III)	200 - 400	µL	Minimal volume for thin-layer mass transfer
Baseline Electrolysis Time (Type I, 100 mg-O<sub>2</sub> L<sup>-1</sup>)	9000	s	Time required for complete decomposition
Optimized Electrolysis Time (Type III, 100 mg-O<sub>2</sub> L<sup>-1</sup>)	360	s	Time required for complete decomposition

Key Methodologies

The core of the research involved optimizing the cell geometry and mass transport mechanisms around the BDD working electrode to accelerate the electrochemical reaction kinetics.

BDD Electrode Synthesis: Boron-Doped Diamond (BDD) films were grown onto conductive silicon wafer substrates using Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD).
Cell Architecture Design: Three distinct cell configurations (Type I, II, and III) were tested, each employing a BDD working electrode, a Pt wire counter electrode, and an Ag/AgCl reference electrode.
Thin-Layer Cell Implementation (Type III): The optimal Type III cell reduced the electrolyte volume significantly (200-400 µL) relative to the 10 mm working electrode area, creating a thin solution layer (approx. 1 mm sample injection distance).
High Positive Potential Application: A constant potential of +2.45 V vs. Ag/AgCl was applied to the BDD electrode to ensure complete anodic decomposition of organic matter (KHP).
Dynamic Solution Mixing: In the Type III cell, mechanical stirring was deliberately omitted. Mixing was achieved effectively using the spontaneous agitation provided by the evolution of gas bubbles (H<sub>2</sub> and O<sub>2</sub>) resulting from the electrochemical decomposition of water at the high applied potential.
Coulometric Measurement: The ECOD value was quantified by integrating the background-subtracted anodic current over time (I-t curve integration) to determine the total electric charge (Q) required for complete decomposition.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials required to replicate and extend this high-performance ECOD research and commercialize related electrochemical sensors. Our expertise in MPCVD growth ensures the quality and consistency necessary for demanding analytical applications.

Applicable Materials

To achieve the wide potential window, chemical inertness, and high current density required for total anodic decomposition (ECOD), Boron-Doped Diamond (BDD) is essential.

Material	Specific 6CCVD Offering	Relevance to Research
BDD Wafers (PCD)	Heavy Boron-Doped Polycrystalline Diamond (PCD) on Si or customized conductive substrates.	Provides the low resistivity (high conductivity) and chemical stability necessary for highly positive potential operation (+2.45 V).
PCD Custom Plates	Wafers up to 125mm in size, customizable thickness (0.1µm - 500µm BDD layer).	Enables production of the large-area, circular working electrodes (6 mm or 10 mm diameter) used in the study, facilitating scale-up.

Customization Potential

The research requires precise electrode geometries and optimized interfacing for stable electrochemical performance. 6CCVD offers end-to-end customization services essential for industrializing this technology.

Custom Dimensions: While the paper utilized 6 mm and 10 mm circular electrodes, 6CCVD can produce plates/wafers up to 125mm (PCD) and offers precision laser cutting services to deliver electrodes of exact custom diameters or unique shapes required for miniaturized flow cells.
Metalization Services: The setup requires robust electrical contact to maintain the highly positive potential (+2.45 V). 6CCVD provides internal metalization capabilities including Ti, Pt, Au, Pd, and Cu layering, ensuring low-resistance contacts critical for stable current measurement and minimized current noise.
Polishing Standards: For high-precision analytical work, surface uniformity is vital. 6CCVD guarantees ultra-low surface roughness, offering Ra < 5nm for inch-size PCD, ensuring consistent mass transfer characteristics across the electrode surface.

Engineering Support

The transition from a laboratory prototype (like the Type III cell) to a robust industrial sensor requires specialized material knowledge.

Electrochemical Sensor Design: 6CCVD’s in-house PhD engineering team can assist clients with material selection, doping level optimization, and substrate integration specifically for high-efficiency Electrochemical Oxygen Demand (ECOD) projects.
Doping Optimization: We provide expertise in tailoring boron doping concentration to balance conductivity requirements versus the need to maintain a wide anodic potential window, maximizing Faradaic efficiency for total organic decomposition.
Global Logistics: Materials are shipped globally, with DDU default and DDP available, guaranteeing secure and timely delivery of high-value custom diamond components to research facilities worldwide.

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

Tech Support

Original Source

DOI: https://doi.org/10.2116/analsci.32.1381