Formation of chlorate and perchlorate during electrochemical oxidation by Magnéli phase Ti4O7 anode - inhibitory effects of coexisting constituents

At a Glance

Metadata	Details
Publication Date	2022-09-23
Journal	Scientific Reports
Authors	Lu Wang, Yaye Wang, Yufei Sui, Junhe Lu, Baowei Hu
Institutions	Nanjing Agricultural University, University of Georgia
Citations	12
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Advanced Electrooxidation

Reference Paper: Wang et al. (2022). Formation of chlorate and perchlorate during electrochemical oxidation by Magnéli phase Ti4O7 anode: inhibitory effects of coexisting constituents. Scientific Reports, 12:15880.

Executive Summary

This research highlights the critical role of anode material selection in electrochemical oxidation (EO) processes, specifically comparing Boron-Doped Diamond (BDD) against Magnéli phase Ti4O7 for wastewater treatment applications involving chloride (Cl-).

BDD as Performance Benchmark: The study confirms that BDD anodes exhibit significantly faster kinetics for the oxidation of Cl- to toxic byproducts (chlorate, ClO3-, and perchlorate, ClO4-) compared to Ti4O7. This rapid transformation rate underscores BDD’s superior oxidative power for general EO applications.
Kinetic Superiority: The fitted pseudo-first-order kinetic constants (k1 and k2) for Cl- conversion were approximately 6 to 8 times higher on BDD than on Ti4O7.
Material Requirement: Replication and extension of this high-performance EO research require high-quality, uniformly doped BDD electrodes, such as those manufactured by 6CCVD via MPCVD.
Customization for EO: The anodes used were large-format plates (10 cm x 5 cm, 78 cm2 total area), demonstrating the need for custom, large-area BDD substrates, a core capability of 6CCVD.
Application Focus: While the paper focuses on minimizing toxic byproducts, BDD remains the material of choice for maximum degradation efficiency in advanced oxidation processes (AOPs).

Technical Specifications

The following hard data points were extracted from the experimental results comparing BDD and Ti4O7 anodes under standard conditions ([Cl-]0 = 1.0 mM, [Na2SO4] = 100 mM).

Parameter	Value	Unit	Context
Anode Materials Compared	BDD (on Si) vs. Ti<sub>4</sub>O<sub>7</sub>	N/A	Electrochemical Oxidation (EO)
Constant Current Density	10	mA cm<sup>-2</sup>	Applied current density
Initial Chloride Concentration	1.0	mM	Reactant concentration
Total Anode Geometric Area	78	cm<sup>2</sup>	Double-sided submerged area
ClO<sub>4</sub><sup>-</sup> Concentration (BDD)	~1000	µM	Achieved after 4.0 h (Near 100% conversion)
ClO<sub>4</sub><sup>-</sup> Concentration (Ti<sub>4</sub>O<sub>7</sub>)	780.0	µM	Achieved after 8.0 h (Slower conversion)
ClO<sub>3</sub><sup>-</sup> Maximum (BDD)	276.2	µM	Temporal maximum reached in 0.5 h
ClO<sub>3</sub><sup>-</sup> Maximum (Ti<sub>4</sub>O<sub>7</sub>)	350.6	µM	Temporal maximum reached in 4.0 h
Kinetic Constant k<sub>1</sub> (BDD)	5.40 x 10<sup>-4</sup>	s<sup>-1</sup>	Cl<sup>-</sup> to ClO<sub>3</sub><sup>-</sup> conversion rate
Kinetic Constant k<sub>1</sub> (Ti<sub>4</sub>O<sub>7</sub>)	8.59 x 10<sup>-5</sup>	s<sup>-1</sup>	Slower rate, confirming BDD superiority

Key Methodologies

The electrochemical oxidation (EO) experiments utilized a standard undivided rectangular cell setup, focusing on controlled current density and material comparison.

Anode Preparation: Silicon-supported Boron-Doped Diamond (Si/BDD) plates (10 cm x 5 cm) were used, sourced from NeoCoat (Switzerland). The total geometric surface area submerged was 78 cm2.
Cell Configuration: An undivided rectangular acrylic cell (10 cm x 5 cm x 2.5 cm) was used. The anode was centered, flanked by two 304 stainless steel plates serving as cathodes, separated by 2.5 cm.
Electrochemical Control: A constant electric current was supplied to maintain a current density of 10 mA cm-2 using a controllable DC power source.
Electrolyte Conditions: Solutions contained 1.0 mM Cl- and 100 mM of various supporting electrolytes (Na2SO4, NaNO3, Na2B4O7, Na2HPO4).
Inhibition Testing: Experiments included spiking the electrolyte with co-existing constituents (Methanol (MeOH), KI, or H2O2) at concentrations up to 1000 mM to assess inhibition of ClO3- and ClO4- formation.
Analysis: ClO3- and ClO4- were quantified using Ultra-High Performance Liquid Chromatography coupled with Electrospray Ionization Mass Spectrometry (UPLC-MS/MS).

6CCVD Solutions & Capabilities

This research validates the superior electrochemical activity of Boron-Doped Diamond (BDD) anodes for advanced oxidation processes. 6CCVD is uniquely positioned to supply the high-quality, customizable BDD materials required to replicate and advance this critical environmental research.

Applicable Materials

To achieve the high oxidative performance demonstrated by the BDD anode in this study, researchers require materials with precise doping and structural integrity.

6CCVD Material	Description & Relevance to Research
Heavy Boron-Doped PCD (BDD)	Required material for high-efficiency EO. 6CCVD offers uniform, high-density boron doping necessary for maximizing the generation of hydroxyl radicals and achieving high current efficiency, crucial for the rapid kinetics observed on BDD.
PCD Wafers/Plates	Used as the substrate material for large-area anodes. We offer Polycrystalline Diamond (PCD) plates up to 125mm in diameter, ideal for scaling up the 10 cm x 5 cm plates used in this study.
Custom SCD/PCD Thickness	We provide BDD films ranging from 0.1 µm to 500 µm, allowing researchers to optimize film thickness based on desired conductivity, lifetime, and cost efficiency for specific wastewater matrices.

Customization Potential for EO Systems

The experimental setup utilized large, double-sided coated plates. 6CCVD specializes in providing custom dimensions and integrated features necessary for industrial and research-scale EO reactors.

Custom Dimensions: We manufacture plates and wafers up to 125 mm in diameter, easily accommodating the 10 cm x 5 cm (50 cm2) plate size used in this research, ensuring scalability for pilot studies.
Substrate Flexibility: While the paper used Si/BDD, 6CCVD can deposit BDD films onto various substrates (e.g., Niobium, Tantalum, Silicon) to meet specific mechanical or electrical requirements.
Metalization Services: For robust electrical contacts and integration into the reactor cell, 6CCVD offers in-house metalization capabilities, including Au, Pt, Ti, and W, ensuring low-resistance connections for high current density applications (10 mA cm-2 and higher).
Surface Finish: We provide polishing services (Ra < 5 nm for inch-size PCD) to control surface roughness, which can influence the mass transport limitations and the formation of adsorbed species (like Clads), thereby optimizing the balance between contaminant degradation and byproduct formation.

Engineering Support

6CCVD’s in-house PhD team provides expert consultation to optimize diamond material selection for complex electrochemical applications, such as minimizing toxic byproduct formation while maintaining high oxidative efficiency.

Doping Optimization: We assist researchers in tuning the boron doping level to control the overpotential and selectivity of the anode, a critical factor in managing the Cl- oxidation pathway (R1-R7).
Surface Termination: We offer control over diamond surface termination (e.g., hydrogen or oxygen termination) to tailor the interaction between the anode surface and reactive species (like HO•), which is key to understanding and mitigating ClO4- formation.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) of sensitive diamond materials, supporting international research collaborations.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-022-19310-5