Abatement of Per- and Polyfluoroalkyl Substances with Electrochemical Oxidation

At a Glance

Metadata	Details
Publication Date	2020-01-01
Journal	Lincoln (University of Nebraska)
Authors	Elise Webb
Analysis	Full AI Review Included

Technical Analysis: Boron-Doped Diamond for PFAS Electrochemical Abatement

This document analyzes the research concerning the electrochemical oxidation of Per- and Polyfluoroalkyl Substances (PFAS) using Boron-Doped Diamond (BDD) electrodes, highlighting 6CCVD’s capability to supply high-performance BDD materials necessary for scaling and optimizing this critical environmental remediation technology.

Executive Summary

The research successfully demonstrated the viability of electrochemical oxidation using Boron-Doped Diamond (BDD) anodes for degrading Perfluorooctanoic Acid (PFOA), a persistent PFAS contaminant.

High Efficacy Achieved: Baseline experiments using BDD anodes achieved up to 61.0% fluoride removal (defluorination) of 10 mg/L PFOA solution in just 2 hours.
Material Validation: BDD was confirmed as the optimal anode material for generating the necessary highly oxidative hydroxyl and sulfate radicals required for breaking the stable C-F bonds in PFAS.
Scalable Dimensions: The optimized experimental setup utilized large-area BDD plates (46.57 cm²), demonstrating the need for industrial-scale electrode dimensions.
Critical Material Failure Identified: A significant challenge was BDD anode erosion/wear, which caused a substantial decrease in treatment efficacy over repeated use (removal rates dropped from 60.4% to 37.5% in repeat 2-hour tests).
Optimization Requirement: Future research must focus on identifying and mitigating BDD plate wear, requiring ultra-high quality, robust MPCVD BDD films for long-term, cost-effective in situ field applications.
Key Electrical Parameters: Optimal baseline conditions utilized a current of 0.4 A and an average voltage of 28 V with a 1 mM Na₂SO₄ electrolyte.

Technical Specifications

The following data points summarize the optimized baseline conditions and performance metrics achieved in the electrochemical degradation of PFOA.

Parameter	Value	Unit	Context
Target Contaminant	PFOA	N/A	Perfluorooctanoic acid (C₈F₁₅O₂H)
Initial PFOA Concentration	10	mg/L	Updated baseline solution concentration
Anode Material	Boron-Doped Diamond (BDD)	N/A	Required for high overpotential oxidation
Anode Surface Area	46.57	cm²	Used in updated, optimized experiments
Cathode Material	Steel Plate	N/A	Matching 46.57 cm² surface area
Electrode Gap	10	mm	Distance between anode and cathode
Electrolyte	Na₂SO₄	N/A	Sodium Sulfate (1 mM concentration)
Applied Current (I)	0.4	A	Baseline condition
Applied Voltage (V)	28	V	Average voltage (Baseline 3/11/20 & 3/27/20)
Best Fluoride Removal Rate	61.0	%	Achieved in 2 hours (using a new BDD plate)
Analytical Confidence (R²)	0.9991 to 0.9997	N/A	R² values for IC calibration curves

Key Methodologies

The optimized experimental procedure focused on electrochemical oxidation (EO) of PFOA, aiming for conditions suitable for eventual in situ remediation.

Solution Preparation: 400 mL of 10 mg/L PFOA solution was prepared using deionized water.
Electrolyte Dosing: 0.5684 g of sodium sulfate (Na₂SO₄) was added to achieve a low, optimized salt concentration of 1 mM.
Electrode Configuration: A BDD plate anode (46.57 cm²) and a matching steel plate cathode (46.57 cm²) were positioned 10 mm apart within the solution.
Power Application: A direct current (DC) power supply (Extech 382275) was used, set to 0.4 A, resulting in an average voltage of 28 V.
Agitation and Duration: The solution was agitated using a magnetic stir bar at 350 rpm. The reaction was run for 2 hours (or 6 hours for extended tests).
Analysis: Degradation was monitored by detecting temporal increases in fluoride (F^-) concentration using Ion Chromatography (IC), providing evidence of PFOA defluorination.
Variable Testing: Other variables tested included reduced current (0.2 A), lowered initial pH (to 2.46 using H₂SO₄), alternative salts (aluminum sulfate, sodium chloride), decreased electrode distance (6 mm), and the addition of potassium persulfate (EAP).

6CCVD Solutions & Capabilities

The research confirms that BDD is indispensable for PFAS abatement but highlights a critical need for highly durable, erosion-resistant electrodes. 6CCVD is uniquely positioned to address the material limitations encountered in this study, ensuring long-term performance and scalability for environmental applications.

Applicable Materials: Addressing BDD Wear

The observed BDD plate erosion is a direct consequence of the highly oxidative environment required for C-F bond cleavage. 6CCVD specializes in producing high-quality MPCVD BDD films engineered for extreme electrochemical stability.

6CCVD Material Solution	Specification & Benefit	Application Relevance
Heavy Boron-Doped PCD (BDD)	High sp³ content, optimized doping profile, and superior adhesion.	Maximizes hydroxyl radical generation and minimizes carbon erosion, extending electrode lifetime significantly for in situ remediation.
Custom BDD Thickness	SCD/PCD films available from 0.1 µm up to 500 µm.	Allows engineers to specify thicker, more robust BDD layers to withstand prolonged high-current density operation and abrasive wear.
Ultra-Low Roughness PCD	Polishing capability to Ra < 5 nm (Inch-size PCD).	Reduces surface defects that can act as initiation sites for erosion and ensures uniform current distribution across the active area.

Customization Potential: Scaling for Field Deployment

The study utilized 46.57 cm² plates. 6CCVD’s manufacturing capabilities easily exceed this requirement, enabling true industrial scale-up.

Large-Area Electrodes: 6CCVD provides BDD plates and wafers up to 125 mm in diameter, allowing for the fabrication of large-format electrode assemblies necessary for high-volume water treatment systems.
Custom Substrates: We offer BDD deposition on various conductive substrates (e.g., Niobium, Silicon) tailored for specific reactor designs and mechanical stability requirements.
Metalization Services: While the study used a steel cathode, future BDD-based systems may require robust electrical contacts. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for reliable integration into electrochemical cells.

Engineering Support: Optimizing Lifetime and Efficiency

The challenge of BDD plate wear (as seen in Figure 11) is a common hurdle in advanced electrochemical oxidation. 6CCVD’s in-house PhD team provides expert consultation to optimize material selection and design parameters for PFAS degradation projects.

Erosion Mitigation Strategies: We assist researchers in selecting BDD films with optimal doping concentrations and surface morphology to maximize radical efficiency while minimizing material loss.
Process Optimization: Consultation on current density limits and electrolyte compatibility to ensure the BDD anode operates within its optimal electrochemical window for maximum longevity.

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

View Original Abstract

Throughout the United States, there is a growing concern for contamination of groundwater with harmful per- and polyfluoroalkyl substances (PFAS). These forever chemicals have no natural degradation pathways and the science community has not had any significant breakthroughs to remediate contaminated sites. Electrochemical oxidation using a boron-doped diamond (BDD) electrode shows excellent potential for becoming an effective therapy for such PFAS contaminated sites. The objective of this research is to provide proof-of-concept that electrochemical oxidation can degrade PFAS, ensure analysis is accurate, and controls of experimental design are optimal. Electrochemical oxidation degraded 10 mg/L perfluorooctanoic acid (PFOA) under a series of controlled conditions. Overall removal rates were measure using ion chromatography and were as high as 60% after 2 hours of an experimental treatment. Unprecedented in similar studies, the technique cause erosion of the BDD anode, and as a result, the efficacy of treatment decreased.

Tech Support

Original Source

DOI: None