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6CCVD Research

Step-by-step guide for electrochemical generation of highly oxidizing reactive species on BDD for beginners

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-01-04
JournalFrontiers in Chemistry
AuthorsG. Xavier Castillo-Cabrera, Caroline I. Pliego-CerdĂĄn, Erika MĂŠndez, Patricio J. Espinoza-Montero
InstitutionsBenemĂŠrita Universidad AutĂłnoma de Puebla, Pontificia Universidad CatĂłlica del Ecuador
Citations18
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research provides a systematic, step-by-step guide for engineers and material scientists to optimize the electrochemical generation of Highly Oxidizing Reactive Species (HORS), primarily the hydroxyl radical (•OH), using Boron-Doped Diamond (BDD) anodes for Advanced Electrochemical Oxidation (AEO).

  • Optimization Methodology: The guide integrates BDD activation, Cyclic Voltammetry (CV) characterization, Sampled Current Voltammetry (SCV), and Tafel analysis to kinetically determine the ideal anodic overpotential (Ρ).
  • Optimal Conditions Identified: An overpotential of Ρ = 1.60 V (vs. Ag/AgCl) was identified as optimal, corresponding to the maximum current limit where charge transfer efficiency is maximized before the Oxygen Evolution Reaction (OER) dominates.
  • Radical Generation: Radical trapping studies (RNO method) confirmed that Ρ = 1.60 V produced the highest concentration of adsorbed hydroxyl radicals (BDD(•OH*)).
  • Degradation Performance: Applying this optimal potential resulted in the highest degradation efficiency for Amoxicillin (AMX), achieving 77.9% Chemical Oxygen Demand (COD) removal in 6 hours in a Na2SO4 medium.
  • Kinetic Insights: Tafel analysis revealed three distinct kinetic regions: a capacitive region (946 mV dec-1), an intermediate HORS generation region (458 mV dec-1), and the OER-predominant region (370 mV dec-1).
  • Efficiency Metrics: The optimal process achieved the highest Instantaneous Current Efficiency (ICE = 0.69) and the lowest energy consumption (0.224 kWh m-3).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Optimal Anodic Overpotential (η)1.60Vvs. Ag/AgCl, for max •OH production
Maximum COD Removal77.9%Amoxicillin (40 ÂľM) degradation (6 h)
Maximum AMX Removal39.9%Amoxicillin (40 ÂľM) degradation (6 h)
Optimal Energy Consumption0.224kWh m-3At Ρ = 1.60 V
Optimal Operating Cost0.022USD m-3Based on Ecuador electricity prices
Maximum Instantaneous Current Efficiency (ICE)0.69DimensionlessAt Ρ = 1.60 V
Tafel Slope (HORS Region)458 Âą 16mV dec-1Intermediate overpotential zone (~1.1 V to ~1.3 V)
Tafel Slope (OER Region)370 Âą 11mV dec-1Overpotential > 1.3 V
BDD Activation Current Density0.1A cm-2Anodic polarization in 0.5 mol L-1 H2SO4
BDD Electrode Area (Effective)6.0cm2Experimental cell setup
Hydroxyl Radical (•OH) Oxidizing Power~2.73Vvs. NHE
Sulfate Radical (SO4•-) Oxidizing Power2.5 to 3.1Vvs. NHE

Key Methodologies

Section titled “Key Methodologies”

The systematic approach for optimizing BDD performance involves five core steps, primarily relying on kinetic electrochemical analysis:

  1. Electrode Activation:

    • New BDD electrodes are activated via anodic polarization (10 min) in 0.5 mol L-1 H2SO4 at 0.1 A cm-2 to ensure an oxygen-terminated surface (O-activated).

  2. Electrode Characterization (CV):

    • Cyclic Voltammetry (CV) is performed in the supporting electrolyte (0.1 mol L-1 Na2SO4) to determine the full potential window and identify the inflection point (onset of OER/intermediate reactions, ~1.20 V vs. Ag/AgCl).
    • CV using the [Fe(CN)6]3-/[Fe(CN)6]4- redox couple is used to confirm surface termination (large ΔEp indicates O-termination).

  3. Kinetic Analysis (SCV and Tafel Plot):

    • Polarization curves (current density, j, vs. time, t) are generated using Sampled Current Voltammetry (SCV) across the oxidation overpotential range (0.4 V to 1.8 V).
    • Small time constants (τ = 0.3 s to 1.0 s) are selected from the SCV data to ensure the measurements are kinetic-controlled (Faradaic current).
    • The Tafel plot (log j vs. Ρ) is constructed to identify the overpotential region (458 mV dec-1 slope) where HORS generation is kinetically favored over OER.

  4. Radical Trapping and Validation:

    • The N,N-Dimethyl-4-nitroso-aniline (RNO) method is used to quantify the concentration of generated •OH radicals at various overpotentials (e.g., 1.45 V, 1.60 V, 1.70 V).
    • The potential yielding maximum •OH concentration (Ρ = 1.60 V) is selected as the optimal limiting potential for AEO.

  5. AEO Performance Evaluation:

    • Amoxicillin degradation is carried out at the optimal overpotential (Ρ = 1.60 V).
    • Performance is quantified by monitoring pollutant removal (AMX concentration), mineralization (COD removal), Instantaneous Current Efficiency (ICE), and energy consumption (kWh m-3).

Commercial Applications

Section titled “Commercial Applications”

The methodologies and findings presented are highly relevant for industrial processes requiring efficient electrochemical oxidation, particularly those utilizing BDD as a stable, non-active anode material.

  • Wastewater Treatment:
    • Pharmaceutical Degradation: Efficient removal and mineralization of persistent organic pollutants (POPs), including antibiotics and endocrine disruptors, from industrial and municipal wastewater streams.
    • COD/BOD Reduction: Optimization of AEO processes for achieving stringent discharge limits by maximizing mineralization efficiency (e.g., 77.9% COD removal demonstrated).
  • Electrode Manufacturing and Quality Control:
    • BDD Surface Engineering: Standardized electrochemical methods (anodic/cathodic polarization) for controlling BDD surface termination (H-activated vs. O-activated) based on application requirements (e.g., O-termination for enhanced HORS generation).
    • Kinetic Benchmarking: Use of Tafel analysis and SCV as reliable, non-RDE (Rotating Disk Electrode) techniques for rapid kinetic benchmarking and quality assurance of new electrode materials.
  • Chemical and Electrochemical Synthesis:
    • Controlled Radical Generation: Utilizing the identified optimal overpotential to selectively generate high concentrations of specific HORS (•OH, SO4•-, Cl•) for use as powerful, in-situ generated oxidants in organic electrosynthesis.
  • Process Scaling and Economics:
    • Limiting Current Determination: The methodology provides a robust way to determine the limiting current density (ilim) necessary for scaling up AEO reactors while maintaining high ICE and minimizing energy costs (e.g., 0.022 USD m-3).
View Original Abstract

Selecting the ideal anodic potential conditions and corresponding limiting current density to generate reactive oxygen species, especially the hydroxyl radical ( • OH), becomes a major challenge when venturing into advanced electrochemical oxidation processes. In this work, a step-by-step guide for the electrochemical generation of • OH on boron-doped diamond (BDD) for beginners is shown, in which the following steps are discussed: i) BDD activation (assuming it is new), ii) the electrochemical response of BDD (in electrolyte and ferri/ferro-cyanide), iii) Tafel plots using sampled current voltammetry to evaluate the overpotential region where • OH is mainly generated, iv) a study of radical entrapment in the overpotential region where • OH generation is predominant according to the Tafel plots, and v) finally, the previously found ideal conditions are applied in the electrochemical degradation of amoxicillin, and the instantaneous current efficiency and relative cost of the process are reported.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2008 - Influence of the surface termination on the electrochemical properties of boron-doped diamond (BDD) interfaces [Crossref]
  2. 2022 - Recent developments in hazardous pollutants removal from wastewater and water reuse within a circular economy [Crossref]
  3. 2022 - Fundamentals and advances on the mechanisms of electrochemical generation of persulfate and sulfate radicals in aqueous medium [Crossref]
  4. 2015 - Standard electrode potentials involving radicals in aqueous solution: inorganic radicals (IUPAC Technical Report) [Crossref]
  5. 2022 - Effect of electrode parameters in the electro-production of reactive oxidizing species via boron-doped diamond under batch mode [Crossref]
  6. 2022 - Electrochemical methods fundamentals and applications
  7. 2023 - Chlorine redox chemistry is widespread in microbiology [Crossref]
  8. 2019 - Electro-oxidation of cyanide on active and non-active anodes: designing the electrocatalytic response of cobalt spinels [Crossref]
  9. 2021 - Synthesis and electrochemical characterization of Si/TiO2/Au composite anode: efficient oxygen evolution and hydroxyl radicals generation [Crossref]
  10. 2009 - Electro-fenton process and related electrochemical technologies based on fenton’s reaction chemistry [Crossref]

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