Parallel paired electrolysis of green oxidizing agents by the combination of a gas diffusion cathode and boron-doped diamond anode

At a Glance

Metadata	Details
Publication Date	2024-02-08
Journal	Frontiers in Catalysis
Authors	Christin M. Hamm, Selina Schneider, Stefanie Hild, Rieke Neuber, Thorsten Matthée
Institutions	Covestro (Germany), Society for Chemical Engineering and Biotechnology
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Paired Electrolysis using BDD Anodes

Executive Summary

This research successfully demonstrates the first proof-of-concept for parallel paired electrolysis combining cathodic Peracetic Acid (PAA) synthesis on Gas Diffusion Electrodes (GDEs) and anodic Peroxodicarbonate (PODIC®) synthesis on Boron-Doped Diamond (BDD) electrodes.

Core Achievement: Simultaneous generation of two high-value “green” oxidizing agents (PAA and PODIC®) in a single electrochemical cell, aiming for a combined current efficiency (CE) of 200%.
BDD Performance: The BDD anode achieved a maximum PODIC® concentration of 42.7 mmol L^-1 with a high half-cell Current Efficiency (CE) of 30.3% at 20 mA cm^-2.
Material Validation: The study confirms BDD as the superior anode material for high-potential electrochemical synthesis, specifically for the stable production of peroxodicarbonates from highly concentrated carbonate solutions (5.0 M K₂CO₃).
Scaling Demonstrated: Experiments were successfully scaled up from 24 cm² planar BDD to a 35 cm² structured BDD electrode on a silicon substrate for flow cell integration.
Future Optimization: While the paired cell CE was lower than half-cell results (14% for PODIC®, 2.0% for PAA), the study identifies pH control and electrode structure optimization as key areas for improvement, directly addressable by 6CCVD’s custom BDD engineering.

Technical Specifications

The following data points were extracted from the half-cell optimization experiments and the final paired electrolysis setup, highlighting the performance metrics achieved using the BDD anode.

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Anodic synthesis of PODIC®
Cathode Material	Carbon Black (CB) GDE	N/A	Cathodic synthesis of PAA/H₂O₂
Max PODIC® Concentration (Half-Cell)	42.7	mmol L^-1	Planar BDD (24 cm²), 5.0 M K₂CO₃
Max PODIC® Current Efficiency (Half-Cell)	30.3	%	Planar BDD (24 cm²), j=20 mA cm^-2
Max PAA Concentration (Half-Cell)	22.6	mmol L^-1	CB GDE (24 cm²), 2.5 M CH₃COOH/CH₃COOK
Max PAA Current Efficiency (Half-Cell)	7.4	%	CB GDE (24 cm²), j=20 mA cm^-2
Paired Cell Electrode Area (Geometrical)	35	cm²	Structured BDD on Si substrate
Paired Cell Current Density (j)	50	mA cm^-2	Applied to 35 cm² area
Paired Cell PODIC® Concentration	75	mmol L^-1	Max concentration achieved (CE 14%)
Optimal Anolyte Composition	5.0 M K₂CO₃	M	For high PODIC® yield
Optimal Catholyte Composition	2.5 M CH₃COOH/CH₃COOK (1:1)	M	For high PAA yield

Key Methodologies

The electrochemical synthesis was conducted in two phases: half-cell optimization followed by integration into a parallel paired flow cell.

Initial Screening: Gas Diffusion Electrodes (GDEs) were screened in an H-cell setup (5 cm² area) using 0.5 M Na₂SO₄ to identify optimal carbon materials (Carbon Black and Carbon Nanotubes selected) for H₂O₂ production.
Half-Cell Optimization (24 cm²): Flow reactors were designed for both the GDE cathode and the BDD anode, separated by a Nafion 115 membrane.
Anodic Optimization (BDD): Planar BDD electrodes (24 cm² geometrical area) were used to investigate PODIC® formation under varying K₂CO₃ concentrations (up to 5 M) at current densities up to 100 mA cm^-2.
Cathodic Optimization (GDE): CB GDEs (24 cm² geometrical area) were used to optimize PAA synthesis via H₂O₂ using various acetate/acetic acid electrolytes.
Paired Cell Integration (35 cm²): A custom flow cell was assembled using a structured BDD electrode on a silicon substrate (35 cm² geometrical area) and a GDE cathode (35 cm² area).
Paired Cell Operation: The cell was operated at a fixed current density of 50 mA cm^-2 for 2 hours, combining the optimal 5 M K₂CO₃ anolyte and 2.5 M CH₃COOH/CH₃COOK catholyte.

6CCVD Solutions & Capabilities

The successful implementation of this paired electrolysis system relies critically on the quality, size, and structure of the Boron-Doped Diamond (BDD) anode. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate and scale this research.

Applicable Materials

To achieve the high current densities and chemical stability required for peroxodicarbonate synthesis, researchers need high-quality, defect-free BDD.

Heavy Boron-Doped PCD/BDD: 6CCVD provides highly conductive, heavy boron-doped polycrystalline diamond (PCD) and single-crystal diamond (SCD) materials. These are essential for maximizing the overpotential required for the anodic formation of PODIC® while maintaining long-term stability against oxygen evolution.
Electrochemical Grade BDD: Our BDD materials are optimized for electrochemical applications, offering superior chemical inertness and stability in highly concentrated, alkaline electrolytes (e.g., 5.0 M K₂CO₃) compared to traditional electrode materials (e.g., Pt).

Customization Potential

The paper utilized both 24 cm² planar BDD and a 35 cm² structured BDD on a silicon substrate. 6CCVD’s manufacturing capabilities directly address these specific requirements, enabling rapid scale-up and design iteration.

Research Requirement	6CCVD Capability	Technical Advantage
Large Area Electrodes	Plates/wafers up to 125mm (PCD/BDD).	Easily accommodates the 35 cm² area used, allowing for future scale-up to pilot or industrial dimensions.
Structured BDD on Si	Custom BDD deposition on various substrates (Si, Ta, Nb).	We can replicate or optimize the structured flow channel design used in the paired cell for improved mass transport and current distribution.
Custom Dimensions	Custom laser cutting and shaping services.	Precise fabrication of electrodes to fit proprietary flow cell designs (e.g., EUT flow cell used in the study).
Metalization Layers	Internal capability for Au, Pt, Ti, W, Cu metalization.	We can apply custom contact layers (e.g., Ti/Pt/Au stacks) directly onto the BDD surface, ensuring low contact resistance for efficient current delivery at high densities (up to 100 mA cm^-2).
Surface Finish	Polishing capability to Ra < 5nm (PCD/BDD).	Optimized surface morphology can be provided to study the effect of roughness on reaction selectivity and stability, addressing the need for improved local current density distribution.

Engineering Support

The observed drop in Current Efficiency (CE) when transitioning from half-cell to the paired cell highlights the complexity of integrating two high-performance reactions. The authors specifically cite changes in pH and electrode structure as potential causes.

6CCVD’s in-house PhD team specializes in MPCVD diamond engineering and can assist researchers in optimizing material selection for similar Paired Electrochemical Synthesis projects:

Doping Optimization: Fine-tuning boron concentration to balance conductivity and electrochemical activity, maximizing the overpotential for PODIC® formation while suppressing parasitic reactions.
Substrate Selection: Consulting on the optimal substrate (e.g., Si vs. Ta) and BDD thickness (0.1 µm to 500 µm) for mechanical stability and thermal management in high-power flow cells.
Flow Cell Design Integration: Providing BDD electrodes pre-metalized and cut to precise specifications, ensuring seamless integration into complex reactor architectures.

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

View Original Abstract

The generation of “green” oxidizing agents by electrochemical synthesis opens the field for sustainable, on-demand, and on-site production, which is often based on non-critical starting materials. In this study, electrosyntheses were carried out on different cathode and anode materials. In half-cell experiments, the cathodic synthesis of peracetic acid (PAA) was investigated on gas diffusion electrodes (GDEs), reaching 22.6 mmol L −1 of PAA with a current efficiency (CE) of 7.4%. Moreover, peroxodicarbonate (PODIC ® ) was produced anodically on boron-doped diamond (BDD) electrodes with concentrations as high as 42.7 mmol L −1 PODIC ® and a CE of 30.3%. Both cathodic and anodic processes were individually examined and improved. Finally, the half-cell reactions were combined as a proof of concept in a parallel paired electrolysis cell for the first time to achieve an increased overall CE.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fctls.2024.1323322

References

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