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

Executive Summary

This research demonstrates the feasibility of a parallel paired electrolysis cell for the simultaneous, sustainable production of two “green” oxidizing agents: Peracetic Acid (PAA) and Peroxodicarbonate (PODIC®).

Core Technology: The system combines a Gas Diffusion Electrode (GDE) cathode for the indirect synthesis of PAA (via H₂O₂) and a Boron-Doped Diamond (BDD) anode for the synthesis of PODIC®.
Optimized Cathodic Performance (Half-Cell): Using a Carbon Black (CB) GDE in 2.5 M CH₃COOH/CH₃COOK, a PAA concentration of 22.6 mmol L^-1 was achieved, corresponding to a Current Efficiency (CE) of 7.4%.
Optimized Anodic Performance (Half-Cell): Using a planar BDD electrode in 5.0 M K₂CO₃, a PODIC® concentration of 42.7 mmol L^-1 was achieved, corresponding to a CE of 30.3%.
Paired Electrolysis Proof-of-Concept: The half-cell reactions were successfully integrated into a 35 cm² flow cell setup, demonstrating simultaneous production of both agents for the first time.
Performance Gap: The combined cell showed significantly reduced efficiency compared to the optimized half-cells (e.g., PAA CE dropped to 2.0% or less), attributed primarily to unfavorable alkaline pH conditions in the catholyte and changes in BDD electrode structure (planar vs. structured).
Future Outlook: The study establishes a promising foundation, highlighting the need for future work focusing on cell design optimization and maintaining stable acidic catholyte conditions.

Technical Specifications

Parameter	Value	Unit	Context
Cathode Material (Screened Best)	Carbon Black (CB)	GDE	H₂O₂ synthesis
Anode Material	Boron-Doped Diamond (BDD)	Electrode	PODIC® synthesis
GDE H₂O₂ CE (Max)	84%	%	CB GDE, j = 20 mA cm^-2
Half-Cell PAA Concentration (Max)	22.6	mmol L^-1	CB GDE, 2.5 M CH₃COOH/CH₃COOK
Half-Cell PAA Current Efficiency (Max)	7.4	%	CB GDE, j = 20 mA cm^-2, 3 h
Half-Cell PODIC® Concentration (Max)	42.7	mmol L^-1	Planar BDD, 5.0 M K₂CO₃
Half-Cell PODIC® Current Efficiency (Max)	30.3	%	Planar BDD, j = 20 mA cm^-2, 2 h
Electrolyte Separator	Nafion 115	Membrane	All half-cell and paired setups
Electrode Area (Half-Cell Optimization)	24	cm²	GDE and BDD setups
Electrode Area (Paired Cell)	35	cm²	Structured BDD and GDE
Current Density (Paired Cell)	50	mA cm^-2	Geometrical surface area basis
Paired Cell Anolyte (PODIC®)	5.0 M	K₂CO₃	150 mL volume
Paired Cell Catholyte (PAA)	2.5 M CH₃COOH/CH₃COOK (1:1)	Mixture	150 mL volume
Paired Cell PAA Concentration (Max)	11.3	mmol L^-1	CNT GDE, 2 h electrolysis
Paired Cell PODIC® Concentration (Max)	75	mmol L^-1	Structured BDD, 2 h electrolysis
Paired Cell Catholyte pH (End)	10 to 11	pH	After 2 h synthesis

Key Methodologies

Initial GDE Material Screening: Five different carbon-based GDEs (Graphite, Carbon Black (CB), Carbon Nanotubes (CNTs), Carbon Fiber, Glassy Carbon, plus Silver-doped CNTs) were screened in an H-cell setup (5 cm² area) using 0.5 M Na₂SO₄ electrolyte for H₂O₂ production.
Half-Cell Optimization (24 cm²): Optimized GDEs (CB and CNT) and planar BDD were tested in a flow reactor setup (24 cm² active area) separated by a Nafion 115 membrane.
PAA Synthesis Optimization: Catholyte composition was varied, testing different aqueous alkaline acetate salt solutions and mixtures (e.g., 2.5 M CH₃COOH/CH₃COOK) to maximize PAA yield at a fixed current density (20 mA cm^-2).
PODIC® Synthesis Optimization: Anolyte concentration was varied up to 5 M K₂CO₃ on planar BDD electrodes to determine the optimal conditions for peroxodicarbonate formation (20 mA cm^-2).
Paired Electrolysis Integration: The optimized half-cell reactions were combined in a custom-designed EUT flow cell (35 cm² geometrical area). This setup utilized a structured BDD anode and a GDE cathode (CB or CNT) separated by Nafion 115.
Process Conditions (Paired Cell): Electrolysis was conducted at a current density of 50 mA cm^-2 for 2 hours, using 5 M K₂CO₃ (anolyte) and 2.5 M CH₃COOH/CH₃COOK (catholyte).
Product Quantification: PAA was quantified via a two-step titration (Ce(SO₄)₂ followed by iodometry). H₂O₂ and PODIC® were quantified via iodine titration.

Commercial Applications

The technology developed, leveraging BDD and GDE in a paired electrolysis setup, is highly relevant for sustainable chemical manufacturing and on-site generation of critical reagents.

Water and Wastewater Treatment: BDD electrodes are highly effective for Advanced Oxidation Processes (AOPs). The ability to generate strong oxidizers (PAA and PODIC®) on-site eliminates transport and storage risks associated with traditional disinfectants.
Disinfection and Sterilization: PAA is a widely used, effective disinfectant in healthcare, food processing, and agriculture. On-demand electrochemical synthesis supports safer, decentralized supply chains.
Green Chemical Synthesis: PODIC® (peroxodicarbonate) is a powerful, eco-friendly oxidizer used for N- and S-oxidations and epoxidations, offering a sustainable alternative to hazardous chemical oxidants.
Electrochemical Reactor Design: The study provides critical data on integrating dissimilar electrode materials (BDD and GDE) and managing complex electrolyte conditions (pH shifts, high salt concentration) in industrial flow cell designs.
BDD Electrode Technology: The use of structured BDD (DIACHEM® by CONDIAS GmbH) highlights its application in high-surface-area flow reactors for high-current-density processes, particularly those requiring high anodic stability.

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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