Continuous Production of Ethylene and Hydrogen Peroxide from Paired Electrochemical Carbon Dioxide Reduction and Water Oxidation

At a Glance

Metadata	Details
Publication Date	2024-03-14
Journal	Advanced Energy Materials
Authors	Sotirios Mavrikis, Matthian Nieuwoudt, Maximilian Göltz, Sophie Ehles, Andreas Körner
Institutions	Schaeffler (Germany), Forschungszentrum Jülich
Citations	17
Analysis	Full AI Review Included

Executive Summary

This research reports the first successful continuous paired electrosynthesis of high-value chemicals: Ethylene (C₂H₄) via Carbon Dioxide Reduction Reaction (CO₂RR) at the cathode, and Hydrogen Peroxide (H₂O₂) via Water Oxidation Reaction (WOR) at the anode.

Core Achievement: Simultaneous production of C₂H₄ and H₂O₂ in a divided flow reactor using a single pass of electric charge, maximizing electron utilization and preventing routine anodic waste (O₂ evolution).
Efficiency Metrics: The paired system achieved a combined Faraday Efficiency (FE) of 120% and a combined Energy Efficiency (EE) of 69% at an industrially relevant current density of 200 mA cm^-2.
Energy Savings: The overall Electrical Energy Consumption (EEC) was reduced by 50% compared to operating the C₂H₄ and H₂O₂ syntheses individually.
Catalyst Stability: The bespoke mixed Copper (Cu) nanowire/nanoparticle GDE cathode demonstrated C₂H₄ FE of 60% over 370 hours, while the Boron-Doped Diamond (BDD-a) anode maintained H₂O₂ FE of 60% over 350 hours (single-pass).
H₂O₂ Concentration: The BDD-a anode accumulated an unprecedented concentration of ~1% w/w H₂O₂ (250 mM) in 4 M K₂CO₃ with 8 g L^-1 Na₂SiO₃ stabilizer.
Economic Impact: A preliminary technoeconomic evaluation projects a 42% increase in Added Value (AV) for the paired system compared to non-paired electrochemical processes, resulting in a positive AV of €0.18 kg^-1Products.

Technical Specifications

Parameter	Value	Unit	Context
Paired System Performance
Combined Faraday Efficiency (FE)	120%	%	50 h stability test
Combined Energy Efficiency (EE)	69%	%	50 h stability test
Electrical Energy Consumption (EEC)	11.77	kWh kg^-1Products	50% reduction vs. non-paired
Applied Current Density (j)	200	mA cm^-2	Paired flow cell operation
Total Cell Voltage (E_cell)	~5	V	Paired flow cell operation
Catholyte Composition	1 M KOH / 2 M KI	-	Cathode compartment
Anolyte Composition	4 M K₂CO₃	-	Anode compartment
Cathode (12e CO₂RR) Performance
C₂H₄ Faraday Efficiency (FE)	60	%	Peak performance (370 h test)
C₂H₄ Stability Duration	370	h	Continuous chronopotentiometry
C₂H₄ EEC (Individual)	84.8	kWh kg^-1C₂H₄	Individual flow cell operation
Catalyst Morphology	Mixed Cu nanowire/nanoparticle	-	Bespoke GDE catalyst
Catalyst Loading	1	mg cm^-2	On Vulcan GDL substrate
Cu Nanowire Diameter	48 (σ = 12)	nm	Average diameter
Cu Nanocube Edge Length	69 (σ = 14)	nm	Average edge length
Anode (2e WOR) Performance
H₂O₂ Faraday Efficiency (FE)	63	%	Peak performance (300 mA cm^-2)
H₂O₂ Concentration (Peak)	250 (0.94% w/w)	mM	4 M K₂CO₃ + 8 g L^-1 Na₂SiO₃
H₂O₂ Stability Duration	350	h	Single-pass flow conditions
H₂O₂ Production Rate (Initial)	135	µmol cm^-2 min^-1	In 4 M K₂CO₃ at 9 V
Anode Material	Boron-Doped Diamond (BDD-a)	-	On Niobium (Nb) plate
BDD-a Boron Doping Level	12600	ppm	Quantified by GDOES
BDD-a Coating Thickness	1.6	µm	Microcrystalline morphology
BDD-a Average Facet Size	0.47	µm	Microcrystalline morphology

Key Methodologies

The paired electrosynthesis was conducted in a customized three-compartment electrochemical flow cell under single-pass, galvanostatic flow conditions.

Cathode Catalyst Synthesis (Mixed Cu):
- Copper nanowires and nanoparticles were synthesized via a chemical reduction method.
- The Cu catalyst ink was prepared by mixing the isolated nanopowder with toluene (1:5 mass ratio) and sonicating for 45 minutes.
Cathode Gas Diffusion Electrode (GDE) Fabrication:
- The catalyst ink was spray-deposited onto a Sigracet SGL 28 BC GDL (Vulcan carbon) using a suction feed airbrush.
- The GDE was coated in a circular motion, rotated 90° each cycle, until a catalyst loading of 1 mg cm^-2 was achieved. No PTFE binder was used in the catalyst layer.
Anode Catalyst Synthesis (BDD-a):
- Boron-Doped Diamond (BDD) films were grown on 1 mm thick Niobium (Nb) plates using a custom-built hot filament Chemical Vapor Deposition (HF-CVD) apparatus.
- The BDD-a variant, optimized for H₂O₂ production, had a boron doping level of 12600 ppm and a microcrystalline morphology (1.6 µm thickness).
Electrolyte Optimization:
- Catholyte (for CO₂RR): Optimized to 1 M KOH / 2 M KI mixture to enhance C₂H₄ selectivity by promoting *CO adsorption and C-C coupling.
- Anolyte (for WOR): Optimized to 4 M K₂CO₃ with 8 g L^-1 Na₂SiO₃ (peroxy-species stabilizer) to maximize H₂O₂ accumulation and stability.
Paired Flow Cell Operation:
- The cell utilized a Nafion 115 Cation Exchange Membrane (CEM) separating the cathode (Mixed Cu/GDE) and anode (BDD-a/Nb).
- The system was operated continuously for 50 hours at a constant current density of 200 mA cm^-2.
- CO₂ gas flowed through the GDE gas compartment (0.1-0.2 L min^-1), and electrolytes flowed through the liquid compartments (10 mL min^-1).
Product Quantification:
- Gaseous products (C₂H₄, H₂, CO, CH₄) were analyzed ex situ using Gas Chromatography (GC).
- Liquid H₂O₂ concentration was quantified using standard Potassium Permanganate (KMnO₄) titration and Quantofix Peroxide test strips.

Commercial Applications

The paired electrosynthesis system produces two high-demand industrial chemicals, C₂H₄ and H₂O₂, efficiently and simultaneously, enabling several key commercial pathways:

Product	Key Industrial Applications	Relevance to Paired System
Ethylene (C₂H₄)	Polymer production (Polyethylene, PVC), Ethylene Oxide (EO), Ethylene Glycol (EG), Styrene.	C₂H₄ is the world’s most produced organic compound; electrochemical synthesis offers a decentralized, low-carbon route.
Hydrogen Peroxide (H₂O₂)	Bleaching (pulp/paper/textiles), Water/Wastewater treatment (advanced oxidation processes), Disinfectant/Sterilization, Chemical synthesis.	On-site, decentralized H₂O₂ generation (avoiding transport risks) is highly desirable, especially for water treatment and sterilization.
Integrated Synthesis	Ethylene Oxide (C₂H₄O) production.	The electrosynthesized C₂H₄ and H₂O₂ can be used immediately for subsequent non-electrochemical transformations, such as the chemical production of C₂H₄O, maximizing atom economy.
Electrode Technology	High-performance flow reactors, Industrial electrochemistry, Wastewater remediation.	The BDD-a anode (optimized for HO˚ radical generation) is highly stable and effective for H₂O₂ production and organic contaminant degradation (demonstrated via Basic Fuchsine dye decolorization).

View Original Abstract

Abstract Paired electrolysis offers an auspicious strategy for the generation of high‐value chemicals, at both the anode and cathode, in an integrated electrochemical reactor. Through efficient electron utilization, routine product misuse at overlooked electrodes can be prevented. Here, an original paired electrosynthetic system is reported that can convert CO 2 to ethylene (C 2 H 4 ) at the cathode, and water to hydrogen peroxide (H 2 O 2 ) at the anode under a single pass of electric charge. Amongst various investigated copper (Cu) nanomorphologies, the bespoke mixed Cu nanowire/nanoparticle catalyst recorded a peak C 2 H 4 Faraday efficiency ( FE ) of 60% following 370 h of electrolysis at 200 mA cm −2 , while the tailored boron‐doped diamond (BDD) anode accumulated an unprecedented ≈1% w/w of H 2 O 2 in 4 m K 2 CO 3 upon applying 300 mA cm −2 for 10 h. When paired, the dual C 2 H 4 ‐H 2 O 2 electrochemical cell attains a combined FE of 120% for 50 h at 200 mA cm −2 , a combined energy efficiency (EE) of 69%, and a 50% decrease in the overall electrical energy consumption (EEC) compared to the individual electrosynthesis of C 2 H 4 and H 2 O 2 .

Tech Support

Original Source

DOI: https://doi.org/10.1002/aenm.202304247