Electrochemical decarboxylation of acetic acid on boron-doped diamond and platinum-functionalised electrodes for pyrolysis-oil treatment
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Faraday Discussions |
| Authors | Talal Ashraf, Ainoa Paradelo RodrĂguez, Bastian Mei, Guido Mul |
| Institutions | Ruhr University Bochum, University of Twente |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Value Proposition: This research establishes a highly stable and tunable electrochemical platform using Boron-Doped Diamond (BDD) electrodes for the decarboxylation of acetic acid, a critical step in upgrading acidic pyrolysis oil feedstocks.
- Bare BDD Performance: Unmodified BDD electrodes promote indirect oxidation via hydroxyl radicals, achieving high Faradaic Efficiency (FE) (up to 90%) towards high-value oxygenates, primarily methanol and methyl acetate.
- Selectivity Tuning (Pt Films): Functionalizing BDD with thin Platinum (Pt) films (thickness >20 nm) successfully shifts the reaction mechanism to Kolbe electrolysis, yielding ethane (a C-C coupling product) with FE >70%.
- Substrate Stability: BDD demonstrated exceptional stability, maintaining a stable potential (3.6 VRHE) and negligible corrosion, making it superior to conventional substrates like Graphite, FTO, and Nickel Foam for high-potential electrolysis.
- Nanoparticle Geometry Impact: The shape of electrodeposited Pt nanoparticles critically determines selectivity. Pt nano-thorns achieved the highest Kolbe selectivity (43% ethane FE) among tested nanoparticles, while porous nanoflowers favored the competitive Oxygen Evolution Reaction (OER).
- Mechanistic Insight (ECMS): Electrochemical Mass Spectrometry (ECMS) confirmed that bare BDD exhibits overlapping OER and decarboxylation onsets, whereas Pt/BDD successfully separates these reactions in potential, enabling better control over Kolbe product formation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| BDD Doping Level | 2000-5000 | ppm | Boron concentration in diamond lattice |
| BDD Coating Thickness | 15 | nm | On 2 mm Tantalum substrate |
| Standard Current Density | 25 | mA cm-2 | Used for batch cell electrolysis |
| Maximum Flow Cell Current Density | 100 | mA cm-2 | Highest tested condition (pH 5) |
| Bare BDD FE (Methanol) | up to 90 | % | Achieved at current densities >50 mA cm-2 |
| Bare BDD Stability Potential | 3.6 | VRHE | Stable potential during chronopotentiometry |
| Pt Thin Film Thickness (Kolbe Selective) | >20 | nm | Required for Ethane FE >70% |
| Pt Thin Film Ethane FE (Max) | >70 | % | For 20, 50, and 100 nm Pt layers on BDD |
| Pt Nano-Thorn (ED-C) Ethane FE | 43 ± 1.9 | % | Highest Kolbe selectivity among NPs |
| Pt Nanoflower (ED-A) OER FE | up to 50 | % | Initial OER dominance |
| Pt/BDD OER Onset Potential | 1.98 | VRHE | 5 nm sputtered Pt/BDD (ECMS) |
| Bare BDD OER Onset Potential | 2.136 | VRHE | ECMS measurement |
| Diamond Phonon Line Shift (Post-Electrolysis) | 1312 to 1323 | cm-1 | Indicates slight change in boron concentration |
| Estimated Boron Doping Concentration | 5.66 x 1020 | cm-3 | Calculated via Raman spectroscopy correlation |
Key Methodologies
Section titled âKey MethodologiesâThe study employed a combination of advanced material fabrication and electrochemical analysis techniques:
- BDD Electrode Preparation: Commercial BDD electrodes (DIACHEMÂź) on tantalum were cleaned using a rigorous protocol: washing, ultrasonication, and anodic polarization (30 minutes in 1 M HClO4).
- Pt Thin Film Fabrication: Platinum layers (5, 20, 50, 100 nm) were deposited onto cleaned BDD substrates using a sputtering system (AJA International).
- Pt Nanoparticle Synthesis (Electrodeposition): Four distinct Pt nanoparticle geometries (ED-A nanoflowers, ED-B dispersed, ED-C nano-thorns, ED-D nanocrystals) were electrodeposited by varying the Pt salt solution (H2PtCl6 or K2PtCl4) and applied potential/time (e.g., -0.24 VAg/AgCl for 15 min for ED-A).
- Electrolysis Setup: Experiments were conducted in a custom-made glass batch cell or a divided flow cell (Condias Synthesis kit) using a Nafion 324 cation exchange membrane.
- Electrolysis Conditions: Constant current (chronopotentiometry) was applied at 25 mA cm-2 (batch) or up to 100 mA cm-2 (flow) in 1 M acetic acid/sodium acetate electrolyte (pH 5).
- Gas Product Quantification: Online Gas Chromatography (GC) was used for continuous monitoring of volatile products (CH4, C2H4, C2H6, H2, O2, CO2) using FID and TCD detectors.
- Liquid Product Quantification: Methanol and methyl acetate were detected by Headspace GC-FID after collecting and neutralizing electrolyte aliquots.
- In Situ Reaction Monitoring: Electrochemical Mass Spectrometry (ECMS) was utilized during Cyclic Voltammetry (CV) to provide instantaneous, potential-dependent detection of volatile and semi-volatile products.
- Surface Characterization: Scanning Electron Microscopy (SEM) was used to visualize Pt morphology and BDD surface structure. Raman spectroscopy was used to assess BDD stability and boron doping levels before and after electrolysis.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology, leveraging the stability and unique electrochemical properties of BDD, is highly relevant for sustainable chemical production and industrial waste treatment:
- Biomass Upgrading and Biofuel Production:
- Pyrolysis Oil Refining: Direct electrochemical reduction of the high carboxylic acid content in crude pyrolysis oil, reducing corrosivity and improving the quality of the bio-oil for subsequent catalytic refining.
- Methanol and Ester Synthesis: Utilizing bare BDD electrodes for the selective conversion of low-value organic acids into high-value chemical intermediates like methanol and methyl acetate.
- Specialty Chemical Synthesis (Kolbe Electrolysis):
- Hydrocarbon Production: Employing Pt-functionalized BDD electrodes to perform the Kolbe reaction, converting organic acids into longer-chain hydrocarbons (e.g., ethane) for use as fuels or chemical building blocks.
- Advanced Electrode Manufacturing:
- High-Stability Anodes: BDD serves as an ideal, corrosion-resistant substrate for depositing active electrocatalysts (like Pt), extending electrode lifetime and efficiency in highly oxidative or acidic industrial environments where traditional metal electrodes fail.
- Wastewater Treatment (General BDD Application):
- While the focus is synthesis, the inherent stability of BDD at high potentials makes it a benchmark material for advanced oxidation processes (AOPs) used in treating recalcitrant organic pollutants.
View Original Abstract
Tuning the surface of boron-doped diamond functionalised with platinum nanoparticles and thin films alters the selectivity of hydroxyl-radical-mediated indirect electrooxidation of acetic acid to the Kolbe product.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2014 - Encyclopedia of Applied Electrochemistry [Crossref]