Photo-assisted electrochemical CO2reduction at a boron-doped diamond cathode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Energy Advances |
| Authors | Goki Iwai, Andrea Fiorani, Jinglun Du, Yasuaki Einaga |
| Institutions | Keio University |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the development and performance analysis of a photo-assisted electrochemical (PEC) system designed for the efficient conversion of carbon dioxide (CO2) into formic acid (FA).
- Core Value Proposition: The system successfully couples photoelectrochemical water oxidation (using TiO2 NTs) with electrochemical CO2 reduction (using BDD) to significantly lower the required electrical energy input.
- High Efficiency: The Electrical-to-Chemical Energy Conversion Efficiency (ηECE) reached a stable 80% in the optimal operating range (1.3-1.5 V).
- Energy Saving: The use of the TiO2 NT photoanode reduced the total cell voltage (Etot) from 2.7 V (required for a dark electrolyzer) to 1.4 V, achieving a 52% saving in electrical energy input.
- Product Selectivity: The Boron-Doped Diamond (BDD) cathode maintained high selectivity, yielding a stable Faradaic Efficiency (FE) for formic acid production of approximately 86%.
- System Performance: The overall Energy Throughput Conversion Efficiency (ηPAE), which accounts for both light and electrical power input, was measured at 5.5%.
- Anode Performance: The TiO2 NT photoanode drove the oxygen evolution reaction (OER) at highly negative potentials (-0.75 V to -0.67 V vs. Ag/AgCl), confirming its effectiveness in reducing the overall cell bias.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Formic Acid Faradaic Efficiency (FEFA) | ~86 | % | Stable above 1.4 V Etot |
| Electrical-to-Chemical Efficiency (ηECE) | ~80 | % | Achieved in the range 1.3-1.5 V Etot |
| Photo-Assisted Electrolysis Efficiency (ηPAE) | 5.5 | % | Maximum overall energy conversion efficiency |
| Cell Voltage (Etot) Reduction | 2.7 to 1.4 | V | 52% saving compared to dark EC cell |
| Light Power Input | 25.2 | mW cm-2 | Used for two-electrode configuration |
| BDD Cathode Area | 9.62 | cm2 | Geometrical area |
| TiO2 NT Photoanode Area | 12.56 | cm2 | Geometrical area |
| TiO2 NT Diameter | 200 | nm | Structure confirmed by SEM |
| TiO2 NT Crystalline Phase | Anatase | - | Confirmed by XRD |
| TiO2 NT Band Gap | 3.4 ± 0.1 | eV | Measured via Kubelka-Munk theory |
| BDD Boron Concentration | 0.1 | % (B/C ratio) | Used during MPCVD deposition |
| Cathode Potential (at 1.4 V Etot) | -2.04 | V | vs. Ag/AgCl, KCl satâd |
| Anode Potential (Water Oxidation) | -0.75 to -0.67 | V | vs. Ag/AgCl, KCl satâd (PEC operation) |
Key Methodologies
Section titled âKey MethodologiesâThe photoelectrochemical system relies on precise fabrication and controlled operation of the BDD cathode and TiO2 NT photoanode:
- BDD Cathode Deposition: Polycrystalline BDD film was deposited on a Si (100) wafer using Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD). The boron concentration was fixed at 0.1% relative to carbon (B/C ratio).
- TiO2 NT Fabrication (Anodization): Titanium foil was oxidized in a fluorine electrolyte consisting of 1 M (NH4)H2PO4 and 0.5 wt% NH4F-HF. A constant DC voltage of 30 V was applied for 3 hours.
- Crystallization: The TiO2 NT plate was annealed at 450 °C for 1 hour to ensure the formation of the Anatase crystalline phase, critical for photoactivity.
- Electrochemical Cell: A two-chamber Polytetrafluoroethylene (PTFE) flow cell was used, separating the catholyte (0.5 M KCl) and anolyte (0.5 M KOH) with a Nafion NRE-212 membrane.
- Gas Saturation: The catholyte was saturated with CO2 (200 mL min-1 for 60 min) after initial N2 purging, and CO2 flow was maintained at 30 mL min-1 during electrolysis.
- PEC Operation: The system was operated in a two-electrode configuration (fixed Etot) under continuous light irradiation (25.2 mW cm-2).
- Characterization: Material quality was confirmed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Raman spectroscopy. The band gap (3.4 ± 0.1 eV) was determined using diffuse reflectance spectra and the Kubelka-Munk theory.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed in this study, leveraging BDD and TiO2 NTs for efficient CO2 conversion, is relevant to several high-value engineering sectors:
- Sustainable Chemical Manufacturing: Direct, low-energy synthesis of C1-synthons (formic acid) from CO2, serving as a key intermediate in the production of fine chemicals, pharmaceuticals, and organic synthesis.
- Renewable Energy Integration and Storage: Utilizing solar energy (via the PEC anode) to drive electrochemical processes, enabling the conversion of intermittent renewable electricity into stable, transportable chemical fuels (Power-to-X).
- Advanced Electrode Technology: The use of Boron-Doped Diamond (BDD) as a cathode material offers exceptional stability, corrosion resistance, and a wide potential window, making it suitable for industrial-scale electrochemical reactors operating under aggressive conditions.
- Photoelectrocatalysis (PEC): The highly efficient TiO2 NT photoanode design provides a blueprint for developing low-bias PEC cells, applicable in solar fuel production and highly efficient water splitting systems for hydrogen generation.
- Environmental Remediation: BDD electrodes are widely used in Advanced Oxidation Processes (AOPs) for wastewater treatment due to their ability to generate powerful hydroxyl radicals, a core application benefiting from the robust electrode development demonstrated here.
View Original Abstract
A photo-assisted electrochemical system converting CO 2 into formic acid by photoelectrochemical water oxidation at TiO 2 nanotubes coupled with electrochemical CO 2 reduction at boron-doped diamond.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2009 - Comprehensive Organic Name Reactions and Reagents