Electrochemical deposition of bimetallic sulfides on novel BDD electrode for bifunctional alkaline seawater electrolysis
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-01-22 |
| Journal | Scientific Reports |
| Authors | Mingxu Li, Genjie Chu, Jiyun Gao, Xiaolei Ye, Ming Hou |
| Institutions | Centre National de la Recherche Scientifique, Université Marie et Louis Pasteur |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel, corrosion-resistant electrode system (CoFeS/Ni/BDD) designed for highly efficient bifunctional alkaline seawater electrolysis.
- Novel Substrate Utilization: Boron-Doped Diamond (BDD) is employed as the substrate due to its exceptional corrosion resistance, addressing the critical issue of metal substrate degradation in harsh seawater environments.
- Enhanced Catalyst Adhesion: A two-step electrodeposition method was developed, utilizing a Nickel (Ni) interlayer to ensure strong adhesion of the active Cobalt-Iron Sulfide (CoFeS) catalyst layer to the BDD surface.
- Optimized Bifunctional Performance: The optimized electrode achieved significantly low overpotentials in alkaline simulated seawater (3 M KOH + 3.5 wt% NaCl) at 100 mA/cm2: 300 mV for the Hydrogen Evolution Reaction (HER) and 383 mV for the Oxygen Evolution Reaction (OER).
- Kinetic Improvement via Concentration: Increasing the KOH concentration from 1 M to 3 M in the simulated seawater significantly enhanced catalytic kinetics, reducing the OER Tafel slope from 182.30 mV/dec to 110.58 mV/dec.
- High Stability: The CoFeS/Ni/BDD electrode demonstrated robust stability over 24 hours in real seawater (1 M KOH), retaining 92.62% of its initial current density for OER.
- Morphological Advantage: The cauliflower-like Ni layer and subsequent CoFeS deposition created a high specific surface area (ECSA of 3.399 x 10-2 mF/cm2), facilitating faster charge transfer (lowest Rct).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Boron-Doped Diamond (BDD) | N/A | Corrosion-resistant base |
| Optimal Co/Fe Ratio | 1.5:1 | N/A | Catalyst Deposition |
| Optimal Deposition Cycles | 15 | Cycles | CV Electrodeposition |
| HER Overpotential (Standard) | 360 | mV | 1 M KOH + Sea, 100 mA/cm2 |
| OER Overpotential (Standard) | 425 | mV | 1 M KOH + Sea, 100 mA/cm2 |
| HER Overpotential (Optimized) | 300 | mV | 3 M KOH + Sea, 100 mA/cm2 |
| OER Overpotential (Optimized) | 383 | mV | 3 M KOH + Sea, 100 mA/cm2 |
| HER Tafel Slope (1 M KOH + Sea) | 130.81 | mV/dec | Reaction Kinetics |
| OER Tafel Slope (1 M KOH + Sea) | 182.30 | mV/dec | Reaction Kinetics |
| Optimized OER Tafel Slope (3 M KOH + Sea) | 110.58 | mV/dec | Fastest OER Kinetics |
| Electrochemically Active Surface Area (ECSA) | 3.399 x 10-2 | mF/cm2 | CoFeS/Ni/BDD |
| OER Stability Retention (24 h) | 92.62 | % | 1 M KOH + Real Seawater |
| HER Stability Retention (24 h) | 84.31 | % | 1 M KOH + Real Seawater |
| Ni3S2 Crystal Spacing | 0.204 | nm | (200) Crystallographic Orientation |
Key Methodologies
Section titled âKey MethodologiesâThe CoFeS/Ni/BDD electrode was synthesized using a two-step electrodeposition process optimized for adhesion and catalytic activity, followed by comprehensive electrochemical and structural analysis.
Electrode Fabrication (CoFeS/Ni/BDD Synthesis)
Section titled âElectrode Fabrication (CoFeS/Ni/BDD Synthesis)â- Nickel Interlayer Electroplating: A Ni layer was deposited onto the BDD substrate to improve the adhesion of the subsequent sulfide layer. This resulted in a cauliflower-like columnar structure, increasing surface area.
- CoFeS Active Layer Electrodeposition: Cobalt-iron sulfide was deposited onto the Ni/BDD using Cyclic Voltammetry (CV).
- Electrolyte: Contained CoCl2, FeCl3, and thiourea (CH4N2S).
- Optimization: The optimal recipe involved a Co/Fe concentration ratio of 1.5, a scan rate of 5 mV/s, and 15 total electrodeposition cycles (scan range: -0.6 V to 0.2 V).
Electrochemical Testing
Section titled âElectrochemical Testingâ- System: Standard three-electrode setup (CoFeS/Ni/BDD working electrode, Hg/HgO or Ag/AgCl reference, carbon rod counter).
- Electrolytes:
- Standard: 1 M KOH solution.
- Simulated Seawater: 1 M KOH + 3.5 wt% NaCl, or 3 M KOH + 3.5 wt% NaCl (for optimization).
- Techniques Used:
- Linear Sweep Voltammetry (LSV) for HER/OER performance and Tafel slope derivation.
- Electrochemical Impedance Spectroscopy (EIS) to determine charge transfer resistance (Rct).
- Chronoamperometry (i-t method) for 24-hour stability testing.
Material Characterization
Section titled âMaterial Characterizationâ- Structural Analysis: X-ray Diffraction (XRD) confirmed the presence of diamond (111), Ni, Ni-Co-S, and Ni3S2 phases. Iron sulfide was assumed to be amorphous.
- Morphology and Composition: Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) confirmed the lamellar CoFeS material dispersed over the columnar Ni structures.
- Microstructural Detail: High-Resolution Transmission Electron Microscopy (HRTEM) identified crystal spacings corresponding to Ni3S2 and Ni-Co-S grains.
- Chemical Bonding: Raman spectroscopy detected characteristic M-S bonds (Fe-S and Co-S stretching vibrations).
- Wettability: Contact angle measurement confirmed the high hydrophilicity of the CoFeS/Ni/BDD surface (20.2°).
Commercial Applications
Section titled âCommercial ApplicationsâThe development of highly stable, bifunctional catalysts on corrosion-resistant BDD substrates is critical for advancing industrial-scale clean energy technologies.
- Green Hydrogen Production: Enables direct, cost-effective hydrogen generation from readily available alkaline seawater, bypassing the energy and cost penalties associated with freshwater purification.
- Industrial Electrocatalysis in Harsh Environments: The BDD substrateâs superior chemical inertness makes this electrode ideal for use in highly corrosive industrial processes (high salinity, high pH, presence of chlorine/sulfur compounds).
- Wastewater Treatment and Remediation: BDD electrodes are already established for electrochemical anodic oxidation in treating difficult-to-degrade industrial wastewater; this bifunctional catalyst expands BDD utility in integrated remediation systems.
- Advanced Energy Storage: The efficient OER kinetics achieved, particularly at high current densities, are relevant for high-performance rechargeable metal-air batteries (e.g., zinc-air batteries).
- Corrosion-Resistant Sensor Technology: BDDâs stability is valuable for sensors operating in corrosive gas or liquid environments (e.g., detection of heavy metal ions, chlorine, or sulfur dioxide).