Engineering interfacial sulfur migration in transition-metal sulfide enables low overpotential for durable hydrogen evolution in seawater
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-07-22 |
| Journal | Nature Communications |
| Authors | Min Li, Kai Li, Hefei Fan, Qianfeng Liu, Yan Zhao |
| Institutions | Chinese Academy of Sciences, Dalian Institute of Chemical Physics |
| Citations | 64 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: High-Performance HER Electrocatalysis
Section titled âTechnical Documentation & Analysis: High-Performance HER ElectrocatalysisâExecutive Summary
Section titled âExecutive SummaryâThis research details a breakthrough in developing highly durable and efficient electrocatalysts for the Hydrogen Evolution Reaction (HER) in challenging alkaline seawater environments, providing a clear pathway for industrial hydrogen production.
- Novel Electrocatalyst: Synthesis of a CN@NiCoS heterostructure (Nickel-Cobalt Sulfides encapsulated in a Nitrogen-Doped Carbon shell).
- Mechanism of Stability: The CN shell prevents the dissolution of active sulfide components into the alkaline electrolyte, addressing the primary degradation mechanism in transition-metal sulfides (TMSs).
- Ultra-Low Overpotential: Achieved remarkably low overpotentials of 4.6 mV (alkaline freshwater) and 8 mV (alkaline seawater) at the benchmark current density of 10 mA cm-2.
- Enhanced Durability: Demonstrated long-term stability up to 1000 hours at 100 mA cm-2 in 1M KOH, significantly surpassing reported TMS-based electrocatalysts.
- Interfacial Engineering: Dynamic sulfur migration creates S-doped CN network and sulfur vacancies (Vs) pairing sites (S/NC@NiCoS-Vs) at the interface, which modulate the d-band center near the Fermi level, accelerating HER kinetics.
- Industrial Relevance: The catalyst maintains high performance even at high current densities (up to 1 A cm-2) in seawater, validating its potential for large-scale industrial seawater electrolysis.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the electrochemical performance analysis of the CN@NiCoS catalyst:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Overpotential (η) | 4.6 | mV | @ 10 mA cm-2 in 1M KOH (Alkaline Freshwater) |
| Overpotential (η) | 8 | mV | @ 10 mA cm-2 in 1M KOH + Seawater |
| Overpotential (η) | 79.8 | mV | @ 100 mA cm-2 in 1M KOH + Seawater |
| Overpotential (η) | 281 | mV | @ 1000 mA cm-2 (1 A cm-2) in 1M KOH + Seawater |
| Tafel Slope | 37.9 | mV dec-1 | 1M KOH (Volmer-Heyrovsky mechanism) |
| Tafel Slope | 68.9 | mV dec-1 | 1M KOH + Seawater |
| Stability Test Duration | 1000 | h | @ 100 mA cm-2 in 1M KOH |
| Stability Test Duration | 200 | h | @ 1 A cm-2 in 1M KOH + Seawater |
| ECSA (Cdl) | 108.6 | mF cm-2 | Electrochemical Activation Surface Area |
| Activation Energy (Ea) | 5.7 | kJ mol-1 | Intrinsic HER activity |
| CN Overlayer Thickness | 1 ~ 1.5 | nm | Encapsulation layer thickness |
| Synthesis Annealing Temp | 350 | °C | In N2 atmosphere |
Key Methodologies
Section titled âKey MethodologiesâThe CN@NiCoS heterostructure electrocatalyst was synthesized via a two-step process involving hydrothermal growth followed by sulfidation and carbon coating.
- Ni Foam Pretreatment: Commercial Ni foam (NF) was cleaned using 1 M HCl solution, acetone, and deionized (DI) water, followed by vacuum drying at 60 °C.
- NiCoLDH/NF Preparation: NiCoLDH was grown hierarchically on the pretreated NF surface using a hydrothermal method.
- Precursors: Co(NO3)2.6H2O, urea, and NH4F dissolved in DI water.
- Hydrothermal Conditions: Sealed and maintained at 120 °C for 10 h.
- CN@NiCoS/NF Synthesis (Sulfidation/Carbon-Coating): The NiCoLDH/NF electrode and thiourea (CH4N2S) powder were annealed in separate ceramic boats.
- Atmosphere: N2.
- Temperature: 350 °C.
- Duration: 2 h.
- Heating Rate: 2 °C min-1.
- Electrochemical Testing: Performed at 25 °C in a typical H-type electrolytic cell (1 cm x 1 cm electrode area).
- Electrolyte: 1M KOH or 1M KOH + natural seawater (pH adjusted to 14 ± 0.2).
- Techniques: Linear Sweep Voltammetry (LSV), Chronopotentiometry (long-term stability), Electrochemical Impedance Spectroscopy (EIS), and Cyclic Voltammetry (CV) for ECSA estimation.
- Advanced Characterization: Structural and electronic properties were confirmed using X-ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), and in situ Raman spectroscopy.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research demonstrates the critical role of highly stable, corrosion-resistant substrates and precise interfacial engineering for achieving durable HER performance in harsh alkaline seawater. While the paper utilizes Ni foam and transition-metal sulfides, Boron-Doped Diamond (BDD) from 6CCVD offers a superior, long-term platform for industrial electrocatalysis due to its unmatched chemical inertness, wide potential window, and tunable conductivity.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this high-stability electrocatalysis research, 6CCVD recommends leveraging the superior properties of our MPCVD diamond materials:
- Heavy Boron Doped Polycrystalline Diamond (PCD):
- Application: Ideal for scaling up industrial seawater electrolysis. PCD offers high conductivity and mechanical robustness.
- Advantage: Available in custom dimensions up to 125mm diameter, allowing for large-area electrode fabrication far exceeding typical lab-scale substrates.
- Thin Film Boron Doped Single Crystal Diamond (SCD):
- Application: Perfect for fundamental research requiring precise control over the catalyst/substrate interface and ultra-low defect density.
- Thickness Control: Available in thicknesses from 0.1 ”m to 500 ”m, enabling optimization of the BDD layer for specific charge transfer requirements.
Customization Potential
Section titled âCustomization PotentialâThe success of the CN@NiCoS catalyst relies on integrating a functional layer onto a conductive substrate. 6CCVD provides comprehensive services to facilitate the integration of advanced electrocatalysts onto diamond platforms:
| Requirement from Research | 6CCVD Capability | Technical Specification |
|---|---|---|
| Substrate for Large-Scale HER | Custom PCD Wafers | Plates/wafers up to 125mm diameter. |
| Low-Resistance Electrical Contact | Custom Metalization | Internal capability for Au, Pt, Pd, Ti, W, Cu deposition. |
| High-Quality Interface | Advanced Polishing | SCD surfaces polished to Ra < 1nm; Inch-size PCD to Ra < 5nm. |
| Robust Electrode Platform | BDD Material | Unmatched stability and corrosion resistance in alkaline/seawater media. |
Engineering Support
Section titled âEngineering SupportâThe paper highlights that HER activity is strongly enhanced by altering the d-band center and creating specific defect sites (sulfur vacancies). 6CCVDâs in-house PhD team specializes in optimizing diamond properties (e.g., boron doping level, surface termination, and defect density) to serve as an optimal foundation for subsequent catalyst deposition.
We offer expert consultation to assist researchers in:
- Selecting the optimal BDD doping level to match the electronic requirements of the CN@NiCoS layer.
- Designing custom metalization schemes (e.g., Ti/Pt/Au stacks) for robust electrical integration in corrosive environments.
- Providing mechanically stable diamond substrates (up to 10mm thick) for long-term, high-current density testing, ensuring the substrate, not the catalyst, dictates the stability limits.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Hydrogen production from seawater remains challenging due to the deactivation of the hydrogen evolution reaction (HER) electrode under high current density. To overcome the activity-stability trade-offs in transition-metal sulfides, we propose a strategy to engineer sulfur migration by constructing a nickel-cobalt sulfides heterostructure with nitrogen-doped carbon shell encapsulation (CN@NiCoS) electrocatalyst. State-of-the-art ex situ / in situ characterizations and density functional theory calculations reveal the restructuring of the CN@NiCoS interface, clearly identifying dynamic sulfur migration. The NiCoS heterostructure stimulates sulfur migration by creating sulfur vacancies at the Ni 3 S 2 -Co 9 S 8 heterointerface, while the migrated sulfur atoms are subsequently captured by the CN shell via strong C-S bond, preventing sulfide dissolution into alkaline electrolyte. Remarkably, the dynamically formed sulfur-doped CN shell and sulfur vacancies pairing sites significantly enhances HER activity by altering the d -band center near Fermi level, resulting in a low overpotential of 4.6 and 8 mV at 10 mA cm â2 in alkaline freshwater and seawater media, and long-term stability up to 1000 h. This work thus provides a guidance for the design of high-performance HER electrocatalyst by engineering interfacial atomic migration.