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 | Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics |
| Citations | 64 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel strategy to engineer interfacial atomic migration in transition-metal sulfides (TMSs) to achieve highly durable and efficient Hydrogen Evolution Reaction (HER) catalysis, particularly in alkaline seawater.
- Core Innovation: Development of a Nickel-Cobalt Sulfide heterostructure encapsulated in a Nitrogen-doped Carbon shell (CN@NiCoS) to break the activity-stability trade-off common in TMSs.
- Engineered Mechanism: The Ni3S2/Co9S8 heterojunction stimulates dynamic sulfur migration, creating sulfur vacancies (Vs) at the interface. The ultrathin CN shell subsequently captures the migrated sulfur atoms via strong C-S bonds, preventing sulfide dissolution into the electrolyte.
- Active Site Enhancement: The dynamically formed S-doped CN shell and sulfur vacancies pairing sites (S/NC@NiCoS-Vs) modulate the d-band center near the Fermi level, significantly accelerating HER kinetics (Volmer-Heyrovsky mechanism).
- Benchmark Performance (Freshwater): Achieved an ultralow overpotential of 4.6 mV at 10 mA cm-2 in 1 M KOH, indicating superior intrinsic activity.
- Seawater Performance: Demonstrated 8 mV overpotential at 10 mA cm-2 in alkaline seawater, confirming robust activity against impurity ions.
- Exceptional Durability: Maintained long-term stability up to 1000 h at a high current density of 100 mA cm-2 in 1 M KOH, surpassing most reported TM-based electrocatalysts.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Overpotential (η) | 4.6 | mV | HER, 10 mA cm-2, 1 M KOH (Alkaline Freshwater) |
| Overpotential (η) | 8 | mV | HER, 10 mA cm-2, 1 M KOH + Seawater |
| Overpotential (η) | 83.9 | mV | HER, 100 mA cm-2, 1 M KOH |
| Tafel Slope | 37.9 | mV dec-1 | HER, 1 M KOH (Dominant Volmer-Heyrovsky mechanism) |
| Tafel Slope | 68.9 | mV dec-1 | HER, 1 M KOH + Seawater |
| Long-Term Stability | 1000 | h | Galvanostatic test at 100 mA cm-2 in 1 M KOH |
| Long-Term Stability | 400 | h | Galvanostatic test at 100 mA cm-2 in 1 M KOH + Seawater |
| Activation Energy (Ea) | 5.7 | kJ mol-1 | CN@NiCoS catalyst (Intrinsic HER activity) |
| Double-Layer Capacitance (Cdl) | 108.6 | mF cm-2 | Proxy for Electrochemical Active Surface Area (ECSA) |
| CN Overlayer Thickness | 1 - 1.5 | nm | HRTEM measurement |
| Ni3S2 Interplanar Spacing | 0.167 | nm | (121) plane |
| Co9S8 Interplanar Spacing | 0.248 | nm | (400) plane |
| S Vacancy Formation Energy | -0.8391 | eV | Ni3S2/Co9S8 heterojunction (Thermodynamically favored) |
| Ni Content (XPS) | 3.65 | wt% | CN@NiCoS/NF |
| Co Content (XPS) | 0.71 | wt% | CN@NiCoS/NF |
Key Methodologies
Section titled âKey MethodologiesâThe CN@NiCoS catalyst was prepared via a two-step hydrothermal-sulfidation/carbon-coating process using Ni foam (NF) as the substrate.
- Precursor Synthesis (NiCoLDH/NF):
- Ni foam was pretreated (1 M HCl, acetone, DI water wash).
- A solution containing Co(NO3)2·6H2O, urea, and NH4F was prepared.
- The pretreated NF was immersed and subjected to hydrothermal treatment at 120 °C for 10 h to grow the NiCoLDH precursor.
- CN@NiCoS Synthesis (Sulfidation/Carbon Coating):
- The NiCoLDH/NF electrode and thiourea (CH4N2S) powder were placed in separate ceramic boats.
- The assembly was annealed in an N2 atmosphere at 350 °C for 2 h, using a heating rate of 2 °C min-1.
- Electrochemical Testing:
- Conducted at 25 °C using a typical three-electrode system (1 cm x 1 cm electrode area).
- Electrolytes used were 1 M KOH (alkaline freshwater) and 1 M KOH + seawater (pH 14 ± 0.2).
- Stability was assessed via chronopotentiometry at high current densities (100 mA cm-2 and 1 A cm-2).
- In Situ Characterization:
- In situ Raman spectroscopy was performed using a 532 nm laser source, monitoring spectral changes under applied potentials ranging from 0 to -0.5 V vs RHE.
- Structural and Compositional Analysis:
- Microstructure was analyzed using Aberration-corrected HAADF-STEM (200 kV) and HRTEM.
- Surface composition and electronic states were determined by High-resolution X-ray Photoelectron Spectroscopy (XPS).
- Sulfur leaching was quantified using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) on post-HER electrolytes.
- Computational Modeling:
- Density Functional Theory (DFT) calculations were performed using the Generalized Gradient Approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) formulation.
- Sulfur migration pathways and energy barriers were determined using the Nudged Elastic Band (NEB) method.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a highly stable and efficient non-precious metal catalyst platform, directly addressing the challenges of large-scale hydrogen production in saline environments.
- Seawater Electrolysis: Enables cost-effective, large-scale green hydrogen production by utilizing abundant seawater feedstock, bypassing the need for extensive freshwater purification.
- Industrial Alkaline Water Electrolysis: Provides a durable, high-performance alternative to expensive Pt-based catalysts for industrial HER processes operating in alkaline media.
- Catalyst Manufacturing: The synthesis strategy offers a scalable method for developing robust, sulfur-migration-controlled Transition-Metal Sulfide (TMS) catalysts for various electrochemical applications.
- Energy Storage and Conversion: Applicable in integrated systems requiring highly efficient and stable hydrogen generation, such as regenerative fuel cells.
- Environmental Engineering: The inhibition of sulfur leaching (sulfide dissolution) makes this catalyst environmentally friendly for large-scale deployment compared to conventional TMSs.
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.