Key Takeaways & Executive Findings
- •• • Co doping in FeS2 generates abundant S2− species by disrupting S–S bond symmetry, accelerating surface reconstruction into FeOOH during OER; this lowers the kinetic barrier for active phase formation, which is critical for reducing overpotential in industrial electrolyzers. • • Post-reconstruction, Co atoms remain integrated in the FeOOH lattice, upshifting the d-band center and optimizing adsorption of oxygen intermediates; DFT calculations confirm a lowered energy barrier for OOH* formation, enhancing intrinsic activity. • • The study provides direct spectroscopic evidence (in situ Raman) linking dopant-induced structural changes to catalytic performance, offering a mechanistic framework for designing pre-catalysts that dynamically transform into active phases. • • The dual functionality of Co dopants—promoting reconstruction and modulating the active phase—addresses the bottleneck of slow kinetics and structural instability in Fe-based OER catalysts, potentially enabling lower overpotentials (ca. 400 mV) and improved durability for large-scale hydrogen production.
Abstract
Heteroatom doping is a widely adopted strategy to enhance the electrocatalytic activity of transition metal compounds, yet the intrinsic role of dopants beyond conventional electronic effects remains unresolved. This study reveals a missed heteroatom-doping effect using a graphene-supported Co-doped FeS2 catalyst for the oxygen evolution reaction (OER). Comprehensive characterization and in situ Raman spectroscopy demonstrate that Co incorporation disrupts S–S bond symmetry and orbital matching within FeS2, generating abundant S2− species that accelerate surface reconstruction into active FeOOH under electrochemical conditions. After reconstruction, Co atoms remain integrated within the FeOOH lattice, upshifting its d-band center and optimizing oxygen intermediate adsorption, as confirmed by theoretical calculations. This dual functionality of Co dopants—facilitating rapid reconstruction in the pre-catalyst and modulating the electronic structure of the active phase—provides novel mechanistic insights into dopant-induced dynamic reconstruction for electrocatalysis. The findings challenge the conventional understanding of doping effects and offer a rational design principle for Fe-based OER electrocatalysts, potentially lowering overpotentials and improving stability for practical water splitting.
1. Introduction
Alkaline water electrolysis powered by renewable energy is a promising route for green hydrogen production, yet the anodic oxygen evolution reaction (OER) remains a bottleneck due to sluggish kinetics and high energy barriers. Non-noble-metal catalysts, particularly Fe-based compounds, are attractive for their abundance and low cost, but they often require high overpotentials (ca. 400 mV) and suffer from structural instability during operation. Pyrite FeS2 is a candidate, but its low intrinsic conductivity and surface oxidation into FeOOH limit its practical use.
Heteroatom doping has been employed to enhance FeS2 performance, traditionally attributed to electronic structure modification. However, recent studies indicate that surface reconstruction into FeOOH is inevitable, and the role of dopants in this dynamic process is overlooked. This work addresses that gap by investigating Co-doped FeS2 supported on graphene, revealing that Co not only accelerates reconstruction but also remains in the active FeOOH phase to optimize its electronic structure. This dual functionality provides a new mechanistic understanding and a design principle for next-generation Fe-based OER electrocatalysts.
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Luhong Fu, Runze He, Shuli Wang, Anantharaj Sengeni, Weiwei Cai, Ligang Feng (2026). Unraveling the Missed Heteroatom-Doping Effect in Pyrite FeS2 for Oxygen Evolution Reaction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3905-9
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Frequently Asked Questions
What is the specific role of Co dopants in the pre-catalyst FeS2, and how does it differ from the conventional electronic effect?
Co doping disrupts S–S bond symmetry and orbital matching within FeS2, generating S2− species that accelerate surface reconstruction into FeOOH. This is distinct from the conventional view that dopants only modify the electronic structure of the pristine catalyst. In situ Raman spectroscopy confirmed the generation of S2− and the accelerated transformation.
How does Co incorporation affect the d-band center of the active FeOOH phase, and what are the implications for OER kinetics?
DFT calculations show that Co atoms integrated in the FeOOH lattice upshift the d-band center, which optimizes adsorption of oxygen intermediates, specifically lowering the energy barrier for OOH* formation. This enhances the intrinsic OER activity of the reconstructed catalyst.
What is the evidence that Co remains in the FeOOH lattice after reconstruction, and why is this important?
Comprehensive characterization, likely including XPS and EXAFS, indicates Co atoms are retained within the FeOOH structure. This is crucial because it means the dopant continues to modulate the active phase's electronic structure, rather than being leached out, ensuring sustained catalytic enhancement.
How does the graphene support contribute to the overall catalytic performance?
Graphene provides electrical conductivity and a high surface area for dispersion of FeS2 nanoparticles, mitigating the low intrinsic conductivity of FeS2. This enhances electron transfer and exposes more active sites, synergistically improving OER performance.
What are the practical implications of this study for industrial OER electrocatalysis?
By revealing the dual role of Co dopants, the study offers a strategy to design pre-catalysts that rapidly transform into highly active FeOOH phases with optimized electronic structure. This could lead to Fe-based catalysts with lower overpotentials and improved stability, reducing cost and energy consumption in alkaline water electrolyzers.
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