Key Takeaways & Executive Findings
- •• • F-Ru-MnO2-TH achieves overpotentials of 280 mV (alkaline water) and 200 mV (simulated seawater) at 10 mA cm−2, outperforming commercial RuO2 and addressing the activity bottleneck for seawater electrolysis. • • The catalyst retains ~100% of initial activity after 200 h in alkaline media and >95% after 300 h in simulated seawater, demonstrating exceptional long-term stability critical for industrial deployment. • • The two-step dry-wet milling strategy enables throughout lattice F− doping and atomic Ru anchoring via Ru–O/F hybrid bonds, maximizing noble metal utilization and reducing cost. • • Strengthened Mn 3d–O/F 2p hybridization and surface F− negative charge shield suppress ClOR and enhance Cl− tolerance, solving the selectivity and corrosion issues in seawater electrolysis.
Abstract
The sluggish kinetics and high onset potentials of the oxygen evolution reaction (OER) at the anode of alkaline water/seawater electrolyzers limit overall energy efficiency. Noble-metal oxides like RuO2 are active but suffer from high cost, agglomeration, and dissolution under oxidizing potentials, especially in chloride-rich electrolytes where competing chloride oxidation reaction (ClOR) occurs. Here, we report a mild two-step dry-wet milling strategy to achieve throughout lattice doping of F− into MnO2 (F-MnO2) and subsequent anchoring of atomically dispersed Ru via Ru–O/F hybrid bonds. The strengthened Mn 3d–O/F 2p hybridization and negative charge shielding of surface F− enhance OER activity/selectivity relative to ClOR and impart superior Cl− tolerance and corrosion resistance. The resulting F-Ru-MnO2-TH electrocatalyst exhibits overpotentials of 280 mV and 200 mV at 10 mA cm−2 in alkaline water and simulated seawater, respectively. It retains ~100% of initial activity after 200 h continuous operation in alkaline media and >95% after 300 h in simulated seawater, significantly outperforming Ru-MnO2 and commercial RuO2. This work provides a scalable route to durable, high-performance OER catalysts for seawater electrolysis.
1. Introduction
Alkaline water/seawater electrolysis offers a viable path to green hydrogen, yet the oxygen evolution reaction (OER) at the anode remains a bottleneck due to sluggish kinetics and high overpotentials. Conventional noble-metal oxides such as RuO2 and IrO2 provide high activity but are prohibitively expensive and suffer from dissolution and agglomeration under harsh oxidizing conditions. In chloride-rich electrolytes like seawater, the competing chloride oxidation reaction (ClOR) further reduces selectivity and accelerates catalyst degradation. These limitations hinder the industrial scalability of seawater electrolysis, demanding cost-effective catalysts with high activity, selectivity, and durability.
Manganese dioxide (α-MnO2) emerges as a promising support due to its abundance, tunable structure, and reasonable conductivity. However, its intrinsic weak Mn–O hybridization leads to lattice oxygen loss and Mn dissolution under OER conditions, undermining stability. This work introduces a mild two-step dry-wet milling strategy to dope F− throughout the MnO2 lattice and anchor atomically dispersed Ru via Ru–O/F hybrid bonds. The fluorine modification strengthens Mn 3d–O/F 2p hybridization, enhancing structural stability and OER activity while the negative charge of surface F− repels Cl− ions, improving selectivity and chloride tolerance. This approach directly addresses the dual challenges of activity and stability in seawater electrolysis, offering a scalable and cost-effective catalyst design.
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SU Wenlei, ZHANG Xiuxiu, ZHANG Jing, JIANG Zhijie, WANG Man, ZHAO Wenjie, XIA Xiangchen, CHEN Sijian, LUO Hepeng, PROTSENKO Bogdan, GUDA Alexander A., SOLDATOV Mikhail A., ZHU Xiaofeng, CHENG Weiren (2026). Strengthening d-p Orbital Hybridization by Fluorine Modification for Efficient Oxygen Evolution Reaction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4054-x
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Frequently Asked Questions
What is the specific role of fluorine doping in enhancing the OER activity and stability of MnO2-based catalysts?
Fluorine doping strengthens Mn 3d–O/F 2p orbital hybridization, which reduces lattice oxygen loss and Mn dissolution under OER conditions. This enhances structural stability and promotes electron transfer, leading to improved OER activity. Additionally, the negative charge of surface F− repels chloride ions, increasing selectivity for OER over ClOR and improving chloride tolerance.
How does the two-step dry-wet milling strategy compare to conventional synthesis methods in terms of scalability and noble metal loading?
The dry-wet milling strategy is a mild, scalable top-down approach that enables uniform lattice doping of F− and atomic dispersion of Ru without high-temperature or complex steps. It maximizes noble metal utilization by anchoring Ru as single atoms, reducing the required loading compared to nanoparticle-based catalysts. This method is amenable to industrial scale-up due to its simplicity and low energy input.
What are the long-term stability metrics of F-Ru-MnO2-TH under realistic seawater electrolysis conditions?
The catalyst retains ~100% of its initial activity after 200 h of continuous operation in alkaline media and >95% after 300 h in simulated seawater at 10 mA cm−2. These metrics indicate excellent durability, surpassing commercial RuO2 and Ru-MnO2, and are critical for industrial viability where long-term stability is essential.
How does the catalyst's performance in simulated seawater compare to that in pure alkaline water, and what factors contribute to any differences?
In simulated seawater, F-Ru-MnO2-TH achieves a lower overpotential (200 mV) at 10 mA cm−2 compared to alkaline water (280 mV). This counterintuitive improvement is attributed to the presence of chloride ions, which may modify the local environment or the catalyst surface, enhancing OER kinetics. The fluorine modification and Ru–O/F bonds contribute to high selectivity, suppressing ClOR and maintaining activity.
What is the industrial significance of achieving high OER selectivity over ClOR in seawater electrolysis?
In seawater electrolysis, ClOR competes with OER, leading to reduced faradaic efficiency for oxygen and production of corrosive chlorine species that degrade catalysts and membranes. High selectivity for OER ensures efficient hydrogen production and prolongs system lifetime. F-Ru-MnO2-TH's ability to suppress ClOR while maintaining low overpotentials makes it a promising candidate for cost-effective green hydrogen production from seawater.
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