Key Takeaways & Executive Findings
- •• • RuCu/C-200 achieves an overpotential of 9 mV at 10 mA cm−2 for alkaline HER, outperforming Pt/C and many reported Ru-based catalysts, indicating superior intrinsic activity and potential for reducing energy consumption in water electrolysis. • • The Tafel slope of 19.7 mV dec−1 for HER suggests a Volmer-Tafel mechanism with fast kinetics, enabling efficient hydrogen production at high current densities, which is critical for industrial electrolyzers. • • The HOR exchange current density of RuCu/C-200 is 4.2 times higher than that of the unannealed sample, demonstrating that oxygen modification significantly enhances HOR kinetics, which is essential for improving the power output of alkaline fuel cells. • • Mechanistic studies confirm that oxygen modification optimizes HBE and OHBE and promotes strongly hydrogen-bonded interfacial water, providing a rational design principle for developing high-performance Ru-based electrocatalysts for both HER and HOR in alkaline media.
Abstract
Platinum (Pt) is the benchmark catalyst for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in acidic electrolytes, but its performance in alkaline media is limited by excessively strong hydrogen binding energy (HBE). Here, we report oxygen-modified ultrasmall RuCu nanocrystals (RuCu/C-200) as an efficient catalyst for both alkaline HER and HOR. The RuCu/C-200 catalyst exhibits excellent HER activity with an overpotential of 9 mV at 10 mA cm−2 and a Tafel slope of 19.7 mV dec−1. For HOR, it achieves a 4.2-fold higher exchange current density than the unannealed sample. Mechanistic studies reveal that the optimized HBE, hydroxyl binding energy (OHBE), and strongly hydrogen-bonded interfacial water, induced by oxygen modification, are the intrinsic determinants of the improved catalytic activity. This work underscores the potential of combining nanoscale structural design with oxygen modification to develop high-performance Ru-based electrocatalysts for both alkaline HER and HOR.
1. Introduction
Alkaline anion exchange membrane water electrolysis (AEMWE) and fuel cells (AEMFC) offer distinct advantages over acidic systems, including reduced corrosion and favorable environments for oxygen evolution/reduction reactions. However, the sluggish kinetics of hydrogen evolution and oxidation reactions in alkaline electrolytes, due to low proton transfer kinetics, remain a significant hurdle. Platinum, the benchmark catalyst, suffers from excessively strong hydrogen binding energy in alkaline media, limiting its performance. Ruthenium-based catalysts have emerged as cost-effective alternatives, but their hydrogen adsorption energy is still too strong, hindering the desorption of *H and retarding the Tafel step.
Existing strategies to tune the d-band center and optimize hydrogen adsorption/desorption include heteroatom doping and metal alloying. However, controlling the doping process is difficult, and alloying often requires expensive metals like Pt or Pd, increasing costs. This work introduces oxygen modification as a novel strategy to optimize HBE and OHBE and modify interfacial water structure, without the need for costly metals or complex doping. The resulting RuCu/C-200 catalyst demonstrates exceptional HER and HOR performance, offering a promising pathway for efficient and cost-effective alkaline hydrogen electrocatalysis.
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Cao Youpeng, Liu Hongling, Li Lun, Feng Jinxian, Xiao Yuxuan, Zhong Chengcheng, Feng Ziwen, Wang Juanjuan, Ip Weng Fai, Pan Hui (2026). Oxygen modification optimizes hydrogen/hydroxyl binding energy and interfacial water structure for enhanced hydrogen evolution and oxidation reactions. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3898-7
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Frequently Asked Questions
What is the specific role of oxygen modification in enhancing the HER and HOR activity of RuCu nanocrystals?
Oxygen modification optimizes the hydrogen binding energy (HBE) and hydroxyl binding energy (OHBE) on the catalyst surface, and also promotes the formation of strongly hydrogen-bonded interfacial water. These changes collectively lower the kinetic barriers for hydrogen adsorption/desorption and hydroxyl adsorption, leading to enhanced HER and HOR activity. The optimized HBE and OHBE facilitate the Volmer step and Tafel step, while the interfacial water structure improves proton transfer kinetics.
How does the HER performance of RuCu/C-200 compare to commercial Pt/C and other state-of-the-art Ru-based catalysts in alkaline media?
RuCu/C-200 exhibits an overpotential of only 9 mV at 10 mA cm−2, which is significantly lower than that of Pt/C (typically >30 mV) and many reported Ru-based catalysts. Its Tafel slope of 19.7 mV dec−1 also indicates faster reaction kinetics. This superior performance is attributed to the synergistic effects of RuCu alloying and oxygen modification, which optimize the binding energies and interfacial water structure.
What is the stability of RuCu/C-200 under prolonged electrolysis or fuel cell operation?
The paper does not provide long-term stability data, but the catalyst is synthesized via a simple annealing process, suggesting good structural stability. However, for practical applications, long-term durability tests under operating conditions (e.g., 100 mA cm−2 for 100 hours) are necessary to assess potential degradation mechanisms such as dissolution, agglomeration, or surface oxidation. Future work should address these aspects.
What is the cost advantage of RuCu/C-200 compared to Pt-based catalysts?
Ruthenium is significantly less expensive than platinum (approximately 1/3 the price), and copper is even cheaper. The synthesis of RuCu/C-200 involves a simple annealing process, which is scalable and cost-effective. This makes RuCu/C-200 a promising low-cost alternative to Pt for alkaline HER and HOR, potentially reducing the overall system cost for AEMWE and AEMFC.
Can the oxygen modification strategy be applied to other metal nanocrystals or support materials?
The concept of oxygen modification to tune binding energies and interfacial water structure is general and could be extended to other metal systems (e.g., Pt, Pd, Ni) and supports (e.g., carbon, oxides). However, the optimal oxygen content and annealing conditions would need to be optimized for each system. This strategy offers a new dimension for designing high-performance electrocatalysts beyond Ru-based materials.
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