Key Takeaways & Executive Findings
- •• • RuCuCe achieves an overpotential of only 18 mV at 10 mA cm−2 in 1.0 M KOH, outperforming Ru-Cu-2 (33 mV) and Ru/C (70 mV), indicating superior intrinsic activity for alkaline HER. • • The apparent activation energy for HER decreases from 47.4 kJ mol−1 (RuCu) to 26.4 kJ mol−1 (RuCuCe), a 44% reduction that directly quantifies the enhanced water dissociation kinetics. • • RuCuCe maintains stable operation for over 100 h at a high current density of 500 mA cm−2 in a membrane electrode assembly, demonstrating industrial viability for sustained hydrogen production. • • The incorporation of ~1 at% Ce into RuCu induces charge redistribution and oxophilic sites, which strengthens H2O adsorption and lowers the kinetic energy barrier for the Volmer step, as confirmed by in situ EIS and pH-dependent measurements.
Abstract
Ruthenium (Ru)-based alloys are promising alternatives to commercial Pt/C catalysts for the hydrogen evolution reaction (HER) owing to their low cost and favorable hydrogen adsorption properties. However, the sluggish water dissociation on Ru catalysts remains a major kinetic bottleneck in alkaline solutions. Herein, we report a rare earth (RE) dilute alloy strategy by incorporating a trace amount of cerium (Ce, ~1 at%) into a RuCu alloy to promote interfacial water activation. The oxophilic Ce sites strengthen H2O adsorption and reduce the energy barrier for water dissociation, thereby accelerating the Volmer step during alkaline hydrogen evolution. Consequently, the RuCuCe catalyst delivers 10 mA cm−2 at an overpotential of only 18 mV in 1.0 M KOH and maintains stable operation for over 100 h at 500 mA cm−2 in a membrane electrode assembly. In situ electrochemical impedance spectroscopy and pH-dependent measurements verify the facilitated Volmer process induced by Ce incorporation. Temperature-dependent analysis further shows that the apparent activation energy decreases from 47.4 kJ mol−1 for RuCu to 26.4 kJ mol−1 for RuCuCe, consistent with enhanced water dissociation kinetics. This work establishes RE dilute metal alloys as an effective platform for boosting the intrinsic activity of Ru-based alloy catalysts, in which RE incorporation promotes water dissociation while inducing charge redistribution in the alloy matrix.
1. Introduction
Alkaline water electrolysis offers a cost-effective route for large-scale hydrogen production, circumventing the need for expensive proton-exchange membranes and enabling the use of non-noble metal components. However, the cathodic hydrogen evolution reaction (HER) in alkaline media suffers from intrinsically slower kinetics compared to acidic conditions, even on platinum (Pt) surfaces, where activity drops by two to three orders of magnitude. This performance gap stems from the additional energy required to cleave the H–OH bond of water molecules, a step that is not rate-limiting in acidic electrolytes. Consequently, the design of efficient alkaline HER catalysts must address both hydrogen adsorption thermodynamics and the kinetics of water dissociation.
Ruthenium (Ru)-based alloys have emerged as promising alternatives to Pt due to their lower cost and favorable hydrogen binding energies. Yet, their alkaline HER activity is still constrained by sluggish water dissociation. This study introduces a rare earth (RE) dilute alloy strategy, incorporating trace cerium (Ce, ~1 at%) into a RuCu alloy. The oxophilic Ce sites enhance water adsorption and reduce the energy barrier for dissociation, thereby accelerating the Volmer step. The resulting RuCuCe catalyst demonstrates a remarkably low overpotential of 18 mV at 10 mA cm−2 and exceptional stability at high current densities, offering a practical solution to the kinetic bottleneck in alkaline hydrogen production.
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ZHAO Jinyuan, LI Ziang, ZHAO Yan, ZHONG Ziyun, JIANG Yong, FU Hao, SAREN Qinggele, ZHANG Bin, LI Yiqun, ZHANG Jiwen, DU Yaping (2026). Rare Earth Dilute Alloys Unlock Fast Water Dissociation for Alkaline Hydrogen Evolution. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4272-3
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Frequently Asked Questions
What is the specific role of cerium in the RuCu alloy, and how does it affect the electronic structure?
Cerium (Ce) at ~1 at% acts as an oxophilic site that strengthens H2O adsorption and facilitates the cleavage of the H–OH bond. This incorporation induces charge redistribution within the alloy matrix, as evidenced by a reduction in apparent activation energy from 47.4 kJ mol−1 (RuCu) to 26.4 kJ mol−1 (RuCuCe), which directly enhances the Volmer step kinetics.
How does the RuCuCe catalyst perform under industrial relevant conditions, such as high current densities?
RuCuCe maintains stable operation for over 100 hours at a high current density of 500 mA cm−2 in a membrane electrode assembly, demonstrating its robustness for practical electrolysis. At 10 mA cm−2, it requires an overpotential of only 18 mV in 1.0 M KOH, outperforming many reported Ru-based catalysts.
What is the mechanistic evidence for the accelerated Volmer step?
In situ electrochemical impedance spectroscopy (EIS) and pH-dependent measurements confirm that Ce incorporation facilitates the Volmer process. Temperature-dependent kinetic analysis shows a significant decrease in apparent activation energy from 47.4 kJ mol−1 for RuCu to 26.4 kJ mol−1 for RuCuCe, consistent with enhanced water dissociation kinetics.
How does the performance of RuCuCe compare to state-of-the-art Ru-based HER catalysts in alkaline media?
RuCuCe achieves an overpotential of 18 mV at 10 mA cm−2, which is lower than many reported catalysts such as Ru-Cu-2 (33 mV), RuIr@NrC (28 mV), Cu-Ru/Ti (23 mV), RuCo@N-C (28 mV), and Ru/C (70 mV). This positions RuCuCe among the most active Ru-based catalysts for alkaline HER.
What are the potential scalability and cost implications of the rare earth dilute alloy strategy?
The use of only ~1 at% Ce minimizes the amount of rare earth material, reducing cost while maintaining significant catalytic enhancement. The synthesis method is compatible with standard alloy preparation techniques, and the demonstrated stability at high current densities suggests feasibility for scale-up in industrial water electrolyzers.
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