Key Takeaways & Executive Findings
- •• Ultrathin 2D MoCoNi medium-entropy alloy (MEA) synthesized via ionic layer epitaxy exhibits exceptional OER performance with an overpotential of only 167 mV at 10 mA/cm² and a Tafel slope of 33.2 mV/dec. • The catalyst achieves an ultrahigh mass activity of 3359.6 A/g, three orders of magnitude higher than commercial RuO₂, significantly reducing noble metal dependence. • The synergy of multiple active metals and ultrathin thickness enhances charge transfer and exposes abundant active sites, driving superior electrocatalytic activity. • The entropy-stabilizing effect ensures outstanding durability, retaining 90% of initial current after 134 hours of continuous operation, promising for sustainable hydrogen production.
Abstract
The development of highly active, durable, and low-cost electrocatalysts is crucial for electrocatalytic hydrogen production. Ultrathin two-dimensional (2D) nanomaterials have extremely large specific surface areas, making them highly desirable electrocatalyst morphologies. Medium-entropy alloys (MEAs) exhibit compositional tunability and entropy-driven structural stability, making them ideal electrocatalyst candidates. In this study, MoCoNi MEA with ultrathin 2D morphology was successfully developed using a facile ionic layer epitaxial method. The ultrathin 2D MoCoNi MEA showed an excellent oxygen evolution reaction (OER) electrocatalytic performance, with a low overpotential of 167 mV at a current density of 10 mA/cm2 and small Tafel slope of 33.2 mV/dec. At the overpotential of 167 mV, the ultrathin 2D MoCoNi MEA exhibited ultrahigh mass activity of 3359.6 A/g, which is three orders of magnitude higher than that of the commercial noble metal oxide RuO2 (1.15 A/g). This excellent electrocatalytic performance was attributed to the synergy of multiple active metal-induced medium entropies, as well as the ultrathin thickness, which considerably shortened the charge-transfer distance and thus significantly promoted charge transfer. Owing to the natural entropy-stabilizing effect, the ultrathin 2D MoCoNi MEA maintained 90% of the initial current after a continuous OER electrocatalytic test for 134 h, showing impressive electrocatalytic stability. This study opens new avenues for the development of high-performance and low-cost electrocatalyst materials by creating MEAs with ultrathin 2D morphology.
1. Introduction
Hydrogen production from environmentally friendly electrocatalytic water splitting satisfies the growing demand for energy and mitigates greenhouse gas emissions [1–3]. However, the overall water electrolysis process faces the bottleneck problems of sluggish oxygen evolution reaction (OER) kinetics and poor electrochemical stability of the electrocatalysts [4]. Meanwhile, the most efficient industrial OER electrocatalysts are expensive and contain scarce noble metals and their oxides, such as Ir/Ru and RuO2/IrO2 [5–6]. Therefore, it is urgent to develop highly active, durable, and low-cost OER electrocatalysts [7].
Ultrathin two-dimensional (2D) nanomaterials with thicknesses of only one or a few atomic layers (less than 5 nm), such as graphene, hexagonal boron nitride, and black phosphorus, have attracted tremendous interest. Compared with zero-dimensional nanoparticles, one-dimensional nanowires, and three-dimensional (3D) macroscopic bulk phases, ultrathin 2D nanomaterials exhibit extremely large specific surface areas and more favorable electronic structures, making them highly desirable catalyst morphologies [8–13]. Their ultrathin atomic-scale thickness and large lateral dimensions enable the maximum exposure of catalytically active sites on the material surface and promote charge transfer in the thickness direction [9,14–16]. Furthermore, their ultrathin atomic thickness corresponds to ultralow mass loading, which can significantly reduce the amount of all elements used in electrocatalytic materials; thus, ultrathin 2D electrocatalytic materials can exhibit ultrahigh mass activity and achieve the optimal electrocatalytic performance with minimal elemental dosage [17].
In recent years, medium-entropy alloys (MEAs) have become a research hotspot in the fields of energy, materials, and chemistry as new cutting-edge alloy material systems that provide new ideas for the development of efficient OER electrocatalysts. MEAs are usually formed by a solid solution of three metal elements in equal or similar molar ratios, resulting in the formation of multiprincipal element alloys with medium configurational entropy [18–19]. They overcome the limitations of the composition design and functional regulation of traditional single-principal element alloys. The synergistic effect of multiple principal elements gives them more abundant catalytic active sites and electronic degrees of freedom to regulate the OER kinetics. Medium configurational entropy and lattice distortion endow MEAs with outstanding structural stability and corrosion resistance [20]. Among the several combinations, MoCoNi alloys have unique compositional advantages and show considerable potential for application as electrocatalysts. Mo, Co, and Ni have similar ionic radii and good solubilities in binary and ternary subsystems, resulting in good structural stability. Strong electronic coupling between these three elements contributes to excellent catalytic activity [21–22].
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Guangyuan Yan, Tianlu Wang, Haoze Xue, Minglei Zhang, Zihan Xu, Fei Chen, Wenbo Yu (2025). Ultrathin two-dimensional medium-entropy alloy as a highly efficient and stable electrocatalyst for oxygen evolution reaction. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3226-3
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Frequently Asked Questions
What is the significance of ultrathin 2D morphology in electrocatalysts?
Ultrathin 2D nanomaterials have extremely large specific surface areas and favorable electronic structures, maximizing exposure of active sites and promoting charge transfer, leading to enhanced electrocatalytic performance.
How does the MoCoNi medium-entropy alloy achieve high OER activity?
The synergy of multiple active metals (Mo, Co, Ni) and the ultrathin thickness shorten charge-transfer distances, significantly promoting charge transfer and providing abundant active sites, resulting in low overpotential and high mass activity.
What is the mass activity of the ultrathin 2D MoCoNi MEA compared to RuO2?
The ultrathin 2D MoCoNi MEA exhibits an ultrahigh mass activity of 3359.6 A/g at an overpotential of 167 mV, which is three orders of magnitude higher than that of commercial RuO2 (1.15 A/g).
How stable is the ultrathin 2D MoCoNi MEA during OER?
Due to the entropy-stabilizing effect, the catalyst maintains 90% of its initial current after a continuous OER test for 134 hours, demonstrating impressive electrocatalytic stability.
What method was used to synthesize the ultrathin 2D MoCoNi MEA?
The ultrathin 2D MoCoNi MEA was successfully developed using a facile ionic layer epitaxial method, which enables the formation of ultrathin two-dimensional morphology.
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