A high-entropy alloy made from iron, cobalt, nickel, chromium and manganese has been transformed into a long-lasting hydrogen-production electrode through a controlled reaction with oxygen, according to a new study published in Advanced Composites and Hybrid Materials. The researchers report that heating FeCoNiCrMn in an oxygen-rich environment reorganizes its surface into an amorphous/crystalline heterostructure: a disordered layer of cobalt, manganese and iron nanosheets develops above the alloy’s crystalline interior. This reconstructed interface enables the electrode to produce hydrogen efficiently in alkaline water while remaining stable at industrially relevant current densities. In one of the most striking results, the electrode operated for 500 hours at 500 milliamperes per square centimeter, a demanding condition that can rapidly degrade many conventional catalysts. The material also showed negligible activity loss in simulated seawater, raising the possibility of durable hydrogen systems that can tolerate harsh electrolytes.
Hydrogen evolution is a central reaction in water electrolysis, but it is kinetically difficult, particularly in alkaline solutions. At the cathode, water molecules must first be split, producing hydrogen intermediates and hydroxide ions. This initial water-dissociation step generally requires more energy than proton reduction in acidic media because the strong O–H bond in water must be activated before hydrogen can form. Electrocatalysts accelerate this process by providing surfaces that bind reaction intermediates at suitable strengths and by facilitating the movement of electrons between the electrode and the electrolyte. The researchers focused on FeCoNiCrMn because high-entropy alloys contain several principal elements rather than one dominant metal. Their chemically complex lattices can offer adjustable electronic structures, high mechanical strength and strong resistance to corrosion. Yet the surface of the original alloy is not necessarily optimized for hydrogen evolution, prompting the team to explore whether its outermost atomic layers could be deliberately rebuilt.
The key strategy was high-temperature oxidation, a treatment more commonly associated with corrosion protection than with catalyst design. Instead of regarding oxygen exposure as a purely destructive process, the researchers used it to trigger a controlled surface reconstruction. Under the treatment conditions, the alloy’s surface developed nanoscale layers rich in cobalt, manganese and iron. Unlike the ordered FeCoNiCrMn substrate beneath them, these layers lacked long-range crystallographic order and therefore behaved as an amorphous material. The resulting electrode, designated HEA/O₂, combined an amorphous catalytic coating with a crystalline high-entropy alloy base. This architecture is important because the two regions perform different functions. The disordered surface offers a chemically diverse population of active sites, while the crystalline substrate provides electrical continuity, structural support and mechanical adhesion. Rather than attaching a separate catalyst powder with a polymer binder, the treatment creates an integrated interface directly on the metal electrode.
Amorphous materials can be especially useful in electrocatalysis because their atoms do not occupy a single repeating arrangement. This structural disorder can expose a broader range of coordination environments, including sites that bind water, hydroxyl species and hydrogen intermediates differently. Such diversity may help the reaction proceed through a sequence of energetically favorable steps instead of forcing every intermediate to interact with an identical surface site. In the HEA/O₂ structure, cobalt, manganese and iron are concentrated in the reconstructed nanosheets, creating a chemically heterogeneous outer layer. The researchers propose that this amorphous region is strongly oxophilic, meaning that it interacts readily with oxygen-containing species from alkaline water. That property is advantageous during water dissociation because hydroxide-related intermediates must be stabilized as the molecule is activated. At the same time, excessive oxygen affinity can trap reaction intermediates and slow later stages of hydrogen formation. The heterostructure’s electronic coupling is therefore critical: it helps balance adsorption and release rather than relying on a single metal’s surface chemistry.
According to the study, the boundary between the amorphous nanosheets and the crystalline FeCoNiCrMn alloy modifies the distribution of electrons across the electrode. Differences in atomic coordination and chemical composition create an interfacial electronic environment in which charge can be redistributed between the reconstructed layer and the metallic substrate. During hydrogen evolution, this arrangement facilitates charge transfer from the conductive alloy toward surface-bound reaction intermediates. In practical terms, the interface acts not only as a physical junction but also as an electronic reaction zone. Such charge modulation can alter the strength with which water, hydroxyl species and hydrogen are adsorbed, potentially lowering the energy required for the rate-limiting steps. The authors describe the surface as an active/passive architecture: the outer layer supplies catalytic functionality, while its strong attachment to the underlying alloy protects the electrode from mechanical failure and dissolution. The approach differs from conventional catalyst optimization, which often focuses on nanoparticle size, composition or support materials. Here, the catalyst is generated by changing the surface of a structurally robust bulk electrode.
The electrochemical performance reported for HEA/O₂ is notable at both moderate and high current densities. In alkaline conditions, the electrode required an overpotential of 137.9 millivolts to reach 10 milliamperes per square centimeter. Overpotential is the additional voltage beyond the thermodynamic potential that must be supplied to drive a reaction at a specified rate; a lower value generally indicates more efficient electrocatalysis. When the current density was increased to 500 milliamperes per square centimeter, the overpotential rose to 275.7 millivolts. That increase is expected because faster hydrogen production demands greater reaction rates and can intensify transport limitations, bubble accumulation and local changes in electrolyte composition. More significant than the low-current result, however, is the electrode’s ability to sustain the much larger current without rapidly losing activity. High-current operation is essential for practical electrolyzers because it allows more hydrogen to be generated from a given electrode area, reducing the size and potentially the cost of the system. Many laboratory catalysts perform well at 10 milliamperes per square centimeter but deteriorate when pushed toward industrially meaningful rates.
Durability was the defining feature of the new electrode. At 500 milliamperes per square centimeter, HEA/O₂ maintained stable hydrogen-evolution performance for 500 hours in alkaline electrolyte. The researchers also tested it in simulated seawater, where chloride ions and other dissolved species can accelerate corrosion, poison active sites or undermine catalyst layers. The electrode again exhibited extraordinary stability, with negligible activity decay over the same 500-hour period. This result is particularly relevant because seawater electrolysis is attracting interest as a way to produce hydrogen without competing directly with freshwater demand. However, seawater introduces complicated challenges: chloride oxidation can generate unwanted products, impurities can foul surfaces, and fluctuating pH and salinity can destabilize materials. The reported test does not by itself establish performance in natural seawater or complete seawater-splitting systems, but it demonstrates that the reconstructed surface can withstand a chemically aggressive simulated environment. The alloy’s corrosion resistance and the mechanically integrated amorphous layer appear to work together to suppress degradation.
The researchers’ findings also point to a broader design principle for transition-metal electrodes. Surface reconstruction is often treated as a complication because the material operating under electrochemical conditions may differ from the material initially synthesized. In this study, reconstruction is intentionally engineered before catalysis begins. Oxygen exposure creates a stable surface that is chemically distinct from the parent alloy, allowing the electrode to acquire new catalytic properties without sacrificing the strength of its metallic core. The method may be attractive for large-scale manufacturing because it does not require elaborate deposition of precious metals, binders or external supports. It relies instead on a thermal treatment that encourages selected elements to reorganize near the surface. The resulting amorphous nanosheets are not simply a passive oxide film; they are presented as a catalytically active Co–Mn–Fe layer coupled to a conductive FeCoNiCrMn foundation. By treating oxidation as a tool for controlling composition, structure and charge distribution, the work turns a familiar materials challenge into a route for designing durable interfaces.
The study arrives as researchers worldwide search for catalysts capable of combining efficiency with the endurance demanded by renewable-energy systems. Wind and solar power fluctuate, so electrolyzers may need to ramp up and down repeatedly while also operating at high current densities when electricity is available. A catalyst that performs well only under ideal laboratory conditions will struggle in that environment. HEA/O₂ offers a potentially useful response because its catalytic surface and structural support are formed as one connected system, limiting the detachment and electrical isolation that often affect coated electrodes. Its performance in simulated seawater further suggests that surface chemistry can be designed for resilience as well as activity. The next questions will involve translating the material into complete electrolyzer architectures, testing it under variable operating conditions and determining precisely which atomic sites control water dissociation and hydrogen release. Even so, the results demonstrate that a high-entropy alloy can be more than a corrosion-resistant metal: through oxygen-activated reconstruction, it can become a self-formed amorphous/crystalline catalytic interface built for sustained hydrogen generation.
Subject of Research: Oxygen-activated surface reconstruction of FeCoNiCrMn high-entropy alloy electrodes for alkaline and simulated-seawater hydrogen evolution.
Article Title: Surface reconstruction of high-entropy FeCoNiCrMn: exploring oxygen-activated amorphous/crystalline heterostructure for robust H2 generation
Article References: Mao, J., Zou, H., Guo, Q. et al. “Surface reconstruction of high-entropy FeCoNiCrMn: exploring oxygen-activated amorphous/crystalline heterostructure for robust H2 generation.” Advanced Composites and Hybrid Materials (2026).
Image Credits: AI Generated
DOI: 10.1007/s42114-026-02037-6
Keywords: Surface reconstruction; transition metals; amorphous/crystalline heterostructure; high-entropy alloy; hydrogen evolution reaction; alkaline water electrolysis; simulated seawater; electrocatalysis.
