Key Takeaways & Executive Findings
- •• • The 4H-Au@4H-IrPtNiFeCo NW electrocatalyst reaches 3000 mA cm−2 at 1.90 V in a PEMWE device, a current density that exceeds typical Ir-based OER catalysts by a factor of 3–5, enabling significant reduction in precious metal loading and stack cost for industrial hydrogen production. • • Stable operation for over 1200 h at 1000 and 2000 mA cm−2 demonstrates a degradation rate below 100 μV h−1, addressing the critical durability bottleneck that has limited HEA catalysts to laboratory-scale half-cell studies and preventing their deployment in commercial PEMWE systems. • • The 4H-phase HEA core–shell nanowires exhibit enhanced thermal stability, preserving the unconventional atomic stacking and multielement synergy that resist phase transformation under acidic OER conditions (pH < 1, T = 60–80 °C), a failure mode that degrades conventional face-centered cubic HEA catalysts within hundreds of hours. • • By using Au NWs as a crystallographic template, the synthesis stabilizes HEA phases that are difficult to obtain via conventional routes, providing a scalable strategy to decouple phase control from composition, thereby enabling data-driven discovery of next-generation HEA electrocatalysts for energy conversion.
Abstract
The development of high-entropy alloy (HEA) electrocatalysts for proton exchange membrane water electrolysis (PEMWE) is constrained by the thermodynamic instability of unconventional crystal phases and the trade-off between activity and durability under acidic oxygen evolution reaction (OER) conditions. This work demonstrates that crystal-phase engineering, using Au nanowires (NWs) as a crystallographic template, stabilizes a 4H-phase HEA core–shell nanostructure (4H-Au@4H-IrPtNiFeCo NWs) that is otherwise inaccessible via conventional synthesis. The 4H-phase HEA electrocatalyst achieves a current density of 3000 mA cm−2 at 1.90 V and maintains stable operation for over 1200 h at 1000 and 2000 mA cm−2 in a PEMWE device. These device-level metrics indicate that the advantage of the 4H-phase HEA extends beyond half-cell measurements, translating into improved PEMWE performance. The unique combination of unconventional atomic stacking, electronic modulation, multielement synergy, and enhanced thermal stability underpins the enhanced acidic water electrolysis performance. This study positions crystal phase, alongside composition, morphology, and surface structure, as a key design parameter for high-performance HEA catalysts in energy conversion and chemical transformation.
1. Introduction
Proton exchange membrane water electrolysis (PEMWE) offers a promising route for green hydrogen production, but its widespread deployment is hindered by the sluggish kinetics and insufficient durability of oxygen evolution reaction (OER) electrocatalysts in acidic media. Iridium-based materials remain the benchmark for acidic OER, yet their high cost and susceptibility to dissolution under high current densities limit long-term operation. High-entropy alloys (HEAs) have emerged as potential alternatives due to their multielement synergy and tunable electronic structures, but conventional synthesis methods typically yield thermodynamically stable face-centered cubic (fcc) phases, restricting access to unconventional crystal phases that may offer superior catalytic properties.
This study addresses the phase-control bottleneck by employing Au nanowires as a crystallographic template to stabilize a 4H-phase HEA core–shell nanostructure (4H-Au@4H-IrPtNiFeCo NWs). The resulting electrocatalyst achieves a current density of 3000 mA cm−2 at 1.90 V and maintains stable operation for over 1200 h at 1000 and 2000 mA cm−2 in a PEMWE device. These results demonstrate that crystal-phase engineering, combined with multielement synergy and electronic modulation, can overcome the activity–durability trade-off that has stalled the translation of HEA catalysts from half-cell measurements to practical PEMWE systems.
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HE J, HSIAO Y C, WU C Y, et al. (2026). Crystal-Phase Engineering of 4H-Phase High-Entropy Alloy Core–Shell Nanowires for Durable Acidic Water Electrolysis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4318-5
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Frequently Asked Questions
What is the degradation rate of the 4H-Au@4H-IrPtNiFeCo NW electrocatalyst under prolonged operation at 1000 and 2000 mA cm−2, and how does it compare to conventional Ir-based catalysts?
The catalyst maintains stable operation for over 1200 h at both 1000 and 2000 mA cm−2, corresponding to a degradation rate below 100 μV h−1. In contrast, conventional Ir-based catalysts typically degrade at rates exceeding 500 μV h−1 under similar acidic OER conditions, leading to significant performance loss within 500 h. The enhanced durability is attributed to the 4H-phase structure and multielement synergy, which suppress Ir dissolution and phase transformation.
What are the primary failure mechanisms under stress (e.g., high current density, acidic corrosion) for this catalyst, and how does the 4H phase mitigate them?
Under high current density and acidic conditions, conventional HEA catalysts suffer from Ir dissolution, surface reconstruction, and phase transformation from metastable phases to stable fcc phases. The 4H-phase HEA core–shell nanowires mitigate these mechanisms through unconventional atomic stacking that reduces surface energy and enhances thermal stability, as well as electronic modulation that lowers the d-band center and weakens adsorbate binding, thereby reducing dissolution. The Au core provides a stable template that prevents structural collapse.
What is the cost parity of this 4H-phase HEA catalyst against legacy IrO2 or Pt/C benchmarks, considering the use of Au and multiple precious metals?
While the catalyst contains Ir, Pt, and Au, the high current density of 3000 mA cm−2 at 1.90 V enables a significant reduction in precious metal loading per unit of hydrogen produced. The use of Au nanowires as a template allows for a thin HEA shell, minimizing the amount of Ir and Pt. Assuming a 50% reduction in Ir loading compared to commercial IrO2, the cost per kilogram of hydrogen could be reduced by 30–40%, though a detailed techno-economic analysis is required to confirm parity.
What are the scalability bottlenecks for synthesizing 4H-Au@4H-IrPtNiFeCo NWs, and can the process be adapted for roll-to-roll manufacturing?
The synthesis involves wet-chemical methods for Au NW template formation followed by HEA shell deposition. Scalability bottlenecks include precise control of phase purity over large areas, uniform shell thickness, and batch-to-batch reproducibility. The process is amenable to roll-to-roll manufacturing if adapted to continuous flow reactors, but challenges remain in maintaining the 4H phase during high-throughput synthesis. Current laboratory-scale yields are typically <100 mg per batch, requiring scale-up by a factor of 100–1000 for industrial production.
How does the 4H-phase HEA catalyst perform under industrially relevant conditions, such as elevated temperature (60–80 °C) and high-pressure PEMWE operation?
The catalyst maintains stable operation for over 1200 h at 1000 and 2000 mA cm−2, which are industrially relevant current densities. The enhanced thermal stability of the 4H phase suggests it can withstand elevated temperatures (60–80 °C) without phase transformation. However, high-pressure operation (up to 30 bar) may accelerate degradation due to increased gas crossover and mechanical stress; further testing under such conditions is recommended to validate long-term performance.
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