Key Takeaways & Executive Findings
- •• • The Ir/WOx NSs achieve a mass activity of 2.34 A mgIr−1 at 300 mV overpotential, 11.1× and 9.8× higher than Ir NSs and commercial Ir/C, respectively, enabling significant reduction in Ir loading for cost-effective PEMWE deployment. • • The catalyst exhibits a low overpotential of 216 mV at 10 mA cm−2geo, surpassing commercial IrO2 and indicating enhanced intrinsic activity for acidic OER. • • In a PEM electrolyzer, Ir/WOx NSs deliver 1.0 A cm−2 at a cell voltage of 1.71 V, meeting ampere-level operational requirements for industrial hydrogen production. • • Long-term stability tests show a potential decay rate of only 2.8 μV h−1, compared to 210 μV h−1 for commercial IrO2, under dynamic current densities (0.2–1.0 A cm−2), demonstrating robust durability essential for intermittent renewable energy integration.
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Abstract
Iridium-based materials remain the only commercially viable anode electrocatalysts for the acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), yet their high cost and insufficient activity necessitate reducing Ir loading while enhancing performance. This work reports the synthesis of ultrathin Ir/WOx hybrid nanosheets (Ir/WOx NSs) featuring abundant two-dimensionally confined heterointerfaces, composed of crystalline Ir nanograins embedded within an amorphous WOx matrix. The Ir/WOx NSs achieve a mass activity of 2.34 A mgIr−1 at an overpotential of 300 mV, approximately 11.1 and 9.8 times higher than Ir NSs and commercial Ir/C, respectively. The 2D-confined interactions establish synergistic bifunctional sites and efficient charge transfer interfaces, accelerating the initial hydrolysis dissociation step. On interfacial Ir atoms, the adsorption of *O and subsequent formation of *OOH intermediates are thermodynamically facilitated, promoting the adsorbate evolution mechanism. The Ir/WOx NSs-based PEMWE delivers a low cell voltage of 1.71 V at 1.0 A cm−2 and exhibits outstanding long-term durability, with a potential decay rate of 2.8 μV h−1 compared to 210 μV h−1 for commercial IrO2. This work demonstrates the engineering of 2D-confined metal-oxide interfacial electrocatalysts for efficient and stable green hydrogen production.
1. Introduction
Proton exchange membrane water electrolysis (PEMWE) offers higher voltage efficiency, ampere-level current density, and superior adaptability to fluctuating renewable energy sources compared to alkaline water electrolysis. However, the acidic oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics due to a complex four-proton-coupled electron transfer process, resulting in significant overpotential. The strongly acidic and oxidizing environment further demands exceptional catalyst stability at high current densities. Iridium-based materials are the only commercially available OER electrocatalysts for PEMWE, but their extreme cost and unsatisfactory performance necessitate urgent improvements to reduce Ir usage while enhancing activity and durability.
Existing Ir-based catalysts primarily follow the adsorbate evolution mechanism (AEM), which involves adsorption and desorption of intermediates such as *O, *OH, and *OOH. The free energy barrier for the rate-determining step (*O → *OOH) often limits overall activity. This work addresses the bottleneck by constructing ultrathin Ir/WOx hybrid nanosheets with abundant two-dimensionally confined heterointerfaces between crystalline Ir nanograins and an amorphous WOx matrix. The 2D-confined interactions create synergistic bifunctional sites and efficient charge transfer interfaces, accelerating the initial hydrolysis dissociation step and thermodynamically facilitating *O and *OOH formation on interfacial Ir atoms. This strategy substantially enhances acidic OER activity and stability, enabling ampere-level PEMWE operation with reduced Ir loading.
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Junlin Cai, Hongpu Huang, Weizhen Chen, Yuhang Peng, Luhong Fu, Shupeng Wang, Zhongyuan Zou, Zhichao Fu, Xiaohong Wang, Zhaoxiong Xie, Shuifen Xie (2025). Two-dimensionally confined Ir/WOx heterointerfaces boost the acidic oxygen evolution reaction for ampere-level stable PEM water electrolysis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3398-9
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Frequently Asked Questions
What is the long-term stability of Ir/WOx NSs under dynamic current density conditions, and how does it compare to commercial IrO2?
Ir/WOx NSs exhibit a potential decay rate of 2.8 μV h−1 during long-term operation under dynamic current densities ranging from 0.2 to 0.5 to 1.0 A cm−2, whereas commercial IrO2 shows a decay rate of 210 μV h−1. This 75-fold reduction in degradation rate indicates superior durability, essential for practical PEMWE systems subjected to intermittent renewable energy inputs.
What are the mass activity and overpotential metrics of Ir/WOx NSs compared to baseline catalysts?
Ir/WOx NSs achieve a mass activity of 2.34 A mgIr−1 at an overpotential of 300 mV, which is 11.1 times higher than Ir NSs and 9.8 times higher than commercial Ir/C. Additionally, the overpotential at 10 mA cm−2geo is only 216 mV, significantly lower than commercial IrO2, demonstrating enhanced intrinsic activity and potential for reducing Ir loading.
How does the 2D-confined heterointerface enhance the acidic OER mechanism?
The 2D-confined interactions between crystalline Ir nanograins and amorphous WOx matrix create synergistic bifunctional sites and efficient charge transfer interfaces. In situ ATR-SEIRAS and theoretical calculations show that these interfaces enhance hydrolysis dissociation and deprotonation steps, increase oxophilicity of proximal Ir atoms, and reduce the free energy barrier for the rate-determining step (*O → *OOH) in the adsorbate evolution mechanism, thereby accelerating OER kinetics.
What cell voltage is required for Ir/WOx NSs to deliver 1.0 A cm−2 in a PEM electrolyzer, and what are the implications for industrial hydrogen production?
The Ir/WOx NSs-based PEMWE achieves a cell voltage of 1.71 V at 1.0 A cm−2, meeting ampere-level operational requirements. This low voltage, combined with outstanding durability, enables efficient and stable green hydrogen production, potentially lowering energy consumption and operational costs for industrial-scale PEMWE deployment.
What are the scalability challenges for synthesizing Ir/WOx NSs, and how might they impact commercial viability?
The synthesis of ultrathin Ir/WOx hybrid nanosheets with abundant 2D-confined heterointerfaces involves elaborate procedures that may pose scalability challenges. However, the substantial reduction in Ir usage (due to high mass activity) and enhanced durability could offset initial synthesis costs. Further optimization of assembly, testing, and analysis of PEMWE devices is expected to improve performance and facilitate scale-up.
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