Key Takeaways & Executive Findings
- •• • Ir@KM achieves a low overpotential of ~280 mV at 10 mA cm−2, outperforming conventional IrO2 and reducing energy losses in PEM electrolysis. • • Mass activity reaches 18,500 A gIr−1 at 1.8 V, 17.6 times higher than IrO2, enabling a drastic reduction in Ir loading and cost (73 $ kW−1 vs. 820 $ kW−1 for IrO2). • • The Ir-skin layer is only 1–2 atomic layers thick, with a low Ir–Ir atomic distance that triggers an oxide path mechanism (OPM), lowering theoretical overpotential to 0.13 V. • • Stability tests show a potential decay rate of 0.27 mV h−1 in the first 50 h, stabilizing to −0.12 mV h−1 after startup, with stable operation at 1.5 A cm−2 and minimal Ir/Mn dissolution.
Abstract
The development of catalysts with highly efficient oxygen evolution performance and low-Ir loading is key to scaling up the application of proton exchange membrane (PEM) water electrolysis technology. Here, an Ir-skin catalyst (Ir@KM) is realized on a potassium-manganese oxide (K0.25MnOx (KM)) using an ion-exchange method. The Ir-skin over the prepared Ir@KM has a low Ir–Ir atomic distance, endowing an energetically favorable oxide path mechanism to allow a low theoretical overpotential of 0.13 V. Ir@KM offers a low overpotential of ~280 mV at a current density of 10 mA cm−2 and provides a high mass activity of up to 18,500 A gIr−1 at a cell voltage of 1.8 V in PEM, which is 17.6 times higher than that of IrO2, demonstrating a significant advantage in reducing the cost of the membrane electrode. The presented Ir-skin concept represents a promising strategy to fabricate low-Ir catalyst with high activity and durability for practical applications of PEM.
1. Introduction
Proton exchange membrane water electrolysis (PEMWE) is pivotal for high-purity hydrogen production, yet its commercial viability is hampered by the reliance on iridium-based catalysts, particularly IrO2, which suffers from high cost and scarcity. The oxygen evolution reaction (OER) at the anode is kinetically sluggish and operates under highly corrosive acidic conditions, necessitating robust and active catalysts. However, the limited global supply of iridium—with consumption potentially reaching 400 kg GW−1—poses a significant economic barrier to large-scale deployment. Nanostructuring and support hybridization have been explored to reduce Ir usage, but these approaches often compromise stability or atomic efficiency. Single-atom catalysts (SACs) maximize utilization but expose support sites to corrosive attack, undermining long-term durability.
This work introduces a rational design of an atomic skin catalyst, Ir@KM, where a 1–2 atomic layer Ir skin is deposited on a potassium-manganese oxide support via ion-exchange. The support's modified electronic structure induces a low Ir–Ir atomic distance, promoting an oxide path mechanism that bypasses conventional scaling relations. This results in a low theoretical overpotential of 0.13 V and exceptional experimental performance: an overpotential of 280 mV at 10 mA cm−2 and a mass activity of 18,500 A gIr−1 at 1.8 V in a PEM cell—17.6 times higher than IrO2. The catalyst also demonstrates robust stability, with minimal degradation over extended operation. This dual-functional design not only enhances intrinsic activity but also protects the support from corrosion, offering a cost-effective and durable solution for PEMWE.
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Zeng Zhen, Hu Yuling, Liu Yun, Zhang Hao, Shi Wenjuan, Kang Zhenye, Yuan Yuliang, Sun Wei, Tian Xinlong (2026). Rational Design of Atomic Skin Layers with Low Ir–Ir Atomic Distance for Highly Efficient OER Catalysts. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3693-0
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Frequently Asked Questions
What is the specific Ir loading in the PEM electrode and how does it compare to conventional IrO2-based electrodes?
The Ir loading is not explicitly stated in the text, but the mass activity of 18,500 A gIr−1 at 1.8 V indicates an extremely low Ir content. Compared to IrO2, which typically requires higher loadings to achieve similar current densities, Ir@KM achieves 17.6 times higher mass activity, implying a proportional reduction in Ir usage. The cost analysis shows Ir@KM requires only 73 $ kW−1 versus 820 $ kW−1 for IrO2, a reduction of over 90%.
How does the low Ir–Ir atomic distance influence the OER mechanism and what is the evidence for the oxide path mechanism (OPM)?
The low Ir–Ir atomic distance on the KM support alters the electronic structure, as evidenced by X-ray absorption spectroscopy showing a high-valence Ir state (4.59+). This configuration promotes an oxide path mechanism (OPM) that bypasses traditional scaling relationships, lowering the theoretical overpotential to 0.13 V. The OPM is inferred from the reduced atomic distance and the observed high activity, which is inconsistent with conventional adsorbate evolution mechanisms.
What are the long-term stability metrics under realistic PEM operating conditions, and how does the catalyst degrade over time?
Chronoamperometry at a current density of 13,800 A (likely mA cm−2? The text says 'j_m of 13,800 A' but likely means 13,800 A gIr−1 or mA cm−2? Clarify) shows a potential decay rate of 0.27 mV h−1 in the first 50 hours, which becomes −0.12 mV h−1 after the second startup, indicating activation and stabilization. Staged tests at 1.5 A cm−2 show stable operation. Post-test SEM confirms nanosheet structure retention, and ICP analysis shows minimal Ir and Mn dissolution, validating practical durability.
What is the economic advantage of Ir@KM over IrO2 in terms of membrane electrode cost, and what are the implications for large-scale PEMWE deployment?
The cost analysis indicates Ir@KM requires only 73 $ kW−1, which is 8.9% of the cost for IrO2 (820 $ kW−1). This dramatic reduction is due to the high mass activity and low Ir loading, making PEMWE more economically viable for large-scale hydrogen production. The catalyst's stability further reduces replacement costs, enhancing its commercial appeal.
How does the ion-exchange synthesis method ensure uniform deposition of the Ir skin and what is the scalability potential?
The ion-exchange method in a low-temperature hydrothermal solvent allows for controlled deposition of Ir atoms onto the KM support, resulting in a uniform 1–2 atomic layer skin as confirmed by STEM. The method is relatively simple and scalable, as it does not require complex equipment or extreme conditions. The use of potassium-manganese oxide as a support is cost-effective, and the synthesis can be adapted for industrial production, though further optimization may be needed for large-scale manufacturing.
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