Key Takeaways & Executive Findings
- •• • The MoIrOx-coated Ti felt PTL achieves a current density of 3.27 A cm−2 at 2 V, a 59.5% improvement over uncoated Ti felts, directly enhancing hydrogen production rate and cell efficiency. • • The coating suppresses the Schottky barrier and pinch-off effect by forming a conductive interlayer that isolates TiOx from the ionomer, reducing charge transfer resistance and enabling stable operation with ultra-low catalyst loadings. • • The MoIrOx coating is applied via scalable spray deposition and thermal treatment, offering a cost-effective route to mitigate corrosion-induced performance degradation in acidic PEMWE environments. • • The work demonstrates a 59.5% increase in current density, which translates to significant energy savings and reduced capital costs for large-scale green hydrogen production, while minimizing reliance on precious metals.
Abstract
Proton exchange membrane water electrolyzers (PEMWEs) are pivotal for sustainable hydrogen production, yet the corrosion-induced TiOx on porous transport layers (PTLs) introduces Schottky contact barriers and pinch-off effects, severely impeding charge transfer and efficiency. Here, a cost-effective MoIrOx coating via spray deposition and thermal treatment on Ti felts is proposed. The coating forms a conductive interlayer that establishes a Schottky barrier staircase, reducing the effective electron transfer barrier and isolating TiOx from the ionomer to mitigate the pinch-off effect. The optimal PTL achieves a current density of 3.27 A cm−2 at 2 V, surpassing uncoated Ti felts by 59.5%. The MoIrOx interlayer suppresses localized electron accumulation at the interface, enabling stable operation with ultra-low catalyst loadings by preventing direct ionomer-TiOx contact. This work demonstrates a scalable strategy to enhance PEMWE efficiency and durability while minimizing precious metal reliance, offering critical insights into interface engineering for electrolyzers.
1. Introduction
The commercialization of proton exchange membrane water electrolyzers (PEMWEs) is hindered by the corrosion of titanium-based porous transport layers (PTLs) under harsh acidic and high-potential conditions. The resulting TiOx passivation layer introduces Schottky contact barriers at the PTL/catalyst interface, impeding electron transfer and causing the pinch-off effect—a nanoscale phenomenon where energy band bending at the semiconductor-electrolyte-catalyst junction increases charge transfer resistance. These interfacial losses degrade cell efficiency and durability, limiting the economic viability of green hydrogen production.
Existing mitigation strategies, such as applying noble metal coatings (e.g., Pt or Ir), are effective but cost-prohibitive for large-scale deployment. This work introduces a cost-effective MoIrOx coating applied via spray deposition and thermal treatment on Ti felts. The coating forms a conductive interlayer that establishes a Schottky barrier staircase, reducing the effective electron transfer barrier and isolating TiOx from the ionomer to mitigate the pinch-off effect. This approach directly addresses the interfacial bottleneck, achieving a 59.5% improvement in current density at 2 V while minimizing precious metal loading, offering a scalable pathway to enhance PEMWE performance and durability.
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Yun Liu, Bingqian Pang, Sihan Mao, Wenjuan Shi, Tianjiao Wang, Peng Rao, Jing Li, Min Wang, Yuliang Yuan, Xiaodong Shi, Xinlong Tian, Zhenye Kang (2026). Suppression of Schottky Effect with Highly Corrosion-Resistant Coating on Porous Transport Layers for Interface Optimization in Proton Exchange Membrane Electrolyzers. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3769-2
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Frequently Asked Questions
What is the specific improvement in current density achieved by the MoIrOx-coated PTL compared to uncoated Ti felt, and what is the underlying mechanism?
The MoIrOx-coated PTL achieves a current density of 3.27 A cm−2 at 2 V, which is 59.5% higher than uncoated Ti felts. This improvement is attributed to the suppression of the Schottky barrier and pinch-off effect. The MoIrOx coating forms a conductive interlayer that creates a Schottky barrier staircase, reducing the effective electron transfer barrier. Additionally, it isolates TiOx from the ionomer, preventing the pinch-off effect that causes energy band bending and increased charge transfer resistance.
How does the MoIrOx coating mitigate the pinch-off effect, and what is the role of the interlayer in preventing direct ionomer-TiOx contact?
The pinch-off effect arises from extensive contact between TiOx (a wide-bandgap n-type semiconductor) and the ionomer, leading to significant energy band bending and increased charge transfer barriers. The MoIrOx coating acts as a conductive interlayer that physically separates TiOx from the ionomer, preventing direct contact. This isolation reduces the nanoscale interaction that causes pinch-off, thereby lowering the charge transfer barrier and improving interfacial conductivity.
What is the scalability of the spray deposition and thermal treatment method for industrial production of coated PTLs?
Spray deposition and thermal treatment are well-established, scalable techniques used in industrial coating processes. The method allows for uniform coating on large-area Ti felts, and the materials (Mo and Ir) can be applied in thin layers to minimize precious metal usage. The demonstrated performance improvement (59.5% increase in current density) suggests that this approach can be economically viable for large-scale PEMWE manufacturing, though further optimization of coating thickness and uniformity is needed for full-scale production.
What is the long-term stability of the MoIrOx-coated PTL under PEMWE operating conditions, and how does it compare to uncoated Ti felts?
The study indicates that the MoIrOx interlayer suppresses localized electron accumulation at the interface, enabling stable operation with ultra-low catalyst loadings. While specific long-term degradation rates are not provided in the abstract, the corrosion-resistant nature of the coating is expected to prevent TiOx formation, thereby maintaining low interfacial resistance over extended operation. Uncoated Ti felts suffer from gradual passivation, leading to performance decay, whereas the coated PTL is designed to mitigate this issue.
How does the MoIrOx coating reduce reliance on precious metals, and what are the implications for cost reduction in PEMWE systems?
The MoIrOx coating uses a combination of molybdenum (a non-precious metal) and iridium (a precious metal) in a thin layer, reducing the overall iridium loading compared to conventional coatings that rely solely on noble metals. This minimizes precious metal reliance, lowering material costs. The improved performance (59.5% higher current density) also means that less catalyst material is needed to achieve the same hydrogen production rate, further reducing system costs. This is critical for the economic viability of large-scale green hydrogen production.
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