Electrochemical Iridium Dissolution: The Primary Failure Mode in PEM Anode Catalysts

Electrochemical dissolution of iridium is the most fundamental and widely documented degradation pathway for IrO₂ in PEM electrolyzer anodes. The PEM environment is equivalent in acidity to approximately 0.5 M H₂SO₄ or 1 M HClO₄, and anode potentials routinely reach 1.8–2.2 V versus the standard hydrogen electrode (SHE) during full-load operation — conditions that drive continuous, thermodynamically favoured iridium dissolution from the catalyst surface.

According to patent disclosures from 苏州朗泰新能源科技有限公司 (2023), iridium and its oxides have an oxidative dissolution potential of approximately 1.9 V vs. RHE at pH = 0, making iridium one of the most corrosion-resistant elements in the periodic table. This is precisely why IrO₂ is favoured over ruthenium oxide (RuO₂), which dissolves at significantly lower potentials. However, even this superior corrosion resistance proves insufficient under the prolonged high-potential, high-current-density conditions of industrial electrolysis. As noted by 中氢能源科技(广东)有限公司 (2021), “Ir and other noble metals as anode catalysts are highly susceptible to corrosion in the strongly oxidizing environment and strongly acidic medium, causing changes in the catalyst and leading to overall performance decay of PEM electrolysis equipment.”

The dissolution process is not merely surface etching. It is a continuous electrochemical process driven by the thermodynamic instability of iridium species above their oxidative dissolution threshold. Low-iridium or iridium-free OER catalysts face even more severe dissolution at current densities above 0.5 A/cm², confirming that IrO₂ remains the only commercially viable choice for PEM anode operation — despite its inherent instability under those very conditions.

The relationship between crystallinity and dissolution behaviour is a recurrent and critical theme in the patent literature. A 2026 disclosure from Carbon Studio (碳工作室有限公司) frames the problem directly: “amorphous iridium oxide exhibits excellent catalytic performance but, due to the characteristics of PEM water electrolysis operation in an acidic atmosphere, some iridium dissolves in water, and thus the durability of such catalysts is poor. In contrast, crystalline iridium oxide shows poor dispersion on the support due to preparation at high temperatures, leading to low catalytic activity, but such catalysts have excellent durability.” This amorphous–crystalline trade-off sits at the centre of every contemporary durability engineering strategy for PEM anode catalysts — a point reinforced by research published through bodies such as Nature and tracked through global filings monitored by WIPO.

“At high current densities, the metallic elements in the catalyst become unstable, undergo dissolution and metal loss, leading to catalyst deactivation and ultimately complete failure of the electrolysis stack.”

Phase Transformation and Over-Oxidation: A Distinct and Underappreciated Deactivation Route

Over-oxidation of active iridium sites is a separate and distinct degradation mechanism from dissolution — one that reduces OER activity without any net loss of iridium mass from the catalyst layer. Under sustained anodic polarization, the active surface IrOₓ species — which may exist as partially hydrated, amorphous phases with high intrinsic activity — are irreversibly oxidized to more stable but less active higher-valence oxides, reducing electrochemical surface area and turnover frequency.

Toyota Motor Corporation’s 2025 patent on grain-boundary-engineered Ir catalysts identifies this mechanism directly: “disordered nanostructured catalysts are easily dissolved or oxidized during the oxygen evolution reaction, causing a sharp drop in catalyst stability.” The Toyota inventors identify grain boundaries as sites where local amorphous IrOₓ species are stabilized and where iridium sites possess better reversible recovery ability, thereby conferring improved stability against over-oxidation. This insight — that nanoscale structural engineering can protect active sites from irreversible oxidation — is now being pursued by multiple assignees as a route to simultaneously high activity and high stability.

Xi’an Jiaotong University’s 2026 patent on IrₓCo₃₋ₓO₄/Ir-Co₃O₄ heterostructure electrocatalysts addresses over-oxidation through a different strategy: cation vacancy engineering and heterostructure design that “effectively improves the electronic structure around Ir active centers, strengthens metal–metal oxide support interactions, and inhibits excessive oxidation of Ir active center atoms, greatly improving the activity and stability of the catalyst.” This confirms that the progressive conversion of active Ir(III/IV) to electrochemically inert higher-valence species is a real and significant deactivation pathway, not merely a theoretical concern.

Metastable-phase IrO₂ materials represent a further dimension of this problem. According to a 2025 patent from China National Petroleum Corporation (中国石油天然气股份有限公司), metastable-phase IrO₂ exhibits superior OER performance compared to thermodynamically stable-phase IrO₂, but these phases are inherently susceptible to structural transformation under operating conditions. Vacancy engineering — including both iridium vacancies and oxygen vacancies — has been identified as a strategy to maintain high activity while improving resistance to phase degradation. Iridium vacancies in particular form rapid proton transport channels that improve both activity and stability, according to this disclosure. This aligns with broader electrochemistry research published by institutions including Nature on defect-engineered oxide catalysts for water splitting.

Interfacial and Mechanical Degradation: How Hotspots, Particle Migration, and Ionomer Encapsulation Deplete the Anode

Significant IrO₂ degradation in PEM electrolyzers arises not from intrinsic catalyst chemistry but from interfacial failures between the catalyst and its surrounding components — the porous transport layer (PTL), the polymer electrolyte membrane, and the ionomer binder. These mechanisms can accelerate effective catalyst loss far beyond what bulk dissolution rates alone would predict.

PTL–Catalyst Contact Hotspots

Robert Bosch GmbH’s 2024 patent on porous transport electrodes with infiltrated ionomer identifies poor surface contact between the PTL and the anode catalyst layer as a root cause of accelerated local degradation: “poor surface contact between the PTL and the anode catalyst layer of the electrolyzer can lead to inefficient utilization of anode catalyst materials… Poor surface contact can also lead to accelerated local degradation at the contact points between PTL and the anode catalyst layer.” The localized stress at these contact points creates electrochemical hotspots where current density — and therefore dissolution rates — are disproportionately elevated relative to the bulk of the catalyst layer.

Physical Catalyst Migration into the GDL

Siemens Energy’s 2024 patent on PEM electrolytic cells addresses a distinct mechanical degradation mechanism: the physical migration of IrO₂ particles from the catalyst layer into the porous transport electrode (GDL) under hydraulic and electrochemical forces during operation. The patent discloses a protective iridium/iridium oxide layer applied selectively at the contact points between the gas diffusion layer and the anode catalyst layer, explicitly “inhibiting the entry of anodic catalyst material” into the GDL mesh structure. This particle migration not only depletes the catalytic layer but can also poison the GDL pores, increasing mass transport resistance over time — a stack-level degradation concern that cannot be addressed by catalyst chemistry alone.

Ionomer Encapsulation and Catalyst Utilization Loss

A 2025 patent from 嘉庚创新实验室 specifically addresses the measurement and consequences of ionomer-driven catalyst utilization loss. Non-uniform Nafion distribution encapsulates IrO₂ particles without forming effective electrolyte interfaces, meaning those catalyst particles cannot participate in the oxygen evolution reaction. Over time, as active particles near interfaces dissolve preferentially, the fraction of encapsulated and inactive iridium increases — accelerating the apparent performance loss in a way that is independent of the absolute iridium dissolution rate. This mechanism is particularly severe in high-loading electrodes where catalyst stacking promotes encapsulation.

Support Corrosion: Why Catalyst Carrier Stability Is Inseparable from IrO₂ Durability

The stability of IrO₂ in PEM electrolyzer anodes is fundamentally coupled to the stability of its support material. Carbon-based supports — widely used in PEM fuel cell cathodes — undergo electrochemical oxidation at the strongly anodic potentials of PEM electrolysis, leading to support corrosion, IrO₂ particle detachment, and agglomeration that accelerates effective catalyst degradation even when the iridium itself remains chemically intact.

Tsinghua University’s 2022 patent specifies that the support must be “oxidation-resistant” and “highly conductive,” because catalyst–support interaction directly governs both activity and stability through synergistic effects. The patent prescribes nanostructured supports in the 10–500 nm particle size range, or mesoporous architectures, to maximise dispersion of active IrO₂ nanoparticles. Poorly dispersed, agglomerated IrO₂ degrades more rapidly due to reduced accessible surface area and increased local current density per active site — a compounding effect where support failure accelerates the primary dissolution mechanism.

The most advanced response to carbon support corrosion identified in the patent dataset is the development of titanium-based oxide supports, particularly Ti₄O₇ (Magnéli phase). A 2025 patent from 无锡威孚环保催化剂有限公司 describes the synthesis of a highly conductive, high-surface-area Ti₄O₇ support that resolves “the problem of poor electrical conductivity of conventional TiO₂ powder.” IrO₂ loaded on this support via molten salt methods produces a porous structure with a high density of hydroxylated edge active sites. These hydroxylated edge sites “can achieve the oxygen evolution reaction through an adsorbate release mechanism involving structural hydroxyls,” providing both high catalytic activity and the structural stability required for long-term operation — without the electrochemical vulnerability of carbon. Standards and certification frameworks for such materials are being developed with input from bodies including ISO, while broader hydrogen technology deployment targets are tracked by the IEA.

Patent Landscape: Who Is Solving IrO₂ Degradation and How

The patent dataset spanning Chinese research institutions, major industrial assignees, and Korean and US academic applicants reveals a clear convergence on the conclusion that IrO₂ is currently the only commercially viable PEM anode catalyst — and that its degradation under operating conditions is the central bottleneck for large-scale deployment. The dominant innovation trend is a shift from pure IrO₂ to alloyed, heterostructured, or defect-engineered Ir-based materials.

Leading Assignees and Their Technical Focus

• Chinese Research Institutions (Tsinghua University, Xi’an Jiaotong University, 嘉庚创新实验室, 无锡威孚, 中氢能源科技, 安徽焓能, 中国石油天然气): Collectively dominate filing volume, focusing on catalyst synthesis, support engineering, heterostructure design, and vacancy engineering as stability enhancement strategies.
• Toyota Motor Corporation: Files patents on grain-boundary-engineered Ir catalysts (2025) targeting the amorphous-phase dissolution problem, reflecting a focus on translating laboratory stability insights into manufacturable catalyst architectures.
• Robert Bosch GmbH: Addresses both interfacial mechanical degradation through porous transport electrode ionomer infiltration (2024) and catalyst compositional stability through ternary oxide formulations (IrₓM₁₋ₓO₂).
• Siemens Energy Global GmbH & Co. KG: Focuses on the mechanical migration of catalyst material into the GDL structure — a uniquely practical stack-engineering degradation concern (2024).
• Heraeus Deutschland GmbH & Co. KG: Files patents focused on synthesis conditions, particularly limiting calcination temperature to below 250°C to preserve amorphous IrOₓ activity while controlling dissolution-prone structural features (2024, 2022).
• W.L. Gore & Associates: Discloses composite electrolysis membranes with catalysts positioned closer to the anode side to manage degradation at the membrane–catalyst interface (2024).

Secondary innovation trends identified across all assignees include: development of alternative corrosion-resistant non-carbon supports (Ti₄O₇, TiO₂, mixed metal oxides); ionomer distribution engineering to recover buried catalyst; and stack-level design interventions (protective layers, modified PTL–catalyst interfaces) to mitigate mechanical degradation pathways. The PatSnap R&D intelligence platform and PatSnap Eureka provide full access to this patent landscape, including assignee-level filing trends and claim-level analysis of degradation mitigation strategies.