Electrochemical Iridium Dissolution: The Primary Failure Pathway

Electrochemical dissolution of iridium is the most fundamental and widely documented degradation pathway for IrO₂ in PEM electrolyzer anodes. The PEM anode 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 forced iridium loss from the catalyst surface.

This dissolution is not merely surface etching. As documented in the patent disclosure from 中氢能源科技(广东)有限公司 (2021), “Ir and other noble metals as anode catalysts, as well as other inorganic oxides, 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 process is electrochemically driven: at potentials exceeding the thermodynamic dissolution threshold, iridium atoms are continuously oxidised and released into the acidic electrolyte, reducing the active catalyst loading over time.

The Pourbaix diagram for iridium is a recurrent reference in the patent literature. According to a 2023 filing from 苏州朗泰新能源科技有限公司, iridium’s oxidative dissolution potential of 1.9 V vs. RHE at pH = 0 is precisely why IrO₂ is favored over ruthenium oxide (RuO₂), which dissolves at significantly lower potentials. However, even this superior corrosion resistance is insufficient under the prolonged high-potential, high-current-density conditions of industrial electrolysis. The same document confirms that low-iridium or iridium-free OER catalysts face even more severe dissolution at current densities above 0.5 A/cm²—a threshold that is routinely exceeded in modern high-performance electrolyzer stacks, as tracked by organisations such as IRENA in their green hydrogen cost roadmaps.

The crystallinity of IrO₂ is directly linked to its dissolution behaviour. A 2026 patent from 碳工作室有限公司 (Carbon Studio) frames this with particular clarity: “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 trade-off is not a marginal engineering consideration—it is the central design dilemma structuring the entire field of PEM anode catalyst development.

“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 of Active Iridium Sites

Beyond mass loss from dissolution, a second and distinct deactivation route operates through the progressive oxidation and phase transformation of active iridium species during sustained electrolyzer operation. Under prolonged anodic polarization, the catalytically active surface IrOₓ species—which may exist as partially hydrated, amorphous phases with high intrinsic activity—are irreversibly converted to more stable but electrochemically inert higher-valence oxides, reducing both electrochemical surface area and turnover frequency without necessarily losing iridium mass from the electrode.

A 2025 Toyota Motor Corporation patent on grain-boundary-engineered Ir catalysts addresses this directly: “disordered nanostructured catalysts are easily dissolved or oxidized during the oxygen evolution reaction, causing a sharp drop in catalyst stability.” Toyota’s approach identifies grain boundaries as sites where local amorphous IrOₓ species are stabilized and where iridium sites possess better reversible recovery ability, thereby conferring improved resistance against over-oxidation. The grain-boundary strategy is a structural approach to constraining the over-oxidation pathway at the nanoscale.

A 2026 patent from 西安交通大学 (Xi’an Jiaotong University) addresses over-oxidation through heterostructure engineering, describing an IrₓCo₃₋ₓO₄/Ir-Co₃O₄ catalyst designed to “suppress the excessive oxidation of Ir active sites.” The disclosure states that the heterogeneous catalyst design “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 inert Ir(VI) species is a real and significant deactivation pathway that operates in parallel with dissolution.

The amorphous-to-crystalline phase transition is also relevant here. A 2025 patent from 中国石油天然气股份有限公司 notes that metastable-phase IrO₂ materials exhibit 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, with iridium vacancies forming rapid proton transport channels that improve both activity and stability simultaneously. This approach is being tracked by bodies including the IEA as part of the broader electrolyzer cost-reduction agenda.

Interfacial and Mechanical Degradation at Catalyst–PTL Contacts

Significant degradation of IrO₂ anode catalysts arises not only from intrinsic electrochemical processes but also from interfacial failures between the catalyst layer and its surrounding components—principally the porous transport layer (PTL) and the polymer electrolyte membrane. These failure modes are mechanical and structural in origin but produce electrochemical consequences that accelerate the dissolution and depletion of active iridium.

A 2024 Robert Bosch 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.” This localized mechanical stress creates electrochemical hotspots where current density—and therefore dissolution rates—are disproportionately elevated relative to the bulk of the electrode.

A 2024 Siemens Energy patent addresses a distinct but related mechanical failure mode: the physical migration of IrO₂ particles from the catalyst layer into the gas diffusion layer (GDL) mesh structure. The patent discloses a protective iridium/iridium oxide layer applied selectively at the contact points between the GDL and the anode catalyst layer, explicitly “inhibiting the entry of anodic catalyst material” into the GDL structure—a failure mode where IrO₂ particles physically migrate under hydraulic and electrochemical forces. This particle migration not only depletes the catalytic layer but can also block GDL pores, increasing mass transport resistance over time and creating a compounding performance loss mechanism.

Catalyst utilisation losses due to ionomer coverage represent a further interfacial degradation vector. A 2025 patent from 嘉庚创新实验室 (Xiamen) documents that non-uniform distribution of perfluorosulfonic acid (PFSA) ionomer—such as Nafion—in the anode catalyst layer causes portions of the IrO₂ to be encapsulated without forming an effective electrolyte interface, meaning those catalyst particles do not participate in the OER. Over time, as active particles near interfaces dissolve preferentially, the proportion of encapsulated and inactive Ir increases, accelerating the effective catalyst loading loss. This mechanism is particularly severe in high-loading electrodes where catalyst stacking promotes encapsulation. W.L. Gore & Associates has also filed patents positioning catalysts closer to the anode side of composite electrolysis membranes specifically to manage degradation at the membrane–catalyst interface.

Support Corrosion and the Stability of IrO₂ Carriers

The stability of IrO₂ anode catalysts is fundamentally coupled to the stability of the support material on which they are dispersed. In conventional carbon-supported catalysts, the carbon carrier itself undergoes electrochemical oxidation at the strongly anodic potentials of PEM electrolysis, leading to support corrosion, catalyst detachment, and particle agglomeration—all of which accelerate the effective degradation of the iridium active phase even if the IrO₂ itself were intrinsically stable.

A 2022 Tsinghua University 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 directly worsens all other degradation mechanisms simultaneously.

The shift to titanium-based oxide supports is now a dominant trend in the patent literature. Ti₄O₇ (Magnéli phase) combines the electrical conductivity necessary for electrode function with the acid and oxidation resistance required to survive PEM anode conditions. The 无锡威孚 patent confirms that IrO₂ loaded on Ti₄O₇ via molten salt methods produces a porous structure with high density of hydroxylated edge active sites. Without a corrosion-resistant support, even intrinsically stable IrO₂ undergoes accelerated effective degradation as its carrier collapses—a coupling that makes support engineering inseparable from catalyst stability engineering. This aligns with durability benchmarks being developed by standardisation bodies including ISO for hydrogen production equipment, and with the broader green hydrogen scaling agenda tracked by WIPO in its annual technology trends reports on clean energy.

Key Assignees and the Direction of IrO₂ Stability Innovation

The patent landscape for IrO₂ anode catalyst degradation mitigation is dominated by Chinese research institutions in terms of filing volume, with major industrial assignees from Germany, Japan, and the United States contributing high-impact disclosures on specific degradation mechanisms. Each major player has converged on a distinct technical focus reflecting their position in the value chain.

Chinese Research Institutions

Tsinghua University (清华大学), Xi’an Jiaotong University (西安交通大学), 嘉庚创新实验室, and industrial applicants including 中氢能源科技(广东)有限公司 and 无锡威孚环保催化剂有限公司 collectively dominate filing volume. Their technical focus spans catalyst synthesis, support engineering, heterostructure design, and vacancy engineering as stability enhancement strategies. The 西安交通大学 heterostructure approach (IrₓCo₃₋ₓO₄/Ir-Co₃O₄, 2026) and the 无锡威孚 Ti₄O₇ support disclosure (2025) represent the frontier of Chinese academic–industrial translation in this space.

Industrial Assignees: Bosch, Siemens Energy, Toyota, Heraeus

Robert Bosch GmbH addresses both interfacial mechanical degradation through ionomer infiltration of porous transport electrodes and catalyst compositional stability through ternary oxide formulations (IrₓM₁₋ₓO₂). Siemens Energy Global GmbH & Co. KG focuses on the physical migration of catalyst material into the GDL—a stack-engineering degradation concern. Toyota Motor Corporation files patents on grain-boundary-engineered Ir catalysts targeting the amorphous-phase dissolution problem, reflecting a focus on translating laboratory stability insights into manufacturable architectures. Heraeus Deutschland GmbH & Co. KG limits calcination temperature to below 250°C to preserve amorphous IrOₓ activity while controlling dissolution-prone structural features—a synthesis-process approach to the activity–stability trade-off.

The dominant innovation trend across all assignees is the shift from pure IrO₂ to alloyed, heterostructured, or defect-engineered Ir-based materials, driven directly by the need to simultaneously address dissolution, over-oxidation, and support corrosion without sacrificing OER activity. Secondary trends 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. These trends are consistent with the technology roadmaps published by PatSnap’s R&D intelligence platform for clean energy materials.

Across the dataset—spanning Chinese research institutions, Siemens Energy, Robert Bosch, Toyota, Heraeus, Carbon Studio, and W.L. Gore—multiple assignees converge on the conclusion that IrO₂ is currently the only commercially viable PEM anode catalyst, yet its scarcity and degradation under operating conditions remain the central bottleneck for large-scale deployment. The PatSnap innovation intelligence platform tracks over 2 billion data points across 120+ countries, providing R&D teams with the patent depth needed to navigate this rapidly evolving competitive landscape.