ALD‐Coated Mesoporous Iridium‐Titanium Mixed Oxides: Maximizing Iridium Utilization for an Outstanding OER Performance

Frisch, Marvin; Raza, Muhammad Hamid; Ye, Mengyang; Sachse, René; Benjamin, Paul R.; Gunder, René; Pinna, Nicola; Kraehnert, Ralph

doi:10.1002/admi.202102035

Cited by 9 publications

(7 citation statements)

References 68 publications

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“…Increasing the amount of inactive titanium would decrease the number of iridium active sites, resulting in poorer OER activity. Therefore, the OER activity of the Ir-TiO x samples increases as the iridium content increases (Ir20 → Ir70), which is in agreement with literature. , − Furthermore, there is a decrease in the E WE at j = 5 mA/cm 2 potential before and after the CP hold at 1 mA/cm 2 (EP step 3.) indicating some increase in OER activity of the material (see the difference in the open and closed circles in Figure b and the E WE at j = 5 mA/cm 2 improvement value in Figure d for each Ir–Ti ratio).…”

Section: Resultssupporting

confidence: 90%

“…Several studies have addressed this issue, successfully demonstrating an increased long-term OER performance for TiO 2 -supported iridium oxides, exploiting viable synthesis methods that achieve conductive and stable OER anode materials. ,, These studies indicate that there is a beneficial relationship between the material’s electrochemical OER activity and stability when mixing rather unstable but active iridium with stable but inactive TiO 2 . However, only a few publications systematically explore the effects of deliberately tuned iridium–titanium composition on the material’s OER activity–stability relationship, with studies mainly focusing on IrO 2 and TiO 2 mixtures. , − …”

Section: Introductionmentioning

confidence: 99%

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The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts

van der Merwe,

Garcia-Diez,

Lahn

et al. 2023

ACS Catal.

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Iridium has emerged as the leading catalyst material for the anodic oxygen evolution reaction (OER) in acidic media. Often, iridium is mixed with more stable materials such as titanium. For these materials, the electronic structure of titanium plays a crucial role since with varying degrees of oxidation titanium transforms to semiconducting or even insulating phases. Yet, the electronic properties of mixed Ir-TiO x catalysts have never been systematically studied. In this study, we correlate the catalytic performance of mixed Ir-TiO x -based OER catalysts with the electronic structure of the surface layers. For this, a thin film material library with a 20−70 at. % Ir (Ir/[Ir + Ti]) compositional gradient was prepared. We used inductively coupled plasma mass spectrometry to test the OER activity and stability of the set of mixed Ir-TiO x catalyst candidate materials. Complementary, Ti L 2,3 -and O K-edge X-ray absorption spectroscopy and depthdependent X-ray photoelectron spectroscopy measurements were performed to correlate the catalytic performance with the composition and electronic property profiles of these mixed Ir-TiO x OER anode catalysts. The spectroscopic analysis reveals that titanium is present as an intermixed matrix of semiconductive but stable TiO 2 , conductive but less stable titanium-suboxides (TiO x ), and highly conductive but highly unstable metallic Ti(0). The extent of the titanium oxidation strongly depends on the titanium content, with a lower degree of oxidation observed for lower titanium (and thus higher iridium) contents. For an iridium loading of 70 at. %, the respective mixed Ir-TiO x catalyst showed a similar OER activity to that of the pure metallic iridium (1.74 vs 1.59 V RHE , respectively) but with a 71% lower iridium dissolution rate relative to the pure metallic iridium. This demonstrates the stabilization effect of titanium addition while maintaining high OER activity.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts

van der Merwe,

Garcia-Diez,

Lahn

et al. 2023

ACS Catal.

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“…In addition to the carbon-based materials, metal oxides were also employed as substrate materials in the catalyst construction, and there are also strong charge redistribution and migration of support oxide species to the metal surface between the metal and metal oxide supports [204,205]. The presence of such interactions could also improve the catalytic stability of supported Ir-based materials under OER conditions [206].…”

Section: Metal Oxide Supportmentioning

confidence: 99%

Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

Wang¹,

Schechter²,

Feng³

2023

Nano Research Energy

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Iridium (Ir)-based catalysts are highly efficient for the anodic oxygen evolution reaction (OER) due to high stability and anticorrosion ability in the strong acid electrolyte. Recently, intensive attention has been directed to novel, efficient, and lowcost Ir-based catalysts to overcome the challenges of their application in the water electrolysis technique. To make a comprehensive understanding of the recently developed Ir-based catalysts and their catalytic properties, the mechanism and catalytic promotion principles of Ir-based catalysts were discussed for OER in the acid condition aimed for the proton exchange membrane water electrolyzer (PEMWE) in this review. The OER catalytic mechanisms of the adsorbate evolution mechanism and the lattice oxygen mechanism were first presented and discussed for easy understanding of the catalytic mechanism; a brief perspective analysis of promotion principles from the aspects of geometric effect, electronic effect, synergistic effect, defect engineering, support effect was concluded. Then, the latest progress and the practical application of Ir-based catalysts were introduced in detail, which was classified into the varied composition of Ir catalyst in terms of alloys, hetero-element doping, perovskite, pyrochlore, heterostructure, core-shell structure, and supported catalysts. Finally, the problems and challenges faced by the current Ir-based catalyst in the acidic electrolyte were put forward. It is concluded that highly efficient catalysts with low Ir loading should be developed in the future, and attention should be paid to probing the structural and performance correlation, and their application in real PEMWE devices. Hopefully, the current effort can be helpful in the catalysis mechanism understanding of Ir-based catalysts for OER, and instructive to the novel efficient catalysts design and fabrication.

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“…Titanium is a potentially useful substituent since TiO 2 is thermodynamically stable under the highly acidic environments (pH ≤1) and high potentials (>1.5 V RHE ) required for OER. , Prior work has investigated Ir–Ti mixed oxides to improve stability and evaluated IrTiO x as a catalyst and support . So-called dimensionally stable anodes (DSAs) synthesized by coating a solution of Ru and Ti salts onto Ti metal followed by thermal decomposition have been utilized industrially for chlorine evolution and explored for OER .…”

Section: Introductionmentioning

confidence: 99%

Titanium Substitution Effects on the Structure, Activity, and Stability of Nanoscale Ruthenium Oxide Oxygen Evolution Electrocatalysts: Experimental and Computational Study

Godínez-Salomón

Ospina-Acevedo

Albiter

et al. 2022

ACS Appl. Nano Mater.

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Proton-exchange membrane water electrolyzers produce hydrogen from water and electricity and can be powered using renewable energy; however, the high overpotential, high cost, and limited supply of the oxygen evolution reaction (OER) electrocatalyst are key factors that hinder wide-scale adoption. Ruthenium oxide (RuO2) has a lower overpotential, lower cost, and higher global supply compared with iridium oxide (IrO2), but RuO2 is less stable than IrO2. As an approach to improve the catalytic stability, we report the effect of titanium substitution at different concentrations within nanoscale RuO2, Ru1–x Ti x O2 (x = 0–50 at. %), on the structure, OER activity, and stability using combined experiments and theory. Titanium substitution within rutile RuO2 affects the electronic structure, resulting in regions of electron accumulation and electron depletion at the surface, and shifts the d-band and O 2p band centers to higher binding energies. Calculations show that the effects of Ti on the electronic structure are highly dependent on not only the concentration but also the specific dopant location. From electrochemical testing and analysis of the electrolyte and simulations, titanium substitution at low concentrations (12.5 and 20 at. %) improves catalyst stability and lowers Ru dissolution. Experiments of OER activity agree with the theory that Ti substitution results in a higher overpotential when averaging over all adsorption sites. Theoretical analysis shows that specific sites predominately act as catalytic sites for the OER, while metal dissolution occurs at different sites. Specifically, OER has the lowest barriers at penta-coordinated Ru sites, while hexa-coordinated Ru sites have the lowest energetic barriers for dissolution.

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ALD‐Coated Mesoporous Iridium‐Titanium Mixed Oxides: Maximizing Iridium Utilization for an Outstanding OER Performance

Abstract: ≈20 to 100 µg cm -2 . The assessment of catalytic OER activity in an RDE setup revealed a linear dependence of nominal Ir loading and current density j at a potential of 1.60 V RHE .

Cited by 9 publications

References 68 publications

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts

Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

Titanium Substitution Effects on the Structure, Activity, and Stability of Nanoscale Ruthenium Oxide Oxygen Evolution Electrocatalysts: Experimental and Computational Study

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ALD‐Coated Mesoporous Iridium‐Titanium Mixed Oxides: Maximizing Iridium Utilization for an Outstanding OER Performance

Abstract: ≈20 to 100 µg cm -2 . The assessment of catalytic OER activity in an RDE setup revealed a linear dependence of nominal Ir loading and current density j at a potential of 1.60 V RHE .

Cited by 9 publications

References 68 publications

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx Oxygen Evolution Reaction Catalysts

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx Oxygen Evolution Reaction Catalysts

Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

Titanium Substitution Effects on the Structure, Activity, and Stability of Nanoscale Ruthenium Oxide Oxygen Evolution Electrocatalysts: Experimental and Computational Study

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The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts

The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiO_x Oxygen Evolution Reaction Catalysts