Chem
Volume 5, Issue 12, 12 December 2019, Pages 3243-3259
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Article
Dissolution-Induced Surface Roughening and Oxygen Evolution Electrocatalysis of Alkaline-Earth Iridates in Acid

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Highlights

  • Significantly increased OER activity with catalyst stability in acid is observed

  • Notable surface roughening on the atomic level is induced by alkaline-earth leaching

  • The formation of rutile-like IrOx nanocrystallites by Sr dissolution is identified

  • Monitoring surface structure variations should be emphasized for OER electrocatalysis

The Bigger Picture

Ir-based oxides are well-known materials used as electrocatalysts for the oxygen evolution reaction (OER). Despite notable catalytic properties, the scarceness and subsequent high cost of Ir are serious disadvantages for actual applications ranging to fuel cells and electrolyzers. To reduce the amount of Ir used per unit mass of a catalyst and to boost the OER activity and stability under acidic conditions, many different types of Ir oxides mixed with other elements have recently been suggested. With a combination of direct atomic-level observations and chemical analyses, this work shows that enormous surface roughening can be induced by alkaline-earth leaching in AIrO3-type iridates (A = Sr and Ba) during the OER in acid, thus making a major contribution to the continuous growth of the OER activity overall without serious degradation.

Summary

Alkaline and alkaline-earth iridates have garnered much attention, as they can outperform traditional IrO2 for oxygen evolution electrocatalysis under acidic conditions. Despite the advantages of their catalytic properties and significant reduction of Ir utilization, dissolution of alkaline and alkaline-earth elements into acid media can be a serious drawback that may confine long-term applications. By using atomic-column-resolved scanning transmission electron microscopy, we demonstrate the surface variations of three alkaline-earth iridates, AIrO3 (A = Sr or Ba). Directly identifying the structural transformation into metastable nanocrystallites or an amorphous state, we elucidate that substantial surface roughening can be induced by alkaline-earth elemental leaching. In particular, ∼20-fold increases in the active surface area in pseudocubic SrIrO3 and monoclinic BaIrO3 are notable structural features. Our findings emphasize both the impact of surface structure on the overall catalytic activity and consequently the important control of chemical leaching to attain a high surface area in iridate-based catalysts.

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SDG7: Affordable and clean energy

Keywords

electrocatalysis
iridium oxides
oxygen evolution reaction
scanning transmission electron microscopy
surface

Cited by (0)

3

These authors contributed equally

4

Present address: Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 02792, Korea

5

Lead Contact