Ir nanodendrites on ATO for acid OER
TTAB-grown Ir nanodendrites on mesoporous ATO outperform Ir black for oxygen evolution in acid and in a PEM electrolyzer.
Source
Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers
Inspect source passages
Ir nanodendrites on ATO for acid OER
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Ir-ND particles are 15–20 nm by TEM
The low resolution TEM image of the as-synthesized material revealed a largely dendritic structure with a narrow size range of 15–20 nm () and high-yield formation.
Crystallite size of Ir-ND is 1.7 nm versus 3.2 nm for Ir black
The crystallite size of Ir-ND and Ir black was estimated to 1.7 nm and 3.2 nm, respectively.
What they did
They reduced H2IrCl6 with NaBH4 in TTAB to make 15–20 nm Ir nanodendrites, deposited them on high-area ATO (or carbon), oxidized the surface electrochemically, and measured OER in 0.05 M H2SO4 and in a 5 cm2 PEMWE single cell.
What they found
Ir-ND crystallites are 1.7 nm versus 3.2 nm for Ir black; BET area is 39.2 versus 18.2 m2 g–1; electrochemical porosity is 34.2% versus 20%. Mass activity is 8 times Ir black at 1.51 V. Ir-ND/ATO reaches 1.50 A cm–2 at 1.8 V in the cell, versus 0.80 A cm–2 for Ir black, and is the most durable in 15 h chronopotentiometry.
The limits
What it doesn't show
Long-term stack lifetime and Ir dissolution rates are not quantified beyond 15 h RDE holds. The 8-fold mass-activity claim is at one overpotential in liquid acid, not a full Tafel comparison across pH. Carbon-supported Ir-ND still faces support corrosion in PEM anodes.
Key terms
- Oxygen evolution reaction (OER)
- Anodic 2 H2O → O2 + 4 H+ + 4 e–; the slow electrode reaction in acid water electrolyzers.
- Nanodendrite
- Branched nanoparticle with many edges/corners, here assembled from tiny Ir seeds.
- ATO
- Antimony-doped tin oxide, a corrosion-resistant oxide support used instead of carbon at the anode.
- PEMWE
- Polymer-electrolyte-membrane water electrolyzer operating in acid with a solid Nafion-type membrane.
- Electrochemical porosity
- Fraction of charge associated with inner, more porous oxide versus outer surface; 34.2% for Ir-ND.
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Quiz yourself
Ir-ND mass activity versus commercial Ir black at 1.51 VRHE is about
Common questions
Why support Ir-ND on ATO instead of carbon?
The anode sees high potential and acid; ATO is more corrosion-resistant than carbon black while still conducting.
How much more active is Ir-ND than Ir black?
About 8 times the Ir-mass activity at 1.51 VRHE (280 mV overpotential).
What cell current does Ir-ND/ATO reach?
1.50 A cm–2 at 1.8 V, versus 0.80 A cm–2 for unsupported Ir black.
How are the dendrites made?
Fast NaBH4 reduction of Ir(IV) in TTAB water at 70 °C self-assembles tiny seeds into 15–20 nm dendrites.
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