Pore diameter flips ORR from kinetic to transport control
Narrower Pt–Ni nanozyme channels raise ORR activity at low overpotential by concentrating protons, but at high overpotential O2 reacts at the pore mouth.
Source
The importance of nanoscale confinement to electrocatalytic performance
What they did
Authors etched Pt–Ni particles with different channel-size distributions, passivated exteriors with oleylamine, measured ORR vs electrolyte concentration, and modelled EDL overlap and O2 depletion.
What they found
69/52/34% of channels <2 nm across three etch ratios. Specific activity 3.3× higher at 0.95 V when only interiors are active. Kinetic regime favors smaller pores; mass-transport regime favors larger pores. EDL ~3, 1, 0.33 nm at 0.01/0.1/1 M HClO4.
The limits
What it doesn't show
Active-site chemical identity inside vs outside is not independently proven; model assumes protons as the confined reactant.
Key terms
- Nanozyme (here)
- Nanoparticle with isolated substrate channels mimicking an enzyme active-site geometry.
- Nanoconfinement
- Altered concentrations/EDL when a pore is comparable to the double-layer thickness.
- Koutecký–Levich
- Analysis that extracts kinetic current by extrapolating to infinite rotation rate.
- EDL overlap
- When electrical double layers from opposite pore walls meet, changing ion profiles.
- Mass-transport limit
- Rate set by O2 diffusion, here localized at the channel entrance.
Flashcards
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Smaller channels help most when:
Common questions
When does smaller pore help?
Under kinetic control (low overpotential).
When does larger pore help?
Under O2 mass-transport control (high overpotential).
Why protons?
They migrate in as counter-ions and are also the ORR reactant.
Why oleylamine?
Passivates the exterior so only channels react.
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