Transition
metal oxides have gained attention as promising oxygen
evolution reaction (OER) electrocatalysts in alkaline electrolytes,
but heterogeneities in typical catalyst samples often obscure key
structure–property relationships that are essential for developing
higher performance materials. Here, we have combined ultrahigh vacuum
surface science techniques, electrochemical measurements, and density
functional theory (DFT) to quantify structure-dependent OER activity
in a series of well-defined electrocatalysts. We describe a direct
correlation between the population of Fe edge-site atoms and the OER
activity of ultrathin Fe2O3 nanostructures (∼0.5
nm apparent height) grown on Au(111) substrates. Hydroxylated Fe atoms
residing at edge-sites along the catalyst/support interface were spectroscopically
identified as key reaction centers, and these Fe edge-site atoms were
estimated to produce OER turnover frequencies approximately 150 times
higher than that of Fe atoms on the catalyst surface at an applied
potential of 1.8 V vs the reversible hydrogen electrode. Impressively,
ultrathin Fe2O3/Au nanostructures with a high
density of catalytically active Fe edge-site atoms outperformed an
ultrathin IrO
x
/Au catalyst at moderate
overpotentials. DFT calculations revealed more favorable OER at edge
sites along the Fe2O3/Au interface, with lower
predicted overpotentials due to beneficial modification of intermediate
binding. Our results demonstrate how a combination of surface science,
electrochemistry, and computational modeling can be used to identify
key structure–property relationships in a well-defined electrocatalytic
system.
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