Microstructural Effects on Electrocatalytic Oxygen Reduction Activity of Nano‐Grained Thin‐film Platinum in Acid Media

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Abstract
The oxygen reduction activity of thin‐film platinum deposits on carbon and its relationship to catalyst microstructure has been investigated using rotating‐disk‐electrode techniques. The thin‐film form of platinum is a viable tool for catalyst study as it can provide intrinsic activity data on finely divided carbon‐supported platinum. Sputtered polycrystalline thin‐film platinum deposits on carbon (loading from 6 to 200 μg/cm2) have been characterized, and their oxygen reduction activity at 25°C in 1M sulfuric acid determined. Catalyst characterization consisted of electrochemical surface‐area measurement and establishing grain size, morphology, and lattice parameter using transmission electron microscopy. Thin‐film platinum exhibits a reduced lattice parameter at very small grain size. Mass activity and specific activity at 0.9 V vs. reversible hydrogen electrode both decrease with increasing grain size (and decreasing specific surface area). Peak mass activity for oxygen reduction was 25 A/g of Pt, and peak specific activity was 0.070 mA/cm2 of Pt surface. The activity trends are attributed to the changes in electronic and geometric properties.

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