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

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.