Impact of film drying procedures on RDE characterization of Pt/VC electrocatalysts

Evaluation of Pt/Vulcan carbon (Pt/VC) electrocatalysts for the oxygen reduction reaction (ORR) is dependent on the quality of the electrocatalyst-coated thin film electrode used for rotating disk electrode (RDE) methodology. Traditionally, films are made by dropping a catalyst ink on an inverted, stationary glassy-carbon electrode, and then air-drying it, but the resulting films are irreproducible and often have poor quality. We present a drying procedure for making reproducible, smooth thin electrocatalyst films, by rotating the electrocatalyst ink on the glassy-carbon electrode substrate at 700 rpm while it is drying. The differences between the morphologies of films made with the rotational versus the stationary drying methods are illustrated with 3D optical profilometry and scanning electron microscopy. Film thickness and uniformity was determined by optical interferometric profilometry for films prepared with both drying methods. The stationary drying method leads to a non-uniform film with thicknesses varying from 0.042 μm in the center of the disk electrode to 4.5 μm towards the edge of the electrode. The rotational drying method yields a uniform film thickness of about 0.8 μm over the entire electrode surface. The difference in these film morphologies is quantified for the ORR electrocatalytic activity of a 19.7% and 40% Pt/VC electrocatalyst. The platinum mass and area-specific activities for the ORR are on average 72% and 56% higher for electrocatalyst made by this rotational drying method, compared to those made from the stationary drying method.

► A simple, fast and reliable method is presented to make thin catalyst films for RDE.
► Stationary drying method leads to non-uniform films with varying thicknesses.
► The novel rotational drying method consistently produces uniform films.
► ORR activity of films prepared with the rotational drying is more reproducible.
► Rotational drying method improves ORR mass and specific activity by 72% and 56%.