OXYGEN REDUCTION ON ELECTRODEPOSITED NANOCLUSTERS OF Pt USING EC-AFM

Studying particle size and shape on a nano metric level plays a key role in understanding catalytic activity of materials. We have used electrochemical atomic force microscopy (EC-AFM) to direct the electrochemical deposition of small aggregates of Pt catalysts. A specially made long tip of 1µm diameter was applied for performing electrodeposition of single and agglomerated nanocluster of Pt on HOPG surface with a size of 80-90nm. Several parameters were controlled during this process including- Pt concentration, tip san rate and line deposition. Further analysis of oxygen reduction reaction (ORR) on electrodeposits Pt on HOPG surface was performed using the same setup. Probing the catalyst at a very short distance from the surface provides unique conditions of examining reaction under a very small volume below the AFM tip, where minimal convection occurs. Short lived intermediates such as hydrogen peroxide (H₂O₂) which is produced by partial reduction of O₂ (2e- process) is measured using tip as an auxiliary electrode, by polarizing this electrode to 0.9V were peroxide is reduced. By this approach, a full mapping of peroxide is obtained from the deposited catalyst. In addition, the working distance between the tip and the surface is 3-4 nm has been shown to provide peroxide current collection efficiency of close to 100%. A correlation of the deposited Pt morphology and the ORR activity is demonstrated via simultaneously current mapping in a single system setup.