Rapid characterization of oxygen-evolving electrocatalyst spot arrays by the substrate generation/tip collection mode of scanning electrochemical microscopy with decreased O2 diffusion layer overlap

A simple approach for the screening of oxygen evolution reaction (OER) electrocatalyst arrays by scanning electrochemical microscopy (SECM) in the substrate generation/tip collection (SG/TC) mode is described. The methodology is based on the application of a series (9-10 replicates) of double-potential steps to a catalytically active substrate electrode, which is switched between potentials where it displays OER activity and inactivity. With an SECM tip coaligned to a given electrocatalyst spot, the dual potential step is applied for a relatively short time in order to restrict the growth of the resulting O2 diffusion layer. The SECM is then able to measure the O2 produced while the potential sequence prevents the overlap of the diffusion layer from neighboring spots. With this approach, each spot of material in an array of Ir:Sn oxide compositions (disk shaped, about 150 μm radius) was examined independently at a constant distance. The method was tested for a series of oxygen evolution catalysts made of SnO2-IrO2 mixtures, with compositions varying between Ir:Sn 100:0 to Ir:Sn 0:100. Optimal conditions for avoiding overlapping of the diffusion profiles generated at each spot of the substrate were evaluated by digital simulation. The results obtained for the activity of SnO2-IrO2 mixtures using this new technique were validated by comparison to reported results using SECM and other techniques.