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Polycrystalline alloy electrodes of Pt with alkaline earth metals (Ca, Sr, and Ba) have been shown to exhibit enhanced electrocatalytic performance for oxygen reduction reaction (ORR) relative to P...

With recent technological advances, the demand for renewable energy is ever growing. Polymer electrolyte membrane fuel cells (PEMFCs) have shown great promise in subduing various environmental and ...

Scanning electrochemical cell microscopy (SECCM) is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle. This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images. Evidently, this becomes impossible for very small nanoparticles and hence, a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles. We show, that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined, the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles.

Complex solid solutions (“high entropy alloys” with a single solid-solution phase) hold great promise in electrocatalysis because of their nearly unlim- ited number of different active sites exposed at the surface. It has been shown by theoretical studies that multiple arrangements of different elements directly neighboring a binding site create millions of differently active catalytic sites. We report a zooming-in approach using scanning electrochemical cell microscopy (SECCM) to distinguish between the averaged electrochemical response of mul- tiple active sites and active site-specific electrochemical response. Using a thin film complex solid solution electrocatalyst and a range of SECCM single bar- rel capillaries with diameters from 1.2 µm to 50 nm, we observed an averaged electrochemical response for the oxygen reduction reaction with minor statisti- cal variations for the larger capillary diameters. In contrast, significant statistical heterogeneity among the measured spots is observed for small capillary diame- ters. This statistical heterogeneity is attributed to the ability of the smaller probe size to address a comparatively smaller number of active sites with high or low activity dominating the measured electrocatalytic currents. &nbsp