Zooming‐in – Visualization of active site heterogeneity in high entropy alloy electrocatalysts using scanning electrochemical cell microscopy. Issue 3 (6th August 2021)

• Record Type: Journal Article
• Authors: Tetteh, Emmanuel Batsa; Banko, Lars; Krysiak, Olga A.; Löffler, Tobias; Xiao, Bin; Varhade, Swapnil; Schumacher, Simon; Savan, Alan; Andronescu, Corina; Ludwig, Alfred; Schuhmann, Wolfgang
• Is Part Of: Electrochemical science advances. Volume 2:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-06
• Subjects: complex solid solution -- high entropy alloy -- oxygen reduction reaction -- scanning electrochemical cell microscopy -- SECCM; Electrochemistry -- Periodicals; Electrochemistry; Periodicals; 541.3705
• DOI: 10.1002/elsa.202100105
• Languages: English
• ISSNs: 2698-5977

Abstract

Abstract: Complex solid solutions ("high entropy alloys" with a single solid‐solution phase) hold great promise in electrocatalysis because of their nearly unlimited 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 multiple active sites and active site‐specific electrochemical response. Using a thin film complex solid solution electrocatalyst and a range of SECCM single barrel capillaries with diameters from 1.2 µm to 50 nm, we observed an averaged electrochemical response for the oxygen reduction reaction with minor statistical variations for the larger capillary diameters. In contrast, significant statistical heterogeneity among the measured spots is observed for small capillary diameters. 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. Abstract : High entropy alloy complex solid solutions have an exceptionally high number of different multi‐element active sites. We investigate the activity of differently sized surface areas to experimentally confirm this concept and to reveal the critical number of sites, which distinguishes between statistically averaged catalytic response and activity differences based on covering only fractions of all possible active sites.