Poster SECM Screening of the Catalytic Activities of AuPd Bimetallic Patterns and their Heterogeneous Electron Transfer Rates Calculation

Abstract

Scanning electrochemical microscopy (SECM) is a good technique for evaluating the local electrocatalytic activity of different catalystssuch as some multimetal catalysts for oxygen reduction, hydrogen oxidation, and hydrogen peroxide reduction [1]. Moreover, SECMis also a powerful electrochemical tool for investigating heterogeneous electron-transfer (HET) reactions at interfaces between anelectrode and an electrolyte[2]. Now we use SECM to batch screening the catalytic activities of different AuPd catalysts for H2O2 andFcMeOH reduction reaction and also confirm the results of SECM by calculated HET rates for the respective AuPd electrodes.The sample of electrocatalyst arrays with various AuPd compositions was prepared by an electrochemical wet-stamping technique.Micropatterned high-strength agarose containing different solutions of chloroauric acid and chloropalladic acid has been used toelectrodeposit and generate patterns of AuPd nanoparticle arrays on ITO. The electrochemical activities of the AuPd alloys for H2O2and FcMeOH reduction reactions have been investigated in both redox-competition and feedback modes by means of SECM. Then weused the SECM approach curves to study the kinetic of heterogeneous reactions on AuPd array substrates.In the following images, AuxPdy represents a simplified form of the AuPd bimetal nanoparticles that were deposited fromelectrolytes containing mixed salts that CHAuCl4:CH2PdCl4=x:y. Fig. 1(a) shows the RC-SECM mode images of H2O2 reduction on a seriesof AuPd electrocatalyst arrays in H2O2 solution. The tip and the substrate were both biased at -0.2 V, at which H2O2 reduction cantake place. In this image, the Au3Pd1 band showed the lowest current among all of the bands which demonstrate the Au3Pd1 bandhave the highest activity for the H2O2 reduction. Fig. 1(b) presents an SECM feedback mode image of FcMeOH reduction and theAu3Pd1 band presents the highest current among all the bands in the respective arrays. Contrary to the RC-mode, the higher currentrepresents a better catalytic activity in feedback mode, so the Au3Pd1 band showed the highest activity for FcMeOH reduction. Fig. 1(c)is the comparison of the experimental (solid lines) and theoretical (symbols) SECM approach curves on AuPd arrays with differentcompositions in FcMeOH solution. The finite element modeling method was used to simulate the tip current response as a functionof the standard HET rate constant (k0) through COMSOL Multiphysics 4.3b, and the simulated probe approach curve with differentvalues of k0 could be readily fitted to the experimental current curves. Because a higher value of k0 indicates better electrochemicalactivity, the Au3Pd1 showed the highest electrocatalyst activitie, this result is in accordance with the SECM image.