Electrochemical Stability and Degradation Mechanisms of Commercial Carbon-Supported Gold Nanoparticles in Acidic Media.

Urša Petek,Francisco Ruiz-Zepeda,Milutin Smiljanić,Marjan Bele,Primož Jovanovič,Miran Gaberšček,Martin Šala,Nejc Hodnik

doi:10.1021/acs.jpcc.0c10033

Abstract

Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investigated by an accelerated stress test (AST), which consisted of 10,000 voltammetric scans (1 V/s) in the potential range between 0.58 and 1.41 VRHE. Loss of Au electrochemical surface area (ESA) during the AST pointed out to the degradation of Au/C. Coupling of an electrochemical flow cell with ICP-MS showed that only a minor amount of gold is dissolved despite the substantial loss of gold ESA during the AST (∼35% of initial value remains at the end of the AST). According to the electrochemical mass spectrometry experiments, carbon corrosion occurs during the AST but to a minor extent. By using identical location scanning electron microscopy and identical location transmission electron microscopy, it was possible to discern that the dissolution of small Au particles (<5 nm) within the polydisperse Au/C sample is the main degradation mechanism. The mass of such particles gives only a minor contribution to the overall Au mass of the polydisperse sample while giving a major contribution to the overall ESA, which explains a significant loss of ESA and minor loss of mass during the AST. The addition of low amounts of chloride anions (10–4 M) substantially promoted the degradation of gold nanoparticles. At an even higher concentration of chlorides (10–2 M), the dissolution of gold was rather effective, which is useful from the recycling point of view when rapid leaching of gold is desirable.

Highlights

Noble metals are irreplaceable for a variety of applications in advanced technologies due to their unique properties, such as high melting point, excellent electrical conductivity, good catalytic activity, high corrosion resistance, and biomedical compatibility
In order to distinguish between the possible degradation mechanisms for the case of carbon-supported gold NPs, potential-resolved dissolution profiles were recorded by electrochemical flow cell (EFC)-ICP-MS, gas evolution was followed by electrochemical mass spectrometry (EC-MS), and identical location scanning electron microscopy (IL-SEM) and identical location transmission electron microscopy (IL-TEM) imaging of the Au/C samples were performed
We studied the stability and degradation mechanism of a commercial carbon-supported gold NPs during accelerated stress test (AST) in 0.05 M H2SO4 in the absence and presence of chloride ions

Summary

INTRODUCTION

Noble metals are irreplaceable for a variety of applications in advanced technologies due to their unique properties, such as high melting point, excellent electrical conductivity, good catalytic activity, high corrosion resistance, and biomedical compatibility. Widespread usage of Pt in electrocatalysis has led to a well-studied electrochemical dissolution of bulk Pt electrodes[13−15] and carbon-supported Pt NPs.[16−21] These studies showed that degradation and the loss of electrochemical surface area (ESA) of Pt catalysts is a complex process that can proceed via several mechanisms, such as particle size growth, dissolution, Ostwald ripening, detachment of the particles, and loss of the electrical contact.[17,20,21] It has been pointed out that Pt is sensitive to the transition between the oxidized and reduced state of the surface (which corresponds to the start/stop conditions in fuel cells) rather than to the potentiostatic exposure to high potentials. Performing the AST with an UPL of 1.41 VRHE in the electrolyte with and without the presence of chloride ions provides an insight into the stability and degradation mechanisms of the Au NPs in the presence of impurities, while testing if the approach by Hodnik and colleagues[42] could be beneficial for recycling of gold. To unambiguously unravel the degradation mechanism responsible for the loss of gold ESA observed during the AST, sequential IL-SEM imaging was performed both in the presence and in the absence of chlorides, while ILTEM imaging was performed before and after AST in the neat 0.05 M H2SO4 electrolyte

METHODS

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES