The expansion/contraction of gold microparticles during voltammetrically induced amalgamation leads to mechanical instability

Abstract

The mechanical stability of gold microparticles during anodic stripping voltammetric (ASV) detection over a large range of mercury concentrations was investigated. Mercury was detected at gold microparticles chemically deposited onto glassy carbon microspheres using ASV. Oxidation was observed at 0.5 and 0.8 V vs. SCE. Which peak was observed was dependent on the concentration of mercury and the deposition potential. The formation of the amalgam was of interest. As mercury was deposited for longer time intervals, scanning electron microscopy (SEM) analysis showed the microparticles increasing in size from 0.76 ± 0.03 μm (initial) to 1.51 ± 0.14 μm (Hg²⁺ deposited for 1980 s at 0.35 V) in diameter. In order to ascertain if multiple expansion and contraction cycles damaged the gold microparticles, cyclic voltammetry was used to monitor the amount of gold on the electrode as mercury was deposited and stripped repeatedly. It was seen that the area under the cathodic gold peak decreased with repetitive scans. SEM analysis revealed that the mechanical stress of repetitive deposition and stripping cycles of mercury caused the gold microparticles to fracture, appearing as irregular cuboid crystals rather than as the orderly polycrystallite formations seen initially. Energy dispersive X-ray (EDX) analysis indicated that the composition of the microparticles changed over the course of repetitive deposition and stripping cycles from gold to an Au–Hg amalgam, which may not be in electrical contact with the carbon support.