Scanning Electrochemical Microscopy for the Electroless Deposition of Gold on Natural Pyrite: Effect of Ferric Ions

Abstract

The local electroless deposition of gold on pyrite is studied by scanning electrochemical microscopy (SECM). The SECM and additional SEM experiments provide kinetic and mechanistic insights on the local galvanic replacement of pyrite by gold. We evidence that individual gold nanoparticles or full coverage of gold on the pyrite surface can be obtained by controlling either the deposition time or the flux of gold ions electrogenerated at the ultramicroelectrode. We also studied the influence of ferric ions, known to be implied on gold etching and pyrite corrosion and therefore, on the overall process of gold deposition on pyrite. We then demonstrate that the presence of ferric ions significantly modifies i) the thermodynamic of the gold electrodissolution, ii) the process of adsorption of auric ions on pyrite in the first instants, iii) the number of nucleation sites on the pyrite surface and, iv) the structure of the deposited gold layer.

Probing the reactive intermediate species generated during electrocatalysis by scanning electrochemical microscopy

“…The RIS (H 2 O 2 ) generated from a reaction of interest (either in the bulk or from a catalytically active NP) is revealed from its homogeneous reaction with a tip-electrogenerated redox mediator (Ru III from a Ru II solution in Figure 1c). This catalytic loop, often analyzed as an EC' mechanism, is probed by the catalytic tip current recorded for the redox mediator conversion [19][20][21][22][23]. It is sensitive to mass transfer of the RIS to the tip, which is controlled by the volume between the tip and an interface (either surface [21] or liquid/liquid [20]).…”

“…The RIS are often detected experimentally by performing approach curves (variation of the tip-interface distance) and their concentration and lifetime can be quantified with the help of numerical simulation of the complex homogeneous reactions involved in the process [20,21]. The SECM tip can also work at fixed distance from the interface, in this case reactive intermediates with  in the ms range can be detected from current transients [19,23] or CVs [22]. To assess more unstable RIS and reach reaction occurring at the nanometer scale, a recent strategy proposed to confine the redox moieties in a thin layer coating the SECM tip, as illustrated in the inset of Figure 1c [24,25].…”

Scanning Gel Electrochemical Microscopy (SGECM): Lateral Physical Resolution by Current and Shear Force Feedback

“…Scanning electrochemical probe techniques are powerful tools for analyzing local electrochemical behavior of interfaces between electrolyte and various materials, such as metals, , metal oxides, − electrocatalysts, − biological species, − as well as minerals. , Among these techniques, scanning electrochemical microscopy (SECM) , and scanning ion conductance microscopy (SICM) − are the most developed, with the concept of using a micro/nano- electrode or capillary scanning over a sample immersed in an electrolyte. Recently, scanning droplet cell techniques (SDC), , such as scanning electrochemical cell microscopy (SECCM), − are also becoming popular.…”

Photoassisted Electrochemical Micropatterning of Gold Film

“…Developing convenient and efficient ways for the micropatterning of gold film is thus of significance for boosting their applications in these fields. − Localized electrochemical etching is a common micromachining method for producing micropatterns in metal films by virtue of its mild conditions and simple operations. − A prepatterned insulating layer on top of the substrate, that is, a mask, was often utilized to selectively protect those regions underneath the protective layer before the desired pattern was formed. , However, the procedures for fabricating masks were usually cumbersome and it was difficult to modify the geometry of mask once it was prepared. A microelectrode probe that can locate on and scan over the substrate was another useful strategy in the electrochemical micromachining. − In this case, the electric field and the reactive reagent were generated around the scanning probe, resulting in highly localized and selective etching or deposition. However, the etching resolution and reproducibility were often compromised by several technical obstacles due to the use of probes, including the reliable fabrication of nanosized scanning probes, the precise controls on the probe–substrate distance, and the inevitable diffusion of electrogenerated reactive species.…”