DECIPHERING THE DYNAMICS OF GALVANIC REPLACEMENT REACTION
TO DESIGN METALLIC CAGES AS FREE-STANDING ELECTROCATALYSTS

Amira BEN ABDERRAHMANE, Sophie TINGRY, David CORNU and Yaovi HOLADE

Institut European des Membranes, IEM UMR 5635, Univ Montpellier, ENSCM, CNRS, Montpellier, France
yaovi.holade@enscm.fr; https://iem.umontpellier.fr/

**Keywords:** Galvanic replacement reaction; Electrochemistry; Gold; Silver; Nanostructured interface

**Summary:**

Galvanic replacement reaction (GRR) occurs spontaneously when the atoms of one metal are in contact with the ions of another metal that has a higher redox potential in solution. Owing to its versatility, GRR has far-reaching technological implications beyond physical chemistry in catalysis, chemistry, physics, biology, and medicine.[1,2]

In the bulk state, silver with E°(Ag⁺/Ag) = 0.8 V vs SHE (standard hydrogen electrode) can be replaced by gold with E°(AuCl₄⁻/Au) = 1.0 V vs SHE according to: 3Ag(s) + AuCl₄⁻(aq) → 3Ag⁺(aq) + 4Cl⁻ + Au(s). Given that the introduction of 1 atom of Au requires the replacement of 3 atoms of Ag (Ag and Au atoms have similar size), GRR generates porous and alloyed structures with unique physicochemical properties.[1-3] Fundamentally, the exact driving force is quantitatively unknown as from a physical chemistry point of view, the understanding of the dynamics of such a redox process, which mixes electrochemical kinetics and mass transport (diffusion), remains a puzzle. Historically, both the synthesis of the initial Ag particles and the GRR are done in solution, making electroanalytical monitoring impossible.

We will discuss our recent methodology allowing to grow surfactant-free Ag particles on GDE and then perform GRR with Au while monitoring the dynamics via the open circuit potential (OCP, **Fig. 1a**).[3] It allows to capture in real time the formation of metallic cages of Ag-Au alloys after a ‘3by1’ atomic exchange. This strategy has led to the fabrication of high performance electrocatalysts where the formation of an alloy phase, the creation of nanoporosity within it and the self-supporting nature amplify, through synergistic and electronic effects, the electrocatalytic activity (Fig. 1b).[1]

<figure><img src="image_1.png" /><figcaption>**Fig. 1.** (a) Open circuit potential (OCP) during GRR (3.5 M NaCl, rt, gentle stirring): inset shows SEM images of the initial GDE-Ag and final GRR-Au<sub>90</sub>Ag<sub>10</sub> electrodes. (b) Comparative performance (CVs at 50 mV s<sup>-1</sup> in 1 M KOH+0.1 M glycerol at 25 °C).</figcaption></figure>

**References:**

1. Jang, H.; Min, D.-H., ACS Nano. **2015**, *9* (3), 2696-2703.

2. Liu, X.; Astruc, D., Adv. Mater. **2017**, *29* (16), 1605-1609.

3. Boukil, R.; Tuleushova, N.; Cot, D.; Rebiere, B.; Bonniol, V.; Cambedouzou, J.; Tingry, S.; Cornu, D.; Holade, Y., J. Mater. Chem. A. **2020**, *8* (18), 8848-8856.