Capturing Electrochemically Galvanic Exchange Events between Silver and Gold in Nonequilibrium and Equilibrium Realms

A new methodology is presented to study the kinetics of the galvanic replacement reaction between silver and gold, allowing, for the first time to our knowledge, real-time monitoring of the dynamics of this redox reaction by quantifying the main driving force, that is, the time- and concentration-dependent redox potential, which cannot be captured by any microscopic, optical, or X-ray method.

The galvanic replacement reaction triggered by the electrochemical potential difference between two metals enables the design of multifunctional nanostructures for catalysis, sensing, and energy. However, there is still limited knowledge of the dynamics in the nonequilibrium and equilibrium realms to maximize material access or prevent structure damage. A methodology is reported to capture galvanic exchange events between atoms of electrodeposited bare Ag particles and aqueous Au^(III)Cl₄ ⁻ species. As the population of Au^(III)Cl₄ ⁻ species increases from the stoichiometric value to two orders of magnitude, the open-circuit potential parameter that determines galvanic exchanges in the nonequilibrium and equilibrium domains follows a quasi-sigmoidal shape. An autocatalytic reaction network mechanism is postulated. The galvanic reaction can be interrupted whenever required to yield stable, separable intermediates that increase the rate of their own formation. The knowledge of the Au^(III)Cl₄ ⁻ concentration-dependent potential-time curves permits to drastically reduce the reaction duration, from 85 to 13 min, while maintaining the material structure and properties, which will undoubtedly inspire new insights into other galvanic exchange processes.

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