Mechanism and kinetics of gold recovery and Au nanoparticle synthesis by Gas-Diffusion Electrocrystallization (GDEx)

Abstract

Standing at the forefront of cutting-edge research, the electrochemical reduction of gases is not only driving the industrial shift towards electrification and decarbonization but also unlocking the immense potential to pioneer uncharted realms of electrochemical conversions, including metal transformations. Carbon monoxide issued from the electrochemical reduction of CO2 on gas-diffusion electrodes (GDEs), was used for the in-situ reduction of AuCl4− ions into elemental gold nanoparticles (NPs). A minimal extent of CO2 reduction on the uncatalyzed activated carbon of the GDEs was sufficient to fully remove the AuCl4− ions from the electrolyte bulk present in the aqueous electrolyte, while steering their complete precipitation as Au0. A maximum current efficiency of 19% towards CO formation was achieved, under a flow-through gas regime. The efficiency for Au0 precipitation was improved by manipulating the gas-flow regime and cathode polarization. The mechanism and kinetic description for gold recovery and nanoparticle synthesis are portrayed for the reactions underpinning the gas-diffusion electrocrystallization process (GDEx).