Inhibition of Ostwald ripening through surface switching species during potentiodynamic dissolution of platinum nanoparticles as an efficient strategy for platinum group metal (PGM) recovery

Efficient recovery of platinum group metals (PGMs) from industrial spent catalysts through electrochemical means using mild conditions is of significant importance from both the industrial and the environmental points of view. Owing to their large surface-to-volume ratio, fast dissolution of PGM nanoparticles is possible through potential cycling between oxidizing and reducing potentials, leading to formation and dissolution of surface-oxide layer (transient dissolution). However, at reducing potentials, reduction of the dissolved metal species on the source nanoparticles leads to enhance the Ostwald ripening process and hence to decrease the overall dissolution efficiency significantly. We report a new concept to accelerate dissolution of Pt nanoparticles by use of surface switching species (SSS), e.g. Cu ions, functioning to selectively block the Pt surface to inhibit redeposition induced particle growth at reducing condition and expose the Pt surface to facilitate dissolution at oxidation condition, respectively. The presence of SSS during potential cycling enhances Pt dissolution by a factor of 2 or more as compared to that without SSS. Such surface self-relegation property to depress unwanted process and assist desired reaction documents an alternative and efficient approach for precious metal electrochemical recovery in dilute acidic baths with/without complexing agents. (C) 2019 Elsevier Ltd. All rights reserved.