Morphology control of noble metal catalysts from planar to dendritic shapes by galvanic displacement

- Pd, Pt, and Au whisker were obtained via one-step galvanic displacement.
- The mechanism of whisker formation was investigated by electrochemical measurements.
- The steep concentration gradient of noble metal ions resulted in the formation of whisker.
- The concentration gradient was controlled by the rates of oxidation and mass transport.
- Pd whisker showed enhanced ethanol oxidation activity compared to planar catalyst.

Noble metal electrocatalysts can simply be prepared via galvanic displacement method on a sacrificial substrate, which is advantageous for preparing a uniform and thin catalyst layer. However, it is difficult to control the morphology of deposited metals via galvanic displacement, therefore, there is a limitation to increase the surface area of electrocatalysts. In this study, we demonstrate galvanic displacement for controlling the morphology of Pd, Pt, and Au from planar to whisker shapes by manipulating the dissolution rate of the sacrificial Cu substrate and the mass transport of noble metal ions. The acceleration of the dissolution of sacrificial substrate increases the reduction rate of noble metal, which develops a steep concentration gradient of noble metal ions near the surface of substrate. This induces the selective deposition of noble metal to form a whisker instead of smooth film. To verify the advantage of whisker-type catalysts, the ethanol oxidation with Pd is investigated. Whisker-type Pd shows 21 times higher electrocatalytic performance than planar Pd due to larger surface area. Therefore, it can be suggested that whisker-type catalysts simply prepared by galvanic displacement is applicable for various electrocatalytic reactions.

192