Electrodeposition and electrocatalytic activity of Pt and Pt-alloy nanoparticles and thin films on highly oriented pyrolytic graphite (HOPG)

Pt and Pt-based alloy catalysts were synthesized by electrodeposition on HOPG. The nucleation and growth, morphology, composition and crystal structure, and electrocatalytic activity (towards relevant reactions in the frame of PEMFCs and DMFCs) of these model electrodes were systematically investigated.; The presence of chlorides inhibits the Pt reduction processes. There is a transition from progressive to instantaneous nucleation with increasing overpotential for the deposition from 1 mM H2PtCl6 electrolytes. The possibility of instantaneous nucleation at large overpotential by using electrolytes with large chloride concentration is advantageous for the growth of small, well dispersed nanoparticles.; The electrochemical data were confirmed by AFM and SEM imaging studies. Relatively narrow size distributed nanoparticles can be obtained from the current system.; While MOR activity decreases with decreasing particle size, the HER and HOR activity of deposited Pt particles increases with decreasing deposition period. The ORR activity first increases then decreases with increasing deposition time.; Interactions between Pt and Ru, or Ni or Co are observed and they form solid solution as verified by XRD. Underpotential deposition occurs for Pt-Ni or Pt-Co co-electrodeposition.; Pt-Ru deposition can be described as progressive nucleation at low overpotential and instantaneous nucleation at high overpotentials. Through direct morphological observations, the Pt-Ni or Pt-Co nucleation can be approximately described as progressive.; Pt-Ru deposits are superior to Pt towards MOR. The optimum Ru content is about 50 at.%.; Pt-Ni and Pt-Co deposits are more active than Pt for ORR. The optimum content is about 30 at.% Ni or 50 at.% Co.; Dealloying of Pt-Ru and Pt-Ni or Pt-Co electrodeposit is observed after electrochemical characterization. The extent of dealloying increases with the content of the alloying element.