Stefanie Schwamborn

Electrochemical Synthesis of Core–Shell Catalysts for Electrocatalytic Applications

A novel electrochemical method to prepare platinum shells around carbon-supported metal nanoparticles (Ru and Au) by pulsed electrodeposition from solutions containing Pt ions is presented. Shell formation is confirmed by characteristic changes in the cyclic voltammograms, and is further evidenced by monitoring particle growth by transmission electron microscopy as well as by energy-dispersive analysis of X rays (EDX). Scanning electrochemical microscopy and EDX measurements indicate a selective Pt deposition on the metal/carbon catalyst, but not on the glassy carbon substrate. The thus prepared carbon-supported core-shell nanoparticles are investigated with regard to their activity in electrocatalytic oxygen reduction, which demonstrates the applicability of these materials in electrocatalysis or sensors.

Pt−Ag Catalysts as Cathode Material for Oxygen-Depolarized Electrodes in Hydrochloric Acid Electrolysis

Pt-Ag nanoparticles were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and tested using cyclic voltammetry and scanning electrochemical microscopy (SECM) with respect to their possible use as catalyst material for oxygen reduction in 400 mM HCl solution. For comparison, a Pt catalyst was investigated under similar conditions. The redox competition mode of scanning electrochemical microscopy (RC-SECM) was adapted to the specific conditions caused by the presence of Cl(-) ions and used to visualize the local catalytic activity of the Pt-Ag deposits. Similarly prepared Pt deposits were shown to dissolve underneath the SECM tip. Pt-Ag composites showed improved long-term stability toward oxygen reduction as compared with Pt even under multiple switching off to open-circuit potential in 400 mM HCl.

Activation/Inhibition Effects during the Coelectrodeposition of PtAg Nanoparticles: Application for ORR in Alkaline Media†

PtAg bimetallic nanoparticles for oxygen reduction reaction (ORR) in alkaline media were prepared by pulse electrodeposition (PED). During PED the reduction of Ag(+) ions predominates, thus an increased Ag content in the co-deposit is accomplished. The mechanism for this anomalous co-deposition was elucidated by potential pulse experiments, which revealed that nuclei formation mainly occurs via the reduction of Pt(2+) ions. The growth of the particles is diffusion controlled leading to the formation of a Ag shell covering a PtAg alloyed region. However, the shell is not growing homogeneously on the PtAg alloy. Hence, regions of the PtAg alloy are exposed, which exhibit an enhanced ORR activity compared to a pure Ag surface.