Adsorbate-Induced Surface Segregation for Core-Shell Nanocatalysts

摘要

Considering the continuously rising price of precious metals, a reduction in the amount of noble metal in catalysts is of great importance for many industrial applications. One approach is to decrease the size of catalyst particles down to the nanometer range to increase the specific surface area per mass, but also to benefit from a change in the electronic structure. Core-shell catalyst structures containing an inexpensive, non-noble core surrounded by a noble-metal shell can bring about further improvements in this respect. Ideally only the catalyti-cally active metal is located at the surface, where the reactions take place; the reaction rate should not suffer as a result of the inactive core material. A promising class of fuel-cell-cathode catalysts are alloys of platinum with other transition metals. For these materials core-shell structures can be achieved by high-temperature annealing chemical leaching of the non-noble material, or electrochemical deposition techniques. All of these methods, however, exhibit significant disadvantages including the loss in active surface area and material, the formation of an incomplete noble-metal shell, and the necessity for potential control during preparation. Herein we present a novel preparation procedure of such core-shell nanoparticles with a platinum shell that overcomes these issues by using an adsorbate-induced surface segregation effect.