The preparation and characterization of novel Pt/C electrocatalysts with controlled porosity and cluster size

Abstract

Small platinum clusters have been prepared in zeolite hosts through ion exchange and controlled calcination/reduction processes. To enable electrochemical application, the pores of the Pt-zeolite were filled with electrically conductive carbon via infiltration with carbon precursors, polymerization, and pyrolysis. The zeolite host was then removed by acid washing, to leave a Pt/C electrocatalyst possessing quasi-zeolitic porosity and Pt clusters of well-controlled size. The electrocatalysts were characterized by TEM, XRD, EXAFS, nitrogen adsorption and electrochemical techniques. Depending on the synthesis conditions, average Pt cluster sizes in the Pt/C catalysts ranged from 1.3 to 2.0 nm. The presence of ordered porosity/structure in the catalysts was evident in TEM images as lattice fringes, and in XRD as a low-angle diffraction peak with d-spacing similar to the parent zeolite. The catalysts possess micro- and meso-porosity, with pore size distributions that depend upon synthesis variables. Electroactive surface areas as high as 112 m² g_Pt⁻¹ have been achieved in Pt/C electrocatalysts which show oxygen reduction performance comparable to standard industrial catalysts.