Solid-state electrochemical generation and characterization of catalytic Pt microcenters within single crystal of heteropoly phospho-12-tungstic acid

Chloroplatinic acid can be incorporated at trace (10(-5)-10(-4) mol dm(-3)) levels into the secondary, hydrated, structure of a single crystal of tetr agonal phospho-12-tungstic acid, H3PW12O40.29H(2)O, without any change of t he primary structure of the system. During partial reduction of hereropoly tungstate units, mixed-valence W(VI, V) sites are generated; they are capab le to mediate the reduction of chloroplatinate to metallic platinum. Conseq uently, trace amounts of highly dispersed Pt microcenters are produced in t he secondary structure of the crystal. Solid-state electrochemical characte rization of the material is accomplished with the use of a carbon fiber ult ramicrodisk electrode. The system's first, most positive, one-electron redo x reaction is virtually not affected by traces of Pt in the crystal. By per forming voltammetric experiments in two time regimes: we have determined co ncentration of mixed-valence sites and an effective diffusion coefficient f or charge propagation,At more negative potentials, intrastructural discharg e of hydronium ions at catalytic Pt microcenters is observed. (C) 1998 Else vier Science Ltd. All rights reserved.