Electrocatalysis for proton reduction by polypyridyl platinum complexes dispersed in a polymer membrane

Catalysis for H+ reduction by polypyridyl platinum complexes (e.g., bis(2,2'-bipyridine) platinum(II) nitrate (Pt(bpy)(2)(2+)) and chloro(2,2':6',2''-terpyridine) platinum(II) chloride (Pt(terpy)Cl+)) dispersed in a Nafion membrane was studied by using a polymer-modified electrode system. These Pt complexes incorporated in the polymer membrane worked as active catalyst for H+ reduction to produce H-2. The cathodic current due to the H+ reduction increased with reaction time indicating that the electrocatalytic reaction does not take place by a simple catalysis of the original Pt complex. The valence state of the Pt complexes after the reduction was investigated by both UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) showing the presence Pt-0 species. Photochemical H-2 formation was investigated in a photochemical H+ reduction system composed of Pt(bpy)(2)(2+) (or Pt(terpy)Cl+), Ru(bpy)(3)(2+) sensitizer, methyl viologen (MV2+) acceptor, and sacrificial donor (EDTA). An induction period for the H-2 evolution was observed, which was ascribed to the formation of active Pt species by MV+ reductant produced by the photochemical reaction. It was concluded that in both the two systems the Pt complexes at first change to active species (zero-valent Pt), and then work as the H+ reduction catalyst. (C) 2001 Elsevier Science Ltd. All rights reserved.