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)22+) 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 H2. 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 Pt0 species. Photochemical H2 formation was investigated in a photochemical H+ reduction system composed of Pt(bpy)22+ (or Pt(terpy)Cl+), Ru(bpy)32+ sensitizer, methyl viologen (MV2+) acceptor, and sacrificial donor (EDTA). An induction period for the H2 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.