ELECTROCHEMICAL AND MICROSCOPIC CHARACTERIZATION OF PLATINUM-COATED PERFLUOROSULFONIC ACID (NAFION-117) MATERIALS

Platinum-coated Nafion 117 structures were characterised using electro chemical measurements of platinum surface area and a number of microsc opy techniques;The morphology and composition of;the platinum deposits were related to their preparation conditions in terms of platinum sal t concentration, electrolyte? flow and the surface I roughness of Nafi on 117. Platinum surface areas achieved were higher than the values pr edicted for ideal spherical platinum particles of average diameter. Th is is due to a fine microstructure, which realises much smaller platin um particles than average (down to about 50 nm) allied to the geometry produced by their clustering to form nodules (about 0.1-1.5 mu m diam eter micro-nodules and about 3-5 mu m macro-nodules). Adherent platinu m deposits with high surface areas were promoted by using roughened Na fion 117 membranes and enhancing the mass transport of chloroplatinate and tetraborohydrate ions by magnetic stirring of the electrolyte. A flow cell produced much more reproducible platinum-coated Nafion 117 s tructures. At best, platinum surface areas of 30-50 m(2) g(-1) Pt were achieved at platinum penetration depths of 5-30 mu m into the membran e surface.