Assembly and electrochemical characterization of nanometer-scale electrode|solid electrolyte interfaces.

A technique is herein described for the assembly and characterization of nanometer-scale metal electrode|solid electrolyte interfaces of variable dimensions. The specific system examined in this work involves a sharp Pt tip attached to the piezo-driven head of a scanning tunneling microscope (STM) allowing the tip to be inserted into (or retrieved from) a Nafion membrane placed normal to the direction of tip travel. The actual Pt|Nafion area of contact was determined by coulometric analysis of the characteristic voltammetric features of Pt, using the tip as the working electrode and a much larger Pt gauze attached to the other side of the Nafion as a counter-reference electrode, yielding for some of the interfaces examined values equivalent to as low as 35 000 Pt surface atoms.

Determination of O[H] and CO coverage and adsorption sites on PtRu electrodes in an operating PEM fuel cell.

A special in situ PEM fuel cell has been developed to allow X-ray absorption measurements during real fuel cell operation. Variations in both the coverage of O[H] (O[H] indicates O and/or OH) and CO (applying a novel Deltamu(L3) = mu(L3)(V) - mu(L3)(ref) difference technique), as well as in the geometric (EXAFS) and electronic (atomic XAFS) structure of the anode catalyst, are monitored as a function of the current. In hydrogen, the N(Pt)(-)(Ru) coordination number increases much slower than the N(Pt)(-)(Pt) with increasing current, indicating a more reluctant reduction of the surface Pt atoms near the hydrous Ru oxide islands.