Nanoporous PtRu alloys for electrocatalysis.

We describe a facile route to the straightforward fabrication of nanoporous (NP) PtRu alloys with predetermined bimetallic compositions. Electron microscopy and X-ray diffraction characterizations demonstrate that selective etching of Al from ternary PtRuAl source alloys generates three-dimensional bicontinuous NP-PtRu alloy nanostructures with a single-phase face-centered-cubic crystalline structure. X-ray photoelectron spectroscopy shows a slight electronic structure modification of Pt by alloying with Ru as well as uniform surface and bulk bimetallic ratio. With characteristic structural dimensions less than 5 nm, these high surface area bimetallic nanostructures show distinct electrocatalytic performance as the Ru content varies within the structure. Among all samples, NP-Pt(70)Ru(30) shows the highest specific activity as well as the most negative onset potential toward methanol oxidation reaction. NP-Pt(50)Ru(50) was found to possess a similar specific activity to the commercial E-TEK Pt(50)Ru(50)/C catalyst, but its onset and peak potentials are about 70 mV more negative. CO stripping experiments demonstrate that the adsorption of CO is the weakest on NP-Pt(70)Ru(30), and further increasing the Ru content actually shifts the CO stripping peak to a more positive potential. Thus, the overall sequence for CO-tolerance is NP-Pt(70)Ru(30) > NP-Pt(50)Ru(50) approximately = Pt(50)Ru(50)/C > NP-Pt(30)Ru(70) > Pt/C.