Dealloyed PtxNi1-x Thin Films for Oxygen Reduction Reaction

Pt cost is a continuing challenge for widespread implementation of PEMFCs, consequently improving durability and increasing Pt mass activity of PEMFCs is essential.  Recently, epitaxial Pt₃Ni (111) with a Pt surface and Ni rich subsurface has demonstrated drastic activity enhancements attributed to reduced interaction between Pt and oxidized species resulting from a shift in the d-band structure.  This work has motivated low cost efforts to produce high surface area analogs of the alloy which we have explored with electrodeposited Pt_xNi_1-x thin films.

In this work nanoporous PtNi thin films over a range of compositions were synthesized by electrodeposition and subsequent dealloying.  High mass activity (0.8A/mg) for oxygen reduction reaction was demonstrated by as-deposited PtNi₃ with a dealloyed composition of Pt₃Ni.  The composition and structure of as deposited and dealloyed Pt_xNi_1-x thin films were probed by hydrogen underpotential deposition, electrochemical quartz crystal microbalance, x-ray diffraction, and scanning electron microscopy.  The dealloying process was shown to be highly dependent on the initial film, creating trends in composition, porosity, shrinkage, specific surface area, and activity.  Select films were further analyzed by small angle x-ray diffraction and transmission electron microscopy to reconcile these differences with structural information and elucidate feature sizes (4-5nm).