Dealloyed Pt 74 Ni 26 and Pt 26 Ni 74 Electrodeposited Thin Film Electrocatalysts for Oxygen Reduction

Electrodeposition and microstructure of thin films close to Pt 75 Ni 25 and Pt 25 Ni 75 stoichiometry are described and their catalytic oxygen reduction reaction performance, dealloying, and strain evolution detailed. Multiple techniques are used to characterize the morphology, crystalline structure, and chemical homogeneity of the as-deposited and dealloyed films. A fine-scale percolating network of lower-density regions is evident in the as-deposited Pt 74 Ni 26 films while the as-deposited Pt 26 Ni 74 films are more homogenous and compact. Electrodeposition is accompanied by development of significant in-plane tensile stress that increases at more negative growth potentials to reach 1.28 GPa for as-deposited Pt 26 Ni 74 . Dealloying of the near-surface regions of Pt 74 Ni 26 is accompanied by limited expansion or opening of the low-density regions while massive dealloying of the highly stressed Pt 26 Ni 74 results in shrinkage, extensive cracking, and formation of a bi-continuous nanoporous structure with an average pore diameter close to 5 nm. Relative to electrodeposited Pt, the alloy films exhibit enhanced area-specific oxygen reduction reaction activity (at 0.95 V vs RHE, iR-corrected) that amounts to a factor of 3.4 for dealloyed Pt 74 Ni 26 and 5.1 for dealloyed Pt 26 Ni 74 while the Pt-based mass activity increased by a factor of 5.1 and 12.3, for the respective films.