Oxide-Stabilized Nanoporous Ni-Pt for Enhanced Durability in ORR Catalysis
Authors: Carter Aliya , Pounds Tyler D. , Gaskey Bernard , Erlebacher Jonah 
Published: February 2020

Improving the lifetime and durability of electrode catalysts is one of the significant barriers to the development of commercially practical hydrogen fuel cells. These issues, along with reduction in material costs associated with precious metal catalysts, are the centerpiece of a major research initiative to investigate new materials and processing techniques for these catalysts. Previous research has demonstrated that (111) Pt3Ni surfaces are superior in oxygen reduction reaction (ORR) electrocatalytic activity compared to pure Pt [1]. Nanoporous nickel-platinum (np-NiPt) formed by dealloying has been shown to possess excellent ORR mass activity compared to Pt3Ni films [2]. Other recent work has shown that incorporation of minority ternary components such as Mo into Pt-Ni alloy nanoparticles can strongly influence their ORR activity [3].
In addition to affecting catalytic activity, the addition of a ternary component to a binary alloy can lead to a more stable nanoporous metal after dealloying, as has been shown in the case of adding small fractions (< 5 at. %) of Pt to Ag-Au alloys [4]. This is because coarsening is mediated by the surface diffusion, and addition of a small amount of Pt to the initial Ag-Au alloy used as a precursor for nanoporous Au leads to a nanoporous Au catalyst with greatly increased structural stability due to the lower mobility Pt atoms acting as pinning points on the surface. Similar behavior is seen in the addition of Ir to Pt-Ni alloys [5].
In this work, we report the results of a survey of ternary components added at a dilute level (2 at. %) to a dealloyable Ni-Pt ingot. Ternary components including Ta, Si, Mo, Ir, and V were incorporated into precursor Ni77Pt23 ingots via RF melting and shaped into rotating disk electrodes (RDEs). These electrodes were dealloyed to a proscribed roughness factor (Rf = HUPD surface area/geometric surface area = 143), and then assessed for ORR activity and stability using rotating disk electrochemistry. These components were chosen because fabrication of these alloys via chemical reduction (e.g., as is used for nanoparticles) is difficult or impossible. Unlike Pt added to Ag-Au alloys, most of the elements of interest here form stable, irreducible oxides during dealloying. Correlations of the ternary component oxide structure to the lengthscale of the nanoporous materials formed during dealloying, as well as the effect of oxide structure on the electrochemically active surface area, will be discussed.
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Acknowledgement: This research is sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy.