New Insights into the ORR Catalysis on Pt Alloy Nanoparticles from an Element Specific d-Band Analysis.

Abstract

Bolstered by their unique atomic structures and tailored compositions, nanoalloys exhibit extraordinary properties making them ideal materials to solve challenges in energy storage and conversion catalysis. However, a quantitative description of the structure-property relationships using an accurate descriptor-based model for nanoalloys, ranging from bimetallic to multimetallic compositions, is needed to drive efficient material design toward high-performance catalysis. In this work, we highlight the electronic property and catalytic activity relationship from an element specific d-band analysis of Pt-based alloy catalysts using X-ray absorption near-edge spectroscopy (XANES). Using a series of L10-MPt/Pt (M = Fe, Co, Ni) core/shell alloy catalysts with well-defined atomic structures, we quantified subtle differences in the Pt d-electron states and correlated the Pt d-band structure to their superior catalytic activity toward the oxygen reduction reaction (ORR). Our analysis used the upper d-band edge position as a predictive descriptor for the mass activity toward the ORR instead of the commonly used d-band center position. Together with density functional theory calculations and Nørskov d-band theory, the upper d-band edge position for the Pt states, derived from experimental measurements, elucidates new physical insights into the ORR performance of the L10-MPt/Pt core/shell catalysts. An element specific Pt d-band analysis using XANES overcomes challenges in traditional X-ray photoelectron spectroscopy-based valence d-band analysis, which cannot distinguish signals from independent elements in nanoalloys. Thus, the insights from the element specific d-band analysis presented in this work are a promising approach to determine structure-property relationships in a variety of transition metal nanoalloys and will be useful in the design of future high-performance catalysts.