Intermetallic hcp-PtBi/fcc-Pt Core/Shell Nanoplates Enable Efficient Bifunctional Oxygen Reduction and Methanol Oxidation Electrocatalysis

Abstract

Two dimensional (2D), ordered intermetallic and core/shell architectures are highly desirable structural features for promoting electrocatalysis on Pt-based nanocrystals in terms of activity, durability, and cost. However, it is currently an extreme challenge to achieve all these features in a single catalytic nanostructure. Herein, we report a new class of 2D nanoplate catalyst composed of intermetallic hcp-PtBi core and ultrathin fcc-Pt shell synthesized by a facile one-pot wet-chemical approach. The unique structural features of PtBi/Pt core/shell nanoplates make them exhibit the highest oxygen reduction reaction (ORR) activity in all the reported PtBi-based catalytic systems and 5 times more active than commercial Pt/C catalyst for ORR. The combination of cyclic voltammograms, X-ray photoelectron spectroscopy, and density functional theory calculations reveals that an optimal oxygen adsorption energy and efficient reduction on both edge surface and interface regions between Pt-shell and PtBi-core from hcp-PtBi/fcc-Pt core/shell nanoplates relative to that on commercial Pt, deriving from the Bi-p empty band suppression at the core/shell interface, is the key to greatly boosting the ORR activity of the PtBi nanocatalyst system. The PtBiPt interface performs at relatively lower overpotential compared with the edge surface because of excellent reduction from OH to the H2O. Thanks to the intermetallic phase and core/shell architecture, hcp-PtBi/fcc-Pt core/shell nanoplates show little loss in electrochemically active surface area and ORR activity during the accelerated durability test. They also show enhanced catalytic performance for the electro-oxidation of liquid fuels in both acid and alkaline electrolytes. This work sheds light on the rational design of new 2D core/shell nanostructured catalysts for enhancing fuel-cell electrocatalysis.