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 PtBi-Pt 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.