Structurally Ordered Pt3Cr as Oxygen Reduction Electrocatalyst: Ordering Control and Origin of Enhanced Stability

Abstract

Ordered intermetallic phases provide predictable control over structure and electronic effects, not afforded by the widely studied alloys. However, because of the lack of a unifying principle or model for controlling the ordering and particle size, it is still a great challenge to synthesize the desired ordered phase (5 nm and smaller). Here, we employ Pt3Cr as a typical ordered intermetallic phase to comprehensively study the factors that control both the ordering and particle size. Ordered Pt3Cr intermetallic nanopartides (similar to 5 nm) are successfully synthesized using a KCl-matrix method in combination with adjusting annealing conditions. Such structurally ordered Pt3Cr/C exhibits superior kinetics toward the oxygen reduction reaction (ORR), relative to disordered PtCr alloy phases and commercial Pt/C. More importantly, the ordered Pt3Cr intermetallic catalyst shows a minimal loss of activity after 5000 potential cycles (14.7%) and a minimal Cr leaching loss after 4 weeks of testing (13.5%). The mechanism for the enhanced stability of ordered phases is discussed and elucidated. The high stability and activity of ordered Pt3Cr/C make it very promising for application as cathode catalysts for fuel cells. This work provides a guide to optimizing the synthesis of ordered intermetallic catalysts and improving their catalytic performance