Enhanced Cycling Stability of Hybrid Li-Air Batteries Enabled By Ordered Pd3fe Intermetallic Electrocatalyst

Hybrid Li-air batteries, in which a solid electrolyte separates the lithium metal anode in an aprotic electrolyte from the air electrode in an aqueous electrolyte, have attracted considerable attention because they possess high theoretical energy density and potentially overcome the problems of conventional aprotic Li-air batteries. However, current hybrid systems still suffer from poor cycling stability. The problem mainly lies in the sluggish kinetics of oxygen reduction reaction (ORR) and poor durability of the cathode catalysts, which actually is also the major limiting factor for other energy conversion and storage technologies such as fuel cells and metal-air batteries. Therefore, it is highly desirable to develop highly active and stable catalysts for the ORR in aqueous media. Herein, we report an ordered Pd₃Fe intermetallic catalyst synthesized with a nanoparticle-KCl matrix method. Such structurally ordered phase can provide predictable control over structure, geometric, and electronic effect, not afforded by disordered alloys.  Further, as the order in intermetallic phases arises from the high enthalpy of mixing, a higher chemical and structural stability than found in its corresponding disordered alloy can be expected. Our results show ordered Pd₃Fe/C catalysts exhibit much higher activity and durability for the ORR in alkaline media than disordered Pd₃Fe/C, Pd/C, and Pt/C. The ordered Pd₃Fe/C catalyst enables a long-term cycling performance of hybrid Li-air batteries over 880 h with only 0.08 V increase in round-trip overpotential. The extraordinarily high performance of ordered Pd₃Fe/C catalyst provides a very promising alternative to the conventional Pt/C catalyst for air cathode in alkaline electrolyte.