Cyano-Bridged Bimetallic Polymer Network-Derived Pd₃Fe Intermetallic for Aqueous Rechargeable Zinc-Air Batteries

The rational design and synthesis of bifunctionally active and durable oxygen electrocatalysts have garnered significant attention for electrochemical energy conversion and storage. Intermetallic nanostructures are particularly promising for these applications due to their unique catalytic properties and exceptional durability. In this study, we present a fascinating synthetic approach for the direct synthesis of a bifunctional oxygen electrocatalyst based on nitrogen-doped carbon-encapsulated ordered Pd₃Fe (o-Pd₃Fe@NC) intermetallic, using a cyano-bridged bimetallic single-source precursor tailored for aqueous rechargeable zinc-air batteries (ZABs). Through temperature-controlled annealing of a bipyridine-containing Pd-Fe cyano-bridged polymer network, a catalytically active o-Pd₃Fe@NC catalyst is obtained. The spatial confinement of Pd(II) and Fe(II) within the polymer network facilitates the controlled growth of the o-Pd₃Fe nanostructure. This intermetallic catalyst exhibits bifunctional activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The o-Pd₃Fe@NC catalyst achieves an ORR onset potential of 0.98 V and demonstrates remarkable long-term stability, sustaining performance over 30,000 cycles in alkaline electrolytes without noticeable degradation. The rechargeable liquid and flexible ZABs constructed with the o-Pd₃Fe@NC air cathode deliver outstanding energy performance, achieving maximum power densities of 212.9 and 109 mW cm^-2, respectively. The liquid ZAB delivers a specific capacity of 816 mAh g_Zn^-1 and exhibits excellent charge-discharge cycling stability, maintaining a consistent charge-discharge voltage gap over 200 h. The flexible ZAB retains its charge-storage performance across all bending angles.