Perovskite oxides have emerged as promising oxygen electrocatalysts for fuel cells and batteries, yet their catalytic activity and long-term stability are under debate because of local surface alterations and instabilities under sustained oxidative potential. Interconnected particles (40 nm) of Ba0.6Sr0.4Co0.79Fe0.21O2.67 (BSCF) are decorated by 10-50 wt % Ni0.6Fe0.4(OH)x [NiFe] layered double hydroxide (LDH) sheets via polyethylenimine linkage. This composite renders modulation of surface charges through Coulombic interaction and provides a leeway for electron mobility between the two components, which bestows relief to the BSCF surface from oxidative degradation. NiFe-LDH (25 wt %) bound to BSCF (BSCF/NiFe-25) is found to be the optimized bifunctional composite after considering the total overpotential of oxygen evolution and reduction reactions. With BSCF/NiFe-25 at the air electrode of a prototype-rechargeable Zn-air battery, a low discharge-charge voltage gap (1.16 V at 10 mA cm-2), unaltered cyclic stability over 100 h, and an energy density of 776.3 mW·h·gZn-1 are achieved. BSCF/NiFe-25 outperforms BSCF and is comparable to 20% Pt/C-RuO2 cathodes in all the standard figures of merit. Our work presents a general strategy to circumvent the reconstructions of perovskite oxide surface under oxidative potentials, by creating highly active, stable, and inexpensive bifunctional composite electrocatalysts for future electrochemical energy storage and conversion devices.
Keywords: Zn−air battery; bifunctional catalyst; layered double hydroxide; perovskite oxide; surface modification.