Surface Charge Modulation of Perovskite Oxide at the Crystalline Junction with Layered Double Hydroxide for Durable Rechargeable Zinc-air Battery.

Abstract

Perovskite oxides have emerged as promising oxygen electrocatalysts for fuel cells and batteries, yet their catalytic activity and long-term stability are under debate due to local surface alterations and instabilities under sustained oxidative potential. 40 nm interconnected particles 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 (PEI) 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. 25 wt% NiFe-LDH 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 (1.16V at 10mAcm-2), unaltered cyclic stability over 100h 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.