NCNT grafted perovskite oxide as an active bifunctional electrocatalyst for rechargeable zinc-air battery

Precious-metal-free electrocatalysts with high activity to bifunctionally activate both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are key enablers for the scalable adoption of zinc-air batteries (ZABs). In this work, a unique hybrid catalyst comprising nitrogen-doped carbon nanotube (NCNT) in-situ grown directly on La_0·8Sr_0·2Ti_0·65Fe_0·35O_3-δ perovskite oxide (denoted as LSTFO/NCNT) has been developed as a bifunctional ORR and OER electrocatalyst for ZAB applications. The compositionally optimized LSTFO/NCNT hybrid delivers remarkable bifunctional oxygen electrocatalysis performances with a characteristic potential gap (ΔE) of 0.76 V. On a device level, the primary and rechargeable homemade ZABs demonstration using such an LSTFO/NCNT hybrid as an air electrode catalyst exhibit reliable electrochemical performances of high peak power density and cycling stability with a final round-trip efficiency of 62.8% at 10 mA cm⁻² during 123 cycles. The active oxygen electrocatalytic activity is believed to be related to the considerable level of pyridinic-N and graphitic-N on NCNT, abundant oxygen vacancies, improved electrical conductivity and the strong electronic interaction between LSTFO and NCNT. The DFT calculation results demonstrated that the electron transfer from NCNT to LSTFO not only reduces the oxygen adsorption and activation energy, but also activates the surface lattice oxygen and favors the formation of O–O bond through reinforcing the Fe/Ti–oxygen covalency, leading to exceptional bi-functionality. This work demonstrates a robust method to obtain exceptional bi-functional oxygen electrocatalysis based on transitional metal oxides for high-performance metal-air batteries.