MOFs encapsulated nanorods derived CoNi@CN composites with open structure as highly efficient bifunctional catalysts for rechargeable Zn-air batteries

Abstract

Constructing highly efficient cathode catalysts is of significance for the practical application of Zn-air batteries, while the accessibility of electrons and electrolyte to catalytic active sites is essential for the electrocatalytic processes of Zn-air battery. Herein, we established a novel strategy to construct CoNi@CN composites with open structure through template-modulating thermal transformation of Co-NRs@Co-Ni-MOF. The internal elongated Co-NRs will convert into carbon nanotubes to create an open channel to the metal active sites needed for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, thereby increasing the O-containing intermediates transmission and boosting the ORR/OER performances. Surprisingly, the optimal Co3Ni1@CN-900 composites deliver excellent ORR/OER activities, affording a high half-wave potential (E1/2) of 0.869 V for ORR and a low overpotential of 366 mV for OER, as well as a narrow potential gap between ORR and OER of 0.727 V. Most impressively, the optimal Co3Ni1@CN-900 based aqueous and solid-state Zn-air batteries achieve outstanding battery properties with high OCVs, enhanced peak power densities and specific capacities, and excellent long-term charge-discharge stabilities. Meanwhile, the Co3Ni1@CN-900 based ZAB also exhibits an impressive practicality.