Ultrathin NiFe-LDH nanosheets strongly coupled with MOFs-derived hybrid carbon nanoflake arrays as a self-supporting bifunctional electrocatalyst for flexible solid Zn-air batteries

Abstract

The construction of a hybrid hierarchical architecture is a promising strategy for optimizing the electrocatalytic activity and the performance of flexible Zn-air battery. However, it still remains a challenging task. This study reports on the use of a simple approach in the preparation of a flexible 3D self-supporting bifunctional catalyst. Ultrathin NiFe-based layered double hydroxide nanosheets (NiFe-LDH) have in this approach been strongly coupled to a metal-organic framework (MOF)-derived carbon nanoflake array, to be used in flexible Zn-air batteries. Importantly, the introduction of Co nanoparticles that were anchored onto the nitrogen-doped porous carbon (Co-NC) nanoflakes provided an abundance of active sites for the oxygen reduction reaction (ORR). Moreover, the catalytic oxygen evolution reaction (OER) process was improved by altering the local electronic structure of the Ni and Fe species in NiFe-LDH. The 3D interconnected conductive network structure, in addition to the strong coupling between NiFe-LDH and Co-NC, was found to give a catalyst with superior electrocatalytic OER performances. The overpotential was only 284 mV at 50 mA cm−2 in an alkaline medium, which is a result that outperforms the commercial RuO2 catalyst. This bifunctional catalyst did also exhibit a good catalytic performance that is comparable to that of commercial Pt/C towards ORR. Interestingly, when this catalyst was used as binder-free air cathode, the assembled flexible solid-state Zn-air battery demonstrated a favorable power density, cycling stability, and mechanical flexibility. The present work offers a facile and efficient strategy for the development and construction of self-supporting bifunctional OER/ORR electrocatalysts, to be used in wearable and flexible electronic devices.