Highly efficient bifunctional nanofiber catalysts with 3D hierarchical nanostructures as building blocks for rechargeable Zn-air batteries

The imperative need for highly active bifunctional electrocatalysts accommodating both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) has intensified for the development of advanced rechargeable Zn-air batteries (RAZBs). Bifunctional catalysts, crucial for simplified processes and enhanced performances, necessitate additional dimensions to host a greater abundance of catalytic sites compared to their monofunctional counterparts. Nanofiber skeletons with multi-dimensional nanostructure building blocks, renowned for structural tunability and high porosity, have garnered significant interest across diverse applications; however, their synthesis remains a formidable challenge. Herein, we present an innovative synthesis strategy to construct nanofiber electrocatalysts with three-dimensional (3D) hierarchical building blocks (CoCNTs/PCNFs), which comprise cobalt nanoparticles embedded in one-dimensional carbon nanotubes growing on porous carbon nanofibers that expand the effective number of OER and ORR active sites. The well-distributed cobalt nanoparticles, coupled with the large specific surface area and high conductivity of the catalyst, contribute to the highly desired catalytic properties of CoCNTs/PCNFs toward both the ORR and OER, resulting in a minimal potential gap Delta E of 0.71 V. Assembled Zn-air batteries (RZABs) incorporating the CoCNTs/PCNFs catalyst demonstrate a high-power density of 262.6 mW cm-2, surpassing the performance of state-of-the-art Pt/C and RuO2 catalysts. This work introduces a promising strategy for designing bifunctional oxygen electrocatalysts, opening avenues for future advancements in the field. The well-distributed cobalt nanoparticles, coupled with the large specific surface area and high conductivity of the catalyst, expand the effective number of active sites to achieve high catalytic activity toward both the ORR and OER.