Bifunctional electrocatalysis with silk cocoon-shaped CdMn2O4 nanoparticles for Zn–air batteries

Abstract

Morphology-controlled catalyst nanoparticles have attracted significant research interest owing to their fundamental and scientific importance. In particular, their crystallographic orientation dependent properties greatly impact their electrocatalytic activity towards the oxygen reduction and evolution reactions. Herein, a CdMn₂O₄ catalyst with silk cocoon-shaped particles is synthesised via a solvothermal approach, and its bifunctional electrocatalytic activity in Zn–air batteries is studied. The catalyst is composed of three-dimensionally interconnected nanoparticles, which provide a highly accessible coordination environment around its surface, and a large number of exposed active sites. Compared with commercial 20 wt% Pt/C and IrO₂ catalysts, the CdMn₂O₄ catalyst exhibits a significantly reduced charge−discharge voltage gap, superior cycling stability and higher round-trip efficiency. Electrochemical redox species are present on the cocoon-shaped catalyst surface without perturbing its structure, and increase the number of reactive sites formed by defective O₂⁻ species, thereby providing sufficient structural stability. This work provides a new understanding that can aid in the design of highly efficient bifunctional electrocatalysts and structural engineering of silk cocoon-shaped materials to replace noble-metal catalysts or non-noble spinel electrocatalysts for Zn–air batteries.

Graphical Abstract