MOF-derived low Ru-loaded high entropy alloy as an efficient and durable self-supporting electrode in rechargeable liquid/flexible Zn-air batteries.

ABSTRACT

Exploiting the high-entropy alloy (HEA) electrocatalysts with the synergistic effect of multi-metal components is an effective approach to address the slow kinetics and undesirable stability of the oxygen evolution reaction (OER) in Zn-air batteries (ZABs), but still faces many challenges. In this study, a multimetallic Metal-organic framework (MOF)-derived HEA catalyst was successfully fabricated on carbon fiber as a flexible self-supporting electrode (denoted as CC@FeCoNiMoRu-HEA/C) for high-performance liquid/flexible ZABs using a facile and cost-effective strategy. The three-dimensional (3D) highly open network framework and hierarchical porous structure accelerate the mass transport of OH-/O2 and charge transfer. The electronic structure adjustment, lattice defects and high entropy effects enable the CC@FeCoNiMoRu-HEA/C catalysts to perform high OER catalytic activity and strong durability while reducing the Ru content and lowering the economic cost. In situ Raman spectra and XPS results reveal the generation of metal-OOH intermediates on the HEA surface during the OER process. In a practical demonstration, the liquid ZAB assembled with CC@FeCoNiMoRu-HEA/C + Pt/C as the air electrode offers stable open-circuit voltage, large power density, excellent specific capacity and satisfactory cycle life, outperforming the commercial RuO2 + Pt/C-based reference ZAB. More attractively, the flexible solid-state ZAB also achieves fast dynamic response, high peak power density, robust cycling stability as well as favorable mechanical flexibility, indicating a promising application prospect in future flexible electronics and wearable devices. This work provides a viable pathway to develop low precious metal-loaded HEAs as advanced OER self-supporting electrocatalysts and realize high-performance flexible energy storage devices.