Atomic Engineering of Single Crystals: Designing High-Efficiency Bifunctional Co/Fe Single-Atom and Alloy Catalysts for Zinc-Air and Zinc-Ion Batteries.

Single-crystalline metal oxides offer well-defined coordination environments to suppress metal migration, yet their application as precursors for bifunctional oxygen electrocatalysis remains limited. In this study, single-crystal x-ray diffraction and Fourier-transform infrared spectroscopy were employed to confirm the atomic structures of the synthesized single-crystalline Fe-CRY and Co-CRY. Subsequently, a localized thermal conversion method was utilized to prepare the functional electrocatalyst (FeCo-DMU-NC) featuring ultralong carbon nanotubes. AC HAADF-STEM and x-ray absorption fine structure (XAFS) spectroscopy, verified the coexistence of atomically dispersed FeN4 and CoN4 sites. In situRaman spectroscopy and density functional theory analyses indicated that FeN4 and CoN4 serve as the main active centers for the oxygen evolution reaction and oxygen reduction reaction, respectively. Moreover, CoFe alloys accelerated OH* desorption, thereby endowing FeCo-DMU-NC with superior bifunctional activity and stability. In practical applications, the material achieved high open-circuit voltages and stable cycling performance when used as the air cathode of Zinc-air batteries and integrated into Zn-ion coin cells. This work provides a green and efficient route for converting single-crystal precursors into high-performance single-atom electrocatalysts.