Dense binary Fe–Cu sites promoting CO2 utilization enable highly reversible hybrid Na–CO2 batteries

Abstract

High-performance and low-cost catalysts are particularly desirable for the exploitation of practical low-overpotential Na–CO₂ batteries with protracted cyclability. Herein, a well-defined morphology of nitrogen-rich graphitic carbon frameworks with dense bimetallic active sites (Fe–Cu–N–C) was facilely prepared by introducing Fe³⁺ and Cu²⁺ to regulate in situ grown carbon nanotubes as an advanced catalyst toward hybrid Na–CO₂ batteries. Through metal content tuning and carbon architecture altering, Fe–Cu–N–C proved to be dramatically more effective than Cu–N–C and Fe–N–C. As the cathodic catalyst of a hybrid Na–CO₂ battery, Fe–Cu–N–C can facilitate the fast evolution and degradation of flocculent discharge products and achieve an excellent long-term cyclability with up to 1550 cycles (over 600 h), which makes it one of the greatest catalysts for hybrid Na–CO₂/air batteries that have been reported to date. The observed outstanding battery performance is attributable to the cross-linked conductive framework affording a “highway” for accelerated electron transport and Na⁺/CO₂ diffusion. Besides, the synergistic effects among defect-rich interfaces, Fe/Fe₃C nanocrystals, and Fe–N_x and Cu–N_x sites derived from nitrogen atom doping enhance the catalytic activity. In addition, the possible growth and decomposition mechanisms of NaHCO₃ products with different morphologies on Fe–N–C, Cu–N–C, and Fe–Cu–N–C electrodes were presented and discussed.