Breaking scaling relations via Fe/Ni diatomic catalysts towards highly efficient electrocatalysts for rechargeable Na-air batteries

Exploiting bifunctional and highly efficient electrocatalysts that can facilitate the reversible formation and decomposition of discharge products is crucial for rechargeable Na-air batteries (SABs). However, restricted by scaling relations, air cathodes based on single metal systems usually exhibit inferior activity and fail to achieve a stable and long cycle life of Na-air batteries. Dual single-atom catalysts (DACs) with two metal sites can circumvent the scaling relations and endow the single-atom catalysts with superior activity. Herein, we present a hollow carbon microsphere loaded with Ni and Fe single atoms (Ni-HCMs-Fe) as a demonstration of DAC air cathodes for SABs. Notably, Na-air batteries with Ni-HCMs-Fe as an air cathode can achieve a low overpotential gap of 530 mV, a high specific capacity of 5382.9 mAh g−1, and an ultralong cycle life of over 450 cycles (1800 hours) with NaO2 as the main discharge product. Due to the different adsorption energies between oxygenated intermediates and Ni/Fe sites, the Ni-HCMs-Fe catalysts can break through the scaling relations and display optimized binding ability towards intermediates, thus boosting the reversible formation and decomposition of NaO2 in SABs. This work pioneers the use of DACs in SABs, paving the way for their practical applications.