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

Abstract

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.