Cu-N-bridged Fe-3d electron state regulations for boosted oxygen reduction in flexible battery and PEMFC

Rational design of hetero-diatomic catalysts (DACs) with tunable electronic structures is an effective approach to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) in metal-air batteries and proton-exchange membrane fuel cells (PEMFCs), which, however, still remains a great challenge to date. Herein, we propose a novel multi-step collaborative synthesis strategy to fabricate the N-bridged Fe and Cu diatomic electrocatalysts (Fe, Cu DAs-NC). Benefitting from the inter-atomic electron transfer and robust graphitized structure, the optimized Fe, Cu DAs-NC catalyst exhibits significantly enhanced ORR performances in both alkaline and acidic media, featuring the half-wave potentials of 0.94 V and 0.80 V, respectively. The established solid-state flexible Zn-air battery and H₂-O₂ single fuel cell using Fe, Cu DAs-NC as cathode deliver an extra-high power density of 83 mW cm⁻² and a maximum power output of 875 mW cm⁻², respectively. In-situ Raman spectroscopy and density functional theory calculations reveal that the strong synergistic interactions between FeN₄ and CuN₄ moieties are responsible for the d-orbital shift of the atomic Fe and Cu sites and charge polarization between them in the N-bridged coordination environment, which results in the well-defined and favorable adsorption free energy regulations and consequent much enhanced catalytic activity of the diatomic catalysts.