Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery.

Fe−N−C materials containing Fe−N x sites have emerged as promising electrocatalysts to substitute precious metal Pt in oxygen reduction reaction (ORR). Nevertheless, in-depth understanding the origin of iron species in Fe−N x sites is essential for the design of promising performance catalysts. Herein, Fe−N−C material composed of Fe and Fe 3 C embedded in bamboo-like nitrogen-doped carbon nanotubes (Fe−Fe 3 C− NCT) have been constructed via a simple pyrolysis strategy and can be used as excellent ORR electrocatalysts. DFT calculations uncover that the interaction between Fe and Fe 3 C could promote the electron density of the center metal iron species, creating a stronger O 2 adsorption and faster ORR kinetics. Furthermore, the oxygen intermediates would more readily dissociate on the Fe−N x sites formed by the coordination of metallic Fe and N. Inspired by these structural characterizations, Fe−Fe 3 C−NCT exhibits a positive onset potential of 0.99 V (vs RHE) and a high diffusion-limited current density of 8.00 mA cm −2 toward ORR, accompanied by an outstanding stability (only 4 mV negative shift after 10 000 cycles). The primary Zn−air battery displays a power density of 195 mW cm −2 and an energy density of 840 mAh g −1 at 10 mA cm −2 , much superior to Pt/C (123 mW cm −2 , 647.7 mAh g −1 ).

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