Isolated FeN₃ sites anchored hierarchical porous carbon nanoboxes for hydrazine‐assisted rechargeable Zn‐CO₂ batteries with ultralow charge voltage

Abstract Zn‐CO 2 batteries (ZCBs) are promising for CO 2 conversion and electric energy release. However, the ZCBs couple the electrochemical CO 2 reduction (ECO 2 R) with the oxygen evolution reaction and competitive hydrogen evolution reaction, which normally causes ultrahigh charge voltage and CO 2 conversion efficiency attenuation, thereby resulting in ~90% total power consumption. Herein, isolated FeN 3 sites encapsulated in hierarchical porous carbon nanoboxes (Fe‐HPCN, derived from the thermal activation process of ferrocene and polydopamine‐coated cubic ZIF‐8) were proposed for hydrazine‐assisted rechargeable ZCBs based on ECO 2 R (discharging process: CO 2 + 2H + → CO + H 2 O) and hydrazine oxidation reaction (HzOR, charging process: N 2 H 4 + 4OH − → N 2 + 4H 2 O + 4e − ). The isolated FeN 3 endows the HzOR with a lower overpotential and boosts the ECO 2 R with a 96% CO Faraday efficiency (FE CO ). Benefitting from the bifunctional ECO 2 R and HzOR catalytic activities, the homemade hydrazine‐assisted rechargeable ZCBs assembled with the Fe‐HPCN air cathode exhibited an ultralow charge voltage (decreasing by ~1.84 V), excellent CO selectivity (FE CO close to 100%), and high 89% energy efficiency. In situ infrared spectroscopy confirmed that Fe‐HPCN can generate rate‐determining *N 2 and *CO intermediates during HzOR and ECO 2 R. This paper proposes FeN 3 centers for bifunctional ECO 2 R/HzOR performance and further presents the pioneering achievements of ECO 2 R and HzOR for hydrazine‐assisted rechargeable ZCBs.