Modulating Electron Transfer From Palladium to Spinel Cobalt Oxide Nanofibers for High‐Efficiency Hydrazine Oxidation‐Assisted Energy‐Saving Nitrate‐to‐Ammonia Conversion

ABSTRACT Integrating the nitrate reduction reaction (NO 3 RR) with the hydrazine oxidation reaction (HzOR) offers a compelling strategy for energy‐efficient ammonia (NH 3 ) synthesis while simultaneously enabling bidirectional nitrogen neutralization. In this work, we develop a high‐performance bifunctional electrocatalyst based on spinel hollow Co 3 O 4 nanofibers decorated with Pd nanoparticles (Pd@Co 3 O 4 NFs) for both NO 3 RR and HzOR in alkaline media. The as‐prepared catalyst exhibits substantially enhanced catalytic activity relative to many previously reported systems. When integrated into a two‐electrode NO 3 RR||HzOR electrolysis cell, the Pd@Co 3 O 4 NFs catalyst enables concurrent hydrazine pollutant degradation and ammonia generation, achieving a markedly reduced power consumption of 8.02 kWh kg −1 NH 3 , a value far below that of the conventional NO 3 RR||oxygen evolution reaction (OER) system (35.17 kWh kg −1 NH 3 ). Theoretical calculations reveal that the enhanced electrocatalytic performance stems from the optimized electronic structure at the Pd‐Co 3 O 4 interface, which facilitates the hydrogenation steps in NO 3 RR and lowers the dehydrogenation energy barrier in HzOR. Collectively, the design principles presented in this study constitute a significant advance in electrocatalyst engineering, directly contributing to sustainable nitrogen cycling through bidirectional nitrogen management, hydrazine waste remediation, and energy‐efficient ammonia synthesis.