Cadmium Sites Accelerate Nitrate-to-Nitrite Kinetics in Cd–Fe 3 O 4 Tandem Electrocatalysts for Ammonia Electrosynthesis

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Abstract
Electrochemical nitrate reduction reaction (NO3RR) proceeds via a well-defined tandem cascade, in which nitrate to nitrite (NO3- to NO2-) conversion is universally identified as the kinetically rate-determining step (RDS). Copper (Cu) is widely recognized as the active site for this critical RDS, yet systematic investigations into the intrinsic NO3- activation activity of metals adjacent to Cu and its diagonal elements in the periodic table remain largely unexplored. Herein, we systematically screen a series of metals (Cu, Ni, Sn, Cd) as dopants in Fe3O4, and demonstrate that trace Cd-doped Fe3O4 (Cd-Fe3O4) delivers superior NO3RR performance over other catalysts. Systematic mechanistic investigations reveal a tandem pathway: Cd sites preferentially catalyze the NO3- to NO2- conversion, while adjacent Fe sites facilitate water dissociation to supply active hydrogen (*H) for subsequent NO2- hydrogenation to NH3. When integrated into a flow cell, Cd-Fe3O4 delivers a high NH3 production rate of 1610 mmol h-1 g-1 cat while maintaining superior Faradaic efficiency. Furthermore, the produced NH3 is successfully recovered as high-purity struvite, demonstrating its potential in practical applications and nitrate value-added processes.
Funding Information
  • Liuzhou Science and Technology Project (2024AA0201G002)
  • Natural Science Foundation of Hebei Province (E2023202141)
  • Natural Science Foundation of Heilongjiang Province (PL2024E008)
  • National Natural Science Foundation of China (52100065)
  • National Natural Science Foundation of China (52203352)
  • Heilongjiang Province key research and development plan guidance project (GZ20210149)

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