Microwave-Assisted Hydrothermal Synthesis of Ce-doped Fe2(MoO4)3 for Low Overpotential Electrocatalytic N2-to-NH3 Reduction

Abstract

Developing efficient catalysts for the electrochemical nitrogen reduction reaction (NRR) under mild conditions remains a key challenge toward sustainable ammonia production. In this work, the microwave-assisted hydrothermal synthesis of Ce-doped Fe₂(MoO₄)₃ is reported as an effective and robust electrocatalyst for N₂ reduction. Structural (X-Ray Diffraction and Raman) and compositional characterization (Energy Dispersive Spectroscopy) confirmed the successful incorporation of nominally 2% cerium into the structure with a homogeneous distribution across the bulk catalyst without significantly altering the crystal structure. Electrochemical tests conducted in phosphate buffer (PBS, 0.1 mol L⁻¹, pH 7.0) saturated with N₂ demonstrated that the 2% Ce–Fe–Mo sample achieved the highest ammonia production: 12.8 µmol/L and 42% Faradaic efficiency for 2 h electrolysis at + 0.022 V vs. RHE. Normalization by mass and electrolysis time revealed that this low overpotential electrolysis effectively suppressing hydrogen evolution, provides a twofold increase in NH₃ production compared to similar processes reported at more negative overpotentials. Chronoamperometry (7 h) followed by post-electrolysis Raman spectroscopy confirmed electrochemical and structural stability under these conditions. The improved performance is attributed to the synergistic interaction between Mo and Ce facilitating N₂ adsorption and conversion. Ce-doped Fe–Mo oxides are promising candidates for ambient N₂-to-NH₃ conversion via electrochemical pathways, combining high efficiency, stability, affordability and significant cost-benefit advantage compared to noble-metal-based systems.

Graphical Abstract