Ultra-dispersed metal oxide nanoparticles on graphitic carbon nitride as functional platforms for electrochemical nitrate valorization

Ammonia is a vital commodity of key importance for global agriculture, but its traditional synthesis via the energy-intensive Haber-Bosch process features a high ecological footprint, contributing to ≈2% of the overall carbon dioxide emission. An eco-friendly and sustainable alternative is offered by electrochemical NO 3 − reduction (e-NO 3 RR), enabling also to simultaneously reduce the concentration of nitrate, a widespread water pollutant. Herein, we report on the ultra-dispersion of CuFe 2 O 4 , NiFe 2 O 4 , or Fe 2 O 3 nanoparticles (NPs) on graphitic carbon nitride (gCN), yielding heterostructured oxide@gCN systems as potential e-NO 3 RR catalysts. The target materials, fabricated by gCN electrophoretic deposition on carbon cloth (CC), followed by radio frequency (RF)-sputtering of oxide NPs in very low amounts, were subjected to a multi-technique characterization aimed at investigating their morphological, structural, compositional, and optoelectronic properties. The results indicate that gCN provides a robust, electronically coupled scaffold anchoring ultra-dispersed oxides, and evidence a gCN → oxide electron donation. Electrochemical tests coupled with ion chromatographic analyses highlight CuFe 2 O 4 @gCN as the best-performing catalyst, affording a Faradaic efficiency towards NH 4 + of 21% at -1.15 V vs. the reversible hydrogen electrode (RHE), together with a comparatively higher ammonium production rate and reduced NO 2 − generation. Altogether, our results may pave the way to the potential implementation of functional catalysts for ammonia generation from nitrate‑containing aqueous media.