Robust Photoelectrochemical Route for the Ambient Fixation of Dinitrogen into Ammonia over a Nanojunction Assembled from Ceria and an Iron Boride/Phosphide Cocatalyst

The nitrogen reduction reaction is of great scientific significance as a hydrogen fuel carrier as well as a source of value-added products; in context to this, photoelectrochemical (PEC) nitrogen fixation emerges as an effective and environmentally benign strategy to meet the need. Hence, the current work reports an effective catalytic system containing a low-cost iron boride-based cocatalyst onto the CeO₂ nanosheet matrix for photoelectrochemical nitrogen reduction reaction. The harmonized electronic property and the ensemble effect of phosphorus and boron in FeB/P with unsaturated metal sites make it a site-selective cocatalyst for nitrogen adsorption and its polarization. Furthermore, the low Fermi level of iron borophosphide enhances the trapping of photogenerated electrons from CeO₂ and productively provides it to the adsorbed nitrogen species. The observed peculiar photocurrent behavior confirms the interaction of photogenerated electrons with adsorbed nitrogen species and its subsequent reduction by the surrounding protonic environment. The optimized CeO₂-FeB/P photoelectrocatalyst exhibited an excellent NH₃ yield velocity, i.e., 9.54 μg/h/cm² at −0.12 V vs RHE with a solar-to-chemical conversion efficiency of 0.046% under ambient conditions. The same catalyst is also very active under near-zero biasing conditions and possesses impressive durability even after multiple uses. This work might strategically direct a promising way for the exploration of new photoelectrocatalytic systems for effective PEC-nitrogen reduction reaction.