Understanding the Nitrogen Reduction Reaction Mechanism on CuFeO2 Photocathodes

This study investigates the reaction pathways for the conversion of \ce{N2} to \ce{NH3} on \ce{CuFeO2} (CFO) by employing density functional theory (DFT) calculations. Concentrating on the most stable (012) surface orientation, two systems were examined: the pristine (012) surface and the corresponding oxygen defective surface. To find the thermodynamic stable pathway, the associative Heyrovsk{\'y} mechanism was considered, containing four different reaction pathways. The reaction intermediates predominantly interact with the iron sites on the surface, following the distal alternating reaction pathway via the formation of hydrazine. Introducing oxygen defects changes the reaction mechanism to a Mars--van--Krevelen--type mechanism, avoiding the formation of hydrazine, while the Gibbs free energy of the first hydrogenation step is lowered by 1.17~eV (from 2.17 to 1.00~eV). Analyzing the charge density distribution reveals that oxygen defective surface enables CFO to facilitate a $\pi$--backdonation between iron sites and the NRR intermediates, increasing the intermediate--surface interaction. This indicates an enhanced catalytic activity for the NRR by generating oxygen lattice defects in CFO.