Mechanistic insights into electrochemical nitrate reduction over d- and p-block Cu-based single-atom alloy catalysts: a DFT study

The electrocatalytic nitrate reduction reaction (NO₃RR) is of great significance for wastewater remediation and ammonia (NH₃) synthesis. However, efficient NO₃RR catalysts and a clear mechanistic understanding are still lacking. A single-atom alloy (SAA) offers a new design space for the NO₃RR with its unique atomic and electronic structures. Here, high-throughput density functional theory (DFT) calculations were performed to systematically investigate the catalytic potential and reaction mechanism of Cu-based SAAs for the NO₃RR to NH₃. A volcano relationship between the descriptor ΔE_*NO - ΔE_*OH and the limiting potential (U_L) was established. The results show that Al/Cu (111) achieves an ultra-low U_L of -0.18 V. The strong hybridization between Al-p and O-p orbitals enables p electrons to be injected more readily into anti-bonding orbitals, thereby effectively weakening the N-O bond and lowering the reaction energies of protonation steps. The stronger O affinity of the Al site allows Al/Cu (111) to break free from the constraints imposed by conventional linear scaling relations and exhibit excellent NO₃RR activity. Moreover, Al/Cu (111) protects the active sites from competitive H adsorption, leading to enhanced selectivity. This work establishes p-orbital engineering as a design principle for Cu-based single-atom alloys beyond conventional d-band tuning, providing valuable theoretical guidance for NO₃RR catalyst design.