Tuning the catalytic preference of ruthenium catalysts for nitrogen reduction by atomic dispersion

Developing cost-effective, high-performance nitrogen reduction reaction (NRR) electrocatalysts is required for the production of green and low-cost ammonia under ambient conditions. Here, a strategy is proposed to adjust the reaction preference of noble metals by tuning the size and local chemical environment of the active sites. This proof-of-concept model is realized by single ruthenium atoms distributed in a matrix of graphitic carbon nitride (Ru SAs/g-C₃N₄). This model is compared, in terms of the NRR activity, to bulk Ru. The as-synthesized Ru SAs/g-C₃N₄ exhibits excellent catalytic activity and selectivity with an NH₃ yield rate of 23.0 μg mg_cat⁻¹ h⁻¹ and a Faradaic efficiency as high as 8.3% at a low overpotential (0.05 V vs the reversible hydrogen electrode), which is far better than that of the bulk Ru counterpart. Moreover, the Ru SAs/g-C₃N₄ displays a high stability during five recycling tests and a 12 h potentiostatic test. Density functional theory calculations reveal that compared to bulk Ru surfaces, Ru SAs/g-C₃N₄ has more facile reaction thermodynamics, and the enhanced NRR performance of Ru SAs/g-C₃N₄ originates from a tuning of the d-electron energies from that of the bulk to a single-atom, causing an up-shift of the d-band center toward the Fermi level.