Modulating Ru-Co bond lengths in Ru₁Co single-atom alloys through crystal phase engineering for electrocatalytic nitrate-to-ammonia conversion.

Abstract

Single atom alloys (SAAs) with maximum atomic efficiency and uniform active sites show great promise for heterogeneous catalytic applications. Meanwhile, crystal phase engineering has granered significant interest due to tailored atomic arrangements and coordination environments. However, the crystal phase engineering of SAAs remains challenging owing to high surface energy and complex phase transition dynamics. Herein, Ru₁Co SAAs with tunable crystal phases (hexagonal-close-packed (hcp), face-centered-cubic (fcc), and hcp/fcc structure) are successfully synthesized via controlled phase transitions. These SAAs exhibit distinct crystal phase-dependent performance towards nitrate reduction reaction (NO₃RR), where hcp-Ru₁Co outperforms its counterparts with a NH₃ Faradaic efficiency of 96.78% at 0 V vs. reversible hydrogen electrode and long-term stability exceeding 1200 h. Mechanistic investigations reveal that the hcp configurations enables shorter Ru-Co distances, stronger interatomic interactions, and more positive surface potential compared to hcp/fcc-Ru₁Co and fcc-Ru₁Co, which enhances the NO₃^- adsorption, reduces the free energy barrier, and suppresses competitive hydrogen evolution.