Synthesis of core/shell nanocrystals with ordered intermetallic single-atom alloy layers for nitrate electroreduction to ammonia

Structurally ordered intermetallic nanocrystals (NCs) and single-atom catalysts (SACs) are two emerging catalytic motifs for sustainable chemical production and energy conversion. Yet, both have limitations in enhancing performance and expanding the materials design space. For example, intermetallic NCs require high-temperature annealing (> 500 °C) to promote atom rearrangement and d-d orbital hybridization, leading to potential aggregation or sintering, while SACs are typically limited by a low metal-atom loading (< 1 wt%) to avoid aggregation of metal atoms. Here, we report a facile, direct solution-phase synthesis of Cu/CuAu core/shell NCs with tunable single-atom alloy (SAA) layers. This synthesis can be extended to other Cu/CuM (M = Pt, Pd) systems, in which M atoms are isolated in the Cu host and can be considered the highest density of single-atom sites. We controlled the density of single-sites and the number of atomic layers and investigated the ligand and strain effects of Cu/CuAu for electrocatalytic nitrate reduction reaction (NO₃RR). The Cu/CuAu densely packed SAAs demonstrated a high selectivity toward NH₃ from NO₃RR with an 85.5% Faradaic efficiency (FE) while maintaining an exceedingly high yield rate of 8.47 mol h^-1 g^-1. This work advances the design of atomically precise catalytic sites by creating a new paradigm of core/shell NCs with SAA atomic layers, opening an avenue for broad catalytic applications in achieving a sustainable energy future.