Crystal Phase Engineering of Ultrathin Alloy Nanostructures for Highly Efficient Electroreduction of Nitrate to Ammonia

Electrocatalytic nitrate reduction reaction (NO 3 RR) toward ammonia synthesis is recognized as a sustainable strategy to balance the global nitrogen cycle. However, it still remains a great challenge to achieve highly efficient ammonia production due to the complex proton‐coupled electron transfer process in NO 3 RR. Here, the controlled synthesis of RuMo alloy nanoflowers (NFs) with unconventional face‐centered cubic (fcc) phase and hexagonal close‐packed/fcc heterophase for highly efficient NO 3 RR is reported. Significantly, fcc RuMo NFs demonstrate high Faradaic efficiency of 95.2% and a large yield rate of 32.7 mg h −1 mg cat −1 toward ammonia production at 0 and −0.1 V (vs reversible hydrogen electrode), respectively. In situ characterizations and theoretical calculations have unraveled that fcc RuMo NFs possess the highest d‐band center with superior electroactivity, which originates from the strong Ru─Mo interactions and the high intrinsic activity of the unconventional fcc phase. The optimal electronic structures of fcc RuMo NFs supply strong adsorption of key intermediates with suppression of the competitive hydrogen evolution, which further determines the remarkable NO 3 RR performance. The successful demonstration of high‐performance zinc‐nitrate batteries with fcc RuMo NFs suggests their substantial application potential in electrochemical energy supply systems.