Atomic coordination environment engineering of bimetallic alloy nanostructures for efficient ammonia electrosynthesis from nitrate

Significance

Ammonia is one of the most significant and indispensable feedstocks for fertilizers and chemicals, and also an important carbon-free energy storge medium. Recently, electrochemical nitrate reduction reaction (NO ₃RR) for ammonia synthesis under ambient conditions has emerged as a promising alternative to the traditional energy-intensive Haber–Bosch process. However, NO ₃RR still suffers from limited ammonia selectivity and yield rate. Although tremendous efforts have been devoted to modulating the size, composition, and morphology of electrocatalysts, little attention is paid to the atomic coordination environment of active sites. Herein, ultrathin nanosheet–assembled RuFe nanoflowers with low-coordinated Ru sites were synthesized, which demonstrated much better electrochemical performance than common Ru-based nanocatalysts, indicating the great potential of atomic coordination environment engineering of metal-based electrocatalysts in NO ₃RR.

Abstract

Electrochemical nitrate reduction reaction (NO ₃RR) to ammonia has been regarded as a promising strategy to balance the global nitrogen cycle. However, it still suffers from poor Faradaic efficiency (FE) and limited yield rate for ammonia production on heterogeneous electrocatalysts, especially in neutral solutions. Herein, we report one-pot synthesis of ultrathin nanosheet-assembled RuFe nanoflowers with low-coordinated Ru sites to enhance NO ₃RR performances in neutral electrolyte. Significantly, RuFe nanoflowers exhibit outstanding ammonia FE of 92.9% and yield rate of 38.68 mg h ⁻¹ mg _cat ⁻¹ (64.47 mg h ⁻¹ mg _Ru ⁻¹) at −0.30 and −0.65 V (vs. reversible hydrogen electrode), respectively. Experimental studies and theoretical calculations reveal that RuFe nanoflowers with low-coordinated Ru sites are highly electroactive with an increased d-band center to guarantee efficient electron transfer, leading to low energy barriers of nitrate reduction. The demonstration of rechargeable zinc-nitrate batteries with large-specific capacity using RuFe nanoflowers indicates their great potential in next-generation electrochemical energy systems.