Entropy-Driven Stabilization of Noble Metal Single Atoms: Advancing Ammonia Synthesis and Energy Output in Zinc-Nitrate Batteries

Abstract

Noble metal single atoms (NMSA) offer exceptional atom utilization and catalytic activity but face challenges like limited stability, low atomic loading, and complex synthesis. This study presents an innovative entropy-driven strategy to stabilize Ru single atoms (SA) on a (CePrYZrHf)O_x high-entropy oxide substrate (Ru_α%-HEO). Due to their defect-rich structure and significant lattice distortion, HEO substrates can accommodate and stabilize more Ru SA than traditional low-entropy oxides (LEO) like CeO₂. This strategy is also effective for achieving high loadings of other NMSAs, such as Pd and Pt. Ru_3%-HEO, as an electrocatalyst for nitrate reduction, achieves a high ammonia yield (5.79 mg h⁻¹ mg_cat.⁻¹) and a Faradaic efficiency (FE) of 91.3%. Density functional theory (DFT) calculations reveal that Ru_3%-HEO exhibits favorable thermodynamics for nitrate reduction, with a lower energy barrier for the rate-determining step of first hydrogenation (^*NO + H⁺ + e⁻ → ^*NOH) and stronger intermediates adsorption compared to RuO₂, enhancing its catalytic efficiency. As a cathode material in a zinc-nitrate battery, Ru_3%-HEO demonstrates a high NH₃ yield rate (1.11 mg h⁻¹ cm⁻²) and FE value (93.4%). This study provides an efficient strategy to produce stable and high-loading SA using high-entropy materials, showcasing their broad applicability in advanced electrocatalysis.