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

Abstract

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 singlesites and the number of atomic layers and investigated the ligand and strain effects of Cu/CuAu for electrocatalytic nitrate reduction reaction (NO 3 RR). The Cu/CuAu densely packed SAAs demonstrated a high selectivity toward NH 3 from NO 3 RR with an 85.5% Faradaic e ciency (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. Full TextAccess to nanoscale multifunctionality and synergistic properties requires the development of heterostructures that assemble nanomaterials with distinctive natures. As an example of heterostructured nanomaterials, well-de ned core/shell metal nanocrystals (NCs) create interfaces between chemically and structurally dissimilar materials and demonstrate tailorable, synergistic functionality from a spatially controlled distribution of chemical compositions 1-3 . Those core/shell NCs often exhibit enhanced or even unconventional physicochemical properties and thus provide new opportunities for many energy-related catalytic processes, such as the reactions involved in fuel cells (oxygen reduction reaction and fuel oxidation reactions) 4-6 , water splitting cells (hydrogen/oxygen evolution reaction) 7,8 , and small molecule transformation schemes (CO 2 reduction) 9,10 . In the ideal scenario, core/shell metal NCs need to be fabricated with a low-cost metal core with precious metal atoms in a thin (≤ 1 nm) shell to enhance atom e ciency and to tune NCs' properties through interfacial electronic and geometric effects 11,12 . In particular, tailoring the thin shell in an ordered intermetallic structure with long-range atomic ordering and strong d-d orbital coupling could open up new avenues for improving the catalytic properties of core/shell NCs [13][14][15] . However, high temperature is involved in the phase transformation, leading to a catastrophic failure in creating such a well-de ned, atomic precise structure.To maximize the atom e ciency of ...

Laser-controlled tandem catalytic sites of CuNi alloys with ampere-level electrocatalytic nitrate-to-ammonia reduction activities for Zn–nitrate batteries

“…The Cu K-edge of the CuNi NPs showed a negative shift toward a lower energy than that of the Cu reference, which meant that the valence state of Cu decreased. 23 In contrast, the Ni K-edge of CuNi NPs showed a slight positive shift as compared with the Ni reference, which indicated an increase in the Ni valence state of the CuNi NPs. 24 These results indicated the electron transfer from Ni to Cu and the strong Cu-Ni coupling in CuNi NPs as compared with the single metal component.…”

Regulating the spin density of CoIIIusing boron-doped carbon dots for enhanced electrocatalytic nitrate reduction

“…3f ). 41 Therefore, we determined that the NH 4 + obtained by the reaction was reduced from the added NO 3 − , excluding the interference of the reaction system or other nitrogen-containing compounds.…”

Intermetallic Single-Atom Alloy In–Pd Bimetallene for Neutral Electrosynthesis of Ammonia from Nitrate

“…25,46−49 For example, Cu/CuAu core/shell nanocrystals with ordered ISAA layers are reported to stabilize a high density of Au single atoms within a Cu matrix, inducing unique ligand effects that optimized the chemisorption of *NO 3 and *N and thus demonstrating a highly selective electrocatalytic NO 3 RR toward NH 3 . 49 In addition, to maximize the exposure of single-atom sites, controlling the nanostructure of the metal host of ISAA is also essential to further increase the AUE of the noble metal. Accordingly, reducing the dimension of metal hosts to atomically thin layers offers effective paths to achieve the utmost surface-to-volume ratio and thus delivers ISAA metallene with single-atom sites of the highest density.…”

“…Metal-based nanostructures are state-of-the-art NO 3 RR electrocatalysts with tunable physicochemical properties to efficiently stabilize the key intermediates in multistep reactions at atomic levels, resulting in a considerable selectivity of NO 3 RR for NH 3 synthesis. − Maximizing the atom utilization efficiency (AUE) of metals is known as the most important strategy to reduce the cost associated with electrocatalysts composed of noble metals without compromising their performance. Although single-atom catalysts (SACs) deliver almost 100% AUE for diverse energy-related catalytic processes, conventional SACs inevitably suffer from insufficient control of metal loading and atom aggregation caused by the Gibbs–Thomson effect. − In contrast, single-atom alloys (SAAs) realize thermodynamically stabilized single-atom centers in a metal matrix with tunable electronic properties for improved catalysis. − More significantly, ordered intermetallic single-atom alloys (ISAAs) are recently deemed to represent a structural motif with the highest density of isolated atoms since the host metal is only composed of the first nearest neighbors of the single atoms. ,− For example, Cu/CuAu core/shell nanocrystals with ordered ISAA layers are reported to stabilize a high density of Au single atoms within a Cu matrix, inducing unique ligand effects that optimized the chemisorption of *NO 3 and *N and thus demonstrating a highly selective electrocatalytic NO 3 RR toward NH 3 . In addition, to maximize the exposure of single-atom sites, controlling the nanostructure of the metal host of ISAA is also essential to further increase the AUE of the noble metal.…”