ABSTRACT The exsolution method has garnered significant attention owing to its high efficacy in developing highly efficient and stable metal nanocatalysts. Herein, a versatile exsolution approach is developed to embed size‐tunable metal nanocatalysts within a conductive metal pnictogenide matrix. The gas‐phase reaction of Ru‐substituted Ni–Fe‐layered‐double‐hydroxide (Ni 2 Fe 1− x Ru x ‐LDH) with pnictogenation reagents leads to the exsolution of Ru metal nanocatalysts and a phase transformation into metal pnictogenide. The variation in reactivity of pnictogenation reagents allows for control over the size of the exsolved metal nanocatalysts (i.e., nanoclusters for nitridation and single atoms for phosphidation), underscoring the effectiveness of the pnictogenation‐driven exsolution strategy in stabilizing size‐tunable metal nanocatalysts. The Ru‐exsolved nickel–iron nitride/phosphide demonstrates outstanding electrocatalyst activity for the hydrogen evolution reaction, exhibiting a smaller overpotential and higher stability than Ru‐deposited homologs. The high efficacy of pnictogenation‐assisted exsolution in optimizing the performance and stability of Ru metal nanocatalysts is ascribed to the efficient interfacial electronic interaction between Ru metals and nitride/phosphide ions assisted by the inner sphere mechanism. In situ spectroscopic analyses highlight that exsolved Ru single atoms facilitate more efficient electron transfer to the reactants than the exsolved Ru nanoclusters, which is primarily responsible for the superior impact of the phosphidation‐driven exsolution approach.

ABSTRACT The exsolution method has garnered significant attention owing to its high efficacy in developing highly efficient and stable metal nanocatalysts. Herein, a versatile exsolution approach is developed to embed size‐tunable metal nanocatalysts within a conductive metal pnictogenide matrix. The gas‐phase reaction of Ru‐substituted Ni–Fe‐layered‐double‐hydroxide (Ni 2 Fe 1− x Ru x ‐LDH) with pnictogenation reagents leads to the exsolution of Ru metal nanocatalysts and a phase transformation into metal pnictogenide. The variation in reactivity of pnictogenation reagents allows for control over the size of the exsolved metal nanocatalysts (i.e., nanoclusters for nitridation and single atoms for phosphidation), underscoring the effectiveness of the pnictogenation‐driven exsolution strategy in stabilizing size‐tunable metal nanocatalysts. The Ru‐exsolved nickel–iron nitride/phosphide demonstrates outstanding electrocatalyst activity for the hydrogen evolution reaction, exhibiting a smaller overpotential and higher stability than Ru‐deposited homologs. The high efficacy of pnictogenation‐assisted exsolution in optimizing the performance and stability of Ru metal nanocatalysts is ascribed to the efficient interfacial electronic interaction between Ru metals and nitride/phosphide ions assisted by the inner sphere mechanism. In situ spectroscopic analyses highlight that exsolved Ru single atoms facilitate more efficient electron transfer to the reactants than the exsolved Ru nanoclusters, which is primarily responsible for the superior impact of the phosphidation‐driven exsolution approach.

Two-dimensional transition-metal dichalcogenide nanosheets made of MoS2 are widely studied owing to their applications as electrocatalysts and electrode materials. To specify key design parameters for optimizing catalytic performance of MoS2, we developed a soft-chemical lattice manipulation strategy to precisely tune their structural, defect, and morphological characteristics via self-assembly of the exfoliated MoS2 nanosheet with various guest cations. Most alkali-metal-restacked MoS2 nanosheets exhibit a layer-by-layer ordered intercalation structure containing water monolayers; however, self-assembly with Li+ ions led to the intercalation of thicker water bilayers, attributed to the higher hydration energy of smaller Li+ ions. Increasing the basal spacing induced a gradual phase transformation from 2H-type bulk MoS2 to 1T MoS2 structure restacked with H+ and Na+ ions and further to a highly distorted 1T′ MoS2 structure restacked with Li+ and Cs+ ions. Additionally, an increase in the guest size led to an increase in the defect concentration. The Cs+-restacked MoS2 exhibited the lowest overpotential and smallest Tafel slope for hydrogen evolution reactions. Correlating the electrocatalytic activity with structural, defect, and morphological parameters revealed that unlike interlayer spacing and crystal phase, the surface area and defect concentration are dominant factors governing the electrocatalytic performance of MoS2. This conclusion was supported by in situ Raman analysis, which indicated enhanced hydrogen adsorption and accumulation on the Cs+-restacked MoS2 surface, suggesting an efficient Volmer–Tafel reaction pathway.

Amorphous materials have garnered significant research interest because of their high structural tolerances and useful functionalities. Here, we develop an effective synthesis method for atomically thin, highly disordered RuO₂ nanosheets that exhibit a promising electrocatalytic performance and a distinct pH-dependent operation mechanism. The poor orbital overlap and coordinatively unsaturated nature of the Ru ions in the highly disordered RuO₂ nanosheets have a synergistic effect on the electrocatalytic performance by enhancing surface adsorption and the activation of lattice oxygen. The highly disordered RuO₂ nanosheets exhibit high electrocatalytic activities in the oxygen evolution reactions (OERs) performed in both alkaline and acidic electrolytes. Various in situ spectroscopic investigations reveal that structural disordering causes a greater contribution of the lattice oxygen participation mechanism in acidic media than in alkaline media. This pH-dependent mechanism can be attributed to the amorphization-induced enhancement of lattice oxygen occupation in the acidic OER medium and increased hydroxide adsorption in the alkaline OER medium. Such disorder-driven pH tuning of the electrocatalytic operation mechanism enables the fabrication of pH-universal high-performance electrocatalysts.

Exsolution is an effective method for synthesizing robust nanostructured metal-based functional materials. However, no studies have investigated the exsolution of metal nanoparticles into metal nitride substrates. In this study, a versatile nitridation-driven exsolution method is developed for embedding catalytically active metal nanoparticles in conductive metal nitride substrates via the ammonolysis of multimetallic oxides. Using this approach, Ti_1-xRu_xO₂ nanowires are phase-transformed into holey TiN nanotubes embedded with exsolved Ru nanoparticles. These Ru-exsolved holey TiN nanotubes exhibit outstanding electrocatalytic activity for the hydrogen evolution reaction with excellent durability, which is significantly higher than that of Ru-deposited TiN nanotubes. The enhanced stability of the Ru-exsolved TiN nanotubes can be attributed to the Ru nanoparticles embedded in the robust metal nitride matrix and the formation of interfacial Ti³⁺─N─Ru⁴⁺ bonds. Density functional theory calculations reveal that the exsolved Ru nanoparticles have a lower d-band center position and optimized hydrogen affinity than deposited Ru nanoparticles, indicating the superior electrocatalyst performance of the former. In situ Raman spectroscopic analysis reveals that the electron transfer from TiN to Ru nanoparticles is enhanced during the electrocatalytic process. The proposed approach opens a new avenue for stabilizing diverse metal nanostructures in many conductive matrices like metal phosphides and chalcogenides.

Boride substitution for defect-introduced MoS 2 nanosheets provides an effective way to tune the crystal structure of MoS 2 and improve the HER electrocatalytic activity.