Metastable phase two-dimensional catalysts provide great flexibility for modifying their chemical, physical, and electronic properties. However, the synthesis of ultrathin metastable phase two-dimensional metallic nanomaterials is highly challenging, mainly due to the anisotropic nature of metallic materials and their thermodynamically unstable ground-state. Here, we report free-standing RhMo nanosheets with atomic thickness and a unique core/shell (metastable phase/stable phase) structure. The polymorphic interface between the core region and shell region stabilizes and activates metastable phase catalysts; the RhMo Nanosheets/C shows excellent hydrogen oxidation activity and stability. Specifically, the mass activities of RhMo Nanosheets/C is 6.96 A mg_Rh⁻¹; this is 21.09 times higher than that of commercial Pt/C (0.33 A mg_Pt⁻¹). Density functional theory calculations suggest that the interface aids in the dissociation of H₂ and the H species can then spillover to weak H binding sites for desorption, providing excellent hydrogen oxidation activity for RhMo nanosheets. This work advances the highly controlled synthesis of two-dimensional metastable phase noble metals and provides great directions for the design of high-performance catalysts for fuel cells and beyond.

亚稳相二维催化剂为改变其化学、物理和电子性质提供了极大的灵活性。然而，超薄亚稳相二维金属纳米材料的合成极具挑战性，这主要是由于金属材料的各向异性性质及其热力学不稳定的基态。在这里，我们报道了具有原子厚度和独特的核/壳（亚稳态相/稳定相）结构的独立式 RhMo 纳米片。核区和壳区之间的多晶型界面稳定并活化亚稳相催化剂； RhMo Nanosheets/C表现出优异的氢氧化活性和稳定性。具体而言，RhMo Nanosheets/C的质量活度为6.96 A mg _Rh ^-1 ；这比商用 Pt/C (0.33 A mg _Pt ^-1 ) 高 21.09 倍。密度泛函理论计算表明，该界面有助于H ₂的解离，然后H物质可以溢出到弱H结合位点进行解吸，为RhMo纳米片提供优异的氢氧化活性。这项工作推进了二维亚稳相贵金属的高度受控合成，并为燃料电池及其他领域的高性能催化剂的设计提供了重要方向。