Emerging Metallenes: Synthesis, Modification, and Application

Metallene is a novel class of 2D materials composed of unsaturated coordinated metal atoms. It features ultrathin thickness (only a few atomic layers), a large specific surface area, a high density of unsaturated surface-coordinated atoms, anisotropic nanosheets formed by isotropic metal bonds, and significant intrinsic catalytic activity. These unique physicochemical properties have enabled metallenes to find widespread applications across various fields. This review summarizes recent advances in the synthesis, modification, and application of metallene materials. First, the synthesis methods of metallenes is discussed, including molecular beam epitaxy, exfoliation, solvothermal synthesis, CO-constrained synthesis, seed-mediated synthesis, ultrasonic synthesis, topologically reduced synthesis, electrochemical replacement synthesis, and template-based synthesis. Second, common strategies for modifying metallene-based catalytic materials are reviewed, such as elemental doping, alloy engineering, composite engineering, loading with nanoclusters or single atoms, amorphization, defect engineering, strain engineering, atomic layer engineering, and self-assembled aerogel formation. Subsequently, the major application directions of metallenes over the past decade are examined, including organic synthesis, sensors, biomedicine, energy catalysis, fuel oxidation, and solid-state hydrogen storage. Finally, the future prospects and key challenges in the development of metallene materials are outlined, with the hope that this review will contribute to advancing the field.