Amorphous metallic ultrathin nanostructures: A latent ultra-high-density atomic-level catalyst for electrochemical energy conversion

Single atom catalysts (SACs) are a kind of up-to-date and important electrocatalysts with the maximum utilization of atoms. The disorder distribution metal atoms on support and specific coordination structure are the basic characteristics of the supported SACs. The newly emerging amorphous metallic ultrathin nanostructured materials (AMUNMs) usually have single or few-atom-layer thickness, disordered metal atom arrangement, abundant vacancy (or micropores), and intensively exposed atomic construction. Herein, a new notion of ultra-high-density atomic-level catalysts (UHD ALCs) is proposed to describe the AMUNMs with optimized atomic exposure ratio. Particularly, the AMUNMs can be regarded as a unique free-standing atomic-level catalyst system without supports. The design philosophy of AMUNMs (including 0-D, 1-D, and 2-D ultrathin nanostructures) are systematically summarized in this perspective review for electrocatalysis applications. The challenges and prospects of this newly UHD ALCs are pointed out as well in the field of electrochemical energy conversion.