Self‐Assembled Cobalt Oxide Nanobeads on the Conducting Van der Waals Semi‐Metal PtTe ₂ for Catalytic Heterostructure

ABSTRACT We report the self‐assembly of cobalt mono‐oxide (CoO) nanobeads on van der Waals (vdW) surface of electrically conducting platinum ditelluride (PtTe ₂ ) as a catalytic heterostructure for enhanced oxygen evolution reaction (OER). We optimize the crystallinity and surface roughness during the thermally assisted conversion (TAC) of platinum (Pt) thin films to PtTe ₂ , achieving an atomically flat vdW surface with ultra‐low surface energy. On these optimized PtTe ₂ templates, Co films are deposited and thermally annealed, allowing residual oxygen in the chamber to oxidize the Co films into CoO. The large surface energy difference between CoO and PtTe ₂ drives the self‐assembly of CoO into spherical nanobeads that are uniformly distributed over the PtTe ₂ surface. Interestingly, chemical interactions at the CoO/PtTe ₂ interface across the vdW gap are evidenced by a reduced gap, a low contact angle of CoO nanobeads, and Te diffusion at the CoO/PtTe ₂ interface. These interactions enhance OER in the CoO/PtTe ₂ heterostructure by improving charge‐transfer efficiency between the catalytically active CoO and conducting vdW PtTe ₂ support, showing comparable catalytic performance of commercial CoO nanoparticles on glassy carbon. These findings present a new synthesis approach for oxide nanostructures on van der Waals surfaces and open new combinations of heterostructures for energy applications.