Self-Assembled Cobalt Oxide Nanobeads on the Conducting Van der Waals Semi-Metal PtTe2 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 (PtTe2) 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 PtTe2, achieving an atomically flat vdW surface with ultra-low surface energy. On these optimized PtTe2 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 PtTe2 drives the self-assembly of CoO into spherical nanobeads that are uniformly distributed over the PtTe2 surface. Interestingly, chemical interactions at the CoO/PtTe2 interface across the vdW gap are evidenced by a reduced gap, a low contact angle of CoO nanobeads, and Te diffusion at the CoO/PtTe2 interface. These interactions enhance OER in the CoO/PtTe2 heterostructure by improving charge-transfer efficiency between the catalytically active CoO and conducting vdW PtTe2 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.