Unprecedented insulator-to-metal transition dynamics by heterogeneous catalysis in Pd-Sensitized single vanadium oxide nanowires

We report an unprecedented insulator-to-metal transition of the Pd-nanoparticle-decorated, single vanadium dioxide nanowires caused by the heterogeneous H₂-Pd catalytic reactions. Upon hydrogen gas exposure, the Pd-VO₂ heteronanostructure shows a remarkably large current increase (∼1000-fold) at a temperature 10 C lower than the insulator-to-metal transition temperature in the bulk. This current increase occurs slowly over the duration of several seconds to several tens of seconds, depending on the Pd coverage, temperature, and hydrogen concentration. After hydrogen flow is shut off, the conductance is not immediately returned to the original value and it takes several hours, indicating that the atomic hydrogens, produced by the dissociative chemisorption on Pd, are incorporated into VO ₂. From the electronic transport measurements and finite element analyses, we suggest that the slow transition is mainly due to the formation of alternating domains of metal and insulator regions of the VO₂ crystal lattice, produced by the generated heat via the exothermic catalytic process. The current response toward hydrogen gas is also found to be reversible after the heating process. This novel finding thus has significant implications for the effective engineering of the physicochemical properties of vanadium dioxide by a heterogeneous catalytic process.