A Versatile Architecture for Electronically Tunable Electrocatalytic Activity: Graphene-Templated Atomically Thin Pt Supported on Oxygen-Deficient Titania

Abstract

Platinum (Pt) is an essential catalyst for many reactions including, but not limited to, oxidation/reduction, hydrogenation, and water gas shift. Despite its common use, the major disadvantages of platinum lies within its high cost due to its low abundance, and propensity for deactivation through poisoning. One way to address this setback is to reduce its loading content in catalyst design. Recently, our group has successfully synthesized a wetted atomic layer- by- layer Pt on carbon-based and noble metal supports via the surface limited redox replacement mechanism. This methodology produced atomically-thin catalyst films on graphene, an architecture that allows for unprecedented through-graphene electronic tuning of the catalyst activity by the support material below. Implementing transition metal oxides as the support with tuned electronic properties (such as work function) can dictate the activity of the surface catalyst atoms through vicinity effects. The research presented here will review the synthesis and structural characterization of atomically thin-filmed platinum overlayers on top of oxygen deficient titanium oxide supports using imaging and spectroscopic techniques. Oxygen deficient titanium oxides supports (TixOy) were used to alleviate corrosion issues caused by the Vulcan XC-72, a known carbon support that is commonly applied in fuel cells. To implement growth of the atomically thin-filmed Pt monolayers, a single layer of graphene was transferred onto TixOy supports before layer-by-layer Pt deposition. Four-point probe measurements, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and ultraviolet photoelectron spectroscopy (UPS) were used to examine the chemical and electrical properties of the TixOy supports. It was revealed that variations in the pulsed laser deposition technique parameters for support synthesis gave rise to Ti2O3- and Ti3O5-like films. The chemical properties of electrochemically deposited Pt on a graphene/TixOy films were found, using XPS, to exist in a metallic state. The functionality of the synthesized catalyst were tested using major (direct methanol) fuel cell reactions including, but not limited to, the oxygen reduction reaction and the methanol oxidation reaction. Overall, varying the stoichiometry of the TixOy supports lead to reaction overpotential tunability.