(Invited) 2D-Functionality in Full 3D: A New Paradigm of Graphene-Metal Epitaxial Systems

Monday, 2 October 2017: 10:00
Chesapeake H (Gaylord National Resort and Convention Center)
F. M. Alamgir (Georgia Institute of Technology)
An unprecedented dual role for graphene in electrochemical systems will be shown in this presentation. First, graphene (GR) plays the role of an enabler, allowing a large-area, fully-wetted, growth of two-dimensional Pt films that are one to several monolayers thick. Next, it also serves the role of a ‘chemically transparent’ barrier that allows catalytic chemistry to take place above it, while protecting the catalyst below it from cyclical loss. In the latter case, we will specifically show that graphene does not restrict access of the reactants for the canonical oxygen reduction reaction (ORR) but does block Pt from dissolution or agglomeration. Using these architectures, we show that it is possible to simultaneously achieve enhanced catalytic activity and unprecedented stability,e.g. retaining full activity for ORR beyond 1000 cycles . Using x-ray photoemission/absorption spectroscopy (XPS/XAS), high resolution TEM, AFM, Raman, and electrochemical methods, we show that, due to intimate graphene-Pt epitaxial contact, Pt/GR hybrid architectures are able to induce a compressive strain on the supported Pt adlayer and increase catalytic activity for ORR. We further investigate graphene as a sandwiched layer between metal films as a membrane that limits interfussion and, therefore, helps retain the integrity of core-shell architectures. We find that at operating temperatures above 100 °C (not uncommon in low-temperature fuel cells), there is appreciable interdiffusion between the primary and support metals of the catalyst system, which can diminish the catalyst activity. A single-layer of graphene acts as a barrier that prevents unwanted surface alloying between layered metals, while allowing interlayer charge transfer. Our demonstration of a the room-temperature, wetted synthesis approach, should allow for efficient transfer of charge, strain, and phonons and photons, impacting not just catalysts, but also electronic, thermoelectric and optical materials.