Stable Pt clusters anchored to monovacancies on graphene sheets
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Research Letter
Stable Pt clusters anchored to monovacancies on graphene sheets Bharat K. Medasani, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland WA 99354, USA Jun Liu, Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland WA 99354, USA Maria L. Sushko, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland WA 99354, USA Address all correspondence to Maria L. Sushko at [email protected] (Received 8 August 2017; accepted 26 September 2017)
Abstract First principles simulations and global optimization predict new mode of binding of Pt clusters with defects on graphene that significantly enhances their stability. Pt clusters were found to firmly bind to monovacancies in configuration transacting the vacancy site, while retaining the integrity of the cluster. Diffusion calculations support tight anchoring of Pt cluster to monovacancy. Pt cluster adsorbed on pristine graphene or other common defects exhibit a different mode of adsorption and only decorate one side of graphene. This study reveals strong influence of defect chemistry on the structure and mobility of Pt nanoclusters adsorbed on graphene and have important implications for catalytic and gas sensing applications.
The unique structural and electronic properties of graphene combined with catalytic properties and chemical selectivity of metal nanoparticles led to a considerable interest in application of graphene decorated with small metal clusters in catalysis[1,2] and gas sensing.[3–5] The catalytic and gas sensing properties of the metal nanoparticles decorating graphene depends on their surface properties and morphology,[1] which, in turn, are strongly influenced by the details of the interactions between metal nanoparticles and graphene. As synthesized graphene is usually not perfect and contains defects that serve as nucleation sites for metal nanoparticles.[6,7] Common defects include monovacancies[8] with one carbon atom missing and divacancies with two carbon atoms missing. More complex reconstruction type defects, where one of the C–C bonds is rotated by 90°, are also frequently observed.[9] Such bond rotation in pristine graphene results in the so-called Stone Wales (SW) or 5-77-5 defect, where the numbers 5 and 7 indicate the presence of pentagon and heptagon rings in graphene as opposed to the regular hexagonal rings [Fig. 1(a)]. Divacancies can adopt one of the 5-8-5, 555-777 or 55556-7777 configurations [Fig. 1(a)]. In higher order defects like tetravacancies, numerous configurations are possible due to structural reconstruction.[10] Point defects also play an important role in bandgap engineering of graphene and other 2D materials like silicene and germanene.[11–13] Simulations suggest that SW defect has the lowest formation energy, defined in Eq. (1), followed by divacancies and the monovacancy. Among divacancies, 555-777 is the most stable followed by 5555-6-7777 and 5-8-5 configurations (Table S1 in SI). Here we investigate how
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