Initial\nCarbonation\nof Ni(111) Surfaces

Understanding the carbon formation\non Ni surfaces is\ncritical for\nthe controlled Ni-based nanofabrication and heterogeneous catalysis.\nDue to the high solubility of carbon in nickel and the complicated\nmigrations of carbon in the near-surface area, achieving a fundamental\nunderstanding of the initial carbonation of a Ni surface at an atomic\nlevel is experimentally challenging. Herein, the initial formation\nof surface carbon adsorbates on Ni(111) from the Boudouard reaction\n(2CO ↔ CO<sub>2</sub> + C) is studied by scanning tunneling\nmicroscopy (STM) in combination with density functional theory (DFT)\ncalculations. The initial carbon formation is site-selective: carbon\nadsorption at step edges is isolated and strongly bonded, acting as\nthe precursor of carbide formation; the adsorption on terrace sites\nis weaker and mobile, acting as the initial graphene clusters on Ni(111).\nThe difference in kinetics of C adsorption on the Ni(111) may play\na role in determining the future growth of carbide or graphene. Upon\nfurther carbon adsorption, new evidence is presented to resolve the\ndebate over the atomic structure of the well-recognized (√39\n× √39) R16.1° carbide structure. Our results based\non combined STM measurements and DFT calculations are further extended\nto other surfaces, such as Ni(110) and Ni(211), and a wide range of\ntemperatures and pressures. This provides valuable insights into controlling\nthe chemical processes related to carbon–nickel interactions.