title: Understanding catalysis in a multiphasic two-dimensional transition metal dichalcogenide.
abstract: Establishing processing-structure-property relationships for monolayer materials is crucial for a range of applications spanning optics, catalysis, electronics and energy. Presently, for molybdenum disulfide, a promising catalyst for artificial photosynthesis, considerable debate surrounds the structure/property relationships of its various allotropes. Here we unambiguously solve the structure of molybdenum disulfide monolayers using high-resolution transmission electron microscopy supported by density functional theory and show lithium intercalation to direct a preferential transformation of the basal plane from 2H (trigonal prismatic) to 1T' (clustered Mo). These changes alter the energetics of molybdenum disulfide interactions with hydrogen (ΔG(H)), and, with respect to catalysis, the 1T' transformation renders the normally inert basal plane amenable towards hydrogen adsorption and hydrogen evolution. Indeed, we show basal plane activation of 1T' molybdenum disulfide and a lowering of ΔG(H) from +1.6 eV for 2H to +0.18 eV for 1T', comparable to 2H molybdenum disulfide edges on Au(111), one of the most active hydrogen evolution catalysts known.
authors.affiliation: Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, USA.
authors.forename: Stanley S
authors.initials: SS
authors.lastname: Chou
authors.affiliation: Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Na
authors.identifier: http://orcid.org/0000-0002-7200-898X
authors.initials: N
authors.lastname: Sai
authors.affiliation: Department of Materials Characterization &Performance, Sandia National Laboratories, Albuquerque, New Mexico 87123, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.affiliation: Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, USA.
authors.forename: Eric N
authors.identifier: http://orcid.org/0000-0002-9382-9373
authors.initials: EN
authors.lastname: Coker
authors.affiliation: Center For Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87123, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Chemical and Biological Engineering, The University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Kateryna
authors.identifier: http://orcid.org/0000-0002-2611-0422
authors.initials: K
authors.lastname: Artyushkova
authors.affiliation: Center For Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87123, USA.
authors.forename: Ting S
authors.initials: TS
authors.lastname: Luk
authors.affiliation: Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, USA.|Department of Chemical and Biological Engineering, The University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Kaehr
authors.affiliation: Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, USA.|Center For Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87123, USA.|Department of Chemical and Biological Engineering, The University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: C Jeffrey
authors.initials: CJ
authors.lastname: Brinker