title: Analysis of atomic force microscopy phase data to dynamically detect adsorbed hydrogen under ambient conditions.
abstract: Characterization of the interactions of hydrogen with catalytic metal surfaces and the mass transfer processes involved in heterogeneous catalysis are important for catalyst development. Although a range of technologies for studying catalytic surfaces exist, much of it relies on high-vacuum conditions that preclude in situ research. In contrast, atomic force microscopy (AFM) provides an opportunity for direct observation of surfaces under or near actual reaction conditions. Tapping-mode AFM was explored here because it expands AFM beyond the usual topographic information toward speciation and other more subtle surface information. This work describes using phase-angle information from tapping-mode AFM to follow the interactions of hydrogen with palladium, polycarbonate, and iron. Real-time AFM phase-angle information allowed for the observation of multiphase mass transfer to and from the surface of palladium at atmospheric pressure and room temperature without the need for complex sample preparation. The AFM observations are quantitatively benchmarked against and confirm mass transfer predictions based on bulk hydrogen diffusion data. Additionally, they support recent studies that demonstrate the existence of multiple hydrogen states during interactions with palladium surfaces.
authors.affiliation: IGERT in Biorefining, Kansas State University , Manhattan, Kansas 66506, United States.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Young
authors.forename: Peter H
authors.initials: PH
authors.lastname: Pfromm
authors.forename: Mary E
authors.initials: ME
authors.lastname: Rezac
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Law
mesh_terms: D000327:Adsorption; D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods; D010165:Palladium / Q000737:chemistry*; D011076:Polycarboxylate Cement / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
chemical_list: D011076:Polycarboxylate Cement; C005506:polycarbonate; D010165:Palladium; D006859:Hydrogen; D007501:Iron