Schematic representation of the most favorable structures of H, OH, and adsorbed separately on (a) Cu(110) and (b) Cu(211) surfaces. 1, 2, 3, 4, and 5 in (a) identify the atop, fourfold hollow (HL), long-bridge (LB), short-bridge (SB) and threefold hollow (SB-HL, namely, the midpoint between the SB and the HL) sites, respectively. 1, 2, 3, and 4 in (b) label the atop, bridge (Bri), and two threefold hcp and fcc positions, respectively. The displayed numbers are the atomic heights in Å relative to the first atomic layer (dashed line). Atomic spheres: dark, O; white, H; gray, Cu. Top panel, side view; lower panel, bird’s eye view.
Side view (upper panels) and bird’s eye view (lower panels) of the adsorption structures of water on copper surfaces. (a) dimer on Cu(110), (b) dimer on Cu(211), (c) monomer on , and (d) monomer on . For the meaning of and , see Sec. III A. 1 (2) designates the H acceptor (H donor) in (a) and (b) or the water molecule (oxygen atom) in (c) and (d). The short arrow directed atom is the dissociating hydrogen atom . For the meaning of atomic spheres, see Fig. 1.
Side view (upper panels) and bird’s eye view (lower panels) of the calculated TS and FS structures of the O–H cleavage of water in dimers (R2) on Cu(110) [(a) and (b)] and Cu(211) [(c) and (d)] and in the most stable water monomers (R6) on [(e) and (f)]. A short arrow identifies the as in Fig. 2. For the IS configurations and the meaning of “1” and “2” and atomic spheres, see Fig. 2.
Energy diagrams for the adsorption and decomposition of water (a) in different aggregate extents on Cu(110) and (b) in dimers on Cu(211) and monomers on . See Table III for reactions R1–R6; for the meaning of PIS and IFS, see Sec. III C. All energies are referenced to the PIS.
Adsorption sites, key geometrical parameters, and adsorption energy for the most stable separate adsorption of the species pertinent to decomposition on copper surfaces. : height of the relative to the averaged height of the first-layer atoms ( except for H species); : shortest distance; : displacement of the Cu atom closest to the adsorbate with respect to the clean relaxed surface; : tilting angle of the OH bond axis for OH species or dihedral angle of the molecular plane with respect to the (110) and (211) planes. For adsorption sites and orientations, refer to Fig. 1. Coverage on Cu(110) and Cu(211) are and ML, respectively. Length in Å, angle in degrees, and energy in kJ/mol.
Geometrical parameters and energetics of the most favorable adsorption structures of water dimers and monomers on copper surfaces. : oxygen height of water molecules with respect to the averaged height of atoms in the first layer; : shortest Cu–O distance; : hydrogen bond length; : distance between O1 and O2; : displacement of the Cu atom closest to water with respect to the clean relaxed surface; : dihedral angle of the molecular plane with respect to the (110) or (211) plane; : interaction energy between adsorbates and ; : adsorption energy. For the adsorption structures and the designation of O1 and O2, see Figs. 2(a)–2(c). Length in Å, angle in degrees, and energy in kJ/mol.
Thermodynamic and kinetic parameters calculated for the O–H bond breaking of water molecules in various aggregate states on copper surfaces. Activation energy and heat of reaction in kJ/mol with ZPE correction are calculated as and , respectively. A negative value of indicates an exothermic reaction. and are the preexponential factor and reaction rate constant in at , respectively.
Key geometrical parameters of the initial states (ISs), transition states (TSs), and final states (FSs) of the dissociation of water in the most stable dimer on Cu(110) and Cu(211) and monomer on surfaces. , , , , and : shortest distances between the pertinent pairs of atomic centers; : dihedral angle of the molecular plane in the IS and TS or tilting angle of the O1H bond axis in the FS relative to the (110) or (211) plane; : displacement of the copper atom closest to O1 relative to the bare relaxed surface. For the definition of labels “1,” “2,” and , see Fig. 2. Length in Å and angle in degrees.
Decomposition of the activation energy for water dissociation on copper surfaces. For the meaning of , , , , , and , see the Appendix. A negative value indicates that the term lowers the barrier.
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