Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals

Abstract

The modification of the electronic and chemical properties of Pt͑111͒ surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts.

Role of Strain and Ligand Effects in the Modification of the Electronic and Chemical Properties of Bimetallic Surfaces

“…As shown for a rectangular band model, if the d-band filling remains constant but the d-band width changes, then the average energy of the d band (the d-band center) must change to conserve both the d-band filling and the total number of d states [6]. Figure 1 shows the correlation between the root mean squared (rms) d-band width and the d-band center for both unrelaxed and relaxed slabs.…”

“…DFT was also recently used to illustrate the ligand effect, by showing that the presence of subsurface 3d metals in Pt(111) surfaces broadens the Pt surface d band. The width of the surface d band was found to be proportional to the interatomic matrix element that describes bonding interactions between the d orbitals of the Pt surface atoms and the d orbitals of the subsurface 3d metal atoms [6]. As a consequence of the band broadening, the average energy of the d band moved down in energy in order to conserve the d-band filling, resulting in modifications of the surface chemical properties.…”

“…We are primarily interested in the proportionality between the interatomic matrix element and the d-band width, so we take ddm to be unity for convenience, and thus treat all of the possible interactions in a lumped manner. Equation (1) was previously used to describe the ligand effect in Pt-3d sandwich structures [6]. In that work, d 12 represented the interlayer spacing between the surface and subsurface layers.…”

Descriptor‐Based Analysis Applied to HCN Synthesis from NH3 and CH4

“…[3][4][5][6][7][8] The underlying principles of the descriptor-based approach are the existence of relations between the surface electronic structure, adsorption energies and activation barriers that result in volcanoshaped activity plots as function of simple descriptors, such as atomic binding energies or the d-band center. [1,6,[9][10][11][12][13][14][15][16][17] Linear scaling relations have been established between the adsorption energies of hydrogen-containing molecules such as CH x , NH x , OH x and SH x and the C, N O and S adsorption energies on transition-metal surfaces. [18] Transition-state energies have also been shown to scale linearly with adsorption energies in a similar fashion.…”

Key Factors Affecting the Performance and Durability of Cathode Electrocatalysts in Polymer Electrolyte Fuel Cells Characterized by In Situ Real Time and Spatially Resolved XAFS Techniques

“…The promoting effects of alloying of Pt with Co, Ni, etc. have been studied by various techniques such as theoretical calculations [58][59][60][61][62], transmission electron microscopy [56][57][58][59][60][61][62][63][64][65][66][67], and photoelectron spectroscopy [55,68,69]. Although these studies have revealed relationships between the ORR enhancements and the bimetal structures, the details of dynamic surface events taking place at the cathode electrocatalyst surface remain unclear, including individual redox processes under PEFC working conditions.…”