Reactivity of bimetallic nanostructured electrocatalysts for the hydrogen adsorption. An atomistic view

Hydrogen Adsorption on Au-Supported Pt and Pd Nanoislands: A Computational Study of Hydrogen Coverage Effects

“…The development and optimization of active and durable nanostructured surface catalysts rely heavily on our understanding of how particle size, site coordination, and substrate effects modulate catalytic properties. − The hydrogen oxidation/evolution reactions (HOR/HER) have been extensively explored to study the effects of particle size, active site coordination, and substrate effects on Pt and Pd nanoparticles supported on Au(111). − The reactivity toward HOR/HER increases considerably when Au(111) with sub-monolayer coverages of Pt or Pd is employed as an electrocatalyst instead of the corresponding Pd and Pt surfaces or their overlayers on Au. − ,− , The supported electrocatalysts are two-dimensional (2D) nanoparticles (nanoislands) with diameters of 2–30 nm. − ,,− , A similarly enhanced electrocatalytic activity for HER has been reported for nanoislands of Rh on Au and Pd surfaces as well as for bimetallic nanoislands of PdRh on Au and Pt surfaces. ,,, Au-supported metal nanoislands are useful model-systems not only for HOR/HER but also for many other catalytic processes, including C–C bond splitting, methanol, and formic acid oxidation, and electro-oxidation of CO …”

“…Au-supported metal nanoislands experience size-dependent compressive stress due to finite-size effects, ,,− resulting in the formation of supported nanoislands that are not aligned with the substrate . As a result, Au-supported metal nanoislands can have a broader range of adsorption sites than regular surfaces. ,− , The works of Liang et al and Liao and Ya show such a broad range of adsorption sites. Liang et al used the electrochemical scanning tunneling microscope (n-ECSTM) technique and showed that the catalytic activity for HER is maximal at the Pd/Au boundary on Pd nanoislands on Au(111) .…”

“…In this regard, various density functional theory (DFT) calculations have been performed to study the adsorption of hydrogen on Pd ,,,,,,, and Pt ,, nanoislands supported on Au(111). The results of these calculations reveal that there are multiple stable adsorption sites for hydrogen on Pd and Pt nanoisland on Au(111) under the low-coverage condition of adsorbed hydrogen.…”

“…The results of these calculations reveal that there are multiple stable adsorption sites for hydrogen on Pd and Pt nanoisland on Au(111) under the low-coverage condition of adsorbed hydrogen. The identified adsorption sites include the hollow sites (hydrogen is 3-fold coordinated), the bridge site (hydrogen is 2-fold coordinated), and the sites at the Pt/Au and Pd/Au boundaries (rim sites). ,,− ,, However, one key factor for an ideal HOR/HER electrocatalysts is to have a free energy of hydrogen adsorption near zero, Δ G (θ H ads ) ≈ 0. ,− Δ G (θ H ads ) is a function of the coverage of adsorbed hydrogen θ H ads . ,− Furthermore, experimental and computational results indicate that HOR/HER at low overpotential on Pt electrodes, for instance, take place under high coverage condition of spectator adsorbed hydrogen. ,,− Therefore, the active sites for HOR/HER on Pt and Pd nanoislands supported on Au(111) are likely metal sites with preadsorbed hydrogen atoms.…”

“…12 As a result, Au-supported metal nanoislands can have a broader range of adsorption sites than regular surfaces. 9,[17][18][19]26 The works of Liang et al 10 and Liao and Ya 12 show such a broad range of adsorption sites. Liang et al 10 used the electrochemical scanning tunneling microscope (n-ECSTM) 36 technique and showed that the catalytic activity for HER is maximal at the Pd/Au boundary on Pd nanoislands on Au(111).…”