Understanding Strain and Ligand Effects in Hydrogen Evolution over Pd(111) Surfaces

Abstract

Pseudomorphic catalytic systems can exhibit enhanced or inhibited activity relative to the pure surface parent metal, based on a combination of strain and ligand effects. In contrast, mechanically strained and dealloyed systems can exhibit pure strain effects. Density functional calculations for hydrogen adsorption at different coverages between 0.25 and 1 monolayer on biaxially strained Pd(111) are carried out to illustrate its differing catalytic behavior for the hydrogen evolution reaction (HER) in comparison to selected pseudomorphic Pd overlayers (Pd/M). The separation of the ligand and strain effects present in Pd/M pseudomorphs and the consequent modification of the binding strengths caused by them individually are estimated. The strain exhibits a systematic contribution to binding energy changes while the ligand effect can act to either intensify or weaken the strain effect. In certain systems (e.g., Pd/Ir) the ligand effect is more pronounced than the strain effect while in others (e.g., Pd/Au) the strain effect is larger. The individual contributions of strain and ligand effects to shifts in the d-band center are also calculated and found to correlate well with the observed binding energy changes. We suggest that in the absence of a ligand effectas would be expected in mechanically strained Pd (111)H binding is tunable, and a differential free energy of hydrogen adsorption of ∼0 eV (at 0 V vs RHE) is achieved at various combinations of strain and coverage. For pure Pd under compressive strain, this leads to a prediction of a broad region of enhanced activity for the HER which may compare favorably to Pd overlayers supported on more expensive metals such as Pt and PtRu.

Exclusive Strain Effect Boosts Overall Water Splitting in PdCu/Ir Core/Shell Nanocrystals

“…[21] Thecompressive strain in our catalytic system can induce the downshift of d-band center relative to the Fermi level to maintain the inherent d occupancy. [24] As the d-band center is shifted down, the antibonding ds tates downshift meanwhile,t hus leading to aweakened adsorption interaction for reaction intermediates, facilitating the enhanced HER activity.T he CV measurements results of PdCu/Ir and PdCuIr nanocrystals in 0.1 M HClO 4 electrolyte are also tested to demonstrate the altered electronic structure,a sw ell as visualize the strain effect ( Figure S10). Thepotential of Hadsorption/desorption peaks of PdCu/Ir is lower than that of PdCuIr,i mplying the weakened hydrogen binding energy (Figure 4d).…”

“…[19,[21][22][23] And it has been exceedingly difficult to disentangle the respective contributions,which is particularly troublesome when the two effects have opposite contributions. [21,24] Indeed, not knowing the relative importance of the two effects has significantly hampered the development of superior core/shell nanocatalysts.…”

“…Xia from the charge transfer between the core/shell materials, while the strain effect arises from the lattice mismatch between them. [24,26,27] Therefore,i fo ne could develop ac ore/shell nanocatalyst with as hell thickness of % 4a tomic layers,o ne can essentially eliminate the contribution of the ligand effect and achieve ac ore/shell system with the exclusive strain effect. Thes eparation of the two effects enables us to derive ac lear picture on how strain could modulate the activity of the core/shell nanocatalysts.T his picture when combined with future study on thinner shells may help us gain better understanding of the ligand effect as well.…”

The Influence of Elastic Strain on Catalytic Activity in the Hydrogen Evolution Reaction

“…15 mV reduction in the overpotential. In ac omputational study,A dit Maark and Peterson [17] studied HER over aPd(111) surface under in-plane biaxial strain and examined the effect of hydrogen coverage.…”

The Influence of Elastic Strain on Catalytic Activity in the Hydrogen Evolution Reaction

“…In their study,t he strain in the shell was estimated indirectly through anomalous X-ray diffraction of nanoparticles before and after de-alloying. In ac omputational study,A dit Maark and Peterson [17] studied HER over aPd(111) surface under in-plane biaxial strain and examined the effect of hydrogen coverage. However,t here are af ew studies that separate the strain effect from the ligand effect.…”