Atomic Ordering-Induced Ensemble Variation in Alloys Governs Electrocatalyst On/Off States.

Area of Science:

• Materials Science
• Catalysis
• Surface Chemistry

Background:

• Catalytic activity is influenced by surface atom arrangements (ensembles).
• Coupling of ensemble effects and electronic structure in conventional materials hinders isolated analysis.
• A novel method is presented to decouple geometric and electronic factors in catalysis.

Purpose of the Study:

• To develop a methodology for separating geometric ensemble effects from electronic structure in catalysis.
• To investigate the role of palladium ensemble size on methanol oxidation reactivity.
• To design catalysts with tunable active site configurations.

Main Methods:

• Comparison of structurally distinct, compositionally identical Pd3Bi intermetallic and solid solution alloys.
• Tuning palladium ensemble size by controlling atomic ordering.
• Characterization of electronic structure using X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES).

Main Results:

• Pd3Bi intermetallics with small ensembles showed no methanol oxidation reactivity.
• Solid solution Pd3Bi with larger ensembles exhibited significant methanol oxidation activity (0.5 mA cmPd-2).
• Reactivity correlated directly with average palladium ensemble size, independent of electronic structure.

Conclusions:

• Catalyst reactivity is strongly dependent on the geometric configuration (ensemble size) of active sites.
• Controlling atomic ordering offers a route to tune ensemble size without altering electronic properties.
• This approach enables more efficient catalyst design by optimizing active site geometry for specific reactions.