Achieving Ultra-High Selectivity to Hydrogen Production from Formic Acid on Pd-Ag Alloys

Area of Science:

• Catalysis science
• Materials science
• Surface chemistry

Background:

• Palladium-silver (Pd-Ag) alloys show promise for CO-free hydrogen production from formic acid, crucial for fuel cell technology.
• Understanding the precise structural factors governing formic acid decomposition selectivity on Pd-Ag alloys remains a challenge.

Purpose of the Study:

• To investigate formic acid decomposition pathways on Pd-Ag alloys with varying atomic configurations.
• To identify specific alloy structures that promote high selectivity for hydrogen (H₂) production.

Main Methods:

• Generation of Pd-Ag surface alloys on a Pd(111) single crystal.
• Characterization using infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT).
• Analysis of reaction pathways using temperature-programmed reaction spectroscopy (TPRS) and DFT.

Main Results:

• Electronic alteration of Ag atoms by neighboring Pd atoms was observed, correlating with the number of Pd neighbors.
• Electronically modified Ag domains facilitate a selective formic acid dehydrogenation pathway.
• Surface Pd atoms, while less prone to CO poisoning, do not enhance selectivity and can produce undesirable byproducts like CO.

Conclusions:

• Surface Ag domains influenced by subsurface Pd are identified as the primary active sites for selective formic acid decomposition.
• Surface Pd atoms negatively impact selectivity for CO-free H₂ production.
• Tailoring Pd-Ag alloy structures offers a route to optimize CO-free hydrogen generation for fuel cells.