Adsorption of formic acid on the Fe₃O₄(001) surface

O. Gamba, H. Noei, J. Pavelec, R. Bliem, M. Schmid, U. Diebold, A. Stierle, G. S. Parkinson

J. Phys. Chem. C 119 (2015) 20459-20465

The adsorption of formic acid (HCOOH) on the Fe₃O₄(001) surface was studied using X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy (IRRAS), low-energy electron diffraction, and scanning tunneling microscopy (STM). At room temperature, HCOOH dissociates to form formate (HCOO-) and hydroxyl groups, facilitated by the close proximity of undercoordinated Fe³⁺/O^2- cation/anion pairs at the Fe₃O₄(001) surface. Bidentate formate species are observed in IRRAS, and their position on Fe-Fe bridge sites can be inferred from STM data. At 70 K, HCOOH is adsorbed both dissociatively and molecularly, suggesting two active sites for dissociation. Our study also demonstrates that IRRAS is possible on Fe₃O₄ single crystals with good sensitivity but that unusual peak shapes occur because the substrate is midway between a perfect conductor and a perfect dielectric.

Corresponding author: Gareth Parkinson (parkinson).

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