Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 45: Poster: Solid-Liquid Interfaces - Structure, Spectroscopy, Reactions and Electrochemistry

O 45.9: Poster

Tuesday, March 13, 2018, 18:15–20:30, Poster A

Electrolysis of CO₂ at Platinum/Ionic Liquid Interfaces — •Andre Kemna and Björn Braunschweig — Institute of Physical Chemistry, WWU Münster, 48149 Münster, Germany

Electrochemical CO₂ reduction reactions (CO2RR) at Pt(poly) and Pt(111)/electrolyte interfaces were studied with cyclic voltammetry (CV). Using different room temperature ionic liquids (RTIL) as electrolytes such as [BMIM][BF₄] and [EMIM][BF₄], we have investigated the influence of both water and the chemical identity of the RTIL as a co-catalyst on the activity for CO2RR. H₂O concentrations between 0.1 and 2 M lead to a substantial rise in activity. In addition, also the surface structure has a significant impact: Compared to polycrystalline Pt, well-ordered Pt(111) electrodes have a substantially lower activity for CO2RR. In order to study the molecular structure of Pt(poly)/[EMIM][BF₄] interfaces in situ and in more detail, we have applied vibrational sum-frequency generation (SFG)[1]. Potentiodynamic SFG spectra reveal a vibrational mode centered at 2355 cm⁻¹ which we attribute to a [CO₂-EMIM] complex at the interface that lifts the inversion symmetry of CO₂ molecules and makes them SFG active. We propose that these interfacial complexes can function as a stable precursor for CO₂ reduction reactions and lead to small overpotentials for CO2RR. Another vibrational band at 2080 cm⁻¹ is due to atop CO as the main reduction product of CO₂ electrolysis on Pt surfaces. Strongly adsorbed CO molecules cause a poisoning of the Pt catalyst and lead to a deactivation over many cycles.

[1] B. Braunschweig et. al. J. Electroanal. Chem., 2017, 800, 144-150