(124c) Operando Attenuated Total Reflection Surface Enhanced Infrared Spectroscopy of the Electrochemical CO2 Reduction Reaction on Gold Thin Films Under Mass Transport Control

The selectivity and activity of the electrochemical CO₂ reduction reaction (ECO­₂RR) is known to be tuned by conditions at the catalyst-electrolyte interface, including the interfacial water structure, local concentration of species, the interfacial electric field, and the presence of adsorbates. The electrified interface has been probed extensively using surface sensitive spectroscopy to study the effect of these on the ECO₂RR. Here we demonstrate for the first time, to our knowledge, the application of operando surface enhanced infrared absorption spectroscopy (SEIRAS) in an attenuated total reflection (ATR) configuration to probe the ECO₂RR.

A platform was developed to enable operando SEIRAS with product collection and quantification with on-line gas chromatography. An electrochemical flow reactor was designed for compatibility with ATR-IR spectroscopy, and hydrodynamic control. Gold thin films were synthesized with electron beam physical vapor deposition (EBPVD) on ATR silicon crystals; the films are electrochemically activated to produce the surface enhanced infrared absorption (SEIRA) effect. This process yields gold thin films that are reproducibly SEIRA active and stable under ECO₂RR conditions.

Operando spectroscopy is demonstrated at various potentials, as negative as -1V vs RHE, and electrolyte flowrates; the local concentration of CO₂ and the interfacial water structure are all investigated as a function of potential or flowrate. Electrochemical ferricyanide reduction is used to calculate the boundary layer thickness as a function of electrolyte flowrate, demonstrating the capacity to control hydrodynamics near the catalyst-electrolyte interface.

This platform allows control of the microenvironment at the catalyst-electrolyte interface to investigate their effect on the ECO₂RR. The platform can be further applied to other catalysts and electrolytes to elucidate on the reaction pathways of the ECO­2­RR reaction, as well as other electrochemical reactions of interest sensitive to mass transport conditions.