Bismuth thin film cathodes exhibit electrocatalytic activity toward reduction of CO2 into CO, in acetonitrile solutions containing milimolar concentrations of alkyl-imidazolium based ionic liquids such as 1-butyl-3-methyl imidazolium triflate ([BMIM]OTf). The reduction of CO2 at the Bi/[BMIM]+ interface is characterized by high selectivity toward CO, Faradaic efficiencies (%FECO) between ~75-90%, current densities (jCO) of 5-25 mA/cm2, and modest overpotentials (h £ 200). Although both Bi and the imidazolium-based ionic liquid are critical to this catalysis, little is known about the fundamental processes responsible for the activation of CO2 at this electrode/electrolyte interface. In this study, we discuss the results of in operando X-ray reflectivity (XR) measurements conducted to investigate the Bi/[BMIM]+ interfacial structure as a function of applied potential. The Bi cathodes consist of thin Bi (001) oriented films (~6 nm thick) sputtered onto graphene-coated SiC (001) substrates. Atomic force microscopy was utilized to screen the surface topography of the samples before conducting electrochemical and X-ray experiments. Low-angle XR and crystal truncation rod (CTR) data obtained at the APS show that these Bi thin film electrodes undergo restructuring during cyclic polarization between open circuit potential (~-0.3 V) and -1.9 V vs. Ag/AgCl in [BMIM]OTf containing solutions, in the presence and absence of CO2. The variation in the reflectivity signal of the Bi (001) film Bragg peak (at Q= 1.56 Å-1) implies that significant structural or conformational changes to the Bi films occur just prior to the onset potential of CO2 activation (~-1.8 V vs. Ag/AgCl). By using multiple characterization techniques, this study provides a more comprehensive assessment of the structural dynamics at the Bi/[BMIM]+ interface under conditions that promote the electroreduction of CO2.

Investigating the structural dynamics of the Bi/[BMIM]+ interface during electrocatalytic reduction of CO2

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.