Physical Chemistry Seminar, Dr. Matthias Waegele, Boston College

Apr 18, 2019 at - | Carol Lynch Lecture HallChemistry Complex

"Elucidating the Molecular Origins of the Product Selectivity of Electrocatalytic Reactions"

"Many electrocatalytic reactions of current interest involve the transfer of multiple protons and electrons. Examples include the oxidations of methane and small organic molecules, as well as the reductions of nitrogen, nitrate, and carbon dioxide. These processes exhibit poor selectivity for  specific  desired  products.  This  poor  product  selectivity  hinders  the  adoption  of  these promising   technologies.   The   aqueous   electrochemical   reduction   of   carbon   dioxide   to hydrocarbons  on  Cu  electrodes  is  prototypical  for  this  class  of  processes.  It  could  potentially provide sustainable pathways to renewable fuels and  valuable commodity chemicals, such  as ethylene. Improving the selectivity for ethylene, the commodity chemical with the highest yearly production  volume,  is  one  of  the  most  critical  challenges  in  carbon  dioxide  reduction.  The reaction selectivity is determined by the electrocatalytic interface, whose properties are jointly determined  by  the  solid  electrode  and  the  liquid  electrolyte.  Often,  these  properties  evolve under operating conditions. To design catalytic interfaces with high selectivity, it is essential to identify the molecular-level origins that are principally responsible for controlling the reaction path. Due to the chemical complexity and dynamic nature of the electrocatalytic interface, this molecular-level understanding is largely lacking to date. To address this challenge, we employ surface-enhanced  infrared  absorption  spectroscopy  (SEIRAS)  for  probing  the  interactions  of surface-adsorbed  carbon  monoxide,  a  key  reaction  intermediate  in  the  reduction  of  carbon dioxide to hydrocarbons, with the Cu electrode surface and the liquid reaction environment. We complement  this  approach  with  differential  electrochemical  mass  spectrometry  (DEMS)  to establish interfacial property/product selectivity relationships. In this talk, we will show that an intermolecular interaction between surface-adsorbed CO and interfacial water is essential for the formation  of  ethylene.  Disruption  of  this  interaction  shuts  down  the  pathway  to  ethylene. Further, we will demonstrate that a pH- and potential-induced reconstruction of the Cu electrode drives the conversion of atop-bound CO to bridge-bonded CO. We found that only atop-bound CO   is   an   on-pathway   intermediate   in   CO   reduction,    whereas   bridge-bonded   CO   is electrochemically  inert.  We  will  discuss  how  these  findings  contribute  to  the  mechanistic understanding of carbon dioxide reduction and how they inform the design of more selective"
"electrocatalytic interfaces."





Host: Dr Gai


inquires rvargas@sas.upenn.edu