Electrified <em>Operando</em>-Freezing of Electrocatalytic CO₂ Reduction Cells for Cryogenic Electron Microscopy

The ability to freeze and stabilize reaction intermediates in their metastable states and obtain their structural and chemical information with high spatial resolution would be very powerful to unravel the fundamentals in many important materials technologies such as catalysis and batteries. Here, we develop an electrified operando-freezing methodology for the first time to preserve these metastable states under electrochemical reaction conditions for cryogenic electron microscopy (cryo-EM) imaging and spectroscopy. Using Cu catalysts for CO₂ reduction as a model system, we observe restructuring of the Cu catalyst in a CO₂ atmosphere while the same catalyst remains intact in an air atmosphere at the nanometer scale. Furthermore, we discover the existence of single valance Cu (1+) state and C-O bonding at the electrified liquid-solid interface of the operando-frozen samples, which are key reaction intermediates that traditional ex situ measurements fail to detect. Finally, this work highlights our novel technique to study the local structure and chemistry of electrified liquid-solid interfaces, which has broad impact for many electrochemical reactions.. Authors: Li, Yanbin [Stanford Univ., CA (United States); SLAC]; Liu, Yunzhi [Stanford Univ., CA (United States)] (ORCID:0000000305244023); Zhang, Zewen [Stanford Univ., CA (United States)] (ORCID:0000000249094330); Zhou, Weijiang [Stanford Univ., CA (United States)] (ORCID:0000000232586005); Xu, Jinwei [Stanford Univ., CA (United States)] (ORCID:000000032185362X). DOE Contract: AC02-76SF00515; SC0022955. Subjects: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; CO2 reduction; catalysis; cryogenic electron microscopy; electrified liquid-solid interfaces; operando-freezing