Graphene Membrane Electrochemical Cell for High-Vacuum SEM Observation of Electrocatalytic Reactions

Understanding morphological changes of electrocatalysts during electrochemical reactions remains challenging in conventional electron microscopy due to the incompatibility between liquid environments and the high vacuum required for scanning electron microscopy (SEM). In this work we focus on the use of ultrathin graphene membrane with the goal of developing a cell enabling electrochemical reactions in liquid and gaseous environments while maintaining high-vacuum conditions for SEM observation. Free standing graphene membranes over a few micrometer diameter windows of a supporting substrate of different materials (Cu, Ni or SiNx) were employed separation to separate a liquid electrochemical chamber from the high vacuum of the SEM measuring chamber. The graphene membrane acts both as an electron-transparent barrier and as a potential working electrode interface for electrochemical reactions in acidic or basic electrolytes. Analysis of the transfer process indicated that premature removal of the PMMA support layer and rapid solvent evaporation produced strong capillary forces that damage the ultrathin graphene films. Process considerations including delayed PMMA removal, critical point drying, and tert-butanol freeze-drying were evaluated as potential strategies to reduce surface-tension-induced damage. To improve reliability, commercially available graphene-coated TEM grids are currently being adopted as the primary membrane platform. Mechanical and thermal factors governing membrane stability were also evaluated. Graphene exhibits a negative thermal expansion coefficient at low temperatures and extremely high intrinsic strength (~130 GPa). For a defect-free monolayer graphene membrane spanning a 10 µm aperture, the estimated differential pressure tolerance is approximately 0.3–0.5 bar, increasing with multilayer thickness. Monte Carlo electron-transport simulations were performed to evaluate electron transmission through a graphene membrane designed to safely sustain differential pressures exceeding 3 atm, at primary beam energies of 10–30 keV. The results indicate that such graphene membranes maintain high electron transparency while providing sufficient mechanical stability for operation under realistic pressure conditions. Future work includes focused ion beam (FIB) sealing of incomplete graphene coverage and high-vacuum SEM investigation of electrocatalyst morphology evolution during electrochemical redox reactions. This platform provides a promising route toward in-situ SEM studies of electrochemical systems using atomically thin graphene windows. 1-Jian-Bin Xu, Rodney S. Ruoff, Hongwei Zhu et al. The physics and chemistry of graphene-on-surfaces 2 -Francesco Bonaccorso1, Antonio Lombardo1, Tawfique Hasan1, Zhipei Sun1, Luigi Colombo2, and Andrea C. Ferrari1,* 1Cambridge University, Engineering Department, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK 2 Texas Instruments Incorporated, 13121 TI Boulevard, Dallas, Texas 75243, US 3 -Interfacial adhesion between graphene and silicon dioxide by density functional theory with van der Waals corrections 4 -Unraveling the strong coupling between graphene/nickel interface and atmospheric adsorbates for versatile realistic applications -https://doi.org/10.1016/j.cartre.2020.10 0 013 5 -Dynamic Imaging of Au-nanoparticles via Scanning Electron Microscopy in a Graphene Wet Cell (Ackerley, C.; Nielsen, C.; Hawkins, C. Microscopy and Microanalysis 2006, 12, 428–429.) 6 -Ishii, M.; Nakamura, H.; Nakano, H.; Tsukigase, A.; Harada, M. Langmuir 2005, 21, 5367 5371 7 -Päivänranta, B.; Langner, A.; Kirk, E.; David, C.; Ekinci, Y. Nanotechnology 2011, 22, 375302. 8- Secondary Electron Hyperspectral Imaging(SEHI) in FIB−SEM for Proton exchange membrane fuel cell (https://doi.org/10.1021/acsomega.5c09325)