Quantifying Aqueous Radiolytic Products in Liquid Phase Electron Microscopy

Liquid phase electron microscopy (LPEM) is rapidly gaining importance for in situ studies of chemical processes. However, radiolysis due to interactions between the liquid medium and the electron beam results in the formation of highly reactive species that influence the studied processes. Our understanding of LPEM radiolysis is currently based on simulations that rely on data collected from measurements at low electron flux intensities, requiring extrapolation by several orders of magnitude to match the intensities utilized in LPEM. We demonstrate direct electrochemical measurements of radiolytic products during in situ LPEM, which allows us to directly assess the high flux accuracy of low-flux radiolysis models. Using a specially designed liquid cell for electrochemical detection, we quantify the primary expected stable radiolysis products H2 and H2O2 in a scanning electron microscope. We find H2 production is rapid and in reasonable agreement with predictions, but H2O2 levels are lower than expected from the low-flux extrapolated radiolysis models. This study demonstrates a new approach to experimentally validate simulations and indicates that the chemical environment may be far more reducing than predicted from current models.