Khim Karki1 , Julio Rodriguez Manzo 1 , Daan Hein Alsem 1 , Norman Salmon 1
1 Hummingbird Scientific Lacey United States
Recent advances in electron microscopy and x-ray instrumentation have made possible to study reactions happening at solid-liquid or solid-gas interfaces with high spatial resolution [1,2]. The challenge is keeping the fluid confined to a small area since vacuum conditions are required for optimal imaging conditions. This requirement is meet by using environmental cells with channels as thin as 0.1µm - 1µm made with microfabricated chips, which contain windows for observation and can be equipped with electrodes for biasing or heating purposes. This in-situ or operando approach, where reactions are induced and simultaneously quantified inside a microscope, is suited to study reactions at interfaces relevant to electrochemical processes. Specifically, with a transmission electron microscopy (TEM) a broad set of techniques (high-resolution imaging, electron diffraction and spectroscopy, etc.) can be used to characterize a reaction.
The process of splitting water into its constituents (hydrogen and oxygen) when an electrical current is passed through it has broad technological implications in devices that use hydrogen-based energy storage strategies. Here we describe an experimental setup to induce and observe water splitting within a TEM. Specifically, we correlate TEM images of gas bubble formation at a biased metal electrode immersed in an electrolyte (phosphate buffer solution) with the corresponding voltammetry analysis. We provide details of the in-situ TEM sample holder, microfabricated electrochemistry cell chips, basic circuitry, and imaging conditions.
We highlight the advantage of using in-situ TEM to study this solid-liquid reaction, by showing that it is possible to observe with nanometer resolution where bubbles are originated, their size and shape, and how they travel away from the active electrode; correlating this data with chemical states dictated by the potential of the active electrode. Finally, we discuss the electron beam effects expected in this type of experiments .