Adapted from a Berkeley Lab press release
A team of Foundry users, working with staff, has invented a technique to study electrochemical processes at the atomic level with unprecedented resolution and used it to gain new insights into a popular catalyst material. Electrochemical reactions – chemical transformations that are caused by or accompanied by the flow of electric currents – are the basis of batteries, fuel cells, electrolysis, and solar-powered fuel generation, among other technologies. They also drive biological processes such as photosynthesis and occur under the Earth’s surface in the formation and breakdown of metal ores.
The scientists have developed a cell – a small enclosed chamber that can hold all the components of an electrochemical reaction – that can be paired with transmission electron microscopy (TEM) to generate precise views of a reaction at atomic scale. Better yet, their device, which they call a polymer liquid cell (PLC), can be frozen to stop the reaction at specific timepoints, so scientists can observe composition changes at each stage of a reaction with other characterization tools. In a paper published June 19 in Nature, the team describes their cell and a proof of principle investigation using it to study a copper catalyst that reduces carbon dioxide to generate fuels.
The scientists tested the PLC approach on a copper catalyst system that is a hot subject of research and development because it can transform atmospheric carbon dioxide molecules into valuable carbon-based chemicals such as methanol, ethanol, and acetone. However, a deeper understanding of copper-based CO2 reducing catalysts is needed to engineer systems that are durable and efficiently produce a desired carbon product rather than off-target products.
The team used the powerful microscopes at the Foundry’s National Center for Electron Microscopy, to study the area within the reaction called the solid-liquid interface, where the solid catalyst that has electrical current through it meets the liquid electrolyte. The catalyst system they put inside the cell consists of solid copper with an electrolyte of potassium bicarbonate (KHCO3) in water. The cell is composed of platinum, aluminum oxide, and a super thin, 10 nanometer polymer film.
Interested in Becoming a Foundry User?
Join our collaborative, multidisciplinary environment.
Learn more >
Using electron microscopy, electron energy loss spectroscopy, and energy-dispersive X-ray spectroscopy, the researchers captured unprecedented images and data that revealed unexpected transformations at the solid-liquid interface during the reaction. The team observed copper atoms leaving the solid, crystalline metal phase and mingling with carbon, hydrogen, and oxygen atoms from the electrolyte and CO2 to form a fluctuating, amorphous state between the surface and the electrolyte, which they dubbed an “amorphous interphase” because it is neither solid nor liquid. This amorphous interphase disappears again when the current stops flowing, and most of the copper atoms return to the solid lattice.
The dynamics of the amorphous interphase could be leveraged in the future to make the catalyst more selective for specific carbon products. Additionally, understanding the interphase will help scientists combat degradation – which occurs on the surface of all catalysts over time – to develop systems with longer operational lifetimes.
Read the full press release
