X-ray spectral microscopy reveals the active edges of the water-splitting material

Newswise – Science

Hydrolysis is a chemical reaction that involves breaking the chemical bonds of water molecules. One of the main types is electrolysis – splitting water into oxygen and hydrogen using electricity. In this study, the researchers used specialized techniques to determine the structure and chemical activity of the electrical conductor involved in electrolysis. The researchers used a method called resonance X-ray absorption microscopy to describe the chemical changes around the electrode's atoms. This allowed them to study the fluid inside and around the electrode while they applied an electrical voltage. They can then create a map of the chemical changes during the electrolysis process.

Influence

Splitting water into hydrogen and oxygen is a key process in energy storage. The chemical transitions involved in water splitting require energy. Researchers are creating more efficient new electrodes with energy savings catalytic properties. This work shows the atomic structure and chemical mechanisms at work as electrical currents rearrange atomic bonds and split water molecules. The understanding gained from this process will help scientists develop better electrodes.

Summary

To understand the transformation of materials under real-world conditions of working energy conversion systems, researchers need analytical tools that can penetrate the working environment without disturbing the process. X-ray absorption microscopy achieves and provides high-resolution chemical maps. In this study, the working electrode was covered with a layer of liquid water. The researchers focused on bright and wide-energy X-rays from the synchrotron source with specialized X-ray lenses. They used a monochromator to select the energy, where the absorption of X-rays depends on the chemical state of the atoms in the electrode. By making and comparing maps taken at specific energies associated with specific chemical states, researchers could identify regions of different chemical activity.

The researchers mapped the electrochemical reaction current, physical structure, and oxidation state of cobalt on single-crystal nanoplatelets while they actively split water. The researchers found that the state of oxygen around the metal atoms in the electrode changes dramatically during electrolysis. The largest changes and the most active sites for oxygen production were at the edges of the electrode nanoplatelets. This information will allow materials engineers to change the chemistry at the edge of the platelets and possibly reduce the energy cost by splitting water to create hydrogen.

financing

The research was funded by the Department of Energy's (DOE) Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. Part of this work was performed at the Stanford Nano Shared Facilities/Stanford Nanofabrication Facility with support from the National Science Foundation. Equipment support was provided by the DOE Office of Science, Office of Basic Energy Sciences, Small Business Innovation Research Program. X-ray work was done Extended light sourceDOE Office of Science User Facility.

Journal link: Nature, May-2021