The faces of iridium: One metal, many reactions

Iridium, a metal similar to platinum and gold, exhibits a variety of chemical behaviors depending on its crystal surface and the surrounding environment. At the atomic level, different crystal faces expose atoms in distinct geometric patterns, impacting how reactions proceed. A single iridium crystal can show varied surface properties when sliced in different ways, much like a diamond cut reveals varied light reflection.

Researchers at the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago investigated how iridium's electrocatalytic performance changes with crystal face exposure and pH levels. They found that different iridium faces are more effective in specific reactions and environments. For example, one face excels at hydrogen-related reactions, while another is better at oxygen reduction, a crucial step in many fuel cells.

Iridium's behavior varies significantly in acidic versus alkaline conditions. In acidic environments, where electricity flows more efficiently, iridium can draw hydrogen directly from protons in the liquid. However, alkaline conditions slow down hydrogen reactions and can lead to increased hydrogen peroxide production, which can reduce efficiency and damage devices. Oxygen reduction rates also change less with pH, but the products formed vary more, impacting device performance.

This study, published in ACS Catalysis, provides crucial benchmark data for iridium surfaces, helping researchers compare iridium with other catalysts like platinum and design improved materials for energy technologies. Understanding these specific iridium behaviors under various conditions can guide the development of more efficient catalysts tailored to specific reactions and environments.