Fuel cells have long held promise as power sources, but low efficiency has created obstacles to realizing that promise. Researchers at the University of Illinois and collaborators have identified the active form of an iron-containing catalyst for the trickiest part of the process: reducing oxygen gas, which has two oxygen atoms, so that it can break apart and combine with ionized hydrogen to make water. The finding could help researchers refine better catalysts, making fuel cells a more energy- and cost-efficient option for powering vehicles and other applications.Led by U. of I. chemistry professor Andrew Gewirth, the researchers published their work in the journal Nature Communications.