A scanning probe microscopy (SPM) method can interrogate oxygen reduction and oxygen evolution reactions on a scale nearly one 100-millionth the size of what is possible with conventional electrochemical methods, according to a study in Nature Chemistry (DOI: 10.1038/nchem.1112). Information derived from the method may lead to design improvements in materials used in air-breathing electrochemical devices such as fuel cells and metal-air batteries. The technique, which was developed by Amit Kumar and Sergei V. Kalinin of Oak Ridge National Laboratory and coworkers, hinges on detecting electrochemically induced strain that results from migration of ionic species in solid ionic conductors such as yttria-stabilized zirconia (YSZ), a common fuel-cell electrolyte. These ionic events, which are central to O2 reduction and O2 evolution reactions, cause short-lived picometer-sized deformations in the conductor surface, which can be measured via SPM. In a key demonstration, the team scanned a YSZ surface coated with platinum nanoparticle electrocatalyst, pausing at each point to electrically pulse the surface and monitor the electrochemical response. The procedure yielded a nanoscale map (shown) that identifies regions of intense electrochemical activity.