Spin states in Co-PI catalysts

Cobalt based oxygen evolution catalysts (Co-PI, PI = electrodeposited from pH 7 phosphate) are studied by resonant photoemission spectroscopy at the Co L3 and O1s edge. For the individual Co3d states, we determine their configuration, their spin, and their energy level relative to the Fermi energy. We identify the Co divalent high spin state and the trivalent low spin state. In addition, we also find the corresponding oxygen-to-metal charge transfer states. We attribute the trivalent charge transfer state to be the active state for the oxygen evolution reaction.