Similar to oxygen at the bridge site, the strong adsorption of oxygen at high negative potentials can be explained by the enhanced coordination of Fe atoms with oxygen due to the electronrich environment created by the negative potentials. As the potential increases (> 1.20V/SHE), neighbouring water molecules become strongly adsorbed onto one of these coordinated Fe atoms, resulting in the formation of a four-coordinate oxygen environment similar to the configuration observed at more negative potentials (Figure ). This dynamic coordination change resulted in the stabilization of oxygen atoms at hollow sites, even at positive potentials.