Oxidation/reduction reactions occurring at the interfaces between semiconductors and electrolyte solutions are often described as simply the movement of electrons (and holes). This presentation will argue that the movement of atoms and ions is often critical as well. Proton-coupled electron transfer (PCET) is critical to solar fuel production, fuel cells, corrosion, and many other processes. Similarly, batteries inherently involve cation-coupled electron transfer. The properties of colloidal ZnO, TiO2, and CeO2 nanocrystals will be described as illustrations of the coupling of electrons with protons and other ions in chemical reactions. For instance, the chemical reaction of reduced ZnO and TiO2 nanocrystals with the nitroxyl radical proceeds by transfer of e– and H+ (a hydrogen atom).