Most oxide materials adopt microporous structures formed by oxometal units tailored to form cage and tunnel cavities. The electrochemistry of metal oxides in contact with aqueous electrolytes is dominated, as briey introduced in Section 3.6, by surface redox reactions involving tightly bound hydrated oxometal groups. Porous oxides, however, can undergo, apart from the above, electron transfer processes coupled with ion insertion issue from/to the electrolyte, with the possibility of adopting interstitial positions or binding to metal centers via formation of hydroxo and aquo groups.