context: When used as cathode materials, anhydrides and imides of tetracarboxylic aromatic acids undergo two-electron reversible reduction, as depicted in Scheme 2. The reduction of the remaining carbonyls occurs at low voltages; it is generally considered irreversible, although some data on using these structures as anode materials indicate the opposite (see Section 3.3).
answer: anhydrides and imides of tetracarboxylic aromatic acids 