Transition metal hydrogenophosphates: a potential source of new protonic and lithium conductors

The research of new frameworks with excellent protonic and lithium ion conduction properties is a topic of high interest for the development of energy storage, as materials in fuel cells and batteries. We review herein, the investigations that have been performed on transition metal hydrogenophosphates, whose hydroxyl (OH) group or (H2O) molecules or (H3O+) cations allow protonic conduction but also precursors for Li ion conduction to be generated, using both H-Li exchange and direct lithium insertion.