CO2-based hydrogen storage – formic acid dehydrogenation

Changing demands on the energy landscape are causing the need for sustainable approaches. The shift toward alternative, renewable energy sources is closely associated with new demands for energy storage and transportation. Besides storage of electrical energy, also storage of energy by generating and consuming hydrogen (H2) is possible and highly attractive. Notably, both secondary energy vectors, electric energy and hydrogen, have practical advantages so that one should not ask “which one is better?” but “which one fits better the specific application?” Molecular hydrogen can be stored reversibly in form of formic acid (FA, HCOOH). In the presence of suitable catalysts, FA can be selectively decomposed to hydrogen and carbon dioxide (CO2). A CO2-neutral hydrogen storage cycle can be achieved when carbon dioxide serves as starting material for the production of the FA. Examples of CO2 hydrogenation to FA are known in the literature. Herein, the formal reverse reaction, the decomposition of FA to H2 and CO2 by different catalyst systems is reviewed and selected examples for reversible storage applications based on FA as hydrogen storage compound are discussed.