Hydrogen is considered as a potential energy storage medium with its only combustion product being water, an environmentally benign material. However, the handling, storage and transportation of hydrogen in large quantities is in itself a challenge. In this study, hydrogen is stored in the form of formate salts, the hydrogenation product of CO2 (a cheap and abundant material). We present for the first time an amine-free and efficient reversible hydrogen storage system that can hydrogenate CO2 or bicarbonate to formate and also generate hydrogen from formate (&gt;90% yield in both directions) by simply varying the pressure under relatively mild conditions without any need for an external pH control or change in solvent or catalyst to reverse the reaction. For instance, carbon dioxide or bicarbonate can be reduced at higher hydrogen pressure to a formate salt using ruthenium-based aliphatic PNP-pincer complexes. The resulting formate salt can then be dehydrogenated to liberate the stored hydrogen at a lower pressure using the same catalyst. Up to six hydrogenation-dehydrogenation cycles were performed and the catalyst performance remained steady with high selectivity (CO free H2/CO2 mixture was produced).

Ruthenium PNP-pincer complex-catalyzed amine-free reversible hydrogen storage in formate salts without pH control or solvent change

250th National Meeting (2015)

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