From catalyst design to recycling studies for the analysis of sodium formate/bicarbonate as a practical system for hydrogen storage

In this manuscript we evaluate the practical advantages and limitations of sodium formate/bicarbonate pair as a Hydrogen Carrier (HC). The catalyst is a hybrid material composed of palladium nanoparticles (PdNPs) supported on carbon-nitride (g-C 3 N 4 ), prepared in a single-step synthesis that provides well-defined and homogeneously distributed nanoparticles. The catalytic performance of PdNPs@C 3 N 4 was investigated in the dehydrogenation of sodium formate under aqueous conditions, showing moderate activity and good stability over multiple reuse cycles. The same catalyst is also effective for the reverse reaction, i.e. the sodium bicarbonate hydrogenation, demonstrating its bidirectional catalytic capability. Catalyst performance and stability were further evaluated through alternating cycles of formate dehydrogenation and bicarbonate hydrogenation, achieving four complete cycles without significant deactivation. Mechanistic insights, supported by labelling deuterium experiments, provide experimental evidence of a plausible pathway involving heterolytic water activation facilitated by the nitrogen-rich support.