Oxygenic photosynthetic organisms reduce CO2 to store energy as sugar. The efficient and catalytic reduction of CO2 has inspired a variety of sustainable energy and chemical-feedstock application, because CO2 is cheap, abundant, and non-toxic. H2 is likely to be used as a fuel in the future. However, utilization of H2 for fuel is limited, mainly because of problems with its storage and delivery. Recently, formic acid has been proposed as a practical liquid fuel for hydrogen storage.Herein, we present recent research using hydroxybipyridine-based iridium catalysts for interconversion of CO2/H2 and formic acid in water. We have developed a well-defined pH-dependent catalysts which have phenolic hydroxyl group in the ligand. Highly catalytic activity showed the hydrogenation of CO2 at basic conditions and dehydrogenation of formic acid at acidic conditions. It was found that the catalyst was activated remarkably by the deprotonation of hydroxyl group, due to the strong electronic effect of the generated oxyanion group. Efficient formation of formate by the reduction of CO2 was performed even under ambient conditions (25 �C and 0.1 MPa). At acidic conditions, H2 by dehydrogenation of formic acid was efficiently evolved without CO (< 10 ppm). In addition, the CO-free pressurized hydrogen gas can be supplied when the reaction was carried out in a closed reaction vessel.We have demonstrated a hydrogen-storage system using a combination of the formation and dehydrogenation of formic acid under mild reaction conditions. Further investigations on the reversible storage and evolution of H2 with improved catalysts based similar ligand motifs are in progress.

Recent advance on interconversion between H<sub>2</sub>/CO<sub>2</sub> and formic acid using hydroxybipyridine-based iridium catalysts

243rd National Meeting (2012)

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Recent advance on interconversion between H2/CO2 and formic acid using hydroxybipyridine-based iridium catalysts

Recent advance on interconversion between H₂/CO₂ and formic acid using hydroxybipyridine-based iridium catalysts