Artificial Photosynthesis

Reversible Hydrogen Storage using CO₂ and a Proton-Switchable Iridium Catalyst in Aqueous Media

Green plants convert carbon dioxide to sugar for energy storage via photosynthesis. We investigated a novel catalyst that uses carbon dioxide and hydrogen to store energy as formic acid. Using a homogeneous Ir catalyst with a proton responsive ligand, we have achieved the first reversible and recyclable hydrogen storage system that operates under mild conditions using CO₂, formate and formic acid. This system is energy-efficient and green because it operates near ambient conditions, uses water as a solvent, produces high-pressure CO-free hydrogen, and uses pH to control hydrogen production or consumption. The extraordinary and switchable catalytic activity is attributed to the multifunctional ligand which acts as a proton-relay and strong π-donor, and is rationalized by theoretical and experimental studies.

Nature Chemistry 2012, 4, 383-388, DOI: 10.1038/NCHEM.1295.