Hydrogen storage with hetero porphyrin aggregates

Hydrogen interaction of porphyrin hetero-pairs has been studied by differential scanning calorimetry (DSC). Aggregates were prepared by spontaneous aggregation of water soluble anionic porphyrins meso-tetra(4-carboxyphenyl)porphine (TCPP) and meso-tetra(4-sulfonatophenyl)porphine (TPPS) with cationic meso-tetra-p-trimethylaminophenyl porphine tetrachloride (TAP). Aggregate formation in solution was investigated via UV–visible spectroscopy at different pH ranges. At neutral to basic conditions, porphyrin pairs formed partially soluble hetero H-aggregates and at low pH, soluble homo J-aggregates was formed. H-aggregates were isolated by centrifuging and freeze-drying. The obtained solids were studied by X-ray powder diffraction. Thermal stability of dry aggregates was determined by thermogravimetric analysis. The TCPP-TAP hetero aggregates exhibited hydrogen uptake between 80 °C and 250 °C. The amount of hydrogen absorbed by the sample corresponds to 0.29% by weight, indicating a potential use of such materials as a solid state hydrogen storage medium.