Photocatalytic covalent organic frameworks for hydrogen production and storage

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COFs are among the most promising hydrogen storage materials, they are lightweight, robust and easily synthesised with high hydrogen storage capacity (>7 wt.%) and are much more stable than metal organic frameworks (MOFs) for long term use. However, like MOFs, these materials are network polymers, often with uniform pore sizes. While this allows gas molecules to enter easily there is little to stop them leaving just as readily, indeed at ambient temperatures the hydrogen storage capacity of both COFs and MOFs is typically around a third of that when measured at cryogenic temperatures.In recent years, photocatalytic polymers and frameworks have also emerged as exciting new candidate in hydrogen evolution from water, the essentially infinite versatility and modular nature of organic molecules allows us to fine tune optical and electronic properties and thereby catalytic performance. This project will produce photocatalytic molecular tectons based on dibenzothiophene-S,S-dioxide - one of the most promising organic fragments in hydrogen production from water - which will anchor over the pores in the surface of the COF through non-covalent interactions to create sites for hydrogen evolution from water and to reduce the size of the pores making them readily permeable to hydrogen but not oxygen to ensure that the COF becomes enriched in hydrogen exclusively, targeting a gravimetric capacity of 5 wt.% at 298K in the first instance. The US DOE has set a target gravimetric capacity of 4.5 wt % by 2020 and 5.5 wt % by 2025 for onboard hydrogen storage for light vehicles and the approach proposed here presents a genuine route to attaining this goal. This approach will increase the thermal stability of the hydrogen enriched COFs at ambient temperatures and ultimately permit controlled generation, storage and release of hydrogen.