Research and Development of Advanced Hydrogen Storage Materials: Sorbents
Recipient National Renewable Energy Laboratory/NREL (PI: Tom Gennett)
Abstract Sorbents, such as metal-organic frameworks, covalent organic frameworks, and carbon-based materials, represent several possible paths forwards towards a hydrogen storage material that can meet the DOE goals for transportation. However, whilst tremendous surface areas for adsorption have been demonstrated in multiple materials, the binding energies and volumetric capacities for hydrogen uptake are still not within the required range. Therefore, the critical objectives with sorbents is to identify modifications to sorbent matrices that can provide a high density of sites with the appropriate binding energy, appropriate temperatures for adsorption/desorption, and decrease void volumes to improve volumetric capacities. This is a team challenge in which theoretical calculations yield pilot assessments of feasibility, connecting binding strength and structure volume calculations to predict upper limits of usable capacity. Interaction with experimental team members at LBNL, NREL, and SNL and theoretical teams at LBNL, PNNL and LLNL will give rise to potentially promising design paradigms, such as specific chemical defect incorporation, multiple hydrogens per metal site, and/or physical modification such as densification/compaction limits, mass transport control and controlled dynamic structure. Such paradigms will be studied relatively rapidly by electronic structure calculations, and further evolved either before, or in tandem with, experimental efforts. Furthermore, as we move towards room temperature sorbent materials it is now evident that the temperature dependence of ΔH and ΔS upon H2 sorption cycles is an additional key to identifying the correct sorbent materials. This is important as most current evaluation thermodynamic properties of H2 binding, were achieved over a narrow cryogenic temperature range (77 – 87K). Therefore, it is imperative that we “re-establish” some of the key parameters and physiochemical properties necessary for materials at the higher temperatures, given this new insight into the different contributions of entropy and enthalpy at the higher temperatures.