Elucidating hydrogen-solid interactions using computational modeling

Hydrogen has significant chemical utility, both as a synthetic reagent and as an energy carrier. As the world moves away from fossil fuels being the predominant energy carrier, the utilization of hydrogen is expected to grow faster than the current industrial framework can support. This situation requires rapid technological advancement in hydrogen production, transport, energy harvesting and storage. Dense hydrogen transport membranes have utility for cost reduction in industrial chemical production (membrane reactors) and for directly harvesting energy from hydrogen (fuel cells). The goal of this work is to improve the understanding of hydrogen-solid interactions in metal and metal oxide hydrogen transport membranes at elevated temperatures. Improving the understanding of what structure-property relations govern hydrogen-dense solid membrane interactions will facilitate material design across the whole hydrogen supply chain. Hydrogen migration through solids involves several processes: adsorption, absorption, diffusion, and desorption. Adsorption and desorption are chemical processes, requiring diatomic hydrogen dissociation (chemisorption) and recombination and desorption of surface bound hydrogen atoms (associative desorption), respectively. Absorption and diffusion are fundamentally the same process. Investigation of how surface and bulk structural features affect hydrogen dynamics in and on metal and metal oxides was accomplished by examining surface behavior of an unusually stable perovskite metal oxide, and applying microkinetic modeling to predict the kinetics of hydrogen flux across dense membranes. Kinetic modeling applied to hydrogen diffusion through palladium metal over the uncertainty range of a set of transport barriers with comparison to published experimental results was utilized to ascertain how robust the model predictions are to uncertainty in the input parameters. Palladium was selected because it has been well studied experimentally due to having a hydrogen flux that is among the highest reported of non-porous hydrogen transport membranes, but has detrimental properties that, combined with high cost, have prevented full scale commercialization. Kinetic modeling of hydrogen diffusion across an InVO₄ membrane was utilized to evaluate the feasibility of InVO₄ as an alternative dense hydrogen separation membrane material. The absorption of hydrogen by dense solids often results in structural and electronic changes. These structural changes may lead to mechanical failure of the material, and hydrogen's reducing abilities can lead to chemical decomposition of metal oxides at elevated temperatures. Design of new materials for hydrogen production, transport, storage, and utilization requires a better understanding of what structure-property relations govern hydrogen diffusion through dense solids. The goal of the present work is to advance this understanding.