Probing Hydrogen Mesosorption by High Pressure Nuclear Magnetic Resonance Spectroscopy

Abstract

Concerns related to fossil fuels as an energy source has driven studies to shift focus to renewable energy. Specifically, the development of hydrogen as an onboard energy carrier. Hydrogen possesses a large amount of energy and has the potential to be a viable renewable energy carrier. Chemisorption and physisorption are two types of material-based interactions researched for hydrogen storage. Physisorption interactions have low binding energies which results in fast kinetics and complete reversibility. However, low binding energies also require liquid nitrogen temperatures to hold the hydrogen to sorbents. Carbon materials have a binding energy of 4-7 kJ/mol to H2, however doped carbon material have shown to improve the binding energy of specific binding sites. Overall, the materials have a relatively low hydrogen storage capacity, but the high energy binding sites supplies valuable information about the possibilities of future dopants. Binding energies needed to facilitate near ambient conditions are found in a region between physisorption and chemisorption, known as mesosorption. Current techniques cannot reliably characterize mesosorption interactions as they are observed on specific high energy binding sites. The technique developed for the observation of strong binding sites utilizes 1H Nuclear Magnetic Resonance (NMR) spectroscopy to examine the change in free and bound hydrogen under high pressures and variable temperatures. Based on the temperature dependent equilibrium, the ΔHdes of a specific high energy binding site was calculated. Studies presented in this dissertation are based on this specialized NMR technique and are used to analyze boron-doped carbon and other materials to identify limitations. Employing high pressure NMR analysis in this manner has shown to be versatile and provides valuable thermodynamic data on compounds typically difficult to investigate.