Structural and chemical characterization of modified graphenes for hydrogen storage

Abstract

The automotive industry is already showing signs of moving beyond a century long dependence on petroleum. The tens of billions of dollars in the electric vehicle (EV) consumer market are a powerful demonstration of this transition. Hydrogen fuel cell electric vehicles also offer a clean alternative to petroleum and have advantages to EVs in some transportation sectors. To grow the hydrogen economy, significant progress must be made in hydrogen storage systems. Adsorbent based storage systems have the potential to lower the pressure requirements while simultaneously improving the storage capacity of these systems. The research presented in this dissertation focuses on the development and characterization of new adsorption storage systems based upon modified graphene. Early work involved substitutional doping of activated carbon with boron to alter the surface chemistry of the adsorbing surface with the goal of improving adsorption strength. Boron-doped samples were characterized with X-ray Photoelectron Spectroscopy to correlate specific boron chemistries to adsorption performance metrics. A maximum of 2% substitutional doping was observed. Later work focused on framework materials built up from graphene oxide and benzene diboronic acid (GOFs). GOFs are an ideal material to study the structural response of an adsorbent during adsorption due to their layered structure and relatively well-defined pore geometry. To study GOF's adsorption-induced structural response, we built a computer-controlled gas handing system for in situ neutron diffraction measurements at the University of Missouri Research Reactor. For the first time, supercritical adsorption-induced structural change was observed. Through correlation of adsorption and structural data, we are able to predict the rate of expansion in GOF based on the critical temperature and vdW diameter of the adsorbate molecule.