Quasi-elastic Neutron Scattering Measurement of Linker and Adsorbed Hydrogen Motion in a Graphene Oxide Framework

Graphene Oxide Frameworks (GOFs) are tunable adsorbent materials composed of graphene oxide layers separated by linker molecules. Recently, neutron diffraction results showed an adsorption-induced increase in GOF layer separation[1]. The changes in the structure upon uptake of hydrogen are expected to impact the dynamics of adsorbed hydrogen. We present Quasi-Elastic Neutron Scattering (QENS) spectra from the GOF linker molecules. The QENS spectra from the linker molecules are fit to rotational motion models and utilized to elucidate the structure of the linkers in the system (layered vs. pillared). Additionally, QENS spectra from molecular hydrogen adsorbed in a graphene oxide framework (GOF) are presented. Two different rates of hydrogen motion were detected with diffusion coefficients separated by an order of magnitude; the fastest hydrogen likely residing in 1.0 to 5.0 nm pores (``macropores'') and the slowest hydrogen residing in pores less than 1.0 nm (``micropores''). The slow hydrogen in micropores increases in diffusion rate as a function of pressure, an effect which may be due to the adsorption-induced changes in the pore structure. Finally, we consider the interaction between rotating linker molecules and the adsorbed hydrogen.
[1] doi.org/10.1021/acsomega.9b02589