Energy Storage in Environmentally Stable Nanoscale Magnesium Hybrid Materials
Authors: Urban Jeffrey J 
Published: February 2020

Energy storage systems are confronted by a paradox: high-energy density materials are, by definition, metastable and able to release energy. However, technological advances require robust, reliable systems to store and deliver energy which mitigates safety concerns. In this talk, I focus on solving this dual challenge of storage vs. stability in a prototype system - nanoscale magnesium nanocrystals embedded in a graphene matrix for high density, stable, hydrogen storage for fuel cell systems. This work (reference below) was recently published in Nature Comms.
Storage of hydrogen on board vehicles is one of the critical enabling technologies for creating hydrogen- fueled transportation systems that can reduce oil dependency and mitigate the long-term effects of fossil fuels on climate change. Stakeholders in developing hydrogen infrastructure (e.g., state governments, automotive OEMs, and industrial gas suppliers) are currently focused on high-pressure storage at 350 bar and 700 bar, in part because no viable solid-phase storage material has emerged. Nevertheless, solid-state materials remain of interest because of their unique potential to meet all DOE/FCTO targets and deliver hydrogen at lower pressures and higher on-board densities. A successful solution would significantly reduce costs and ensure the economic viability of a U.S. hydrogen infrastructure.
In this talk, I present work highlighting advances in the performance and viability of nanoscale metal hydrides (Cho et al. Nature Communications, 2016) by using graphene-based materials as both hydrogen-specific barrier materials and catalytic functional groups to enhance the performance of nanoscale magnesium hydride. Historically, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. In this work, we report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage surpassing that of compressed hydrogen (we report 6.5wt% and 0.105kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments and have implications for other classes of energy storage devices. I will also discuss future and ongoing work using chemically synthesized versions of graphene nanobelts to co-localize dopant moieties on the surfaces of metal hydrides using a related materials architecture.
Reference: “Graphene oxide/metal nanocrystal laminates: the atomic limit for safe, selective hydrogen storage”, Eun Seon Cho, Anne M. Ruminski, Shaul Aloni, and *Jeffrey J. Urban
, Nature Communications (2016)