WFU Physics Colloquium

TITLE: Understanding and Improving Hydrogen Storage Materials with ab initio Methods

SPEAKER: Evan Welchman

TIME: Wednesday April 05, 2017 at 2:00 PM

PLACE: Room 101 Olin Physical Laboratory

This work outlines some of the current issues driving the development of methods for using hydrogen as an energy carrier. I argue that suitably storing hydrogen is the key technological challenge to this effort. I describe the technical requirements for what constitutes a suitable hydrogen storage material and explain the three primary mechanisms by which these materials can operate. In many cases, the relevant physical and electronic properties of these materials can be modeled computationally with density functional theory, and I describe some of the myriad assumptions and methods necessary to do that.

I successfully apply that formalism to study both chemical and adsorption-based hydrogen storage materials. In NH₃BH₃ (ammonia borane or AB), I reveal the cause of experimentally-observed disorder. I also propose improving the material’s hydrogen storage properties by switching out one hydridic hydrogen atom with Cu. In metal borohydrides and metal borohydride ammoniates, I more fully describe how decomposition mechanisms change after ammoniation, and propose a new decomposition mechanism for a subset of these materials. Moving on to study adsorption-based storage as well, I fully characterize the crystal structure and bonding of a high-pressure mix of AB and H₂ (the most hydrogen-dense material fully characterized in the literature to date), and describe a general scheme that could be used to characterize other hydrogen-dense materials. I also assist in proposing a novel decoration to the organic linkers in Zn-MOF-74 that would quintuple the material’s hydrogen storage capacity and suggesting a new class of hydrogen storage materials based on alkane chains.