Development and Exploration of Electrochemical Cascades for Titanium-Mediated Nitrogen Reduction to Ammonia

The Haber-Bosch process, invented at the turn of the 19th century, revolutionized agriculture by providing a way to make ammonia—an important component of fertilizer—from nitrogen and hydrogen. It's been estimated that without artificial ammonia synthesis, up to half the population would starve. However, this miracle chemistry comes with costly downsides, responsible for the consumption of an estimated 2% of global energy and for up to 1.6% of global carbon dioxide emissions. Therefore, the development of new methods of ammonia synthesis that are compatible with a greener society is a task of paramount importance. In this thesis, one such method for doing so—an electrochemical cascade reaction involving a plated alkali metal and a homogeneous titanium compound—is developed and explored. Electrochemically-generated sodium naphthalenide in conjunction with titanium isopropoxide is shown to enable a high rate of ammonia synthesis, but low selectivity. By contrast, potassium metal with titanium isopropoxide allows for much higher selectivity at the cost of rate. It is found that the rate-determining step of these reactions is usually electrochemical reductant generation, a powerful discovery that allows for precise tuning of rate via changing applied current density. This spatially-decoupled reaction paradigm is also applied to other alkali metal and transition metal compounds in order to open up a wider chemical space. While much remains unknown about the mechanism of this system, the novel reactivity demonstrated in this work will have immense impacts on the field of sustainable ammonia synthesis.