Crude oil has excellent energy storage characteristics, such as a very high energy density of 45 mega-joules per kilogram as well as the ability to be moved from one place to another safely and conveniently by almost any means of transportation. Our challenge lies in understanding and developing new mechanisms and materials for storing and transporting energy safely. At present, our primary work on energy storage focuses on two directions: materials for hydrogen storage and materials for direct sunlight-to-chemical storage. 

Ideally hydrogen will be stored in a lightweight and compact manner for mobile applications. Apart from the often-cited weight percent of hydrogen that a material can store, a number of other criteria are important. One of these is the amount of energy required to get the hydrogen out of the storage material. Our effort in this area is aimed at understanding and optimizing both the storage weight as well as the desorption temperature general, which is quite challenging as these two properties are often inversely related in bulk materials.

Our work in the area of solar fuels is focused on a class of molecules that can convert sunlight directly into "stored heat" in the form of chemical bonds.  These molecules undergo a reaction upon exposure to light that is reversible with either a catalyst or heat. In some cases a considerable amount of energy can be stored. While there are many examples of molecules that can do this once or perhaps several times, only one case has been shown to date to be able to do this reversibly many times, with no degradation: a di-ruthenium fulvalene complex. In this case, the mechanism shown in the figure, the Ru-Ru bond and the C-C bond are broken upon light exposure, and the molecule effectively “flips”. This stored chemical energy is highly stable, with a large back-reaction barrier, and can then be released in a very straightforward manner. In addition to understanding and predicting the details of both the forward photoisomerization step as well as the back-reaction heat release step, we are more broadly interested in identifying new classes of molecules (based on cheaper, more abundant materials) that can undergo the same kind of reaction as robustly.