The Past and Present Quest for Storing Solar Energy as Fuel

The full potential of solar energy cannot be realized unless there is method to store it and use it as fuel.  Despite large efforts in the past and the present there has been very little progress in the quest to develop a practical, inexpensive and efficient photoelectrochemical solar fuel device.  In this talk I will give both a brief historical look at the past efforts to solve this problem and provide some options and opinions about the way forward.  I will explain the reasons that photoelectrochemical production of hydrogen from water is preferable to large-scale carbon dioxide reduction for solar fuel production.  Given this it is clear that materials that are stable and have the proper band gaps for an efficient photoelectrochemical water splitting device are currently unknown.  In addition these materials need to be catalytic for water oxidation or reduction reactions or have catalyst layers deposited on their surfaces.  I will discuss combinatorial methods for discovering new oxide semiconductors and solid-state catalysts that might be further optimized to be useful in a solar water splitting device.  Researchers need to focus on quickly evaluating the many new materials that will emerge from the combinatorial searches to identify a few that have the potential to be stable, efficient and inexpensive.  An example of collaborations between my laboratory and laboratories will be given as an example.  A new concept for storing solar energy that is a simpler and potentially more efficient than a water splitting system will also be described.