Using solar power to produce hydrogen could be a big part of a clean energy future, but the idea has been stymied for decades. This work found a solution to a major technical problem. A voltage applied between two electrodes can separate water into hydrogen and oxygen gases, but photovoltaic electrodes that use sunlight to provide part of the driving force for this reaction are usually made of silicon. Silicon corrodes and fails when exposed to the oxygen, as do other high-quality semiconductors. This research used atomic layer deposition to coat silicon with ultrathin and pinhole-free layers of titanium dioxide and iridium.
The result of this work was a corrosion-resistant and efficient solar cell for splitting water far exceeding the performance of previously reported silicon photovoltaic anodes for water splitting. The resulting hydrogen gas can be stored. Later, when the sun is not shining, the hydrogen can be allowed to react with oxygen to form water again and release a portion of the solar electricity. Such inexpensive storage will be needed if solar power is to provide a significant amount of the world’s electricity. The new, protected silicon anode may prove to have other possible applications, like producing other kinds of fuels besides hydrogen by using feed stocks that include chemicals other than water, possibly even carbon dioxide.
Atomic layer deposition is well-established in semiconductor device fabrication, but it is only now being investigated for applications in energy. Based on the results obtained in this project, investigators are pursuing research in which ALD enables sophisticated devices for even more efficient photosynthesis of hydrogen, and the fabrication of novel catalyst alloys for more economical water splitting at high rates.