TITLE: Solar hydrogen -- theoretical modeling of photocatalytic water oxidation

SPEAKER: Dr. Philip B. Allen

TIME: Thursday March 4 at 3 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

There is no law forbidding use of sun-light to split water to fuels like H2 with 10% efficiency at a cost far less than photovoltaic cells. For example, plants are cheap, but unfortunately natural photosynthesis has less than 1% efficiency. This seminar reports work by a consortium called SWaSSiT (solar water splitting simulation team) involving Stony Brook and Brookhaven National Laboratory. The surface of the semiconductor alloy GaN/ZnO appears to be a good catalyst for water oxidation, using electronic excitations from solar photoexcitation in the interior of the same alloy. The overall process is 4hf + 2H2O --> 2H2 + O2. The four solar photons create electrons and holes (4hf  4h+ +4e-). The electrochemistry takes place as two separate half-reactions. We focus on the more difficult oxidation process, 4h+ +2H2O --> O2 + 4H+. The reduction process, 4e- + 4H+  2H2, requires a separate catalyst. Our density functional calculations suggest a route for the oxidation catalysis, with a candidate active site, thermodynamically favored reaction intermediates, and tentative identification of the rate-limiting process.