the chemistry
of renewable energy
Solar fuel reactions require the coupling of multielectron processes to protons, and they are energetically uphill, thus requiring a light input. The Nocera group has pioneered each of these areas of science. Examples of multielectron photoreactions originate from the research group with the generalization of the concept of the multielectron excited state, most prominent of which has a parentage of two-electron mixed-valency. The Nocera group has also created the field of proton-coupled electron transfer (PCET) at a mechanistic level by timing the electron and proton with ultrafast lasers. With the frameworks of multielectron chemistry and PCET in place, the Nocera group has created the first HX (X = halide) splitting photocatalysts to produce hydrogen from homogeneous solution. The group has also created new H2O splitting catalysts. As has been widely discussed, the production of oxygen from water has been the primary barrier to efficient water splitting. The Nocera group has overcome this challenge with the discovery of cobalt and nickel catalysts that duplicate the solar fuels process of photosynthesis outside of the leaf - an artificial photosynthesis. Like the oxygen evolving catalyst (OEC) of photosynthesis, the new catalysts in the Nocera labs self assemble from water to form a partial cubane structure, they are self-healing and they split water to hydrogen and oxygen using light from neutral water, at atmospheric pressure and room temperature. The catalyst operates at 100 mA/cm2 at 76% efficiency. Moreover it can operate out of any water source including the Charles River in front of MIT. Finally, the ability to split neutral water has led to the discovery on an inexpensive H2 producing catalyst that operates at 1000 mA/cm2 at 35 mV overpotential. These catalyst discoveries have enabled the construction of inexpensive water splitting devices that may be coupled to either a photovoltaic panel or coupled directly to the surface of a semiconducting substrate (thus eliminating the module costs associate with a photovoltaic panel). This science discovery sets a course for the large scale deployment of solar energy by providing a mechanism for its storage as a fuel, especially for those in the non-legacy world.