In a recent study from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, plant biology has helped design a method to transform water into hydrogen and oxygen. During this chemical process, two membrane-bound protein complexes were made to react using energy from the sun.
The method is based on prior research (2011) which was conducted on the protein complex Photosystem I. This protein complex forms a membrane that uses electrons elicited from light and feeds them to an inorganic catalyst which enables hydrogen production. This, however, is only half of the process needed for hydrogen production.
Follow-up research (2015) focused on the direct binding of molecular catalysts to the Photosystem I protein. Originally, platinum nanoparticle catalysts were used for initiating the reaction, but they were soon replaced by cobalt or nickel-containing catalysts. Due to their surface chemistry and size, the latter can better adhere to Photosystem I molecules when excited electrons accumulate.
Further studies (most notably in 2018) showed how Photosystem I and Photosystem II proteins can be linked in photosynthetic membranes. When the Photosystem I complex is exposed to light, an electron momentarily enters from a ground state into an excited state, where it is separated from the atom with the help of a catalyst. One of the main challenges is that the electron remains excited only for a very short period of time during which the catalyst needs to “grab” it in order to initiate the reaction. The second protein complex, Photosystem II, then splits water atoms using energy from light and takes electrons from it, which are then re-introduced into Photosystem I.
The two protein complexes are embedded in thylakoid membranes, which are similar to the oxygen-creating chloroplasts in plants. This membrane forms a pathway for exchanging electrons between the two proteins.
The next step in the research, according to Argonne chemist Lisa M. Utschig, involves incorporating the membrane-bound prototype into a living system. “Once we have an in vivo system — one in which the process is happening in a living organism — we will really be able to see the rubber hitting the road in terms of hydrogen production,” Utschig explains.
A main advantage of this design lies in its simplicity, as “you can self-assemble the catalyst with the natural membrane to do the chemistry you want”, the scientist claims. Also, the cobalt or nickel-containing catalysts could reduce the costs of producing hydrogen.
Furthermore, this process of sunlight-driven production of hydrogen from water could be the first step towards an alternative fuel to fossil fuels. It generates protein complexes which can convert water directly into hydrogen by using sunlight, thus creating an inexpensive solar fuel-producing system which helps to make solar fuels become a suitable energy source. These studies are an important step toward generating living photosynthetic systems for hydrogen production. Further research will have to be carried out on in vivo systems to demonstrate the employability of this novel process in the energy sector.