The solution to the demands of transport goes through solar fuels. This is the name given to those fuels that use only sunlight, water and atmospheric carbon dioxide for their synthesis. According to this definition, wood is a solar fuel. But that is not an option: it is a liquefiable fuel, such as hydrogen and hydrocarbons. In all cases they are obtained by a fundamental previous step: the rupture of the water molecule. Something simple.
A water molecule, H2O, is composed of two hydrogen atoms and one oxygen atom. Separating hydrogen atoms from oxygen is something that is very expensive energy, so it is necessary to use catalysts, compounds capable of reducing the necessary energy to levels where the action of sunlight is sufficient. Once the hydrogens are separated, they can be joined to form molecular hydrogen, H2, or combine them with carbon dioxide, CO2, to obtain hydrocarbons.
To create practical solar fuels, an attempt has been made to develop low cost and efficient catalyst materials, generally known as photo-anodes, which are capable of breaking the water molecule using visible light as an energy source. In the last four decades, 16 of these photo-anodes have been identified. At that rate, the chances of finding the catalyst that solves one of our most serious environmental problems are the same as finding a needle in a haystack by putting your arm down and tempting with your hand. Not null, but close.
That is why the work that a group of researchers from the California Institute of Technology and the Lawrence Berkeley National Laboratory (USA) has just published is so interesting. In it they present a method that has allowed them to identify 12 photophores in just two years.
The previous material identification processes were based on a very tedious experimental verification of specific chemical compounds to evaluate their potential to be used in specific applications. In the new method, computational studies and experimentation are combined in the laboratory to, in the first place, make intelligent searches in databases to find compounds with the potential to be photo-nodes, in second to filter the compounds found according to the structural and synthesis characteristics of the compounds and, finally, check them experimentally with a high performance methodology.
To fine-tune the method they focused on vanadates, compounds that contain only three types of atoms: vanadium, oxygen and a third. 174 compounds came to the final evaluation.
The researchers found that the nature of the third element dramatically affects the properties of the material, which allowed them to learn how to "fine-tune" those properties to obtain a better photo-node.
The methods and processes are as important as the materials themselves in achieving a useful application. Thanks to this it is very possible that we are closer to an environmentally better future.
Quimin Yan et al (2017) Solar fuels photoanode materials discovery by integrating high-throughput theory and experiment. PNAS doi: 10.1073/pnas.1619940114
