CEA researchers have made a step towards the preparation of a lasting photo-electrode for hydrogen production. It is based on a hybrid architecture, based on a semiconductor interfaced with a molecular catalyst. The electrode contains only elements found in abundant quantities in the earth’s crust.
Hydrogen (H 2 ) is a promising fuel and a good means of storing renewable energies that it will subsequently restore by combustion with molecular oxygen (O 2 ) in fuel cells. Its carbon footprint will then be zero: this reaction only produces water! Green hydrogen can thus be produced from water and solar energy in a process mimicking photosynthesis. The sustainability of this future technology, however, rests on the development of new materials that are both active, stable and based on abundant and inexpensive elements.
As part of the “ Make Our Planet Great Again ” initiative , researchers from CEA-Irig, in collaboration with the Institut néel and EPFL, have taken another step towards preparing a durable photoelectrode for the production of hydrogen. It is based on a hybrid architecture, based on a p-type semiconductor which absorbs light and which is interfaced with a molecular catalyst. The whole contains only non-toxic elements found in abundant quantities in the earth’s crust.
The strategy is to use a mixed oxide semiconductor composed of iron and copper to absorb visible light and generate a flow of electrons from the electrode where it is deposited to its surface with an aqueous solution. This material, composed only of elements abundantly found on Earth, has been protected from corrosion by a thin layer of amorphous (non-crystalline) titanium oxide (TiO 2 ) less than 10 nm thick deposited by Atomic Layer Deposition (ALD), a benchmark process used to deposit very thin films. This thin layer of TiO 2also allows the transfer of electrons to a molecular catalyst, a cobaloxime grafted to its surface. This catalyst and its grafting have been previously developed and described by these researchers.
Collaboration with researchers from the Néel Institute and EPFL has enabled a detailed characterization of the architecture of this photoelectrode and a better understanding of its performance. This hybrid photoelectrode is thus capable of producing hydrogen from aqueous solutions when a much more positive potential is applied to it than what thermodynamics requires for the electrolysis of water. This value makes it possible to quantify the capacity of the system to store solar energy in the form of hydrogen. The photo-current generated is another important parameter which quantifies the fraction of photons actually converted and therefore the rate of hydrogen production.
Future work will improve the performance of the photocathode and to integrate it into a complete photo-electrochemical system comprising a photo-anode capable of producing electrons and protons from water and a complementary portion of the spectrum solar energy to produce autonomous solar hydrogen production.