The production of solar fuels – in particular solar hydrogen – is one of the stated objectives of the green transition. Photoelectrochemical processes offer an attractive solution for the decentralized production of "green" hydrogen from water and solar energy, but their current performance and cost prohibit their large-scale use.

In order to make progress in this area, researchers at Irig and their partners at the University of Science and Technology of Hanoi (Vietnam) have developed an artificial "leaf" based on a photovoltaic "core" (a triple-junction silicon cell).

They developed a photochemical process to deposit, in a single step and from a single precursor, the two catalysts that promote the evolution of hydrogen and oxygen resulting from water splitting, each on a specific side of the leaf. When immersed in a neutral salty medium, the device is then capable of converting solar energy into chemical energy (here in the form of hydrogen) with a 2% conversion yield, thus mimicking the natural photosynthetic activity of leaves.

To further their understanding of the phenomena limiting this conversion, the researchers equipped both sides of the leaf so as to independently measure the electrochemical potential of each catalyst as well as the current flowing through the cell, and to quantify the production of hydrogen.

This operando characterization highlighted the impact of defects in the protective layers of the core triple junction solar cell and led the scientists to propose new ways to optimize the efficiency of their artificial leaf.

This work is part of the European project SUNER-C (starting in June 2022), powered by SUNERGY, co-coordinated by the CEA (DRF) and also involving the CEA's Energy and Technology Research Divisions. These projects aim to develop the European solar fuels and chemistry community, and to prepare a large-scale joint European effort in the form of a public-private partnership.