Publication in J. Am. Chem. Soc.

Iron, a sustainable alternative to rare metals for solar fuels


Although solar energy can be efficiently converted into electricity with photovoltaic panels, its storage remains a major challenge so that it can be used independently of the diurnal cycle. Batteries are a form of storage that has several advantages but also some limitations (storage capacity, lifespan, environmental impact, manufacturing and waste management, etc).

An alternative is to store solar energy in chemical bonds by forming "solar fuels" such as hydrogen (H2), which is very promising for enabling large-scale energy storage and distribution. Hydrogen production can be photo-induced but also obtained through the splitting of halohydric acids (HX). The latter is advantageous because it simultaneously generates of a second solar fuel in the form of the corresponding halogen X2. However, the oxidation of halides often requires the use of photosensitizers based on rare metals, such as ruthenium and iridium, which severely limits its implementation.

Teams led by Ludovic Troian-Gautier (WEL Research Institute - UCLouvain) and Benjamin Elias (UCLouvain) developed a photosensitizer based on iron, one of the most abundant elements in the Earth's crust, to enable the oxidation of halides. Using various spectroscopic methods, these researchers demonstrated that it is possible to oxidize halides (iodide, bromide, and chloride) using the energy stored in the excited state of this iron-based photosensitizer. In addition to measuring the efficiency of this process, the team determined that ~90% of stored energy led to the regeneration of the initial reactants, pointing to a large range of opportunities for optimizing these photo-induced processes.

Reference : De Kreijger et al, Investigation of the Excited-State Electron Transfer and Cage Escape Yields Between Halides and a Fe(III) Photosensitizer, J. Am. Chem. Soc. (2024) 146: 10286–10292

Illustration : With authorization from Ludovic Troian-Gautier

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