LEAF - Decoupled production of solar fuels

The LEAF project targets the design and development of a modular photoelectrochemical system for the decoupled production of solar fuels and implementation of a carbon-neutral energy landscape. In a conventional photoelectrochemical cell for water photolysis, hydrogen and oxygen are produced concomitantly in the cathodic and anodic compartments of the same cell, respectively. On the other side, the LEAF approach aims to decouple hydrogen and oxygen production in time and/or in space. This is realized by two steps: the first one consists of a photoelectrochemical cell where water oxidation is coupled to the reduction of a redox mediator. In step 2, the so-obtained reduced form of the redox mediator is used to drive water reduction with (type A) or without (type B) an external photovoltage. In particular, in type A system, step 2 is performed in a photoelectrochemical cell where the re-oxidation of the redox mediator is coupled to water reduction: this is the case in which the reduced form of the redox mediator is not thermodynamically able to drive water reduction. On the other hand, type B system comprises a redox mediator with a sufficiently negative reduction potential to be able to directly reduce water in the presence of catalyst.

The main advantages of the LEAF approaches compared to direct water splitting are: (i) rate of the hydrogen evolution reaction not limited by the oxygen evolution reaction, which is usually the bottleneck of the entire process for direct water electrolysis; (ii) no mixing of hydrogen and oxygen gases by physical separation of the two processes, thus reducing energy needed for the separation, safety concerns, cost of the membranes used in the photoelectrochemical cells; (iii) operation under milder conditions, without interference by possible production of oxygen reactive species.

The LEAF project is targeted at the realization of an efficient and stable device for sun-driven production of hydrogen with solar-to-hydrogen conversion efficiency of 3%. The research efforts are thus devoted to: (i) the realization of efficient (high Faradaic efficiency) and stable photoelectrodes made of earth-abundant materials and obtained by sustainable production processes; (ii) the characterization of all the investigated molecular and nanostructured materials by advanced structural and (photo)electrochemical techniques; (iii) the selection of the best catalysts and redox mediators in terms of efficiency and stability; (iv) dissemination and communication activities to the scientific community as well as to the citizens to make them aware of the most advanced solutions for the use of renewable energy sources.