The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. Actually, the amount of solar energy reaching the Earth is several orders of magnitude greater than that required for human development so that even low conversion efficiency would be sufficient to solve the upcoming energetic crisis. The issue now is to find a way to store this energy since worldwide energy demand does not correlate with the availability of sunlight.
Hydrogen production, through the reduction of water in electrolyzers is currently one of the most convenient ways to durably store solar energy, first transformed in electrical power through photovoltaics. While electrolysis is a mature and robust technology, the most promising devices, based on proton exchange membranes, rely on the use of platinum as electrocatalysts to accelerate both hydrogen evolution (1) and water oxidation (2). However, this rare and expensive metal is not itself a renewable resource so that the viability of a hydrogen economy depends on the finding of new efficient and robust electrocatalytic materials based on earth-abundant elements. In natural systems, (1) and (2) are efficiently catalyzed by enzymatic sites such as the dinuclear NiFe and FeFe clusters in hydrogenases or the oxygen–evolving center (OEC) of photosystem II.
Our group develops bio-inspired catalysts based on the current understanding of the structure and function of these enzymes. This encompasses the design of molecular systems as active site analogues, the preparation of artificial enzymes and the study of solid-state electrodeposited materials. Combining the bio-inspired approach with nanochemical tools allowed for the preparation of the first platinum-free materials able to catalyse both hydrogen evolution and uptake. Similar efforts are currently pursued for water-oxidation catalysts.
Another issue resides in using sunlight directly as the energy source for water splitting, without the intermediate production of electricity, thereby reproducing the direct light-to-chemical energetic transduction achieved by photosynthetic organisms. Interestingly, cyanobacteria or micro-algae are even able to photosynthesize hydrogen, in a fully sustainable way, called “light-driven water splitting” and shown in (3).
Taking inspiration from this naturally occurring process, we develop several projects aiming to the preparation of light-driven systems for hydrogen evolution based on the above mentioned catalysts. Here again we employ, as light-harvesting components, both solid-state systems (semi-conductors) and molecular photosensitizer (metal-organic and fully organic dyes) grafted onto conducting material. Practical applications of such photocatalytic systems require that they are obtained in the form of photoelectrode materials that can be implemented into technological devices such as electrolysers or photoelectrochemical (PEC) cells for water splitting.
The next challenge for artificial photosynthesis will consist in converting atmospheric CO2 into a liquid fuel, which also requires breakthroughs in the design of electrocatalytic materials. This constitutes the lastly launched project in the group, with the ambition both to develop novel electrode materials for CO2 electroreduction and the development of light-driven systems towards the production of solar fuels.