One of the more challenging issues chemistry will have to face during the next century will be the replacement of energetic technologies based on oil consumption. Over millions of years of evolution, living organisms have developed clean and efficient strategies to solve the energetic issue: (i) during the photosynthesis, two molecules of water are oxidized to form molecular oxygen and sunlight energy is transformed into protons and electrons which are then used in the reduction of CO2 to form carbohydrates; (ii) in aerobic respiration, the cytochrome c oxidase (CcO) promotes the reduction of O2 to H2O (4e- + 4H+), generating ATP. Consequently, almost all the energy produced in living organisms involves three basic elements, light, water and oxygen, sources widely available in Earth. Different authors have pointed to the development of fuel cells using H2 and O2 as sustainable alternative to energy sources based on fuel combustion: the use of low-weight bioinspired model systems of the active center of the CcO attached to the surface of the electrode could catalyze at low potentials the reduction of O2.During the outgoing phase, the research plan we will focus on the development of new bioinspired heme/copper systems (active center of CcO) in order to reveal structural and mechanistic details of the O2 reduction performed by CcO. During the returning phase, the applicant will take advantage of the knowledge acquired during the outgoing phase to develop new heme/non-heme diiron systems as potential catalysts for O2 reduction.Due to the excellence of the host groups, this project will suppose a significant advance in the career of the applicant, giving him all the required skills to continue his career as independent researcher. Moreover, this project may provide crucial knowledge for the development of new green, economical and sustainable energy sources, a crucial issue for the socio-economic development of the European Union for the next century.