From the beginning of the project to its conclusion, the project successfully addressed fundamental challenges in designing novel molecular complexes inspired by the nitrogenase enzyme, as well as exploiting fundamental properties observed in such model complexes to design new catalysts for ammonia electrosynthesis.
On the molecular side, the project achieved critical advances in bio-inspired catalysis by investigating electron and proton transfer processes mediated by iron-sulfur clusters. The development of a complete biomimetic redox series of iron-sulfur cubanes provided a detailed understanding of how oxidation state and covalency govern catalytic reactivity. These findings, published in PNAS and JACS Au, were complemented by the elucidation of gated electron transfer mechanisms in synthetic analogs, published in Chem. This work established key mechanistic insights into the function of iron-sulfur clusters as redox mediators, paving the way for their use in catalytic systems, as well as providing strategies for the synthesis of larger clusters inspired by the FeMoco and P-clusters of nitrogenase.
In addition, the potential use of FeS clusters as concerted proton-electron transfer (CPET) mediators was demonstrated and particularly exploited as a novel strategy to generate highly reactive metal hydride species. This study, published in Nature, demonstrated the potential of CPET-mediated strategies to be incorporated into electrocatalytic pathways and used to promote highly efficient CO2 reduction.
Furthermore, the synthesis of low-valent molybdenum complexes revealed novel reactivity pathways for small-molecule activation, such as CO2 and CS2, as published in Chemical Science and Chemical Communications.
In the area of heterogeneous catalysis, we demonstrated that a bimetallic Fe-Mo carbide MXene catalyst exhibited enhanced nitrate reduction activity due to synergistic interactions between Fe and Mo sites. This study, which included in-depth in situ XAS investigations, was published in Angewandte Chemie.
Building on this initial discovery of the high activity of Mo-based materials for nitrate reduction, we pursued the development of supported dendritic molybdenum oxide catalysts. These materials set a benchmark in electrochemical nitrate reduction, achieving a Faradaic efficiency of 99% and maintaining operational stability for over 3,100 hours. Patented and subsequently published in Advanced Energy Materials, this work highlighted the role of oxygen vacancies in enabling efficient nitrate binding and reduction.
Overall, the accomplishments of the project were disseminated, to date, through 13 high-impact publications, 1 patent, and over 30 conference presentations, fostering new collaborations and advancing the understanding of bio-inspired catalysis for N2 and NOx reduction.
