Periodic Reporting for period 4 - HEINE (Hybrid Electrocatalysts Inspired by the Nitrogenase Enzyme)
Periodo di rendicontazione: 2024-04-01 al 2024-09-30
Artificial nitrogen reduction to ammonia using the Haber-Bosch process directly supports half of the global food production and accounts for 2% of global energy consumption. This large energy consumption originates mostly from the use of H2 (derived from fossil fuels) as a reductant and from the high pressure and temperature required to carry out the Haber-Bosch process.
Electrochemical synthesis of ammonia, using a proton and electron source combined with an electrocatalyst at room temperature to reduce N2 or NOx, presents an appealing, energy-efficient alternative. However, despite years of research, the few currently available catalysts exhibit very limited efficiency and selectivity for ammonia production.
Drawing inspiration from biochemistry and using the tools of coordination chemistry, catalysis, and surface chemistry, this project explored original strategies to develop catalysts for the reduction of N2 and NOx, inspired by the nitrogenase and nitrate reductase enzymes.
The objectives of HEINE have been twofold: We focused on understanding the fundamental elementary steps critical for the reduction of N2 and NOx in these enzymatic systems, namely electron and proton transfers driven by iron-sulfur clusters. In addition, an important related objective of the project was to develop accurate mimics of the nitrogenase active site, in particular the assembly of large iron-sulfur clusters, as well as the exploration of low-valent, octahedral Mo complexes.
On the more applied side, the project aimed to develop new heterogeneous catalysts inspired by the elementary components of nitrogenase and nitrate reductase to catalyze the electrochemical synthesis of ammonia.
Electrochemical synthesis of ammonia, using a proton and electron source combined with an electrocatalyst at room temperature to reduce N2 or NOx, presents an appealing, energy-efficient alternative. However, despite years of research, the few currently available catalysts exhibit very limited efficiency and selectivity for ammonia production.
Drawing inspiration from biochemistry and using the tools of coordination chemistry, catalysis, and surface chemistry, this project explored original strategies to develop catalysts for the reduction of N2 and NOx, inspired by the nitrogenase and nitrate reductase enzymes.
The objectives of HEINE have been twofold: We focused on understanding the fundamental elementary steps critical for the reduction of N2 and NOx in these enzymatic systems, namely electron and proton transfers driven by iron-sulfur clusters. In addition, an important related objective of the project was to develop accurate mimics of the nitrogenase active site, in particular the assembly of large iron-sulfur clusters, as well as the exploration of low-valent, octahedral Mo complexes.
On the more applied side, the project aimed to develop new heterogeneous catalysts inspired by the elementary components of nitrogenase and nitrate reductase to catalyze the electrochemical synthesis of ammonia.
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.
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.
The project advanced the state of the art by integrating bioinspired design with advanced synthetic and mechanistic studies. Through the fundamental investigation of electron and proton transfer processes in FeS cluster systems, we identified key parameters that could be exploited to develop novel catalytic systems. The incorporation of CPET strategies, particularly demonstrated in FeS cluster-mediated CO2 reduction, introduced a novel approach to activating challenging substrates under mild conditions.
Similarly, the detailed understanding provided by the in-depth investigation of the reactivity of low-valent molybdenum complexes supported the development of Mo-based heterogeneous systems, such as the MoOx/NiNF and Fe-Mo MXene catalysts. These materials demonstrated the potential of bioinspired materials to achieve high performance in nitrate electroreduction and offer a practical pathway for sustainable ammonia production, providing scalable and energy-efficient alternatives to traditional methods.
Similarly, the detailed understanding provided by the in-depth investigation of the reactivity of low-valent molybdenum complexes supported the development of Mo-based heterogeneous systems, such as the MoOx/NiNF and Fe-Mo MXene catalysts. These materials demonstrated the potential of bioinspired materials to achieve high performance in nitrate electroreduction and offer a practical pathway for sustainable ammonia production, providing scalable and energy-efficient alternatives to traditional methods.