CO2 Reduction and Water Oxidation: Catalysts and Mechanisms Related to Solar Liquid Fuels
Javier Concepcion a
a Brookhaven National Laboratory, Chemistry Department, Upton, NY, USA, 11973, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2024 Conference (MATSUS24)
#ProMatSol - Exploring Material Properties for Advanced Solar Energy Applications
Barcelona, Spain, 2024 March 4th - 8th
Organizers: Marina Freitag and Elizabeth Gibson
Invited Speaker, Javier Concepcion, presentation 427
DOI: https://doi.org/10.29363/nanoge.matsus.2024.427
Publication date: 18th December 2023

In nature, solar energy is captured and stored in chemical bonds by activating small molecules such as CO2 and H2O. This requires catalysts capable of carrying out CO2 reduction and water oxidation catalysis. In this presentation, molecular catalysts and mechanisms related to these two processes will be discussed. CO2 reduction to C1 products has received considerable attention as part of many efforts to try to address the devastating effects of climate change. Among various C1 reduction products, liquid fuels such as formic acid and methanol are particularly important to achieve carbon-neutral cycles. But the underlying chemistry to generate liquid fuels from CO2 efficiently and selectively has yet to be developed, particularly in the case of methanol. Cascade strategies using a combination of catalysts that can carry out some of the required multistep reactions are being pursued because achieving this goal with a single catalyst is difficult. One of these strategies involves CO2 reduction to CO by one catalyst and further reduction of CO to a liquid fuel by another catalyst or a combination of catalysts.  In this presentation, a strategy for the generation of methanol efficiently and selectively from CO is discussed, with a transition metal-organic hydride combination. Using NMR, IR and mass spectrometry, together with labeling studies, chemical synthesis of authentic samples of intermediates and theoretical calculations, selective and efficient conversion of CO to methanol is demonstrated. The key to the high selectivity is the use of organic hydride donors that are inactive towards direct CO2 reduction and hydrogen generation. These organic hydride donors are inexpensive and renewable and are a promising platform for solar fuels generation from CO2. In the water oxidation front, a new mechanism for water oxidation catalysis with molecular catalysts will be presented. In this mechanism, the transition metal participates in the redox chemistry but not in the thermally activated processes, which take place on the ligands. In the oxygen evolution step, the ligands are returned to their original state and, as a result, these catalysts are very robust because they follow a “self-healing” mechanism. In addition, because the mechanism is ligand-based, no open coordination site is required and this enables the development of highly active molecular catalysts for water oxidation with first-row transition metals.

This research at Brookhaven National Laboratory is supported by the U.S. Department of Energy, Office of Science, Division of Chemical Sciences, Geosciences & Biosciences, Office of Basic Energy Sciences under contract DE-SC0012704 and as part of the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0021173.

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