A tale of two metals: switching selectivity towards CO2 reduction in heptacoordinate complexes
Solar fuels, i.e. fuels generated by using sunlight as a source of energy, are the most promising alternatives to fossil fuels, both because of their availability and of their reduced environmental impact. CO2 reduction, in particular, is one of the most popular strategies to obtain solar fuels. However, protons and efficient catalysts are necessary to respectively decrease the thermodynamic and kinetic barrier. These conditions often also trigger the reduction of protons to hydrogen, which represents a competitive process. We have recently found that a heptacoordinate Co complex (known to efficiently produce hydrogen) can also catalyze CO2 reduction in acetonitrile/water solutions, although with low selectivity, the hydrogen generation being the predominant process. Remarkably, replacement of the Co(II) center with Fe(II) induces a switch in selectivity towards CO2 reduction. The resulting heptacoordinate Fe(II) catalyst is extremely active and it reaches selectivities > 90% in carbon-based products (CO + formate) in the presence of 1-10% H2O as proton source. In this talk we will present our results concerning the electrochemical, photochemical and computational investigations of these two catalysts.
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