MECHANISM PATHWAY FOR THE ELECTROCATALYTIC REDUCTION OF CO2 BY [Mn(bipyridyl)(CO)3X] DERIVATIVE

For more than a century human activities have caused an increase in air pollutants inducing an excess of greenhouse gases. In addition, the depletion and rising costs of fossil fuels, due to the increase in energy demand driven by global growth, leads to the search for alternative raw carbon sources. In this particular context, the transformation and utilization of carbon dioxide is today under great consideration as it could both reduce the environment impact of CO2 and create valuable products at the same time. For instance, conversion of CO2 into carbon monoxide (CO) or formic acid (HCOOH), the simplest products from a two-electron two-proton reduction, could be an attractive alternative solution for synthesizing useful chemicals and energy rich products. Indeed, HCOOH is a convenient liquid for H2-storage and for Direct Formic Acid Fuel Cell (DFAFC) in which energy can be recovered in an electrical form. Nevertheless, CO2 reduction still remains challenging since CO2 is a stable molecule. If a renewable carbon-free energy source is used, to power CO2 reduction in water (proton source), ElectroCatalytic Reduction (ECR) could be regarded as a sustainable artificial method to activate and transform CO2. In the past thirty years several transition metal complex catalysts able to convert CO2 by ECR have been studied [1]. This includes polypyridyl carbonyl complexes based on Re, Ru and Os. Just a few molecular electrocatalysts based on cheap metals naturally abundant in the earth’s crust like Fe and Mn have already been reported [2]. Herein, we present [Mn(L)(CO)3Br] molecular electrocatalysts (L = bipyridyl derivatives). We show their efficiency, selectivity and stability catalytic properties towards CO2 ECR [3]. We focus particularly on the catalytic mechanism which has been highlighted mainly by spectroelectrochemistry [4].