Turning it off! Disfavouring hydrogen evolution to enhance selectivity for CO production during homogeneous CO2 reduction by cobalt–terpyridine complexes

International audienceUnderstanding the activity and selectivity of molecular catalysts for CO 2 reduction to fuels is an important scientific endeavour in addressing the growing global energy demand. Cobalt–terpyridine compounds have been shown to be catalysts for CO 2 reduction to CO while simultaneously producing H 2 from the requisite proton source. To investigate the parameters governing the competition for H + reduction versus CO 2 reduction, the cobalt bisterpyridine class of compounds is first evaluated as H + reduction catalysts. We report that electronic tuning of the ancillary ligand sphere can result in a wide range of second-order rate constants for H + reduction. When this class of compounds is next submitted to CO 2 reduction conditions, a trend is found in which the less active catalysts for H + reduction are the more selective towards CO 2 reduction to CO. This represents the first report of the selectivity of a molecular system for CO 2 reduction being controlled through turning off one of the competing reactions. The activities of the series of catalysts are evaluated through foot-of-the-wave analysis and a catalytic Tafel plot is provided