Electrochemically Mediated Separation of Carbon Monoxide Using a Ni-Based Redox Couple

Carbon monoxide in industrial waste gases is often burned and is responsible for about 8% of industrial CO2 emissions. In contrast to CO2 capture, no conventional technologies are available for separating CO from nitrogen at scale. Here, we show that the difference in the CO binding affinity between [NiI(cyclam)]+ and [NiII(cyclam)]2+ can be leveraged in an electrochemical separation method: cycled capture and release of CO through potential control. The carrier, [NiI(cyclam)]+, has a binding constant with CO that was estimated to be 7 × 103 M–1 through the deconvolution of cyclic voltammetry curves. An electroswing between −1.7 V and −1.5 V vs ferrocene is sufficient to switch between the capture and release of CO. A more positive release potential can increase the release rate of CO albeit at the expense of the current efficiency. This work shows that a [Ni(cyclam)]Cl2 carrier can selectively separate and concentrate CO from nitrogen electrochemically.