Rising atmospheric carbon dioxide (CO2) emissions from anthropogenic sources demonstrate the need for carbon neutral energy generation. Electrocatalytic CO2 reduction is of increasing interest to address this because it can use CO2 as a source valuable C1 synthons, including carbon monoxide (CO) and formate. Hydrogen evolution often competes with CO2 reduction in electrocatalytic systems, but independently, the hydrogen evolution reaction (HER) can be an alternative method of generating carbon-neutral energy as a fuel source or as the cathodic half-reaction in fuel cells. A molecular chromium (III) complex with a 2,2-bipyridine-based ligand was evaluated as an electrocatalyst for CO2 reduction. Electrochemical investigations show that upon reduction by two electron equivalents, the resulting chromium complex is active for CO2 reduction to CO with a Faradiac efficiency of 96 ± 8% and turn over frequencies of 1.89 x 104 s-1 at low overpotential (110 mV) in the presence of phenol (PhOH) as a proton donor.These results suggest that electrocatalytic CO2 reduction by early transition metals is possible and comparable to the reactivity seen with late transition metals. In order to improve the efficacy of transition metal catalysts bearing these 2,2-bipyridine based ligand frameworks, a similar, ligand framework was developed. Its influence on catalytic activity was evaluated for a molecular nickel (II) complex because Ni is a prominent earth-abundant transition metal used in several well-studied CO2 reduction and HER catalysts. This work reports the electrochemical analysis of this Ni complex, which suggests that it can act as an electrocatalyst for the HER.

Earth abundant transition metal complexes for electrocatalytic CO2 reduction and the hydrogen evolution reaction

ACS Fall 2021

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