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.

Julia M. Dressel

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