Work

Transforming Unidirectional CO2 to CO Reduction Catalysis into a Bidirectional One via Rational Ligand Engineering

Year: 2026

Type: preprint

Abstract: Developing molecular catalysts capable of bidirectional CO2/CO conversion is crucial for advancing carbon‐neutral energy technologies, yet achieving such bidirectionality remains a formidable challenge. In recent years, several complexes, including [Co(II)(bpy)]2+, have been shown to catalyze the two-electron reduction of CO2 to CO selectively but not the reverse reaction of CO oxidation. One of the key features of metal complexes demonstrating bidirectionality (see e.g. ACS Catal. 2021, 11, 5934), is the access to a range of oxidation states. Since accessing high oxidation states for a Co centre is usually quite energy demanding, one alternative solution is to design ligands that can stabilize low oxidation states. Redox non-innocent ligands can stabilize formally very low oxidation states by storing the excess electrons on the ligands. Here, we present a cobalt complex bearing two redox‐non‐innocent bis(2‐(phenylazo)pyridine) (PAP) ligands that enables energy‐efficient, bidirectional CO2/CO electrocatalysis under mild conditions. Cooperative electron redistribution between the cobalt centre and the PAP ligand manifold facilitates multielectron storage and proton‐coupled electron transfer, allowing seamless switching between CO2 reduction and CO oxidation with minimal structural reorganisation. The catalyst displays a pronounced bias toward CO2 reduction, operating at an overpotential as low as 0.27 V with a turnover frequency of ~30 s-1 and Faradaic efficiency of 85%, while selectively oxidising CO back to CO2 with comparable activity. Spectroelectrochemical characterisation and multireference computational analysis reveal a mechanistic landscape governed by ligand‐centred redox flexibility and shared catalytic intermediates. This work introduces a rare example of a homogeneous, bidirectional cobalt catalyst, establishing a general design principle for next‐generation molecular systems that operate near thermodynamic potentials and close the carbon cycle through bidirectional electrocatalysis.

Source: ChemRxiv

DOI: 10.26434/chemrxiv.15010363/v1