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Large conjugated carbon framework has been incorporated as the diimine ligand for Re(α-diimine)(CO)3Cl complexes with a pyrazinyl linkage, either to increase energy efficiency or to turn them into heterogeneous catalysts for selective electrocatalytic CO2 reduction. However, there exists a nonmonotonic dependence of CO2 reduction overpotential on the conjugation size of the ligands. Understanding its origin could facilitate heterogenization of molecular catalysts with improved energy efficiency. Here, we show that the conjugated pyrazinyl moiety plays a crucial role in catalysis by enabling a proton-coupled, lower-energy pathway for CO2 reduction. With ligands of moderate size, the pathway leads to previously unknown intermediates and decreases CO2 reduction overpotential. Because the pathway hinges on the basicity of the pyrazinyl nitrogen, we propose that it imposes a limit on the conjugation size of the ligand for the pathway to be effective. 

Electrochemical conversion of CO₂to value‐added products is an attractive approach to mitigating environmental impacts caused by human consumption of fossil fuels. While many molecular complexes have shown excellent selectivity in reducing CO₂to CO, herein we report on mononuclear Mo(Diimine)(CO)₄complexes that can electrocatalyze CO₂reduction to formate with high selectivity. By increasing conjugation size of the diimine ligands we achieved a faradaic efficiency of 93 (±5) % with an overpotential of 0.2 V.

 

Graphite monofluoride (GF) can undergo reductive defluorination in the presence of weak, non-nucleophilic reductants. This leads to a new approach to GF–polyaniline composites as cathode materials for significantly improving the discharge capacity of primary lithium batteries. We postulate that the reduction is mediated by residual π-bonds in GF.