Oxidation-State Control of Cobalt Electrocatalysts Enables Selective Hydrogenation of Nitrogen-Containing Aromatics

Kinetic analysis and density functional theory calculations indicate that pyridine hydrogenation proceeds through a Langmuir–Hinshelwood-type pathway, in which the mixed Co(0)/CoO_<i>x</i> surface provides an electronically suitable environment for pyridine adsorption and hydrogenation. This electronically tuned Co(0)/CoO_<i>x</i> surface enables selective hydrogenation of a broad range of nitrogen-containing aromatic compounds, including pyridines, quinolines, pyrazines, nitriles, and nitroarenes, while suppressing undesired hydrogenation pathways observed with Rh-based catalysts.

Guided by the operando insight, intermittent electrolysis was introduced to prevent catalyst over-reduction during prolonged operation, enabling gram-scale conversion of pyridine to piperidine in 89% yield with stable cell voltage. These results highlight the importance of maintaining an intermediate Co(0)/CoO_<i>x</i> state for selective electrocatalytic hydrogenation with earth-abundant cobalt catalysts.