Identifying Highly Active and Selective Cobalt X‐Ides for Electrocatalytic Hydrogenation of Quinoline

Abstract Earth‐abundant Co X‐ides are emerging as promising catalysts for the electrocatalytic hydrogenation of quinoline (ECHQ), yet challenging due to the limited fundamental understanding of ECHQ mechanism on Co X‐ides. This work identifies the catalytic performance differences of Co X‐ides in ECHQ and provides significant insights into the catalytic mechanism of ECHQ. Among selected Co X‐ides, the Co 3 O 4 presents the best ECHQ performance with a high conversion of 98.2% and 100% selectivity at ambient conditions. The Co 3 O 4 sites present a higher proportion of 2‐coordinated hydrogen‐bonded water at the interface than other Co X‐ides at a low negative potential, which enhances the kinetics of subsequent water dissociation to produce H*. An ideal 1,4/2,3‐H* addition pathway on Co 3 O 4 surface with a spontaneous desorption of 1,2,3,4‐tetrahydroquinoline is demonstrated through operando tracing and theoretical calculations. In comparison, the Co 9 S 8 sites display the lowest ECHQ performance due to the high thermodynamic barrier in the H* formation step, which suppresses subsequent hydrogenation; while the ECHQ on Co(OH)F and CoP sites undergo the 1,2,3,4‐ and 4,3/1,2‐H* addition pathway respectively with the high desorption barriers and thus low conversion of quinoline. Moreover, the Co 3 O 4 presents a wide substrate scope and allows excellent conversion of other quinoline derivatives and N ‐heterocyclic substrates.