Researchers reveal the mechanisms behind cobalt X-ide electrocatalysts

The unsung heroes of electrochemical reactions—electrocatalysts—can assist in optimizing factors such as the reaction’s speed, yield, and energy consumption. As such, these electrocatalysts are crucial for optimizing large-scale production in the pharmaceutical, agrochemical, and petrochemical industries.

Researchers at Tohoku University and Nanjing Normal University conducted a deep dive on the performance of an emerging category of electrocatalysts: cobalt oxides (Co X-ides). The work is published in the journal Advanced Materials.

The research team sought to use Co X-ides for the electrocatalytic hydrogenation of quinoline (ECHQ). This process is an attractive alternative to other methods, as it can be conducted under ambient temperatures and can result in a net zero carbon footprint.

In comparison, conventional methods to hydrogenate quinoline release undesirable byproducts, and require the storage and transportation of highly flammable hydrogen—which is equal parts dangerous and costly.

“Previous research on ECHQ focused more on the optimization of catalytic activity, whereas for ECHQ reaction mechanisms and reaction path explorations, we might as well be starting with a blank page,” explains Tianyi Wang from Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR).

“One goal of this study was to try and find which Co X-ide was ‘the best’ one,” says Hao Li of WPI-AIMR, “However, we also need to be able to understand why certain catalysts perform differently.”

It was found that among selected Co X-ides, Co₃O₄ was the winner. It demonstrated the best ECHQ performance with a high conversion of 98.2% and selectivity of 100% under ambient conditions.

The Co₃O₄ 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*.

In comparison, the Co₉S₈ sites displayed the lowest ECHQ performance due to the high thermodynamic barrier in the H* formation step, which suppressed subsequent hydrogenation. Co(OH)F and CoP sites also had a low conversion of quinoline, due to high desorption barriers.

This study will help significantly advance our understanding of the catalytic mechanisms in ECHQ.