Modulating the Electrocatalytic Hydrogenation of Benzaldehyde on Cu@C Electrode Materials

Abstract

Electrocatalytic hydrogenation (ECH) is a promising route toward a more sustainable synthesis of fuels and chemicals. State-of-the-art catalysts are still reliant on precious metals and new electrocatalysts based on low cost materials would be desired. Copper has shown good activity in ECH applications; however, its ability to promote carbon coupling reactions yields mixed product feeds. Different ways to moderate the selectivity have been proposed, for example, alloying the copper with precious metals. Herein we report on carbon-covered copper electrodes and their activity in the ECH of benzaldehyde as a diagnostic organic substrate. Material synthesis using sequential dc-magnetron sputtering of copper and carbon did not yield chemical changes of the copper or the carbon layer. Electrochemical investigation suggests that the electrocatalytic activity of the copper is largely maintained. Studies on the ECH give a similar picture, with the faradaic efficiency and the amount of reduced benzaldehyde seemingly independent of the carbon coverage. However, the selectivity is influenced by the carbon, with a complex trend, giving increased selectivity toward benzyl alcohol for moderate carbon coverage. We propose that the carbon influences the relative surface concentration between adsorbed hydrogen and adsorbed benzaldehyde/ketyl radical. Two possible routes for this have been outlined. We think that this approach to modulate selectivity is promising, as it uses low cost materials and a scalable technology, and could make copper and other transition metals more attractive for ECH applications.