Bifunctional catalysis in the Electrochemical Reduction of CO2 to Multicarbon Products.

01/12/2016 - 01/12/2022

The development of energy-efficient catalysts for the electrochemical CO2 reduction reaction (CO2RR) to CO and ethylene has reached several critical milestones recently, making industrial implementation of the technique more relevant than ever before. Within this scope, we investigate an important class of non-noble metals as potential industrial electrocatalysts for the selective conversion of CO2 to ethylene and alcohols, namely carbon-supported copper-based electrodes (Cu/M-C).

Bifunctionality and bimetallic interactions are two important pillars in this project, since they have proven paramount in many heterogeneous catalysts and industrial systems in the past. We achieve bifunctionality by integrating copper nanoparticles with CO-generating carbon-support materials that are doped with several elements, such as nickel and nitrogen, in order to render them selective to CO – an important intermediate in the formation of ethylene on copper. In order to enhance copper’s activity and surface area, nanoparticles are tailored to a limited size range (5 – 30 nm), either by means of an ammonia-driven deposition precipitation method in aqueous solution or by means of colloidal protocols using organic solvents. Enhancement of C2 selectivity is hypothesized to be affected by the interaction of copper with the support, or with its interaction with a second metal M, that can be introduced controllably into the catalytic system. Using the said colloidal methods, we synthesize Cu/Ag particles – notably in the core-shell morphology – with Cu as the core and Ag as the shell material. On the one hand, the morphology and the atomic arrangement of these particles and Cu-metal/metal-carbon interfaces are studied in more depth using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDXS). On the other hand, the electrochemical performance of these catalysts is investigated in both a liquid cell configuration (H-Cell) and gas-liquid cell configuration (CO2 electrolyzer), under industrially relevant high overpotential and high current density reaction conditions. Electrochemical metrics are complemented by in-line gas chromatography gas product analysis and a variety of material characterization tools such as H2-temperature-programmed reduction, thermogravimetric analysis, X-ray diffraction and UV-Vis spectroscopy.