Nanoporous Cu Thin Films for Electrochemical CO₂ Reduction

Abstract

Copper catalysts have been extensively researched as catalysts for electrochemical reduction of CO 2 (CO 2 RR) due to their capability to catalyze production of hydrocarbons. The selectivity and activity of Cu catalysts for CO 2 RR are greatly dependent on the surface structure of the catalysts, and due to this dependence, many forms of Cu (ranging from high quality single crystals to densely populated arrays of supported nanostructures) have been investigated as CO 2 RR catalysts. Nanoporous (np) metals, which are produced through selective dissolution of an element from a parent alloy or compound, have inherent properties not typically present in other nanostructured materials that can strongly affect their catalytic properties, including concave surfaces with unique surface structures and open porosity that can cause mass transport effects during catalysis. Nanoporous Au and Ag, have been demonstrated as efficient and selective catalysts for oxidation of CO and reduction of CO 2 to CO relative to their bulk metals. However, np-Cu has yet to be comprehensively studied as a CO 2 RR catalyst. To date, np-Cu has been primarily produced from homogeneous bulk materials which are not well suited for practical use as a potential CO 2 RR catalyst due to long dealloying treatments required to produce np-Cu that remains stable, without continued dealloying of the non-noble metal, at low CO 2 RR overpotentials. In this work, we demonstrate new electrochemical methods for producing fully dealloyed thin films of high-quality, crack-free np-Cu on inert substrates in significantly shorter processing times compared to bulk samples. We examine the activity and selectivity of np-Cu film catalysts produced by several dealloying methods for CO 2 RR. These results are presented in relation to other Cu catalysts with focus on the catalytic effects of the unique structural properties of np-Cu and the effects of post dealloying treatments to tune pore and ligament sizes of the np-Cu films. In addition to np-Cu films, we discuss how the presented techniques offer a path for production of stable thin films of other nanoporous metals on complex geometries. This work is supported by the Department of Energy award number DE-SC0008686.