• Pardo Pérez, Laura C.

Abstract

<jats:p>In the field of electrochemical CO<jats:sub>2</jats:sub> conversion, the development of earth-abundant catalysts which are selective for a single product is a central challenge. Cu-Sn bimetallic catalysts have been reported to yield selective CO<jats:sub>2 </jats:sub>reduction towards either carbon monoxide or formate. To advance the understanding of possible synergetic effects between Cu and Sn which direct product selectivity, a thorough investigation of the catalyst structure and composition in its active state is desired. We present an X-ray spectroscopy investigation of oxide-derived Cu-Sn catalysts prepared by functionalization of Cu(OH)<jats:sub>2</jats:sub> nanowire arrays with ultrathin SnO<jats:sub>2</jats:sub> overlayers. This method allows precisely tunable Sn composition, which enables synthesis of composite catalysts with high selectivity toward either CO or formate. Under CO<jats:sub>2</jats:sub> reduction conditions, the materials undergo significant transformations before reaching their catalytically active forms. Complementary information on the electrocatalysts’ dynamic bulk and surface structure was revealed via correlating observations from multiple X-ray spectroscopy methods. <jats:italic>In situ</jats:italic> investigations of Cu K-edge revealed that in the bulk Cu is fully reduced from Cu<jats:sup>2+</jats:sup> to Cu° after a pre reduction step. <jats:italic>Quasi in situ</jats:italic> XPS demonstrated that, at the catalyst surface, Cu is also present exclusively as Cu°, whereas significant differences in Sn quantification and speciation were observed between the CO- and formate-selective catalysts. After CO<jats:sub>2</jats:sub> electrolysis, CO-selective catalysts exhibited a surface Sn content of 13 at. % predominantly present as Sn oxide, while the formate-selective catalysts had a Sn content of ~70 at. % consisting of both metallic Sn° and Sn oxide<jats:sub> </jats:sub>species. Our study reveals the complex dependence of catalyst structure, composition, and speciation with applied electrochemical bias in Sn-functionalized nanostructured Cu catalysts.</jats:p>

Topics

• impedance spectroscopy
• surface
• Carbon
• x-ray photoelectron spectroscopy
• composite
• functionalization
• X-ray spectroscopy