Nanophase-Separated Copper-Zirconia Composites for Bifunctional Electrochemical CO₂ Conversion to Formic Acid

A copper-zirconia composite having an evenly distributed lamellar texture, Cu#ZrO₂, was synthesized by promoting nanophase separation of the Cu₅₁Zr₁₄ alloy precursor in a mixture of carbon monoxide (CO) and oxygen (O₂). High-resolution electron microscopy revealed that the material consists of interchangeable Cu and t-ZrO₂ phases with an average thickness of 5 nm. Cu#ZrO₂ exhibited enhanced selectivity toward the generation of formic acid (HCOOH) by electrochemical reduction of carbon dioxide (CO₂) in aqueous media at a Faradaic efficiency of 83.5% at -0.9 V versus the reversible hydrogen electrode. In situ Raman spectroscopy has revealed that a bifunctional interplay between the Zr⁴⁺ sites and the Cu boundary leads to amended reaction selectivity along with a large number of catalytic sites.