Facet- and structure-dependent catalytic activity of cuprous oxide/polypyrrole particles towards the efficient reduction of carbon dioxide to methanol

The preparation of cost-effective, stable catalysts for the selective reduction of carbon dioxide (CO₂) to C₁ products such as methanol is extremely important because methanol can be used directly as a fuel or it can be converted into other value-added products. However, the catalysts currently used for the reduction of CO₂ to methanol exhibit poor selectivity, poor stability and very low faradaic efficiency. Herein, we used low-cost, stable cuprous oxide/polypyrrole (Cu₂O/Ppy) particles having structures of octahedra and icosahedra (microflowers) that were prepared on linen texture (LT) papers for the selective reduction of CO₂ to form a value-added single C₁ product, methanol. The Cu₂O/Ppy particles possessing both octahedral and microflower shapes with exposed low-index (111) facets and high-index (311) and (211) facets are denoted as Cu₂O_(OL-MH)/Ppy particles. The as-prepared Cu₂O_(OL-MH)/Ppy particles exhibited high catalytic activity and selectivity towards the electrochemical reduction of CO₂ at -0.85 V vs. RHE to form methanol, with a faradaic efficiency of 93 ± 1.2% and an average methanol formation rate of 1.61 ± 0.02 μmol m^-2 s^-1. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the pyrrolic nitrogen atoms present in the Ppy shell played a dominant role as active sites for CO₂ molecules. The Raman bands of Ppy and Cu₂O did not shift even after being subjected to electrolysis for several hours, suggesting superior stability of the Cu₂O_(OL-MH)/Ppy particles. The high resolution microscopic, spectroscopic, diffraction and electrochemical analysis results clearly revealed that the Ppy shell protected the Cu₂O particles and avoided corrosion, dissolution, and structural and crystal facet changes, leading to greater stability. The low-cost, durable, flexible, and catalytically active Cu₂O_(OL-MH)/Ppy LT paper holds great potential for catalytic, photocatalytic and energy storage applications.