Nanosheet Synthesis of Mixed Co₃O₄/CuO via Combustion Method for Methanol Oxidation and Carbon Dioxide Reduction

This paper represents a study of mixed Co₃O₄/CuO nanosheet (NS) synthesis via solution combustion synthesis for oxidation of methanol and carbon dioxide (CO₂) conversion. The mixed oxide NS of Co₃O₄/CuO is a hybrid structure of Co₃O₄ and CuO NSs. We applied this mixed oxide NS of Co₃O₄/CuO for methanol oxidation and carbon dioxide (CO₂) conversion, and the results revealed that the activity of the mixed oxide NS surpassed the activity of the corresponding individual Co₃O₄ and CuO metal oxide NSs, both in methanol oxidation and in CO₂ conversion. The mass activity of the mixed Co₃O₄/CuO NS produced at 0.627 V versus Ag/AgCl during methanol oxidation (0.5 M) was 12 mA g^-1, which is 2.4 times better than that of Co₃O₄, whose mass activity is 5 mA g^-1, and 4 times better than that of the CuO NS, whose mass activity is 3 mA g^-1. The methanol oxidation peak at 0.62 V versus Ag/AgCl was also more intense than individual oxides. The trend in performance of methanol oxidation follows the order: Co₃O₄/CuO > Co₃O₄ > CuO. In the case of CO₂ reduction, we experienced that our product was formate, and this was proved by formate oxidation (formate is formed as a product during the reduction of CO₂) on the surface of the Pt ring of a rotating ring-disc electrode. Similar to methanol oxidation, Co₃O₄/CuO also showed superior activity in carbon dioxide reduction. It was experienced that at -1.5 V, the current density rises to -24 mA/cm² for the Co₃O₄/CuO NS, that is, 0.6 times that of the CuO NS, which is -15 mA/cm², and 3 times more than that of the Co₃O₄ NS, which is 8 mA/cm². The trend in performance of CO₂ reduction follows the order: Co₃O₄/CuO > CuO > Co₃O₄.