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

Abstract

This paper represents a study of mixed Co 3 O 4 /CuO nanosheet (NS) synthesis via solution combustion synthesis for oxidation of methanol and carbon dioxide (CO 2 ) conversion. The mixed oxide NS of Co 3 O 4 /CuO is a hybrid structure of Co 3 O 4 and CuO NSs. We applied this mixed oxide NS of Co 3 O 4 /CuO for methanol oxidation and carbon dioxide (CO 2 ) conversion, and the results revealed that the activity of the mixed oxide NS surpassed the activity of the corresponding individual Co 3 O 4 and CuO metal oxide NSs, both in methanol oxidation and in CO 2 conversion. The mass activity of the mixed Co 3 O 4 /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 Co 3 O 4, 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: Co 3 O 4 /CuO > Co 3 O 4 > CuO. In the case of CO 2 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 CO 2 ) on the surface of the Pt ring of a rotating ring-disc electrode. Similar to methanol oxidation, Co 3 O 4 /CuO also showed superior activity in carbon dioxide reduction. It was experienced that at −1.5 V, the current density rises to −24 mA/cm 2 for the Co 3 O 4 /CuO NS, that is, 0.6 times that of the CuO NS, which is −15 mA/cm 2, and 3 times more than that of the Co 3 O 4 NS, which is 8 mA/cm 2 . The trend in performance of CO 2 reduction follows the order: Co 3 O 4 /CuO > CuO > Co 3 O 4 .