Uranyl N 2 O 2 -Schiff base complex as co-catalyst in ethanol electro-oxidation: synthesis, crystallographic, spectroscopic, electrochemical, and DFT characterization, and catalytic investigation

• Published in: New journal of chemistry 2023-09, Vol.47 (37), p.17393-17405
• Main Authors: Barbosa, Elizomar Medeiros, Soares, Kaique Souza, Cruz, Julianna Ferreira, Doring, Thiago Henrique, de França, Igor Vinicius, Mello, Lucas dos S., Nagurniak, Glaucio R., Parreira, Renato L. T., Alvarenga, Meiry Edivirges, Martins, Felipe Terra, Dockal, Edward Ralph, Souza, Elson Almeida, Maia, Paulo José Sousa, da Cruz, José Wilmo
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D3NJ01561K

Direct Ethanol Fuel Cells (DEFCs) are important clean energy conversion systems which can reach high energy densities using inexpensive and non-toxic fuels. One of the main obstacles to using DEFC systems is the high cost of platinum or platinum-alloy electrodes traditionally used in these systems. However, other less expensive co-catalysts, e.g. , transition metal complexes, can be used to partially replace platinum or platinum-alloys in Pt-based electro-catalysts. The aim of this study is to describe and analyze the use of a new uranyl salen-type complex as co-catalyst in ethanol electro-oxidation. To this end, the structural and spectroscopic properties of the co-catalyst in question was investigated by single-crystal X-ray diffraction, DFT, elemental analysis (CHN), FTIR, UV-Vis, and 1 H and 13 C NMR. Cyclic voltammetry indicated a quasi-reversible redox pair at 0.97/0.69 V ( E 1/2 = 0.83 V) along with an anodic process at 1.14 V, both associated to the phenolate/phenoxyl radical couple. Six PtSn-based catalysts were produced by varying the PtSn:uranyl complex molar ratio. The ethanol oxidation reaction was investigated in acidic media via cyclic voltammetry and chronoamperometry. Direct scanning of the samples indicated that the peak-current density for the 6 : 1 PtSn/C : [UO 2 (3-OMe- c -salcn)H 2 O] catalyst was higher than that for other catalyst ratios. Moreover, as compared to the pure PtSn catalyst, 6 : 1 PtSn/C : [UO 2 (3-OMe- c -salcn)H 2 O] exhibited better catalytic activity in ethanol electro-oxidation reaction (EOR); it decreased the onset potential during ethanol oxidation. In addition, this catalyst exhibited peak-current densities about 2.3 times that of PtSn/C. pH affected the catalytic system performance, which decreased as pH increased (maximum efficiency at pH 0.3). Ethanol oxidation catalyzed by 6 : 1 PtSn/C : [UO 2 (3-OMe- c -salcn)H 2 O] was also investigated using cyclic voltammetry and chronoamperometry at different ethanol concentrations, indicating that the EOR peak increased as ethanol concentration increased.