Uranyl Salen-Type Complex as Co-catalyst for Electrocatalytic Oxidation of Ethanol

Direct ethanol fuel cells (DEFCs) are considered a viable alternative power source for both stationary and mobile applications. Obstacles to widespread use of DEFCs include the slow kinetics of ethanol electro-oxidation, which has been countered by using Pt-based electrocatalysts. Pt-based electrocatalysts are produced by partially or totally replacing the platinum alloys with other less expensive materials such as transition metal complexes. This study describes the synthesis and characterization of the electrochemical properties of a new uranyl complex, whose molecular structure has been previously elucidated by FTIR, elemental analysis (CHN), and 1 H NMR. Its cyclic voltammogram indicates two reversible redox pairs at 0.69/0.56 V ( E 1/2 = 0.63 V) and 0.85/0.77 V ( E 1/2 = 0.81 V) vs. RHE, attributed to ligand processes such as two successive oxidations of phenolate to phenoxyl radicals. The use of UO 2 (3-OMe- t -salcn)H 2 O as catalyst for ethanol oxidation reaction in acidic media was also investigated via cyclic voltammetry and chronoamperometry. Six PtSn-based catalysts were produced by adjusting the molar ratio of the PtSn:UO 2 -complex. Direct scanning of the samples indicated that the peak-current density for the 6:1 PtSn/C:[UO 2 (3-OMe- t -salcn)H 2 O] catalyst was higher than that for mixed catalysts. Moreover, as compared to the pure PtSn catalyst, 6:1 PtSn/C:[UO 2 (3-OMe- t -salcn)H 2 O] exhibited better catalytic activity for ethanol electrooxidation; i.e., it decreased the onset potential during the oxidation of ethanol. Moreover, this catalyst exhibited peak-current densities (j) at 34.53 mA cm −2 ; i.e., ~ 5.2-fold that of PtSn/C. In addition, chronoamperometry data indicated higher catalytic activity at 0.6 V for PtSn/C:[UO 2 (3-OMe- t -salcn)H 2 O]-based catalysts. Graphical Abstract