Enhancement of Urea Electrooxidation on PbO2-Ni/C and Bi2O3-Ni/C Nanocomposites in Alkaline Medium

Development of efficient catalysts for urea electrooxidation is a current issue due to its ability to generate H 2 and its use as fuel for low-temperature fuel cells. In this work, non-precious Ni and Ni-metal oxide (PbO 2 and Bi 2 O 3 ) nanocomposites were prepared by electrodeposition technique and used as anodes for urea electrooxidation in NaOH solution. The surface characterizations were carried out by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The electrocatalytic activity was investigated by applying different electrochemical techniques. Remarkable catalytic activities and stabilities toward urea electrooxidation were recorded for PbO 2 -Ni/C and Bi 2 O 3 -Ni/C nanocomposites more than that of Ni/C. The recorded oxidation peak current densities on PbO 2 -Ni/C, Bi 2 O 3 -Ni/C and Ni/C are (80 mA cm −2 at +570 mV), (27 mA cm −2 at +460 mV), and (18.5 mA cm −2 at +440 mV), respectively. The onset potentials of the oxidation processes shifted to lower potentials by values of +40 mV and +150 mV on Bi 2 O 3 -Ni/C and PbO 2 -Ni/C, respectively compared to that on Ni/C. Electrochemical impedance spectroscopy (EIS) showed charge transfer resistance values of 6.8, 28.9 and 42.2 Ω cm 2 for PbO 2 -Ni/C, Bi 2 O 3 -Ni/C and Ni/C, respectively in urea solution at +356 mV. Higher catalytic activity, exchange current density, diffusion coefficient, electron transfer rate and lower charge transfer resistance toward urea electrooxidation were recorded for Bi 2 O 3 -Ni/C and PbO 2 -Ni/C nanocomposites. The electrocatalytic performance was found in the order of PbO 2 -Ni/C > Bi 2 O 3 -Ni/C > Ni/C. Application of these nanocomposites in applications related to H 2 production, direct urea fuel cells, and water treatments is possible.