Enhanced Urea Activity of Oxidation on Nickel-Deposited Tin Dendrites

Urea oxidation has gained tremendous research interest, owing to its application in direct urea fuel cells and urea electrolyzers. In this work, the electrochemical oxidation of urea on a Ni/Sn dendrites catalyst is investigated. Ni and Ni/Sn dendrites are synthesized through electrodeposition on porous Toray^© carbon paper. The prepared catalysts were characterized by scanning electron microscopy, X-ray diffraction, and inductively coupled plasma−optical emission spectroscopy. The Ni/Sn dendrites oxidized 0.33 M urea in alkaline solution at an onset potential of 0.34 V vs. Ag/AgCl with a current density of 44 mA cm⁻²@0.55 V, which is higher than that of electrodeposited Ni/TC (31 mA cm⁻² @0.55 V). In situ Raman spectroscopic measurements indicate that urea oxidation on Ni/Sn dendrites is initiated by Ni(III)OOH species. Electrochemical impedance spectroscopy patterns of Ni/Sn dendrites in the presence of urea displayed a single depressed semicircle at potentials of 325 mV and two semicircles above 325 mV with a decreased total charge-transfer resistance. The Ni/Sn dendrites electrode shows lower resistance at the tested potentials, indicative of faster urea oxidation kinetics.