Electrochemical fabrication of carbon fiber-based nickel hydroxide/carbon nanotube composite electrodes for improved electro-oxidation of the urea present in alkaline solutions

Abstract

Abstract A Ni(OH)2/carbon nanotube (CNT)/carbon fiber (CF) composite electrode was developed, and its electrode kinetics were investigated to improve its urea oxidation reaction (UOR) performance. The fabrication of the electrode was done using electrophoretic co-deposition combined with hydrothermal reaction. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used to examine the electrode properties, while cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) were used to study the electrode kinetics. The prepared catalyst that had a flake-like structure was an α phase Ni(OH)2 catalyst, which mixed well with the CNTs to form a composite layer on the CF substrate. The α-Ni(OH)2/CNT/CF electrode displayed satisfactory UOR performance because it had a higher oxidation current and a lower overpotential than those of either the α-Ni(OH)2/CF electrode or CF electrode. These improved properties of the α-Ni(OH)2/CNT/CF electrode can be because of the active and reversible Ni2+/Ni3+ redox reaction, which has high rate constant and anodic transfer coefficient, of the α-Ni(OH)2/CNT composite. Moreover, compared with α-Ni(OH)2/CF or CF electrodes, the α-Ni(OH)2/CNT/CF electrode has a low charge transfer resistance because of the increase in the reaction surface area and electrical conductivity caused by the CNTs. Overall, the composite electrode combines the advantages of the α-Ni(OH)2 catalyst, CNT conductive network, and CF current collector for improved UOR performance, which will be beneficial for urea pollution mitigation and H2 production.