LAUSR

Abstract This study reports the facile fabrication of a three-dimensional (3D) spherical composite of NiII, FeIII-layered double hydroxides (NiFe-LDHs)/carbon nanotube (CNT) via the urea synthesis method without any surfactants or organic solvents and applies it to an ethanol electrooxidation reaction for the first time. The spherical composite showed a particle size of approximately 4 μm with NiFe-LDHs sheets that were closely arranged on the sphere surfaces. The formation mechanism of the composite was inferred. First, NiII and FeIII ions were adsorbed on the CNT surface. Simultaneously, the CNT agglomerated into interwoven clusters to form a conductive network. Sequential hydrolysis and polycondensation of FeIII in the presence of urea were kinetically beneficial to the precipitation of amorphous iron hydroxide. Then, an in situ phase transition from amorphous iron hydroxide to α-FeOOH/Fe(OH)3 nanoflakes occurred. Surface-adsorbed NiII was doped into the α-FeOOH/Fe(OH)3 flakes. Finally, the NiFe-LDHs nanoflakes continued to crystallize and formed a NiFe-LDHs/CNT spherical composite. Compared to the NiFe-LDHs powder sample, the NiFe-LDHs/CNT composite had enhanced electrocatalytic activity (approximately 5 times), showed a smaller electron transfer resistance of 15.7 Ω, and increased the long-term stability of ethanol oxidation, which could be deduced from the synergistic effect between NiFe-LDHs and CNT.