Battery-like behavior of Ni-ceria based systems: Synthesis, surface defects and electrochemical assessment

NiO, CeO2 and respective composites are extensively used in energy storage devices due to mostly their high electrochemical activity. However, the assessment of battery-like behavior of Ni-ceria based systems comprising (Ni or Gd)-doped ceria combined with Ni0 seems to be neglected in the literature. In this work, NiO and ceriabased solid solutions composite powders were obtained by a co-precipitation synthesis method. The structure and particle size of the calcined powders were investigated by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM), respectively. Oxidative states of composites were inspected by X-ray photoelectron spectroscopy (XPS). The electrochemical performance of powders was evaluated by cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy. Refinement of the XRD patterns showed that powders have nanosized crystallites and mean size of particles within 20- 70 nm were revealed by FESEM. The improved specific capacity of the NiO-CeO2 electrode material (about 2.5 times higher than that of NiO-CGO at 5 mV s(-1)) is due to an increase in Faradic reactions taken place on its surface with a higher fraction of defects (namely Ni3+, Ce3+ and oxygen vacancies), as determined by XPS. The superior electrochemical performance of the NiO-CeO2 electrode is also confirmed by electrochemical impedance spectroscopy.