Cerium oxide decorated on nickel hydroxide anchored on reduced graphene oxide (Ce-Ni(OH)2/rGO) composite with hexagonal structures were synthesized by facile hydrothermal method. Fourier transform infrared spectroscopy (FT-IR), highresolution transmission electron microscopy with selected area diffraction (HRTEM-SAED), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer– Emmett–Teller (BET) surface area analysis and electrochemical technology were used to characterize the composite. Due to its unique two-dimensional structures and synergistic effect among Ce2O3, Ni(OH)2 and rGO components indicated twodimensional hexagonal nano Ce-Ni(OH)2/rGO composite is promising electrode material for improved electrochemical H2O2 sensing application. From 50 to 800 μM, the H2O2 concentration was linearly proportional to the oxidation current, with a lower detection of limit of 10.5 μM (S/N = 3). The sensor has a higher sensitivity of 0.625 μA μM−1 cm− 2. In addition, the sensor demonstrated high selectivity, repeatability and stability. These findings proved the viability of the synthetic method and the potential of the composites as a H2O2 sensing option.

The potential application of ultrafine cerium oxide (ceria, ) as an oxygen gas sensor has been investigated. Ceria was synthesized by a thermochemical process: first, a precursor powder was prepared by spray drying cerium-nitrate solution. Heat treatment in air was then performed to evaporate the volatile components in the precursor, thereby forming nanostructured having a size of approximately 20 nm and specific surface area of 100 . After sintering with loosely compacted samples, hydrogen-reduction heat treatment was performed at 773K to increase the degree of non-stoichiometry, x, in . In this manner, the electrical conductivity and oxygen-response ability could be enhanced by increasing the number of oxygen vacancies. After the hydrogen reduction at 773K, was obtained with nearly the same initial crystalline size and surface. The response time measured at room temperature was extremely short at 4 s as compared to 14 s for normally sintered . We believe that this hydrogen-reduced ceria can perform capably as a high-performance oxygen sensor with good response abilities even at room temperature.

The nanostructured cerium oxide powders were synthesized by spray thermal decomposition process for the use as the raw materials of resistive oxygen sensor. The synthesis routes consisted of 1) spray drying of water based organic solution made from cerium nitrate hydrate () and 2) heat treatment of spray dried precursor powders at in air atmosphere to remove the volatile components and identically to oxidize the cerium component. The produced powders have shown the loose structure agglomerated with extremely fine cerium oxide particles with about 15 nm and very high specific surface area (). The oxygen sensitivity, n ( and the response time, measured at in the sample sintered at , were about 0.25 and 3 seconds, respectively, which had much higher performances than those known in micron or sized sensors.