ORIGINAL PAPER Impedimetric sensing of humidity and temperature using CeO 2 –Co 3 O 4 nanoparticles in polymer hosts Sher Bahadar Khan 1,2 & Khasan S. Karimov 3,4 & Muhammad Tariq Saeed Chani 1,2 & Abdullah M. Asiri 1,2 & Kalsoom Akhtar 5 & Noshin Fatima 3 Received: 26 February 2015 /Accepted: 12 May 2015 # Springer-Verlag Wien 2015 Abstract Humidity and temperature sensors were fabricated from a nanocomposite consisting of CeO 2 -Co 3 O 4 hybrid nanoparticle-silicone adhesive and CeO 2 -Co 3 O 4 hybrid nanoparticle-polymer adhesive, respectively, to fix the mate- rial on a glass supported copper electrode. The impedance of the sensor decreases by a factor of 960 at a working frequency of 100 Hz, and by a factor of 800 at 1 kHz, on increasing relative humidity (RH) from 30 to 90 %. In parallel, the ca- pacitances increase by factors of 567 and 355, respectively, under the same experimental conditions. The effect of temper- ature in the range from 25 to 70 °C on impedance (again at 100 Hz and 1 kHz) was also studied and found to decrease with increasing temperature. On going from 25 to 70 °C, the impedance measured at 100 Hz and 1 kHz decreases 2.22 and 1.58 times, respectively, in surface type sensors, while in sand- wich type sensors this decrease is 3.0 and 2.08 times. The calculated average sensitivity to temperature is -1.02 and -0.8 % °C -1 for the surface type and -1.5 and -1.2 % °C -1 for the sandwich type sensors at frequencies of 100 Hz and 1 kHz, respectively. Keywords Surface type sensor . Sandwich type sensor . Nanoparticles . Polymer . Impedance . Capacitance . Resistance Introduction Humidity can be determined by methods and devices such as psychrometer (wet- and dry-bulb hydrometers), mechanical hy- grometers (exploiting the change in dimensions of porous ma- terials such as paper and hair), dew point sensors, electrolytic sensor, spectroscopic sensors and hygrometers where capacity or resistance are measured. The last method is one of the most suitable from practical point of view because the electric sen- sors may have small sizes, short response and recovery times, high reliability, the possibility to use them in telemetry systems and low costs. Humidity sensors are widely used in semicon- ductor, automobile, medical, pharmaceutical, health caring, tex- tile, paper, agriculture and food industry [1-2]. Commercially available humidity sensors are fabricated by conventional sensing materials like alumina, ceramics and electrolytic metal oxides. Depending upon the nature of ma- terials these sensors may be expansive or require high opera- tional power/temperature and high cost of maintenance [3]. To make the sensor suitable for commercialization; the wide range sensitivity, linear response, small hysteresis, short re- sponse and recovery time, low cost and low power along with long term physical and chemical stability are the required characteristics [4, 5]. The development of humidity sensor with high sensitivity, linear response, short response and recovery time, low hyster- esis, physical and chemical stability, wide sensing range and low cost is needed [5, 6]. To developed humidity sensor with good assets, different types of materials have been explored because for humidity sensors, nature of sensing material and * Sher Bahadar Khan sbkhan@kau.edu.sa 1 Chemistry Department, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589, Saudi Arabia 2 Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, P.O. Box 80203, Saudi Arabia 3 GIK Institute of Engineering Sciences and Technology, Topi 23640, Swabi, Pakistan 4 Physical Technical Institute, Aini St. 299/1, Dushanbe 734063, Tajikistan 5 Division of Nano Sciences and Department of Chemistry, Ewha Womans University, Seoul 120-750, South Korea Microchim Acta DOI 10.1007/s00604-015-1529-1