Insights about sensing mechanisms with Nickel oxide based gas sensors

Project Director: Dr. Cristian Eugen Simion

Among different types of sensors, those based on semiconducting metal oxides stands out through their: robustness, selective sensitivity, low fabrication costs and infield operation (presence of the relative humidity, variable temperature, the presence of potential interfering gases, etc.).

The idea of the current project proposal consists in exploring the intrinsic nature of Nickel Oxide (NiO) as sensitive material together upon inspired chemical synthesis pathways, merging towards extracting the insights of its gas sensing performances towards different target gases (CO, CO2, NO2, CH4, NH3, SO2, H2S) adapted to work under infield conditions.

The research work employs interdisciplinary vision of the team spanning from: chemical-physics and theoretical physics.

The novelties brought by the project are:

  • Structure-functioning relationships will be highlighted by understanding the role of sensing and transducing features with multi-dimensional NiO nanostructured based sensors. Through inspired chemistry synthesis, NiO morphologies will be tailored to maximize the gas sensing performances.
  • The challenge is to fuse the theoretical predictions with the realistic gas sensing outputs into an overview image about the nature of gas surface interactions.

The outputs from phenomenological and catalytic investigations will guide the theoretical modeling towards extending the gas surface model of NiO sensors.

1. NiO materials with controlled morphology.

2. Complete electronic library with NiO network parameters, elemental composition, crystallite size distribution, volume and pore size distribution.

3. Different batches of NiO-based sensors accompanied by fully documented procedures.

4. Selection of gas-sensitive layers without surface cracks and agglomerations as a result of optical inspection.

5. Selection of sensors following the evaluation of the parameters of: sensitivity, selectivity, response time and return time as well as electricity consumption.

6. Selection and separation of NiO-based materials according to the nature of the layers (completely or partially enriched in majority charge carriers) in accordance with the theoretical analysis of gas-sensitive properties.

7. Distinction between physisorption and ionosorption processes, individually represented for NiO sensors partially or completely enriched in majority load carriers.

8. Quantification of surface reactions using the formalism of quasi-chemical equations

9. Modeling the effects associated with load exchange processes by using the concepts of solid state physics (for example, load loading statistics, theory of transport phenomena, etc.)

Cristian Eugen Simion
Adelina Stanoiu
Cosmin Istrate
Catalina Mihalcea
Ovidiu Gabriel Florea
Corneliu Ghica
Andrei Cristian Kuncser
Ion Viorel Dinu
Daniela Ghica
Ionel Florinel Mercioniu
Simona Somacescu

Complete chemical synthesis route, can be found here:

Complete XRD report can be found here:

XRD pattern and data library:

MaterialCalcination temperatureCrystalline phase
Lattice parameter
Particle size
NiO-1400°CCubic Fm-3m (225)a = 0.4178 ± 0.0001 nmd = 11 ± 2 nm
NiO-1500°CCubic Fm-3m (225)a = 0.4178 ± 0.0001 nmd = 18 ± 2 nm
NiO-2400°CCubic Fm-3m (225)a = 0.4178 ± 0.0001 nmd = 18 ± 2 nm
NiO-rGO400°CCubic Fm-3m (225)

Hexagonal C-2H (grafit 2H) P63/mmc

aNiO = 0.4177 ± 0.0001 nm

agrafit = 0.2460 ± 0.0001 nm și cgrafit = 0.6707 ± 0.0001 nm



dNiO = 7 ± 2 nm

dgrafit = 35 ± 4 nm

SEM investigations:

TEM and HRTEM investigations:


Specific surface BET (Brunauer, Emmett, Teller) data:

MaterialCalcination temperature
Pore volume


Pore size (nm)Specific surface




Purpose of the procedure: Obtaining batches of four planar sensors based on Nickel oxide, fully prepared for the development of the stages of evaluation of sensitive gas performance. Field of application: Gas sensors based on thick and porous films of semiconductor metal oxides. Nickel oxide powders obtained by different chemical routes are transported and stored in specially designed plastic containers. They must meet the following conditions: - Must not chemically or physically affect the NiO sample; - It must ensure a tight closure so that there is no loss of material, both during transport and when stored; - NiO samples will not be exposed to direct sunlight and will be stored in laboratory conditions. 

Weigh 59 mg of each material or 57.5 mg of organic solvent, which is then mixed in a mortar and pestle with minimal roughness and absorption (preferably agate). Grind very well for 10 minutes, so as to obtain a paste with medium viscosity, which is to be transferred to Al2O3 supports, by the following method:


After transferring the paste to the alumina supports, they are placed in the oven at 60 ° C for 18 hours. The final heat treatment consists of the progressive heating of the sensors in a programmable oven, according to the graph below:

In order to determine the operating temperature of the gas-sensitive material, it is needed as an initial a calibration of the Platinum heater takes place, depending on the voltage applied to it, using the electrical configuration below. The optical pyrometer used is of the Lumasense IN-5L Plus type, which is able to detect an infrared emission of the NiO type material, as a result of the heat transfer from the Platinum heater to the gas-sensitive layer. The IR emission was corrected with the NiO emissivity coefficient (ε = 0.95).

The obtained results are in good agreement with those provided in Work Plan of Stage 1.

In conclusion, the objectives and activities proposed for Stage 1/2021 were fully achieved.


1. A. Stanoiu, A.C. Kuncser, D. Ghica, O.G. Florea, S. Somacescu, C.E. Simion, Sensing Properties of NiO Loaded SnO2 Nanoparticles - Specific Selectivity to H2S, Chemosensors 2021, 9, 125,

2. C.E. Simion, C. Ghica, C.G. Mihalcea, D. Ghica, I. Mercioniu, S. Somacescu, O.G. Florea, A. Stanoiu, Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors-The Influence of Humidity, Chemosensors 2021, 9, 244,

3. A. Sobetkii, R.E. Irimescu, A.E. Slobozeanu, C.F. Ciobota, U. Cindemir, L. Osterlund, A. Stanoiu, C.E. Simion, R.M. Piticescu, Deposition and characterization of thin films based on nanostructured NiO as sensorial element for detection gases, Workshop on "Contemporary Solutions for Advanced Catalytic Materials with a High Impact on Society", 11-15 October 2021, Bucharest, Romania,

4. C.E. Simion, Special Issue "Advanced Materials for Gas Sensors" Editorial, Materials 2021, 14, 6765,

5. A. Stanoiu, C. Ghica, C.G. Mihalcea, D. Ghica, S. Somacescu, O.G. Florea, C.E. Simion, Effects of Calcination Temperature on CO-Sensing Mechanism for NiO-Based Gas Sensors, Chemosensors 2022, 10, 191,

6. C. Ghica, C.G. Mihalcea, C.E. Simion, I.D. Vlaicu, D. Ghica, I.V. Dinu, O.G. Florea, A. Stanoiu, Influence of relative humidity on CO2 interaction mechanism for Gd-doped SnO2 with respect to pure SnO2 and Gd2O3, Sens. Actuators B. Chem. 2022, 368, 132130,

Nr. Crt.Name and surname
e-mailID Brainmap
1GHICA Corneliucghica@infim.roU-1700-029U-5827
2STANOIU Adelinaadelina.stanoiu@infim.roU-1700-038M-8092
3GHICA Danielaghica@infim.roU-1700-035Y-0481
4SIMION Cristian Eugensimion@infim.roU-1700-030F-9765
5KUNCSER Andrei U-1700-032N-6988
6MERCIONIU Ionel Florinelimercioniu@infim.roU-1700-039E-8823
7ISTRATE Marian U-1900-061U-8873
8MIHALCEA U-1900-062F-0766
9FLOREA U-1700-032D-4435
10DINU Ion Viorelvdinu@infim.roU-1700-030A-3912
11SOMACESCU Simonasomacescu.simona@gmail.comU-1700-039T-4737



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