Sensor	Cristallite size(nm)	Grain size(nm)	Resistivity(10^²)	Gas ResponseS H_₂ concentration(1000 ppm)	Gas ResponseS H_₂ concentration(15000 ppm)
undoped CuO	35	32	1.22	0.23	1.40
CuO :Pd(2 %)	24	23	1.11	0.53	2.10
CuO :Pd (6 %)	20	17	1.04	0.35	4.10

Table 1: Overview about of different morphological, electrical and H₂ sensing properties of CuO-based sensors

Table 2: Comparison of hydrogen gas sensor performance with reported data

Table 1

Table 2

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 1: (a) (b) X-ray diffraction patterns for CuO, CuO: Pd 2%, and CuO: Pd 6% thin films

Figure 2: SEM images of CuO and Pd-doped CuO thin films as a function of Pd doping: (a) 0%, (b) 2% and (c) 6%

Figure 3: Response of the undoped CuO sensor to hydrogen at 180 °C operating temperature, for the hydrogen concentration range 15 000 – 1000 ppm.

Figure 4: Illustration of hydrogen sensing mechanism of by CuO-based sensor and relevant energy band diagram

Figure 5: Sensor response of undoped CuO with respect to hydrogen concentration for various operating temperatures

Figure 6: Maximum response of CuO, CuO: Pd 2% and CuO: Pd 6% sensors to different hydrogen concentrations for an operating temperature of 160 °C

Figure 7: Comparison of the response of the sensors CuO: Pd 2% and CuO: Pd 6% to different hydrogen concentrations at 60°C