# Effect of Platinum Doping on the Morphology and Sensing Performance for CuO-Based Gas Sensor
## 1 Introduction  
Hydrogen sulfide (H\({}_{2}\)S) is a toxic, harmful, and malodorous gas, which is usually produced by petroleum refining, as well as agricultural and biogas production [1; 2; 3]. The threshold limit value for H\({}_{2}\)S gas (recommended by the American Conference of Government Industrial Hygienists) is 10 ppm [4]. Furthermore, H\({}_{2}\)S gas is liable to explode at a high temperature. Therefore, it is urgent to develop a new type of sensors for detecting H\({}_{2}\)S with a low operating temperature. Although researchers have developed some detecting methods, such as fluorescent probes [5], electrogenerated chemiluminescene [6], and chemical methods [7] to detect H\({}_{2}\)S, these methods still have shortcomings such as complex detection process, and high cost. Among the various detection methods, metal oxide semiconductor gas sensors have been widely used in the detecting of toxic, flammable, and explosive gases; monitoring air quality; and food processing, due to their simplicity, high sensitivity, low cost, and compatibility with modern electronic devices [8; 9]. In recent years, many researchers have utilized metal oxide semiconductor sensors to detect H\({}_{2}\)S gas, including CuO [10; 11], In\({}_{2}\)O\({}_{3}\)[12], ZnO [13; 14] SnO\({}_{2}\)[15], and WO\({}_{3}\)[16]. Cupric oxide (CuO), as a typicalp-type semiconductor with a band gap of 1.2 eV [17], has been widely investigated in lithium-ion batteries [18], super-capacitors [19], heterogeneous catalysts [20], and particularly in gas detection devices. The gas sensitivity of CuO-based gas sensors has been widely reported. [PERSON] et al. [10] reported H\({}_{2}\)S gas sensors based on CuO thin films, and the results showed that the response of CuO thin films to sub-ppm (100-400 ppb) H\({}_{2}\)S at room temperature was highly reversible. However, once the concentration was higher than 400 ppb, the response became irreversible. To improve the performance of sensors, loading metal oxides with catalytic metals or noble metals nanoparticles on the surface has proved to be a very effective method [21]. For example, [PERSON] et al. [22] reported that 2.2 wt % Cr added to CuO nanostructures by a solvothermal reaction significantly increased the responses to 100 ppm NO\({}_{2}\) from 7.5 to 134.2. [PERSON] et al. [23] prepared Pd functionalized one-dimensional CuO nanostructures, which revealed a high response of 167 at 50 ppm. However, the operating temperature was relatively high (300 \({}^{\circ}\)C). Therefore, there is still a great demand to develop a H\({}_{2}\)S gas sensor with excellent sensing performance, such as fast response/recovery time, good selectivity, high sensitivity, low detection limit, and relatively low operating temperature [24]. Pt as a catalytic additive has been proven to be effective in improving gas-sensing performance. [PERSON] et al. [25] has shown that the Pt-doped SnO\({}_{2}\) material is less resistant, more sensitive, and shows faster response to ethanol than pure SnO\({}_{2}\); what's more, the response of the Pt-doped sensors was between 2 and 55 times higher than the commercial one. [PERSON] et al. [26] prepared \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles doped with different amounts of Pt. Compared with the pure \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) based sensor, the Pt-doped \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) based sensors showed the enhanced excellent sensing performance and good selectivity for H\({}_{2}\)S gas. However, reports on the gas-sensing performance of Pt-doped CuO are rather rare. We expected that Pt doping could be an efficient way to enhance the sensing properties of pure CuO. In the present work, the pristine and Pt-doped CuO based H\({}_{2}\)S gas sensors were designed. The Pt-doped CuO has been prepared using a facile one step method. For the purpose of comparison, the gas sensing performance of CuO sensors with different Pt concentrations was evaluated.