The international collaboration between the researchers of the Technical University of Moldova (UTM) and their colleagues from universities in Germany, the Netherlands, Great Britain and India, concluded with the publication of an remarkable scientific paper in the prestigious journal ACS Applied Materials & Interfaces, 2020, with impact factor 8.8. 

“A single CuO / Cu2O / Cu micro-wire covered by a nano-wire network as a gas sensor for the detection of battery hazards” is a work of great magnitude, with 80 pages of manuscript. Through the results of the reflected scientific investigations, the authors aim to contribute to the development of cost-effective microsensors for electric transport with portable batteries, especially for modern electric cars and bicycles.

This remarkable success was achieved due to the joint effort, during the past five years, of the teams of researchers led by prof., Dr. Oleg LUPAN (Center of Nanotechnologies and Nanosensors, Department of Microelectronics and Biomedical Engineering, Faculty of CIM, UTM), prof., Dr. Rainer ADELUNG (Institute for Materials Science, Germany), prof., Dr. Franz FAUPEL (Christian Albrechts University of Kiel, Germany), prof., Dr. Lorenz KIENLE (Faculty of Engineering, Kiel University, Germany), prof., Dr. Nora H. de LEEUW (Utrecht University, the Netherlands, and Cardiff University, UK) and prof., Dr. Abhishek Kumar MISHRA (University of Petroleum & Energy Studies, India).

It is known that the use of batteries in various equipment as portable energy sources, is continuously increasing, especially in transportation, bicycles, scooters and modern electric cars. Their volume and complexity is constantly escalating, and producers are consistently improving them, in accordance with the rigors of the international market (e.g. obtaining Li-ion batteries based on nanowires-microwires, by applying new nanotechnologies with lithium ions). Various new, significantly improved chemical combinations are introduced every 4-6 months, and with such rapid progress, it is extremely difficult to assess how quickly the battery will “age”, how it will behave and how safe its further utilization will be. Thus, there is an urgent need for cost-effective sensors with high accuracy and long battery life. Hence the need to monitor the evolution of gas and the process of decomposition of electrolytes in the battery, because any change in temperature or environment has a direct impact on its electrical performance and long-term stability. With this simple and very reliable approach to the manufacture of a sensor, it is possible to integrate it into the classic battery cell to monitor the condition of a Li-ion battery.

The authors of this study have developed a new, extremely simple strategy for manufacturing and integrating CuO/Cu2O/Cu microwire sensors into battery sensors, which are completely covered by a nanowire network of only 20 nm, using a simple thermal oxidation process. The CuO/Cu2O/Cu-microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. These sensors show different dominating gas responses with operating temperatures, for example, higher sensitivity to ethanol at 175 oC, higher sensitivity to 2-propanol at room temperature and 225 oC, and higher sensitivity to hydrogen gas at ~ 300 °C, respectively. In this context, the authors propose the sensing mechanism of this 3-in-1 sensor based on CuO/Cu2O/Cu. The crystal structure of the Cu2O-shell/Cu-core and the CuO-NWs networks on the surface were confirmed with TEM, HRTEM, and SAED, where (HR)TEM micrographs reveal the monoclinic CuO phase. DFT calculations bring valuable inputs to the interactions of the different gas molecules with the most stable surface of CuO, revealing strong binding, electronic band gap changes and charge transfer dueto the gas molecule interactions with the surface, thus confirming the experimental data. This research shows the importance of the non-planar CuO/Cu2O layered hetero-structure as a bright nanomaterial for the detection of various gases, controlled by the working temperature, and the insights presented in this work will be of significant value in the fabrication of new p-type sensing devices through simple nanotechnology, a plan proposed by professors from UTM and carried out in an international collaboration through detailed scientific research.

The paper is part of a larger research project on “Nanotechnologies for nanosensory devices”, conducted under the scientific guidance of Dr. Oleg LUPAN. Students of the university cycles I, II, and III, and those eager to experiment and work on new things, can join this team within the Center for Nanotechnologies and Nanosensors, the Department of Microelectronics and Biomedical Engineering, Faculty of Computers, Informatics and Microelectronics of UTM, at all times. Thus, UTM students and collaborators have the opportunity to put their knowledge to the test by developing new electronic and biomedical devices, but also to engage in international collaborations.

This internationally acclaimed research was partially supported by the NATO Science for Peace and Security Programme (SPS) Project under grant G5634 “Advanced Electro-Optical Chemical Sensors” AMOXES, conducted at the Technical University of Moldova.

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