Study on the Ozone Gas Sensing Properties of rf-Sputtered Al-Doped NiO Films

Al-doped NiO (NiO:Al) has attracted the interest of researchers due to its excellent optical and electrical properties. In this work, NiO:Al films were deposited on glass substrates by the radio frequencies (rf) sputtering technique at room temperature and they were tested against ozone gas. The Oxygen content in (Ar-O2) plasma was varied from 2% to 4% in order to examine its effect on the gas sensing performance of the films. The thickness of the films was between 160.3 nm and 167.5 nm, while the Al content was found to be between 5.3 at% and 6.7 at%, depending on the oxygen content in plasma. It was found that NiO:Al films grown with 4% O2 in plasma were able to detect 60 ppb of ozone with a sensitivity of 3.18% at room temperature, while the detection limit was further decreased to 10 ppb, with a sensitivity of 2.54%, at 80 °C, which was the optimum operating temperature for these films. In addition, the films prepared in 4% O2 in plasma had lower response and recovery time compared to those grown with lower O2 content in plasma. Finally, the role of the operating temperature on the gas sensing properties of the NiO:Al films was investigated.

Towards sustainable and efficient p-type metal oxide semiconductor materials in dye-sensitised photocathodes for solar energy conversion

In order to meet the ever-growing global energy demand for affordable and clean energy, it is essential to provide this energy by renewable resources and consider the eco-efficiency of the production and abundance of the utilised materials. While this is seldom discussed in the case of technologies still in the research stage, addressing the issue of sustainability is key to push research in the right direction. Here we provide an overview of the current p-type metal oxide semiconductor materials in dye-sensitised photocathodes, considering element abundance, synthetic methods and large scale fabrication as well as the underlying physical properties that are necessary for efficient solar harvesting devices.

Adsorption Dynamics of Redox Active Species onto Polarized Surfaces of Sensitized NiO

Mesoporous NiO films were deposited by means of a screen printing technique onto fluorine-doped tin oxide transparent electrodes and consequently sensitized with Erythrosin B (EryB) dye. The obtained colored NiO material was used as a working electrode in a three-electrode cell to study the evolution of the triple semiconductor/dye/electrolyte interface upon electrochemical polarization in dark conditions. The electrolyte was a solution of I₃ ^-/I^- in acetonitrile, with the redox couple representing the typical redox shuttle of dye-sensitized solar cells (DSCs). The adopted electrochemical conditions were devised in order to simulate the actual electrical environment of the NiO/dye photocathode in a light-soaked DSC. The use of a benchmark sensitizer EryB and of the most widely used redox mediator I₃ ^-/I^- is particularly meaningful for the study of the adsorption dynamics and the determination of possible degradative phenomena on the basis of the behavior of numerous analogue systems. Therefore, for the first time, the evolution of the NiO/EryB/I₃ ^-/I^- multiple interface was investigated combining the electrochemical characterization with ex situ spectroscopic analysis by means of X-ray photoelectron spectroscopy. The resulting picture shows that EryB in the immobilized state promotes the redox processes based on the I₃ ^-/I^- couple. Moreover, the EryB sensitizer inhibits the phenomena of recombination between the metal oxide semiconductor and the redox couple.

Electrochemical and Photoelectrochemical Properties of Nickel Oxide (NiO) With Nanostructured Morphology for Photoconversion Applications

The cost-effective production of chemicals in electrolytic cells and the conversion of the radiation energy into electrical energy in photoelectrochemical cells (PECs) require the use of electrodes with large surface area, which possess either electrocatalytic or photoelectrocatalytic properties. In this context nanostructured semiconductors are electrodic materials of great relevance because of the possibility of varying their photoelectrocatalytic properties in a controlled fashion via doping, dye-sensitization or modification of the conditions of deposition. Among semiconductors for electrolysers and PECs the class of the transition metal oxides (TMOs) with a particular focus on NiO interests for the chemical-physical inertness in ambient conditions and the intrinsic electroactivity in the solid state. The latter aspect implies the existence of capacitive properties in TMO and NiO electrodes which thus act as charge storage systems. After a comparative analysis of the (photo)electrochemical properties of nanostructured TMO electrodes in the configuration of thin film the use of NiO and analogs for the specific applications of water photoelectrolysis and, secondly, photoelectrochemical conversion of carbon dioxide will be discussed.