No abstract

Hydrogen produced from the photocatalytic splitting of water is one of the reliable alternatives to replace the polluting fossil and the radioactive nuclear fuels. Here, we provide unequivocal evidence for the existence of blue- and red-shifting O-H covalent bonds within a single water molecule adsorbed on the MgO surface as a result of asymmetric displacement polarizabilities. The adsorbed H-O-H on MgO gives rise to one weaker H-O bond, while the other O-H covalent bond from the same adsorbed water molecule compensates this effect with a stronger bond. The weaker bond (nearest to the surface), the interlayer tunneling electrons and the silver substrate are shown to be the causes for the smallest dissociative activation energy on the MgO monolayer. The origin that is responsible to initiate the splitting mechanism is proven to be due to the changes in the polarizability of an adsorbed water molecule, which are further supported by the temperature-dependent static dielectric constant measurements for water below the first-order electronic-phase transition temperature.

In this paper, we report a comparison between the most commonly used single harmonics (sine voltage waveform) and the original multiple harmonics AC-driven atmosphericpressure plasma jet. The designed multiple harmonics source was applied to a single-electrode plasma jet. In this research, we characterized and studied the advantages of a single-electrode jet which was powered with multiple harmonics voltage waves, fundamental frequency was varied between 5 and 60 kHz. Optical emission spectroscopy, electric probes and plasma jet visible length measurements lead to the conclusion that the optical emission intensity of emitting plasma species correlates with the discharge current RMS (Root Mean Square), whereas the jet visible length correlates with the electrode discharge voltage amplitude. These properties of the plasma jet cannot be obtained with single harmonics AC-driven plasma jets.

Inductively coupled RF water vapour plasma generated in a linear glass tube was studied by means of optical emission spectroscopy. Low pressure water vapour plasma was created by an 8 turn coil with an EM field oscillating at 13.56 MHz. Various total pressures (5–14 Pa) and discharge powers (100–300 W) were investigated. Excitation temperatures (between 0.6 and 1.0 eV) of the plasma discharge were determined from emission spectra by employing the Boltzmann plot method. E- and H-modes of plasma and transitions among them were observed. Hysteresis effects were observed by the change in water vapour pressure and discharge power through monitoring of O, H and OH spectral features.

Samples of PVC foils are exposed to an early afterglow of gaseous plasma created by an electrode‐less RF discharge in predominant H‐mode using Ar, H2 and O2 gases. Sample temperature is measured with a pyrometer while the presence of reaction products is determined with an optical spectrometer. The temporal evolution of major radiative species is measured. The results show that the samples are rather immune to the Ar afterglow. H2 afterglow causes substantial heating of the sample due to heterogeneous surface recombination of H‐atoms, while O2 plasma treatment results in etching of the material which is substantial already at room temperature. The specific behaviour of reactive species is explained by taking into account spectrometer calibration curves, excitation energies and radiative species lifetimes. magnified image