Understanding the Photocatalytic Properties of Pt/CeOx /TiO2 : Structural Effects on Electronic and Optical Properties

Structural, dielectric, and antimicrobial evaluation of PMMA/CeO2 for optoelectronic devices

In the current report, we have successfully synthesized nanocomposites of PMMA incorporating different doping of CeO2 through a chemical approach. XRD results reflects decent matching for CeO2 nanoparticles with 29 nm crystallite size. FTIR spectroscopy demonstrates the characteristic functional groups validating the successful formation of the composite. The optical study of PMMA and the nanocomposites has proven that the optical properties such as band gap, refractive index, optical permittivity, and loss tangent factor are affected by adding CeO2 to the PMMA matrix.The peak residing around 420 nm by UV measurements is allocated to occurring electrons photoexcitation from the valence to conduction band inherent in CeO2. The dielectric measurements were achieved using broadband dielectric spectroscopy upon a wide span of frequencies (10-1-107 Hz) and within temperatures from - 10 to 80 °C with a step of 10 °C. The permittivity decreases by adding CeO2 and the dielectric parameters are thermally enhanced, however, the temperature influence is based on CeO2 content, the higher the CeO2 amount, the higher the influence of temperature. The results of the nanocomposites revealed antibacterial activity counter to gram-positive bacteria strain (S. aureus, and B. subtilis), and gram-negative bacteria (E. coli, and K. pneumoniae), yeast (C. albicans, as well as fungi (A. niger). Inherently, the change in CeO2 concentration from 0.01 to 0.1 wt% delivers maximum influence against gram-negative bacteria. These PMMA CeO2-doped composites are beneficial for optoelectronic areas and devices.

Active Pt-Nanocoated Layer with Pt-O-Ce Bonds on a CeO x Nanowire Cathode Formed by Electron Beam Irradiation

A Pt-nanocoated layer (thickness of approx. 10-20 nm) with Pt-O-Ce bonds was created through the water radiolysis reaction on a CeO _x nanowire (NW), which was induced by electron beam irradiation to the mixed suspension of K₂PtCl₄ aqueous solution and the CeO _x NW. In turn, when Pt-nanocoated CeO _x NW/C (Pt/C ratio = 0.2) was used in the cathode layer of a membrane electrode assembly (MEA), both an improved fuel cell performance and stability were achieved. The fuel cell performance observed for the MEA using Pt-nanocoated CeO _x NW/C with Pt-O-Ce bonds, which was prepared using the electron beam irradiation method, improved and maintained its performance (observed cell potential of approximately 0.8 V at 100 mW cm^-2) from 30 to 140 h after the start of operation. In addition, the activation overpotential at 100 mA cm^-2 (0.17 V) obtained for MEA using Pt-nanocoated CeO _x NW/C was approximately half of the value at 100 mA cm^-2 (0.35 V) of MEA using a standard Pt/C cathode. In contrast, the fuel cell performance (0.775 V at 100 mW cm^-2 after 80 h of operation) of MEA using a nanosized Pt-loaded CeO _x NW (Pt/C = 0.2), which was prepared using the conventional chemical reduction method, was lower than that of MEA using a Pt-nanocoated CeO _x /C cathode and showed reduction after 80 h of operation. It is considered why the nanocoated layer having Pt-O-Ce bonds heterogeneously formed on the surface of the CeO _x NW and the bare CeO₂ surface consisting of Ce⁴⁺ cations would become unstable in an acidic atmosphere. Furthermore, when a conventional low-amount Pt/C cathode (Pt/C = 0.04) was used as the cathode layer of the MEA, its stable performance could not be measured after 80 h of operation as a result of flooding caused by a lowering of electrocatalytic activity on the Pt/C cathode in the MEA. In contrast, a low-amount Pt-nanocoated CeO _x NW (Pt/C = 0.04) could maintain a low activation overpotential (0.22 V at 100 mA cm^-2) of MEA at the same operation time. Our surface first-principles modeling indicates that the high quality and stable performance observed for the Pt-nanocoated CeO _x NW cathode of MEA can be attributed to the formation of a homogeneous electric double layer on the sample. Since the MEA performance can be improved by examining a more effective method of electron beam irradiation to all surfaces of the sample, the present work result shows the usefulness of the electron beam irradiation method in preparing active surfaces. In addition, the quantum beam technology such as the electron beam irradiation method was shown to be useful for increasing both performance and stability of fuel cells.