Rok: 2020

Ti3+ doped anodic single-wall TiO2 nanotubes as highly efficient photocatalyst

MOTOLA, Martin – ČAPLOVIČOVÁ, Mária – KRBAL, Miloš – SOPHA, Hannah – THIRUNAVUKKARASU,  Guru Karthikeyan – GREGOR, Maroš – PLESCH, Gustáv – MACAK, Jan M.

In Electrochimica Acta. Vol. 331, (2020)

https://doi.org/10.1016/j.electacta.2019.135374

Abstract

In this work, a two-step treatment of TiO2 nanotube (TNT) layers towards enhanced photocatalytic performance is presented. TNT layers with a thickness of ∼7 μm and an average inner diameter of ∼190 nm were prepared via electrochemical anodization of Ti foil in a fluoride containing ethylene glycol-based electrolyte. To improve the photocatalytic activity of the produced TNT layers a two-step post-treatment was conducted. First, the inner shell of the native double-wall TNT layers was removed via a mild pre-annealing followed by a selective etching treatment of the inner shell in piranha solution yielding single-wall TNT layers. Second, reduction via annealing in H2/Ar atmosphere was performed. The resulting Ti3+ doped single-wall TNT layers possess 100% enhancement of photocatalytic activity compared to their non-treated counterparts.

Properties of sputtered BaSi2 thin films annealed in vacuum condition

TIAN, Yilei – MONTES, Ana Rita – VANČO, Ľubomír – ISABELLA, Olindo – ZEMAN, Miro

In Japanese Journal of Applied Physics. Vol. 59, SF (2020)

https://doi.org/10.7567/1347-4065/ab5b59

Abstract

As a potential absorber candidate for high-efficient solar cell applications, BaSi2 films are confronted with issues of surface oxidation associated with the high-temperature annealing. Herein, BaSi2 films are deposited by the sputtering technique. A vacuum annealing process is subsequently carried out to crystallize sputtered BaSi2 films. Raman spectroscopy is used to study surface structures and crystalline quality. Elemental depth profile is measured by Auger Electron spectroscopy to understand the compositions of films. Optical and electrical properties are further investigated to reveal the effects of annealing condition. Applying vacuum annealing condition can effectively suppress diffusions of Ba and ensures a stochiometric BaSi2 layer. However, surface oxidation still occurs even in the vacuum environment owing to the high reactivity of Ba. Further attempts to prevent BaSi2 surface oxidation may focus on the combination of other methods, such as capping layer and reducing atmosphere, with vacuum (or low-pressure) annealing condition.

A systematic study of MOCVD reactor conditions and Ga memory effect on properties of thick InAl(Ga)N layers: a complete depth-resolved investigation

CHAUHAN, Prerna – HASENÖHRL, Stanislav – VANČO, Ľubomír – ŠIFFALOVIČ, Peter – DOBROČKA, Edmund – MACHAJDÍK, Daniel – ROSOVÁ, Alica – GUCMANN, Filip – KOVÁČ, Jaroslav jr. – MATKO, Igor – KUBALL, Martin – KUZMÍK, Ján

In CrystEngComm. Vol. 22, iss. 1 (2020)

https://doi.org/10.1039/C9CE01549C

Abstract

Thick InAlN layers (In-molar fraction >0.37) on GaN buffer layers were prepared using a close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor. This work provides a discussion of the dependence of reactor parameters (pressure, ammonia flow and temperature) and unintentional Ga-incorporation on structural, optical and chemical properties of those layers down to the nanoscale. Rutherford back-scattering spectrometry, Auger electron spectroscopy, and transmission electron microscopy with the energy dispersive X-ray analysis were used for in-depth chemical analysis of layers. A diminishing Ga-auto-incorporation in thick InAlN layer creates a chemically graded InAl(Ga)N interlayer that assists in releasing of interfacial strain and paves the way toward In-rich InAlN layer. The rate of unintentional Ga-auto-incorporation in InAlN layers increases with decreasing of growth temperature, and increasing of reactor pressure and ammonia flow during growth. Raman and photoluminescence spectroscopy were used to get the crystal structural fingerprint influenced by Ga-incorporation. We suggested that Ga could incorporate at nitrogen vacancies at high reactor pressures (≥200 mbar). Screw dislocations and/or N-vacancies in InAl(Ga)N layers may be energetically favorable sites for In-incorporation and lead to compositional fluctuation and local In-rich InAl(Ga)N phase.

A comparative life cycle assessment of graphene and activated carbon in a supercapacitor application

COSSUTTA, Matteo – VRETENÁR, Viliam – CENTENO, Teresa A. – KOTRUSZ, Peter – MCKECHNIE, Jon – PICKERING, Stephen J.

In Journal of Cleaner Production. Vol. 242, iss. 1 (2020)

https://doi.org/10.1016/j.jclepro.2019.118468

Abstract

Graphene shows substantial promise in improving the technical performance of a range of applications. For its development and before its potential mass adoption, it is critical to understand the associated cradle-to-grave life cycle environmental impacts. Previous studies on graphene environmental performance do not include end of life and the potential environmental credits generated by graphene reuse. This study undertakes a cradle-to-grave approach to evaluating graphene applications, considering a case study of supercapacitors manufactured with graphene and activated carbon active materials. The analysis includes active materials commercial-size production, supercapacitors production, supercapacitors use phase in an automotive application, and their end of life in which both devices are recycled. With current material performance and energy mixes, the graphene-based supercapacitor would increase impacts in all environmental categories analysed, ranging from 27% higher human toxicity to 213% greater ozone depletion and showing a 48% increase in GHG emissions. This unfavourable result arises due to the tested graphene material exhibiting inferior specific capacitance to the activated carbon comparator, as well as a more energy-intensive production process. Prospective analysis considers hypothetical performance where both active materials reach their theoretical specific capacitance, and the decarbonisation of electricity generation. The environmental impacts of both the activated carbon and graphene supercapacitors are reduced in these prospective scenarios, with the graphene based supercapacitor becoming the least impacting solution due to its lower active material requirements. The graphene-based device shows 36% lower GHG emission and overall shows lower impacts ranging from 14% less mineral, fossil and renewable resource depletion to 43% less photochemical ozone formation. These results support graphene as a valid candidate material for substituting activated carbon in supercapacitors provided graphene technical performance is improved, production optimised, and recycling developed.