Egon Kecsenovity

Enhanced Photoelectrochemical Performance of Cuprous Oxide/Graphene Nanohybrids

Combination of an oxide semiconductor with a highly conductive nanocarbon framework (such as graphene or carbon nanotubes) is an attractive avenue to assemble efficient photoelectrodes for solar fuel generation. To fully exploit the possible synergies of the hybrid formation, however, precise knowledge of these systems is required to allow rational design and morphological engineering. In this paper, we present the controlled electrochemical deposition of nanocrystalline p-Cu2O on the surface of different graphene substrates. The developed synthetic protocol allowed tuning of the morphological features of the hybrids as deduced from electron microscopy. (Photo)electrochemical measurements (including photovoltammetry, electrochemical impedance spectroscopy, photocurrent transient analysis) demonstrated better performance for the 2D graphene containing photoelectrodes, compared to the bare Cu2O films, the enhanced performance being rooted in suppressed charge carrier recombination. To elucidate the precise role of graphene, comparative studies were performed with carbon nanotube (CNT) films and 3D graphene foams. These studies revealed, after allowing for the effect of increased surface area, that the 3D graphene substrate outperformed the other two nanocarbons. Its interconnected structure facilitated effective charge separation and transport, leading to better harvesting of the generated photoelectrons. These hybrid assemblies are shown to be potentially attractive candidates in photoelectrochemical energy conversion schemes, namely CO2 reduction.

Influence of synthesis parameters on CCVD growth of vertically aligned carbon nanotubes over aluminum substrate

In the past two decades, important results have been achieved in the field of carbon nanotube (CNT) research, which revealed that carbon nanotubes have extremely good electrical and mechanical properties The range of applications widens more, if CNTs form a forest-like, vertically aligned structure (VACNT) Although, VACNT-conductive substrate structure could be very advantageous for various applications, to produce proper system without barrier films i.e. with good electrical contact is still a challenge. The aim of the current work is to develop a cheap and easy method for growing carbon nanotubes forests on conductive substrate with the CCVD (Catalytic Chemical Vapor Deposition) technique at 640 °C. The applied catalyst contained Fe and Co and was deposited via dip coating onto an aluminum substrate. In order to control the height of CNT forest several parameters were varied during the both catalyst layer fabrication (e.g. ink concentration, ink composition, dipping speed) and the CCVD synthesis (e.g. gas feeds, reaction time). As-prepared CNT forests were investigated with various methods such as scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. With such an easy process it was possible to tune both the height and the quality of carbon nanotube forests.

Ellipsometric Analysis of Aligned Carbon Nanotubes for Designing Catalytic Support Systems

Vertically aligned CNT carpets combined with inorganic semiconductors are expected good prospect in practical applications, especially in photocatalysis. If these devices are in production, a fast and non-invasive characterization method will be required. Ellipsometry is widely used in industry as an in-line monitoring tool, so in this study the applicability of ellipsometry for characterizing CNT carpets is investigated. It is shown that ellipsometric evaluation can provide information about the density and the optical properties of the nanotubes; however, the properties of the individual nanotubes (diameter, wall number) can not be taken into account during ellipsometric modeling. To overcome these limitations, numerical simulations are also presented.

CCVD preparation of highly uniform carbon micro- and nanocoil fibers

Micro- and nanosized carbon fibers with special helical structure have many promising applications. These structures can be used as reinforcing materials in polymer composites, wave absorption or tactile sensor elements. In this fiber preparation method the applied catalyst precursor were nickel (II) oxide nanoparticles. Sulfuric modification of nickel containing catalyst grain yields carbon fibers with special coiled structures in acetylene decomposition. The preparation of carbon fiber coils by the CCVD method was carried out between 700- 800 C using thiophene impurity. The catalyst particles and the observed structures were studied by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The lengths of fibers can even reach millimeter size and the average fiber diameter is 1 μm. The diameter of coils is 1-20 μm, the coil pitch is 0.5-1.5 μm. Carbon microcoils might have interesting applications in the near future.