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Olli Pitkänen

Bio: Olli Pitkänen is an academic researcher from University of Oulu. The author has contributed to research in topics: Carbon nanotube & Carbon. The author has an hindex of 12, co-authored 38 publications receiving 516 citations.

Papers
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TL;DR: Lightweight carbon foam–carbon nanotube/carbon nanofiber nanocomposites that are synthesized in a two-step robust process including a simple carbonization of open-pore structure melamine foams and subsequent growth of carbon nanotubes/nanofibers by chemical vapor deposition are demonstrated.
Abstract: High-performance electromagnetic interference shielding is becoming vital for the next generation of telecommunication and sensor devices among which portable and wearable applications require highly flexible and lightweight materials having efficient absorption-dominant shielding. Herein, we report on lightweight carbon foam–carbon nanotube/carbon nanofiber nanocomposites that are synthesized in a two-step robust process including a simple carbonization of open-pore structure melamine foams and subsequent growth of carbon nanotubes/nanofibers by chemical vapor deposition. The microstructure of the nanocomposites resembles a 3-dimensional hierarchical network of carbonaceous skeleton surrounded with a tangled web of bamboo-shaped carbon nanotubes and layered graphitic carbon nanofibers. The microstructure of the porous composite enables absorption-dominant (absorbance ∼0.9) electromagnetic interference shielding with an effectiveness of ∼20–30 dB and with an equivalent mass density normalized shielding ef...

93 citations

Journal ArticleDOI
TL;DR: In this paper, nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method.
Abstract: Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocata ...

58 citations

Journal ArticleDOI
TL;DR: In this paper, the template growth of tungsten carbide and sulfide on vertically aligned carbon nanotubes (CNTs) is demonstrated for a facile construction of three-dimensional electrocatalyst nanostructures.
Abstract: Direct growth of tungsten carbide and sulfide on vertically aligned carbon nanotubes (CNTs) is demonstrated for a facile construction of three-dimensional electrocatalyst nanostructures. A thin layer of tungsten was first deposited on free-standing CNT forests followed by annealing in an inert atmosphere or in the vapor of sulfur for obtaining tungsten carbide or disulfide, respectively. Besides structural characterization of the composites by means of scanning and transmission electron microscopy, Raman spectroscopy and X-ray diffraction, the produced CNT–catalyst composites are also evaluated in the hydrogen evolution reaction and compared to Pt as well as to the original and W coated CNT forests. The results indicate that the template growth of catalyst nanostructures on vertically aligned CNT forests is a suitable approach for catalytic electrode fabrication, which for example may find use in the hydrogen evolution reaction.

58 citations

Journal ArticleDOI
TL;DR: In this article, a scalable and CMOS compatible synthesis of robust diamond-like carbon (DLC) -multi-walled carbon nanotube (MWCNT) hybrid electrodes was demonstrated.
Abstract: In this study we demonstrate a scalable and CMOS compatible synthesis of robust diamond-like carbon (DLC)–multi-walled carbon nanotube (MWCNT) hybrid electrodes. MWCNTs were grown directly on top of DLC thin film electrodes by utilizing Al/Co/Fe tri-layer catalyst structure at 550 °C. The structure of the hybrid material was characterized in detail by utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman investigations and X-ray photoelectron spectroscopy (XPS). After a very simple activation step with nitric acid the material was shown to exhibit a wide stable water window, almost reversible electron transfer kinetics and high sensitivity as well as selectivity towards dopamine (DA) in the presence of ascorbic acid (AA). Thus, it can be argued that the electrochemical properties of DLC and MWCNT were combined in a unique way in this new hybrid nanomaterial. The possible reasons behind the observed behavior are discussed in considerable detail. Despite the fact that present results are valid only for this particular hybrid material synthesized under conditions described in this paper, we anticipate that by utilizing the concept of DLC–MWCNT hybrids, several other novel carbon based electrode materials may be introduced for a wide variety of electrochemical and other applications.

52 citations

Journal ArticleDOI
11 Jan 2017
TL;DR: In this paper, the structural, interfacial, optical, and transport properties of large-area MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated.
Abstract: Structural, interfacial, optical, and transport properties of large-area MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated. A relatively simple growth strategy is demonstrated here that simultaneously promotes superior interfacial and bulk MoS2 properties. Few layers of MoS2 are established using x-ray reflectivity, diffraction, ellipsometry, and Raman spectroscopy measurements. Layer-specific modeling of optical constants show very good agreement with first-principles calculations. Conductivity measurements reveal that few-layer MoS2 films are more conducting than many-layer films. Photo-conductivity measurements reveal that the sputter deposited MoS2 films compare favorably with other large-area methods. Our work illustrates that sputtering is a viable route for large-area device applications using transition metal dichalcogenides.

50 citations


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01 Nov 2000
TL;DR: In this paper, the authors compared the power density characteristics of ultracapacitors and batteries with respect to the same charge/discharge efficiency, and showed that the battery can achieve energy densities of 10 Wh/kg or higher with a power density of 1.2 kW/kg.
Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

2,437 citations

Journal ArticleDOI
TL;DR: Various cocatalysts, such as the biomimetic, metal-based,Metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area.
Abstract: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

1,365 citations

Journal ArticleDOI
TL;DR: In this Review, recent progress in the synthesis and electrochemical application of transition metal carbides and nitrides for energy storage and conversion is summarized andvantages and benefits of nanostructuring are highlighted.
Abstract: High-performance electrode materials are the key to advances in the areas of energy conversion and storage (e.g., fuel cells and batteries). In this Review, recent progress in the synthesis and electrochemical application of transition metal carbides (TMCs) and nitrides (TMNs) for energy storage and conversion is summarized. Their electrochemical properties in Li-ion and Na-ion batteries as well as in supercapacitors, and electrocatalytic reactions (oxygen evolution and reduction reactions, and hydrogen evolution reaction) are discussed in association with their crystal structure/morphology/composition. Advantages and benefits of nanostructuring (e.g., 2D MXenes) are highlighted. Prospects of future research trends in rational design of high-performance TMCs and TMNs electrodes are provided at the end.

971 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the surface modification of TiO2 for photocatalytic CO2 reduction, including impurity doping, metal deposition, alkali modification, heterojunction construction and carbon-based material loading, is presented.

930 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the fundamentals of water electrolysis, current popular electrocatalysts developed for cathodic hydrogen evolution reaction and anodic oxygen evolution reaction (OER), and strategies to improve catalytic activity, long-term durability and endurance to electrochemical erosion.
Abstract: Hydrogen is an ideal candidate for the replacement of fossil fuels in the future due to zero emission of carbonaceous species during its utilization. Water electrolysis is a dependable link of primary renewable energy and stable hydrogen energy. In this work, the fundamentals of water electrolysis, current popular electrocatalysts developed for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in liquid electrolyte water electrolysis are reviewed. The main HER catalysts include noble metals, non-noble metals and composites, noble metal-free alloys, metal carbides, chalcogenides, phosphides and metal-free materials while the OER catalysts are focused on efficient Co-based, Ni-based materials and layered double hydroxide (LDH) materials. The strategies to improve catalytic activity, long-term durability and endurance to electrochemical erosion are introduced. The main challenges and future prospects for the further development of electrodes for water electrolysis are discussed. It is expected to give guidance for the development of novel low-cost nanostructured electrocatalysts for electrochemical water splitting.

747 citations