Papers by Dijana Simkunaite
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
International Journal of Hydrogen Energy, Dec 1, 2018
This work presents the study of catalytic activity of the fiber-shaped Co decorated with low amou... more This work presents the study of catalytic activity of the fiber-shaped Co decorated with low amounts of Au or Pt nanoparticles for the hydrolysis of sodium borohydride in alkaline conditions. The morphology, structure and composition of the prepared catalysts were examined using Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Optical Emission Spectroscopy. It was found that the decoration of the fiber-shaped Co with the Au or Pt nanoparticles allows enhancing of catalytic activity for the hydrolysis of sodium borohydride, compared with that of the pure fiber-shaped Co.
Meeting abstracts, Nov 23, 2020
In this study, we report a facile electrochemical approach for fabrication of flexible catalysts ... more In this study, we report a facile electrochemical approach for fabrication of flexible catalysts for the electro-oxidation of hydrazine with the aim to use them as the anode material in direct hydrazine fuel cells (DHFCs). A fiber-shaped cobalt coating has been electroplated on the copper coated polyimide surface (labeled as Cofiber/Cu/PI) using the electrolyte containing CoSO4, NaOH and N-(2-Hydroxyethyl) ethylenediamine. For comparison, the cobalt layer that has the smooth structure has been also electrodeposited on the flexible Cu/PI surface (labeled as Cosmooth/Cu/PI). Additionaly, the fabricated flexible catalysts have been decorated with gold (Au), manganese (Mn) or gold-manganese (AuMn) nanoparticles via electrochemical deposition. The morphology, structure and composition of the fabricated flexible catalysts have been characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and inductively coupled plasma optical emission spectroscopy. The activity of catalysts has been investigated with respect to the electro-oxidation of hydrazine in an alkaline medium using cyclic voltammetry and chrono-techniques. It was found that the deposition of Au, Mn or AuMn nanoparticles on Cofiber/Cu/PI and Cosmooth/Cu/PI results in significantly enhanced electrocatalytic activity of Cofiber/Cu/PI and Cosmooth/Cu/PI towards the electro-oxidation of hydrazine. Moreover, the prepared flexible catalysts seem to be a promising anode material for DHFCs.
Chemija, Sep 24, 2019
The graphene (GR) supported platinum-tungsten (PtW) catalysts with Pt:W molar ratios, equal to 1.... more The graphene (GR) supported platinum-tungsten (PtW) catalysts with Pt:W molar ratios, equal to 1.6:1, 2.3:1 and 7.1:1, were prepared by a rapid microwave-assisted heating method. The activity of the catalysts was investigated for the electro-oxidation of methanol in an alkaline medium by means of cyclic voltammetry (CV) and chronoamperometry (CA). It has been determined that the rate of methanol oxidation depends on the Pt:W molar ratio in the PtW/GR catalysts. From the CV measurements it follows that the highest current density values, specific and mass activities are obtained for the PtW/GR catalyst with the Pt:W molar ratio equal to 1.6:1. Similarly, the chronoamperometry measurements point to the best performance of the PtW/GR catalyst with the same Pt:W molar ratio. Moreover, in all cases the synthesized PtW/GR catalysts, regardless of different Pt:W molar ratio, show an enhanced electrocatalytic activity towards the direct electro-oxidation of methanol when compared with that for the bare Pt/GR and W/GR catalysts.
Journal of Solid State Electrochemistry, Jul 26, 2005
The early stages of Cu electrodeposition onto Pt(poly) have been investigated in 0.5 M H 2 SO 4 +... more The early stages of Cu electrodeposition onto Pt(poly) have been investigated in 0.5 M H 2 SO 4 + 0.01 M CuSO 4 solution without or with H 2 SeO 3 when a molar concentration ratio [Cu(II)]/ [Se(IV)] ‡ 2•10 2 using electrochemical and ex situ AFM techniques. The overpotential deposition of Cu has been performed onto a Pt surface precovered independently with Cu in amount close to an equivalent monolayer. Chronoamperometric results have been shown to follow an instantaneous 3D nucleation and diffusion-controlled growth model. The values of diffusion coefficient D for Cu 2+ , number of nuclei N and average nuclei radius r av have been calculated. In the local regions of the surface, the separate large agglomerates composed of the different diameter clusters have been revealed in both cases, but, in the presence of the H 2 SeO 3 , they attained a distinct chain-like configuration. Some morphological characteristics have been reported.
Meeting abstracts, May 1, 2020
Herein, the electrochemical oxidation of glucose has been investigated on the Co and CoB alloy co... more Herein, the electrochemical oxidation of glucose has been investigated on the Co and CoB alloy coatings, which were deposited on the copper substrate (Cu) and subsequently modified with a small amount of Au nanocrystallites (termed as the AuCo/Cu and AuCoB/Cu catalysts), with the aim to use them as the anode catalysts for direct glucose fuel cells (DGFCs). The catalysts have been prepared via a simple electroless Co deposition method followed by a spontaneous Au galvanic displacement from the Au(III)-containing solution. The activity of the prepared catalysts for the oxidation of glucose in an alkaline medium has been examined by cyclic voltammetry and chrono-techniques. In conclusion, the Co and CoB alloy coatings, which were modified with a small amount of Au nanocrystallites in the range from 11 to 14 µg Au cm–2, exhibit a significantly higher activity for the oxidation of glucose as compared to that of bare Au, Co and CoB alloy catalysts. Furthermore, the process of glucose oxidation has been significantly shifted to more negative potential domain at the both AuCo/Cu and AuCoB/Cu catalysts, indicating the higher activity of the latter catalysts as compared to that of the unmodified Co/Cu and CoB/Cu catalysts and the bare Au electrode. In addition, approximately 22 and even 67 times higher glucose oxidation current density values have been obtained at the AuCo/Cu and AuCoB/Cu catalysts, respectively, as compared to those for the unmodified CoB/Cu and Co/Cu. The prepared AuCo/Cu and AuCoB/Cu catalysts, which have been prepared with very small amount of Au nanocrystallites, seem to be a promising anode material for DGFCs.
Elsevier eBooks, 2021
Abstract Direct hydrazine fuel cells (DHFCs) are one type of direct liquid fuel cells (DLFCs), wh... more Abstract Direct hydrazine fuel cells (DHFCs) are one type of direct liquid fuel cells (DLFCs), where hydrazine is used as a fuel. DHFCs can be operated using a non-precious metal catalyst, which potentially contributes to cost reduction of the hydrazine fuel cell technology. Despite the tremendous progress made in the development of an active catalyst for DHFCs, however, available perfect catalyst able to meet the power output requirements for commercial fuel cell vehicles is still an issue. In this chapter, we summarize the recent advances in the development of catalysts for direct hydrazine fuel cells (DHFCs). The challenges and perspectives in this field are also discussed.
Journal of The Electrochemical Society, Nov 1, 2019
Catalysts, Aug 13, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Meeting abstracts, 2014
Among chemical hydrides sodium borohydride is widely used as a source for a hydrogen generation d... more Among chemical hydrides sodium borohydride is widely used as a source for a hydrogen generation during its catalytic hydrolysis. This attention is determined by its features such as a high hydrogen storage capacity, nontoxicity, good storability, easily controlled hydrogen generation rate. The development of new catalysts with high activity in the hydrolysis reaction of borohydride and durability plays an important role in the hydrogen generation for fuel cells. This work presents the study of catalytic activity of cobalt with a fiber structure deposited on the copper surface and modified with gold nanoparticles towards the hydrolysis of borohydride. Cobalt coatings with the thickness of ~3 µm were deposited from the electrolyte described in Ref. [1]. Au crystallites were deposited on the Co/Cu surface (denoted as Au(Co)/Cu) via the galvanic displacement technique. The Co/Cu catalysts were immersed into the 1 mM HAuCl4 + 0.1 M HCl solution at 25 oC for 0.5, 1 and 5 min, respectively [2]. The morphology, structure and composition of the prepared catalysts were examined by means of Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray diffraction and Inductively Coupled Plasma Optical Emission Spectroscopy. It has been determined that the Au loadings were 10.8, 22.4 and 84.4 µg cm-2 in the prepared Au(Co)/Cu catalysts after the immersion of Co/Cu into the gold-containing solution for 0.5, 1 and 5 min, respectively. The data of hydrogen generation from an alkaline sodium borohydride solutions using the Co/Cu and different Au(Co)/Cu catalysts under various conditions are presented. It has been determined that the temperature and amount of catalysts have exceptional influence on the rate of hydrogen generation from alkaline sodium borohydride solutions. References [1] E. Juzeliunas, S. Lichusina. Patent of the Republic of Lithuania No. 5481 26.03.2008. [2] L. Tamasauskaite-Tamasiunaite, A. Jagminiene, A. Balciunaite, A. Zabielaite, J. Vaiciuniene, A. Selskis, R. Juskenas, E. Norkus. Int. J. Hydrogen Energy 38 (2013) 14232-14241.
Meeting abstracts, 2014
In the present study the Co sublayers with different structures were used for the deposition of A... more In the present study the Co sublayers with different structures were used for the deposition of Au crystallites (denoted as Au(Co)/Ti). The smooth Co layer was deposited on the titanium surface via electroless deposition [1]. Cobalt coatings with a fiber structure were deposited from the electrolyte described in Ref. [2]. Au crystallites were deposited on the Co/Ti surface by immersion of Co/Ti into the 1 mM HAuCl4 + 0.1 M HCl solution at 25 oC for 0.5, 1 and 5 min, respectively [3]. The morphology, structure and composition of the prepared catalysts were examined by means of Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray diffraction and Inductively Coupled Plasma Optical Emission Spectroscopy. Electrocatalytic activity of the prepared catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry. It was found that the gold particles deposited on the cobalt with a fiber and smooth structures show enhanced electrocatalytic activity towards the oxidation of borohydride in an alkaline medium as compared to that of bare Au and Co deposited on the Ti surface with smooth and fiber structures. References [1] A. Vaskelis, A. Jagminiene, I. Stankeviciene, E. Norkus. “Electroless deposition of cobalt alloys”. US patent 7,794,530 B2 (2010). [2] E. Juzeliunas, S. Lichusina. Patent of the Republic of Lithuania No. 5481 26.03.2008. [3] L. Tamasauskaitë-Tamasiunaite, A. Jagminiene, A. Balciunaite, A. Zabielaite, J. Vaiciuniene, A. Selskis, R. Juskenas, E. Norkus. Int. J. Hydrogen Energy 38 (2013) 14232-14241.
Materials
A Pt-coated Ni layer supported on a Ni foam catalyst (denoted PtNi/Nifoam) was investigated for t... more A Pt-coated Ni layer supported on a Ni foam catalyst (denoted PtNi/Nifoam) was investigated for the electro-oxidation of the formic acid (FAO) in acidic media. The prepared PtNi/Nifoam catalyst was studied as a function of the formic acid (FA) concentration at bare Pt and PtNi/Nifoam catalysts. The catalytic activity of the PtNi/Nifoam catalysts, studied on the basis of the ratio of the direct and indirect current peaks (jd)/(jnd) for the FAO reaction, showed values approximately 10 times higher compared to those on bare Pt, particularly at low FA concentrations, reflecting the superiority of the former catalysts for the electro-oxidation of FA to CO2. Ni foams provide a large surface area for the FAO, while synergistic effects between Pt nanoparticles and Ni-oxy species layer on Ni foams contribute significantly to the enhanced electro-oxidation of FA via the direct pathway, making it almost equal to the indirect pathway, particularly at low FA concentrations.
Pt-coated Ni layer supported on Ni foam catalyst (denoted PtNi/Nifoam) was investigated for the o... more Pt-coated Ni layer supported on Ni foam catalyst (denoted PtNi/Nifoam) was investigated for the oxidation of the formic acid (FAO) in acidic media. The prepared PtNi/Ni foam catalyst was studied as a function of the formic acid (FA) concentration at bare Pt and PtNi/Nifoam catalysts. The catalytic activity of the PtNi/Nifoam catalysts, studied on the basis of the ratio of the direct and indirect current peaks (jd)/(jnd) for the FAO reaction, showed values about 10 times higher compared to those on bare Pt, particularly at a low formic acid concentrations, reflecting the superiority of the former catalysts for the oxidation of FA to CO2. Ni foams provide a large surface area for the FOR while synergistic effects between Pt nanoparticles and Ni-oxy species layer on Ni foams contribute significantly to the enhanced oxidation of FA via the direct pathway, making it almost equal to the indirect pathway, particularly at low formic acid concentrations.
Materials
This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN)... more This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN) using annealing, microwave-assisted and hydrothermal syntheses, and their employment in hydrogen and oxygen evolution (HER and OER) reactions. Composition, surface morphology, and structure were examined using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of Co-modified gCN composites for the HER and OER were investigated in an alkaline media (1 M KOH). Compared to the metal-free gCN, the modification of gCN with Co enhances the electrocatalytic activity towards the HER and OER. Additionally, thermal annealing of both Co(NO3)2 and melamine at 520 °C for 4 h results in the preparation of an effective bifunctional Co3O4/gCN catalyst for the HER with the lower Eonset of −0.24 V, a small overpotential of −294.1 mV at 10 mA cm−2, and a low Tafel slope of −29.6 mV dec−1 in a 1.0 M KOH solution and for the OER...
This study presents the synthesis of graphitic carbon nitride (g−C3N4) and its nanostructures wit... more This study presents the synthesis of graphitic carbon nitride (g−C3N4) and its nanostructures with cobalt ferrite oxide (CoFe2O4) and silver nanocubes (Ag) using the combined pyrolysis of melamine and polyol method. The resulted nanostructures were tested as electrocatalysts for hydrogen and oxygen evolution reactions in alkaline media. It was found that the Ag/CoFe2O4/g−C3N4 shows the highest current density and gives the lowest overpotential of −259 mV for HER to reach a current density of 10 mA cm−2 in 1 M KOH. Overpotentials to reach the current density of 10 mA·cm−2 for OER are 370.2 mV and 382.7 mV for Ag/CoFe2O4/g−C3N4 and CoFe2O4/g−C3N4, respectively. The above results demonstrate that CoFe2O4/g−C3N4 and Ag/CoFe2O4/g−C3N4 materials could act as a bifunctional catalyst due to the notable performance towards HER and OER and for total water splitting in practical applications is a promising alternative to noble metal-based electrocatalysts.
Materials
Herein, we present a synthesis route for high-efficiency nitrogen-doped carbon materials using kr... more Herein, we present a synthesis route for high-efficiency nitrogen-doped carbon materials using kraft pulping residue, black liquor, and wood charcoal as carbon sources. The synthesized nitrogen-doped carbon materials, based on black liquor and its mixture with wood charcoal, exhibited high specific surface areas (SSAs) of 2481 and 2690 m2 g−1, respectively, as well as a high volume of mesopores with an average size of 2.9–4.6 nm. The nitrogen content was approximately 3–4 at% in the synthesized nitrogen-doped carbon materials. A specific capacitance of approximately 81–142 F g−1 was achieved in a 1 M Na2SO4 aqueous solution at a current density of 0.2 A g−1. In addition, the specific capacitance retention was 99% after 1000 cycles, indicating good electrochemical stability.
Chemija, 2019
The electrochemical oxidation of glucose was investigated on the Co and CoB alloy coatings, which... more The electrochemical oxidation of glucose was investigated on the Co and CoB alloy coatings, which were deposited on the copper substrate (Cu) and subsequently modified with a small amount of Au nanocrystallites. The catalysts were prepared via a simple electroless Co deposition method followed by a spontaneous Au galvanic displacement from the Au(III)-containing solution. The activity of Co and CoB alloy coatings modified with Au crystallites towards the oxidation of glucose was examined by the cyclic voltammetry method. It has been determined that the Co and CoB alloy coatings, which were modified with a small amount of Au crystallites, exhibit a significantly higher activity for the oxidation of glucose as compared to that of bare Au, Co and CoB alloy catalysts. The process of glucose oxidation is significantly shifted to a more negative potential domain at the both Co/Cu and CoB/Cu catalysts modified by Au nanocrystallites, indicating the higher activity of those catalysts as com...
Bulletin of Electrochemistry, 2002
The formation of Cu adlayers and the initial stages of Cu deposition from 0.5 M H 2 SO 4 + 0.01 M... more The formation of Cu adlayers and the initial stages of Cu deposition from 0.5 M H 2 SO 4 + 0.01 M CuSO 4 solution onto a bare and Se-modified smooth polycrystalline Pt electrodes have been studied by cyclic voltammetry andpotentiostatic step techniques. It has been obtained with the Se-modified Pt electrode that the specific voltammetric pattern of Cu UPD observed for the bare Pt electrode disappeared and a new current peak at potentials much closer to bulk Cu deposition was formed. In this regard, the results obtained agree well with those reported earlier in the case of more dilute CuSO 4 solution. It has been established that, at potentials more negative than the equilibrium potential for the couple Cu/Cu 2 + , the initial stages of Cu deposition onto the bare Pt and Se-modified Pt electrodes occurred likely through the instantaneous 3D nucleation and growth under diffusion control model by Scharifker and Hills. For the deposition of Cu onto the Se-modified Pt electrode, the inte...
Chemija, 2020
State Research Institute Center for Physical Sciences and Technology, 3 Saulėtekio Avenue, 10257 ... more State Research Institute Center for Physical Sciences and Technology, 3 Saulėtekio Avenue, 10257 Vilnius, Lithuania In this study, the carbon powder supported gold nanoparticles composites (AuNPs/C) were prepared via the chemical reduction method by employing sodium citrate or a complex mixture of glucose and ascorbic acid as reducing agents in the presence of small amounts of different halide ions (Cl–, Br–, I–). The electrocatalytic activity of the synthesized composites was evaluated for the electro-oxidation of glucose in an alkaline medium using cyclic voltammetry, whereas the morphology and composition of composites were characterized using field emission scanning electron microscopy and inductively coupled plasma optical emission spectroscopy. The electrochemical measurements demonstrate the enhanced electrocatalytic performance of the AuNPs/C composites prepared by the help of different reducing agents coupled with halide ions for the electro-oxidation of glucose as compared...
ECS Meeting Abstracts, 2020
In this study, MnOx modified fiber-shaped Co nanocomposites have been fabricated via electrochemi... more In this study, MnOx modified fiber-shaped Co nanocomposites have been fabricated via electrochemical deposition with the aim to use them as electrocatalysts in direct hydrazine fuel cells (DHFCs). The electrocatalytic activity of the MnOx modified fiber-shaped Co nanocomposites towards the electro-oxidation of hydrazine in an alkaline medium has been investigated using cyclic voltammetry and chrono-techniques. Scanning Electron Microscopy, X-ray diffraction and Inductively Coupled Plasma Optical Emission Spectroscopy have been used for the characterization of the surface morphology, structure and composition of the prepared catalysts. It was found that the MnOx modified fiber-shaped Co nanocomposites have significantly higher catalytic activity towards the electro-oxidation of hydrazine as compared to that of the bare fiber-shaped Co. Moreover, modification of the fiber-shaped Co coating with MnOx leads to the rather pronounced shift in the hydrazine electro-oxidation potential to m...
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Papers by Dijana Simkunaite