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Carbonization of biomass residues followed by activation has great potential to become a safe process for the production of various carbon materials for various applications. Demand for commercial use of biomass-based carbon materials is growing rapidly in advanced technologies, including in the energy sector, as catalysts, batteries and capacitor electrodes. In this study, carbon materials were synthesized from hardwood using two carbonization methods, followed by activation with H3PO4, KOH and NaOH and doping with nitrogen. Their chemical composition, porous structure, thermal stability and structural order of samples were studied. It was shown that, despite the differences, the synthesized carbon materials are active catalysts for oxygen reduction reactions. Among the investigated carbon materials, NaOH-activated samples exhibited the lowest Tafel slope values, of -90.6 and -88.0 mV dec-1, which are very close to the values of commercial Pt/C at -86.6 mV dec-1.
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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 with the onset overpotential of 286.2 mV and overpotential of 422.3 mV to achieve a current density of 10 mA cm-2 with the Tafel slope of 72.8 mV dec-1.
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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.
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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.
RESUMEN
Nitrogen-doped activated carbons with controlled micro- and mesoporosity were obtained from wood and wastes via chemical processing using pre-treatment (pyrolysis at 500 °C and hydrothermally carbonization at 250 °C) and evaluated as oxygen reduction catalysts for further application in fuel cells. The elemental and chemical composition, structure and porosity, and types of nitrogen bonds of obtained catalyst materials were studied. The catalytic activity was evaluated in an alkaline medium using the rotating disk electrode method. It was shown that an increase in the volume of mesopores in the porous structure of a carbon catalyst promotes the diffusion of reagents and the reactions proceed more efficiently. The competitiveness of the obtained carbon materials compared to Pt/C for the reaction of catalytic oxygen reduction is shown.
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In this study, NiMo catalysts that have different metal loadings in the range of ca. 28-106 µg cm-2 were electrodeposited on the Ti substrate followed by their decoration with a very low amount of Au-crystallites in the range of ca. 1-5 µg cm-2 using the galvanic displacement method. The catalytic performance for hydrogen evolution reaction (HER) was evaluated on the NiMo/Ti and Au(NiMo)/Ti catalysts in an alkaline medium. It was found that among the investigated NiMo/Ti and Au(NiMo)/Ti catalysts, the Au(NiMo)/Ti-3 catalyst with the Au loading of 5.2 µg cm-2 gives the lowest overpotential of 252 mV for the HER to reach a current density of 10 mA·cm-2. The current densities for HER increase ca. 1.1-2.7 and ca. 1.1-2.2 times on the NiMo/Ti and Au(NiMo)/Ti catalysts, respectively, at -0.424 V, with an increase in temperature from 25 °C to 75 °C.
RESUMEN
One of the methods to improve the performance of a heterogeneous electrocatalyst is the dispersion of a catalytic material on a suitable substrate. In this study, femtosecond laser ablation was used to prepare very rough but also ordered copper surfaces consisting of vertical, parallel ridges. Then, a molybdenum sulfide coating was electrochemically deposited onto these surfaces. It was observed by profilometry that the average roughness of the surface after coating with MoS2 had decreased, but the developed surface area still remained significantly larger than the projected surface area. The electrodes were then used as an electrocatalyst for the hydrogen evolution reaction in acidic media. These were highly efficient, reaching 10 mA cm-2 of HER current at a -181 mV overpotential and a Tafel slope of ~39 mV dec-1. Additionally, scanning electrochemical microscopy was used to observe whether hydrogen evolution would preferentially occur in certain spots, for example, on the peaks, but the obtained results suggest that the entire surface is active. Finally, the electrochemical impedance spectroscopy data showed the difference in the double-layer capacitance between the ablated and non-ablated surfaces (up to five times larger) as well as the parameters that describe the improved catalytic activity of fs-Cu/MoS2 electrodes.
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Six cobalt gold (CoAu) electrodes were prepared by electroless deposition using different gold-containing solutions (acidic and weakly acidic) and different Au deposition times. Characterization of CoAu electrodes was done by scanning electron microscopy with energy-dispersive X-ray spectroscopy, N2-sorption, and X-ray powder diffraction techniques. The possibility of using the prepared electrodes in environmental applications, i.e., for the electrochemical sensing of a trace amount of arsenic(iii) in weakly alkaline media was assessed. Employing the CoAu electrode (prepared by immersing Co/Cu into 1 mM HAuCl4 (pH 1.8) at 30 °C for 30 s) under optimized conditions (deposition potential -0.7 V and deposition time of 60 s), a low limit of detection of 2.16 ppb was obtained. Finally, this CoAu electrode showed activity for arsenic oxidation in the presence of Cu(ii) as a model interferent as well as in real samples. Furthermore, the use of CoAu electrode as an anode in fuel cells, namely, direct borohydride - hydrogen peroxide fuel cells was also assessed. A peak power density of 191 mW cm-2 was attained at 25 °C for DBHPFC with CoAu anode at a current density of 201 mA cm-2 and cell voltage of 0.95 V, respectively. The peak power density further increased with the increase of the operating temperature to 55 °C.
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In this study, Mn-based multicomponent catalysts supported by two different carriers (lightweight expanded clay aggregate and the Ukrainian clinoptiolite) were prepared by electroless metal deposition method and tested for the selective catalytic reduction of NO with ammonia (NH3-SCR de-NO). Prior to the activity test, all the catalysts prepared were characterized by inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray mapping, X-ray photoelectron spectroscopy, H2-TPR and NH3-TPD techniques. The particular interest of the present study was focused on the investigation of the carrier's role in the NO catalytic reduction and the promoting effect provided by the incorporation of the small amount of Pt (0.1 wt.%) in the Mn-based catalytic layer. The results revealed that the carrier's role in the NO catalytic conversion can be considered as a factor determining the effectiveness of the conversion process. Ukrainian clinoptiolite was proved to be a more attractive carrier for the preparation of the effective SCR de-NO catalysts due to its intrinsic sorption capacity, surface acidity and the redox potential. The high NO conversion efficiency provided by the Mn-based clinoptiolite-supported catalysts can be explained by the synergistic effect between the carrier and the active species deposited. It was shown that both the Mn97.6Cu2.4/clinoptiolite and the Mn97.5Co2.5/clinoptiolite catalysts can be successfully applied as the low-temperature (100-300°C) catalysts for NH3-SCR de-NO. When the NO removal efficiency varies in the range of 86-91%, the additional incorporation of Pt in the active layer in the amount of 0.1 wt.% can enhance the NO reduction by about 5% on average.
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In this study, sodium borohydride oxidation has been investigated on the platinum nanoparticles modified copper/titanium catalysts (PtNPsCu/Ti), which were fabricated by employing the electroless copper plating and galvanic displacement technique. ICP-OES, XRD, FESEM, and EDX have been used to characterize PtNPsCu/Ti catalysts' composition, structure, and surface morphology. The oxidation of sodium borohydride was examined on the PtNPsCu/Ti catalysts using cyclic voltammetry and chrono-techniques.
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In the present work, the kinetics of electroless deposition of Pt, using a cobalt ion redox system (Co3+/Co2+) as a reducing agent, has been investigated. The deposition rate of Pt depends on the pH, concentration of reactants, and temperature. The deaeration and bubbling of the plating solution with argon play an essential role. It was found that 0.11 mg cm-2 of Pt films could be deposited on the surface of a roughed glass sheet in one hour without replenishing the solution. Additional data have been obtained on the grounds of electrochemical quartz crystal microbalance experiments. The bubbling (agitation) of the electroless Pt plating solution with argon during the deposition of Pt results in a higher deposition rate and is ca. 3 µg cm-2 min-1. The Pt deposition rate is far less, and is as low as 0.14 µg cm-2 min-1 when the electroless Pt plating solution is not bubbled with argon during the deposition of Pt.
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In this work, the possibilities of increasing the rate of electroless silver plating without a rise in the concentration of reactants or elevation of temperature were studied. The effect of halide additive, namely chloride ions, on the rate of electroless silver deposition was investigated, using conventional chemical kinetics and electrochemical techniques. It was found that the deposition rate of electroless silver increased 2-3 times in the presence of 10-20 mM of chlorides, preserving sufficient stability of the solution.
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Bimetallic cobalt (Co)-based coatings were prepared by a facile, fast, and low-cost electroless deposition on a copper substrate (CoFe, CoMn, CoMo) and characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Prepared coatings were thoroughly examined for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution (1 M potassium hydroxide, KOH) and their activity compared to that of Co and Ni coatings. All five coatings showed activity for both reactions, where CoMo and Co showed the highest activity for HER and OER, respectively. Namely, the highest HER current density was recorded at CoMo coating with low overpotential (61 mV) to reach a current density of 10 mA·cm-2. The highest OER current density was recorded at Co coating with a low Tafel slope of 60 mV·dec-1. Furthermore, these coatings proved to be stable under HER and OER polarization conditions.
RESUMEN
In this recent decade, great interest has risen to develop metal-free and cheap, biomass-derived electrocatalysts for oxygen reduction reaction (ORR). Herein, we report a facile strategy to synthesize an electrochemically active nanocarbon material from the renewable and biological resource, wood biomass. The ORR activity of the catalyst material was investigated in 0.1 M KOH solution by employing the rotating disc electrode method. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy were employed to obtain more information about the catalyst material's morphology and composition. The material exhibits outstanding electrocatalytic activity with low onset potential and high current density, similar to that of a commercial Pt/C catalyst in an alkaline medium. The results clearly ascertain that wooden biomass can be easily transformed into novel carbon nanostructures with superior ORR activity and possibility to be used in fuel cells and metal-air batteries.