RESUMEN
Due to their low cost and excellent electrocatalytic performance, nickel-based hydroxides are widely used as hydrogen evolution catalysts for large-scale hydrogen production by water electrolysis. In this study, a heterostructured composite with improved electron transport and modulated electron surface density was prepared by combining Ni(OH)2 with two-dimensional layered Ti3C2Tx (Ti3C2Tx-MXene). Ni(OH)2 nanosheets were formed on nickel foam (NF) substrates using acid etching, followed by the longitudinal growth of negatively charged Ti3C2Tx-MXene on positively charged Ni(OH)2/NF via electrophoretic deposition. The resulting structure facilitates spontaneous electron transfer from Ti3C2Tx-MXene to Ni(OH)2/NF by means of the Mott-Schottky heterostructure effect and establishes a continuous electron transport path which effectively increases the concentration of active sites, improving hydrogen evolution during water electrolysis. The obtained electrode is characterized by an HER overpotential of 66 mV (vs. RHE) and a Tafel slope of +105 mV dec-1 at a current density of 10 mA cm-2, combined with good electrochemical stability.
RESUMEN
Metals and their compounds effectively suppress the polysulfide shuttle effect on the cathodes of a lithium-sulfur (Li-S) battery by chemisorbing polysulfides and catalyzing their conversion. However, S fixation on currently available cathode materials is below the requirements of large-scale practical application of this battery type. In this study, perylenequinone was utilized to improve polysulfide chemisorption and conversion on cobalt (Co)-containing Li-S battery cathodes. According to IGMH analysis, the binding energies of DPD and carbon materials as well as polysulfide adsorption were significantly enhanced in the presence of Co. According to in situ Fourier transform infrared spectroscopy, the hydroxyl and carbonyl groups in perylenequinone are able to form O-Li bonds with Li2Sn, facilitating chemisorption and catalytic conversion of polysulfides on metallic Co. The newly prepared cathode material demonstrated superior rate and cycling performances in the Li-S battery. It exhibited an initial discharge capacity of 780 mAh g-1 at 1 C and a minimum capacity decay rate of only 0.041% over 800 cycles. Even with a high S loading, the cathode material maintained an impressive capacity retention rate of 73% after 120 cycles at 0.2 C.
RESUMEN
The development of electrode materials with abundant active surface sites is important for large-scale hydrogen production by water electrolysis. In this study, Fe/Ni NWs/NF catalysts were prepared by hydrothermal and electrochemical deposition of iron nanosheets on nickel chain nanowires, initially grown on nickel foam. The synthesized Fe/Ni NWs/NF electrode possessed a 3D layered heterostructure and crystalline-amorphous interfaces, containing amorphous Fe nanosheets, which demonstrated excellent activity in the oxygen evolution reaction (OER). The newly prepared electrode material has a large specific surface area, and its electrocatalytic performance is characterized by a small Tafel slope and an oxygen evolution overpotential of 303 mV at 50 mA cm-2. The electrode was highly stable in alkaline media with no degradation observed after 40 h of continuous OER operation at 50 mA cm-2. The study demonstrates the significant promise of the Fe/Ni NWs/NF electrode material for large-scale hydrogen production by water electrolysis and provides a facile and low-cost approach for the preparation of highly active OER electrocatalysts.
RESUMEN
Electrolysis of seawater using solar and wind energy is a promising technology for hydrogen production which is not affected by the shortage of freshwater resources. However, the competition of chlorine evolution reactions and oxygen evolution reactions on the anode is a major obstacle in the upscaling of seawater electrolyzers for hydrogen production and energy storage, which require chlorine-inhibited oxygen evolution electrodes to become commercially viable. In this study, such an electrode was prepared by growing δ-MnO2 nanosheet arrays on the carbon cloth surface. The selectivity of the newly prepared anode towards the oxygen evolution reaction (OER) was 66.3% after 30 min of electrolyzer operation. The insertion of Fe, Co and Ni ions into MnO2 nanosheets resulted in an increased number of trivalent Mn atoms, which had a negative effect on the OER selectivity. Good tolerance of MnO2/CC electrodes to chlorine evolution in seawater electrolysis indicates its suitability for upscaling this important energy conversion and storage technology.
RESUMEN
Rational design and synthesis of high-performance electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are critical for practical application of Zn-air batteries (ZABs). In this work, the bifunctional composite Cu-Fe2O3/PNC was prepared by a simple and effective wet-hydrothermal coupled dry-annealing synthesis strategy. The Cu-Fe2O3/PNC displayed excellent catalytic activity in ORR and OER with a potential difference of 0.63 V. More importantly, the ZAB assembled with Cu-Fe2O3/PNC exhibited a high-power density of 138.00 mW cm-2 and an excellent long-term cyclability. X-ray photoelectron spectroscopy (XPS) demonstrated that the excellent performance is due to the strong electronic interaction between Cu and Fe2O3 that arises as a result of the fast electron transfer through the Cu-O-Fe bond and the higher concentration of surface oxygen vacancies. Meanwhile, the spillover factor Bsp/2zF of Cu/PNC and Cu-Fe2O3/PNC obtained by the rotating disk experiment was 1.00 × 10-7 and 1.10 × 10-7 cm2·s-1, respectively, indicating that the oxygen spillover effect between Cu and Fe2O3 lowers the energy barrier, increases the number of active sites, and alters the rate-determining reaction step. This work demonstrated the significant potential of Cu-Fe2O3/PNC in energy conversion and storage applications, providing a new perspective for the rational design of bifunctional electrocatalysts.
RESUMEN
Since urea is commonly present in domestic sewage and industrial wastewater, its use in hydrogen production by electrolysis can simultaneously help in water decontamination. To achieve this goal, the development of highly active and inexpensive urea electrolysis catalysts is necessary. This study deals with the preparation of multilayered nickel and copper phosphides/phosphates (NiCu-P/NF and NiCu-Pi/NF) supported on Ni foam (NF) and their application as new electrocatalyst types for the electrolysis of urea-containing wastewaters. In these materials, Cu atoms induce the formation of multilayer nanostructures and modulate electron distribution, allowing for the exposure of additional active sites and acceleration of the process kinetics. NiCu-P/NF is used as a cathode and NiCu-Pi/NF as an anode in an electrolysis cell and exhibits significant catalytic activity and stability in the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER). The NiCu-Pi/NF||NiCu-P/NF electrolysis cell, operating with an alkaline urea-containing aqueous electrolyte, achieves a current density of 10 mA cm- at a potential of 1.41 V, which is less than required by the RuO2||Pt/C cell utilizing commercial noble metal-based electrodes. The study provides a novel strategy for designing efficient catalysts to produce hydrogen by urea electrolysis.
RESUMEN
The development of multi-component bi-functional electrocatalysts is necessary for commercialization of high-performance zinc-air batteries. Herein, foamed carbon-supported nickel-iron oxides interspersed with bamboo-like carbon nanotubes are prepared as bi-functional electrocatalysts for this battery type. During high temperature synthesis, edges of carbon sheets comprising the foamed carbon structure become involuted to form short carbon nanotubes. The composite of carbon nanotubes and network carbon confer high specific surface area and high electrical conductivity on the newly prepared materials. The supported NiFe2 O4 phase improves the oxygen reduction reaction (ORR) activity by fixing more N atoms, and high-valent Ni oxide (Ni2 O3 ) promotes the formation of OO bonds, which is conducive to the oxygen evolution reaction (OER). The optimized material exhibits excellent bi-functional electrocatalytic activity toward both ORR and OER, and its use in the assembled zinc-air battery cell results in a high power density of 150 mW cm-2 with long discharge stability.
RESUMEN
Metal substrates are frequently used as current collectors and supports for electrochemically active materials, but their effect on the physical and electrochemical performance of electrocatalysts is rarely investigated. In this study, the electrodeposition method was used to coat four different metal meshes with three-dimensional nickel porous structures using hydrogen bubbles as a template. The significant influence of the metal substrates on the morphology of deposited nickel was demonstrated. 3D porous structures formed on nickel, iron, copper, and titanium meshes via the hydrogen bubble template method varied significantly. It was found that differences in the physical adsorption of hydrogen and electrochemical hydrogen evolution on metal substrates are the fundamental reasons behind the diverse morphology of the coatings. Lattice matching of the substrate and the active material also plays an important role during the electrodeposition process. Electrocatalytic performance of the newly prepared materials in water electrolysis was evaluated using the hydrogen and oxygen evolution reactions (HER and OER). The results demonstrate the high electrocatalytic activity of Ni/FeM in the OER and HER, and the good stability of Ni/TiM in HER.
RESUMEN
Porous carbon-supported transition metals and their compounds have attracted much attention as sulfur host materials for cathodes of lithium-sulfur batteries, due to their high chemisorption capacity and ability to catalyze the conversion of polysulfides. However, actual activity of these materials is not very high because of low specific surface areas of transition metal compounds synthesized at high temperatures. In this study, ultra-fine vanadium nitride particles with an average particle size of ca. 4 nm (VN/M/NC) are successfully grown on the surface of nitrogen-doped three-dimensional carbon using sp2 nitrogen atoms, resulting from melamine pyrolysis in the presence of ammonium metavanadate, as anchor points to lock vanadium atoms in the VN/M/NC material. When used as a cathode for lithium-sulfur battery, VN/M/NC demonstrates initial discharge specific capacity of 1080 mAh g-1 at 0.2 C, and retains a discharge capacity of 475 mAh g-1 at a high rate of 2 C. With capacity attenuation of only 0.037% per cycle after 500 cycles at 1 C, the newly obtained VN/M/NC can be a promising cathode material for lithium-sulfur batteries.
RESUMEN
Effective fabrication of electrocatalysts active in anchoring and converting lithium polysulfides is critical for the manufacturing of high-performance lithium-sulfur batteries (LSBs). In this study, original Fe3O4 nanospheres with diameters close to 12 nm were finely dispersed over a porous nitrogen-doped carbon matrix by the freeze-drying method to produce a three-dimensional composite material (nano-Fe3O4/PNC) suitable for application as a sulfur host in LSBs. Nano-Fe3O4/PNC loaded with sulfur (S@nano-Fe3O4/PNC) was used as a cathode in a Li-S cell, whose initial discharge specific capacity reached 1256 mA h g-1 at a 0.1 C rate. After 100 charge-discharge cycles at a 0.2 C rate, the reversible capacity of S@nano-Fe3O4/PNC remained at 745 mA h g-1, demonstrating a capacity retention rate of 70%. Importantly, a high Coulombic efficiency of more than 99% was achieved, indicating effective inhibition of the polysulfides' "shuttle effect" by nano-Fe3O4/PNC. The use of electrolytes containing lithium nitrate further reduces the "shuttle effect" of polysulfides. This study demonstrates the synergistic effect between metal oxide nanoparticles and N-doped carbon, which plays an important role in promoting the adsorption and conversion of polysulfides in LSBs.
RESUMEN
Hydrogen generation by water splitting using various renewable energy sources will play an important role in the sustainable green energy supply of the future. Unfortunately, wide industrial adoption of this process is currently impeded by the necessity to use noble metal based electrolysis catalysts. In this study, a low-cost and highly efficient water electrolysis catalyst active in the hydrogen evolution reaction (HER) taking place in alkaline medium is developed. The catalyst preparation procedure consists of electrodeposition of a rough nickel layer onto a smooth copper mesh, followed by the growth of hierarchical Ni nanowires on its surface. The rough nickel layer provides plenty of active sites for nanowire formation, resulting in a synergetic effect between copper and nickel in the copper mesh supported nickel nanowire array, which effectively enhances the HER electrocatalytic performance of this novel material. The catalyst demonstrated an HER overpotential as low as 317 mV in 1 M KOH electrolyte at a current density of 1 A cm-2. The copper substrate's superior electrical conductivity to that of nickel is responsible for the excellent HER performance of the catalyst at high current density, making it a promising candidate to replace highly expensive noble metal based electrodes.
RESUMEN
Urea electrolysis is a promising hydrogen generation and urea-rich wastewaters treatment technology, which requires the development of highly active electrocatalysts. In this study, porous hetero-structured nanosheet electrocatalyst (NiO/Ni2P/NF), composed of crystalline NiO and Ni2P, is prepared via the in-situ acid etching and gas-phase phosphating method, and the obtained NiO/Ni2P/NF material is applied as efficient urea oxidation and hydrogen evolution catalyst for the overall splitting of urea-containing wastewaters. An electrolyzer containing NiO/Ni2P/NF||NiO/Ni2P/NF electrode pair in an alkaline urea aqueous solution requires a potential of just 1.457 V to reach a current density of 10 mA cm-2, lower than that of 1.490 V needed for a Pt/C/NF||RuO2/NF electrolyzer to operate under the same current density. The study demonstrates the synergistic effect between NiO/Ni2P nanosheets as well as their uniform pore structure formed by the Kirkendall effect, resulting in enhanced electrocatalytic performance in hydrogen production by urea electrolysis.
RESUMEN
Lithium-sulfur batteries are promising secondary energy storage devices that are mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe2 nanoparticles (CoSe2 -PNC) is developed as a cathode for lithium-sulfur battery. A combination of CoSe2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6â mAh g-1 at a current density of 0.2â C. After 100â cycles, its capacity remained at 865.7â mAh g-1 thus corresponding to a capacity retention of 75.97 %. In a long-term cycling test, discharge specific capacity of 546.7â mAh g-1 was observed after 300â cycles performed at a current density of 1â C.
RESUMEN
To obtain a highly active, stable, and binder-free electrode based on transition-metal compounds for water splitting, nickel foam-supported 3D NiMoO4 nanosheet arrays modified with 0D Fe-doped carbon quantum dots (Fe-CQDs/NiMoO4 /NF) are synthesized. The structure characterizations indicated that 0D Fe-CQDs are evenly dispersed onto the NiMoO4 sheets of the arrays. The contact angle analysis confirmed that the surface hydrophilia of the arrays is improved after the 0D Fe-CQDs are deposited 3D on the NiMoO4 sheets. Here, both the activity and durability in electrochemical water splitting are significantly enhanced with the Fe-CQDs/NiMoO4 /NF catalysts. At a current density of 10â mA cm-2 , the resultant Fe-CQDs/NiMoO4 /NF revealed an overpotential of only 117â mV for the hydrogen evolution reaction (HER), a relatively low overpotential of 336â mV toward the oxygen evolution reaction (OER), and a Faraday efficiency of up to 99 %. This performance can be attributed to the unique 3D nanosheet array structure, the synergistic effect, and the optimal hydrophilia for gas evolution evolved from the electrode surface.
RESUMEN
Cost efficient bifunctional air cathodes possessing high electrocatalytic activity are of great importance for the development of secondary Zn-air batteries. In this work, cobalt nanoparticles are encapsulated within a 3D N-doped open network of carbon tubes (Co@N-CNTs) by a molten-salt synthesis procedure conducted at a high temperature. Physical characterization demonstrates that Co@N-CNTs are comprised of Co particle inserted carbon tubes with mesoporous tube walls, providing significant active surface area for electrochemical reactions. High electrocatalytic activity of Co@N-CNTs towards both oxygen evolution and oxygen reduction reactions is due to its well-developed active surface and a synergistic effect between N-doped carbon and Co nanoparticles. Both primary and secondary Zn-air battery cells assembled using Co@N-CNTs as an air cathode show higher electrochemical performance than similar cells containing commercial Pt/C and Pt/C +RuO2 , making the newly developed material a promising alternative to existing metal-based air cathodes.
RESUMEN
Porous Ni(OH)2 nanoflakes are directly grown on the surface of nickel foam supported Ni3 Se2 nanowire arrays using an in situ growth procedure to form 3D Ni3 Se2 @Ni(OH)2 hybrid material. Owing to good conductivity of Ni3 Se2 , high specific capacitance of Ni(OH)2 and its unique architecture, the obtained Ni3 Se2 @Ni(OH)2 exhibits a high specific capacitance of 1689 µAh cm-2 (281.5 mAh g-1 ) at a discharge current of 3 mA cm-2 and a superior rate capability. Both the high energy density of 59.47 Wh kg-1 at a power density of 100.54 W kg-1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni3 Se2 @Ni(OH)2 as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L-1 at a power density of 83.62 W L-1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm-2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni3 Se2 @Ni(OH)2 composite can become a promising electrode material for energy storage applications.
RESUMEN
NixCoy alloy pompoms formed by the aggregation of nano ultrathin sheets were prepared by simultaneous reduction of NiCl2 and CoCl2 with NaBH4via a liquid-liquid interface reaction. Ni1Co3 pompoms produced markedly higher activity and stability as hydrazine oxidation catalysts than Ni, Co and other NixCoy pompom catalysts.
RESUMEN
The design of amorphous noble metallic nanoparticle electrocatalysts is an important fundamental and applied research challenge because their surface is rich in low-coordination sites and defects which could act as the active sites in various catalytic processes. Here we describe new findings on the amorphous platinum-nickel-phosphorous nanoparticles supported on carbon black (PtNiP(a)/C) and the comparison between their catalytic activity and that of the nanoscale crystalline and phase-segregated PtNiP nanoparticles. The nanoscale amorphous, crystalline and phase-segregated catalysts were probed as a function of surface composition, particle size, and thermal treatment conditions using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, selected area electron diffraction and electrochemical characterization. The results provide the experimental evidence in support of nanoscale amorphous, crystalline, and phase-segregated PtNiP nanoparticles evolution dependence on the catalyst synthesis temperature. More importantly, the results of the electrochemical performance investigation showed that the amorphous structure has not only better catalytic activity for methanol oxidation but also stronger tolerance to carbon monoxide poisoning compared to the crystalline and phase-segregated structure. Besides, the thermal control of the formation of nanoscale amorphous, crystalline and phase-segregated structured catalysts provided the opportunity for establishing the correlation between the nanoscale phase structures of the catalysts and their electrocatalytic activity in methanol oxidation reaction, which plays an important role in developing highly active electrocatalysts for direct methanol fuel cells.
RESUMEN
The conjunction of the PdSn alloy and SnO2 is of interest for improving catalytic activity in formic acid oxidation (FAO). Here, we report the synthesis of PdSn-SnO2 nanoparticles and a study of their catalytic FAO activity. Different degrees of interfacial contact between SnO2 and PdSn were obtained using two different stabilizers (sodium citrate and EDTA) during the reduction process in catalyst preparation. Compared to the PdSn alloy, PdSn-SnO2 supported on carbon black showed enhanced FAO catalytic activity due to the presence of SnO2 species. It was also found that interfacial contact between the PdSn alloy and the SnO2 phase has an impact on the activity towards CO oxidation and FAO.
RESUMEN
Two structural forms of a ternary alloy PtRuIr/C catalyst, one amorphous and one highly crystalline, were synthesized and compared to determine the effect of their respective structures on their activity and stability as anodic catalysts in methanol oxidation. Characterization techniques included TEM, XRD, and EDX. Electrochemical analysis using a glassy carbon disk electrode for cyclic voltammogram and chronoamperometry were tested in a solution of 0.5 mol L-1 CH3OH and 0.5 mol L-1 H2SO4. Amorphous PtRuIr/C catalyst was found to have a larger electrochemical surface area, while the crystalline PtRuIr/C catalyst had both a higher activity in methanol oxidation and increased CO poisoning rate. Crystallinity of the active alloy nanoparticles has a big impact on both methanol oxidation activity and in the CO poisoning rate.