Electrocatalysis最新文献

The objective of this work is to employ chemometric tools to investigate the influence of the synthesis parameters in platinum electrodeposition on a titanium substrate using cyclic voltammetry. Through a 2² factorial design, using as response the maximum peak current density during the ethanol electro-oxidation, one can observe that the number of cycles and the scan rate are both significant, but the interaction between them is not. The maximum peak current density is observed for the electrode obtained with NC = 20 cycles and SR = 200 mV s⁻¹. The structural characterization indicates that the surface irregularity of the substrate causes an uneven growth of the (200) and (220) crystallographic planes, which present different performances in the electro-oxidation of ethanol. The response surface methodology indicates that the best experimental condition is that obtained with 10 cycles and 218 mV s⁻¹. The Pt/Ti electrodes prepared with the optimized parameters are promising.

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A 2² factorial design was applied to prepare Pt/Ti for ethanol eletro-oxidation. Pt electrodeposits have shown an atypical “house of cards” morphology. Preferential orientation of Pt on Ti surface are related to better activity. Response surface methodology points 10 cycles at 218 mV s⁻¹ as the best condition.

The influence of Pd nano-layers electro-deposited onto Pt(111) single crystal has been systematically studied toward the formic acid electrochemical oxidation reaction in H₂SO₄ and HClO₄. The studied Pd_xML/Pt(111) surfaces (x = 1, 2, 5, and 16 monolayers (ML)) are all more active than Pt(111) toward formic acid oxidation, even if the activity is very sensitive to the Pd film thickness and morphology. In sulfate solution, the competitive adsorption of long-range ordered (bi)sulfate on the pseudomorphic Pd terraces effectively hinders the formic acid oxidation only on the thinnest films. We could observe the different roles of the (bi)sulfate adsorption on the first and on the following deposited Pd layers. The sulfate adsorption competitive role rapidly fades away beyond about 5 ML of equivalent thickness, due to the surface roughness increasing and terraces width diminishing. In perchlorate media, anions do not adsorb competitively with formic acid intermediates, allowing a larger activity of the formic acid oxidation up to about 5 ML. At higher thicknesses, the difference in activity between the two electrolytic media is reduced, and it drops in both electrolytes close to 0.5 V vs. RHE, where Pd surface oxides are formed. Coupling the electrochemical results with the Pd layer structural description previously obtained from in situ SXRD experiments, the outstanding activity of Pd_1ML/Pt(111) observed in perchloric solution can be explained by the ligand effect of the underlying platinum atoms on the first pseudomorphic Pd layer. This advantageous effect is lost for Pd deposits thicker than 1 ML.

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The La_1.5Nd_0.3Pr_0.2NiO_4.16 material was prepared by the citrate method and used as a cathode for a solid oxide fuel cell (SOFC). The study was carried out in the presence of a thin interfacial layer composed of 50% GDC10 and 50% 8YSZ deposited on both surfaces of the GDC10 (Ce_1.9Gd_0.1O_1.95) electrolyte. The purity of the materials was studied by X-ray diffraction, while X-ray photon-electron spectrometry (XPS) was used to characterize the surface chemical state of the synthesized material; the morphology of the electrode and cross-sectional images of the cell were obtained by scanning electron microscopy (SEM). Iodometric titration has also been performed to evaluate oxygen over-stoichiometry. Cross-sectional SEM images have shown good adherence between all the cell components, and the cationic character of the cathode material was confirmed by the XPS and iodometric analysis. The use of these materials as an oxygen cathode has shown interesting electrochemical properties with an area-specific resistance (ASR) value of the order of 0.060 (Ω.cm²) at 600 °C and 0.022 (Ω.cm²) at 700 °C. The activation energy (Ea) of the LNPNO5 material is very low and is of the order of 0.96 eV.

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1. An anionic character of La_1.5Nd_0.3Pr_0.2NiO_4.16 was determined; an important property for easy displacement of oxide ions in these materials.

2. At 600 and 700 °C, the ASRs of La_1.5Nd_0.3Pr_0.2NiO_4.16 were as low as 0.06 Ω.cm² and 0.022 Ω.cm², respectively.

3. The presence of the new interfacial layer (8YSZ (50%) + GDC10 (50%) is of interest to operate at intermediate temperatures for SOFCs.

4. La_1.5Nd_0.3Pr_0.2NiO_4.16 can be qualified to be an excellent cathode material for SOFC fuel cells operating at intermediate temperatures, 600 – 700 °C.

Abstract

Surface coverages of ionomer on Pt and carbon support are key properties to clarify the ionomer distribution in cathode catalyst layer of polymer electrolyte fuel cells. However, their measurement is highly challenging especially for carbon, where Faradaic charge is not visible in voltammograms. Conventionally, the capacitance measured by voltammetry or electrochemical impedance spectroscopy is used to determine the ionomer coverage. In these methods, surface coverages are obtained by comparing the double layer capacitance at wet condition with that at dry condition; Pt and carbon surfaces covered by ionomer and water contributes to the capacitance at wet condition, while surfaces covered only by the ionomer contributes at the dry condition because of the absence of water. However, when measured capacitance is converted to surface area, the methods assume that the specific capacitance (capacitance per surface area) is independent of the humidity although it significantly changes in reality, because the double layer structure of ionomer changes. Here, we propose an alternative method that significantly suppresses the change in specific capacitance. The method was applied to porous and nonporous carbon supports with Pt nanoparticle catalyst. The measurement also indicates that the surface coverages on both Pt and carbon are reduced in the case of the porous carbon.

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In order to explore the effects of morphology, specific surface area and relative content of Cu/Cu-oxide in “CuO-derived Cu” electrocatalysts on the current density and product formation during electrochemical carbon dioxide reduction reaction (eCO₂RR), CuO electrocatalysts were synthesized via solution combustion and hydrothermal routes, possessing different morphologies. The as-synthesized CuOs were first reduced to Cu at − 0.8 V (vs. RHE), till the currents got stabilized; thus, forming “CuO-derived Cu”. Subsequently, eCO₂RR was carried out via bulk electrolysis at different potentials between − 0.6 and − 1.6 V (using 0.1 M KHCO₃ solution), leading to the formation of seven liquid/gaseous products, viz., CO, methane, ethylene, formate, acetate, and ethanol (in addition to H₂). It was interesting to note that the type of products and associated faradic efficiencies (FEs) were governed by the Cu-content of the “CuO-derived Cu” electrocatalysts (i.e., Cu:CuO ratio), as obtained post the pre-reduction step and looked into here as one of the starting conditions of the electrocatalysts. Higher initial Cu-content of the pre-reduced CuOs resulted in higher FEs at lower negative potentials. Furthermore, high Cu-content (even for simple equiaxed morphology), as opposed to any special morphology (say, rod/whisker-type), has been found to be particularly important for the formations of methane and formate; yielding a maximum FE of ~ 18.6 ± 1.2% at − 1.0 V for the latter. Accordingly, the present work reveals the relative roles of specific surface area and Cu/CuO-content of “CuO-derived Cu” electrocatalysts on the current densities, product formation and associated FEs on eCO₂RR.

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In the bipolar-type alkaline water electrolysis powered by renewable energy, electrocatalysts are degraded by repeated potential change associated with the generation of reverse current. If an electrode has large discharge capacity, the opposite electrode on the same bipolar plate is degraded by the reverse current. In this study, discharge capacity of various transition metal-based electrocatalysts was investigated to clarify the determining factors of electrocatalysts on the reverse current and durability. The discharge capacities from 1.5 to 0.5 V vs. RHE (Q_dc,0.5) of electrocatalysts are proportional to the surface area in most cases. The proportionality coefficient, corresponding to the specific capacity, is 1.0 C·m^–2 for Co₃O₄ and 2.3 C·m^–2 for manganese-based electrocatalysts. The substitution of Co³⁺ in Co₃O₄ with Ni³⁺ increased Q_dc,0.5. The upper limit of theoretical specific capacity for Co₃O₄ is estimated to be 1.699 C·m^–2, meaning the former and latter cases correspond to 2- and 1-electron reactions, respectively, per a cation at the surface. The discharge capacities of the elctrocatalysts increased because of the dissolution and recrystallization of nickel and/or cobalt into metal hydroxides. The increase in the capacities of Co₃O₄ and NiCo₂O₄ during ten charge–discharge cycles was below 2–9% and 0.5–38%, respectively. Therefore, if a cathode electrocatalyst with relatively low redox durability is used on the one side of a bipolar plate, it is necessary to control optimum discharge capacity of the anode by changing surface area and constituent metal cations to minimize the generation of reverse current.

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This paper reports the development of a simple and new photoelectrochemical (PEC) aptamer-based sensor for ultrasensitive determination of the concentration of diazinon (DZN) using the surface plasmon resonance effect (SPR) of gold nanoparticles (AuNPs) deposited on a titanium dioxide (TiO₂) film. A thin layer of flourin tin-oxide (FTO) was covered on the surface of glass plates during the spray pyrolysis process, and the resulting FTO plates were modified layer by layer with TiO₂ film and AuNPs as the photoactive nanomaterials. The AuNPs were utilized to increase the absorption rate of visible light through the formation of hot electrons. The prepared AuNPs/TiO₂ nanocomposite revealed a higher photoelectro catalytic activity compared to the pure TiO₂. In order to improve the selectivity of the proposed PEC sensor, the thiolated aptamer was conjugated to the AuNPs/TiO₂ nanocomposite through S–Au bonds. Upon exposition of the fabricated PEC apatasensor to DZN molecules, the formation of the aptamer-DZN complex restricted the electron transfer at the surface of the PEC sensor; therefore, the photocurrent signal decreased. The simultaneous usage of the PEC technique and aptamer led to the improvement of the analytical performance of the proposed sensor in terms of sensitivity, selectivity, reproducibility, and stability for the quantitative determination of diazinon with a wide linear range of 0.2 to 1000 nM and a low detection limit of 0.04 nM. In addition, the prepared PEC aptasensor was used for the determination of diazinon in water and biological samples, and satisfactory results were obtained which confirms the practical application of the proposed PEC aptasensor.

Considering the widespread use of alkaline water electrolysis (AWE) in the chemical industry and the growing need to design and manufacture low-cost and efficient electrodes, the optimization of a Ni-Mo-coated stainless steel substrate is investigated in the present work to use this substrate as a cathode of an alkaline water electrolyzer. The crystallographic structure, surface morphology, and composition of the optimized coating are characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and surface elemental mapping. The electrocatalytic activity for the hydrogen evolution reaction (HER) is evaluated by making electrochemical measurements. In addition, the optimization of the electrodeposition bath is investigated to promote the HER activity. The results show that nickel-molybdenum (1:2) alloy exhibits a higher HER activity, and a current density of 180 mA cm⁻² is achieved at −1.7 V vs. Ag/AgCl using this coating. Also, the polarization curves of the electrolysis cell demonstrate that using the optimized cathode, the cell operates at 1.9 V at a current density of 1.5 A.cm⁻² and the operating temperature of 60 °C, which is suitable for use in large-scale industrial AWE units.

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Synthetic organic dyes contaminate the aquatic environment. A fast and efficient preparation of catalysts plays a vital role in wastewater treatment to reduce costs and increase its market. In this study, we prepared different Si-rich ZSM-5 catalysts (Si/Al = 200) through the one-pot synthesis and impregnation technique that include Fe species. The catalysts were applied in heterogeneous electro-Fenton (HEF) to remove methylene blue (MB), an organic dye which is a model compound for water contaminants. The parent and modified catalysts were characterized by XRD, FT-IR, FE-SEM, NH₃-TPD, and N₂ adsorption–desorption methods. The results showed the well crystalline framework (89%), high surface area (359 m² g⁻¹), mesopore structure (0.05 cm³ g⁻¹), and uniform distribution of the Fe species. The optimum operating conditions for the [Fe]-ZSM-5 catalyst were pH = 4, applied current of 100 mA, and catalyst concentration of 0.1 g L⁻¹, which resulted in the highest MB removal (98%) in 15 min through the HEF process. The results confirm the applicability of the one-pot synthesis of the [Fe]-ZSM-5 catalyst.