Electrocatalysis最新文献

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.

Graphical Abstract

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.

Graphical Abstract

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.

Graphical Abstract

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.

Graphical Abstract

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.

Nitrobenzene(NB) is frequently utilized in the production of numerous products and aromatic compounds. Highly toxic nitrobenzene (NB) and its derivatives mix with water resources and cause various serious effects on human health and the environmental ecosystem. It is vital to accurately detect highly dangerous aromatic nitro compounds in the water medium for the sake of safeguarding both human health and environmental safety. Hence, the detection of NB and its derivatives is one focus of electrochemical sensor development. In this work, a sensitive NB sensor has been developed using Ag-CuSe composite. The prepared Ag-CuSe composite modified with a glassy carbon electrode (GCE) has been used for the detection of NB and real sample analysis. In addition, the morphology, crystallinity, and functionality of the Ag-CuSe composite have been determined by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and elemental mapping. The electrocatalytic reduction mechanism and kinetic parameters of the NB at the GCE/Ag-CuSe electrode have been evaluated by cyclic voltammetry, differential pulse voltammetry, and amperometry in 0.05 M phosphate buffer solution (pH 7.0). The GCE/Ag-CuSe-modified electrode exhibited excellent electrochemical activity toward the detection of NB with a low limit of detection (S/N = 3) of 0.01 µM, good sensitivity of 3.64 µA µM⁻¹ cm⁻², and a linear response range of 0.1 to 400 µM. Moreover, the Ag-CuSe-modified electrode has excellent selectivity, repeatability, reproducibility, and anti-interference ability, as well as good stability. The prepared GCE/Ag-CuSe electrode has been successfully applied to the removal of pollutants from various real water samples with good recovery results. The proposed GCE/Ag-CuSe electrode has been used for the trace-level detection of nitrobenzene in environmental samples.

The high cost of catalyst materials suitable for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWE) is still a major hurdle that needs overcoming before commercial PEMWE can have a meaningful impact as a technology in the hydrogen economy. Metal oxides based on precious metals are currently still the most reliable and most used materials as catalysts in PEMWE; however, alternative or modified materials are desirable to help reduce the cost associated with the catalyst component. In this study, we report on binary metal oxide catalysts based on Ru and Ni. Ni-based electrodes are typically used in alkaline water electrolyzers due to their high performance, robustness and low cost; however, Ni and NiO electrodes do not show promising performance in acidic environments due to corrosion. By combining NiO with acid stable RuO₂, we have demonstrated that the performance of the RuO₂ catalyst can be improved and due to the lower cost of Ni, the cost of the catalyst can ultimately be reduced. The Ni addition was limited to 10 mol% to achieve improved OER performance followed by noticeable performance degradation as the Ni composition was increased. The metal oxide catalysts were synthesized via a modified Adams fusion method that produced nano-sized catalysts with superior performance compared to a state-of-art commercial RuO₂ catalyst. Physical characterizations were performed via high-resolution transmission electron microscopy, X-ray diffraction, energy dispersive X-ray, and Brunauer Emmett Teller analyses. OER performances were evaluated via cyclic voltammetry, linear sweep voltammetry, chronopotentiometry, and chronoamperometry analyses.

Graphical Abstract

The low-cost and high-performance electrocatalysts, especially metal (oxy)hydroxides, for the oxygen evolution reaction (OER) have attracted considerable attention due to their promising OER activity. Amorphous electrocatalysts are often superior to their crystalline counterparts due to their more actives and structural flexibility. However, using traditional preparation techniques still presents a significant barrier. Herein, the amorphous NiFe (oxy)hydroxides on nickel foam (NF) with large surface area and small charge transfer resistance were fabricated by electrodeposition technique. The as-fabricated NiFe (oxy)hydroxides (Ni:Fe = 1:3) exhibited remarkable electrocatalytic activity and stability for OER with a low overpotential of 245 mV at a current density of 100 mA cm^–2, a small Tafel slope of 76.9 mV dec⁻¹, which was superior to that of noble metal electrocatalysts (RuO₂) and most NiFe-based electrocatalysts. This work provides a facile and effective way to synthesis metal (oxy)hydroxide catalysts towards high-efficiency water splitting.