Higher Anodic Current Density Research Articles

New type nanocomposite based on metal-organic frameworks decorated with nickel nanoparticles as a potent electrocatalyst for methanol oxidation in alkaline media

Methanol oxidation reaction (MOR) is used to provide electrical energy via direct methanol fuel cell (DMFC), which requires a practical design of electrocatalysts to accelerate the sluggish MOR. In this study, we successfully fabricated the carbon black nanoparticles/graphite ceramic electrode (CBNPs/GCE) supported metal-organic frameworks (MOFs) and decorated with nickel nanoparticles (NiNPs) as a new type nanocomposite modified electrode (NiNPs/MOFs/CBNPs/GCE) via a chemical and an electrochemical process, respectively. The surface morphology and structure of the synthesized nanocomposite materials and modified electrodes were characterized using field emission scanning electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. Then, the NiNPs/MOFs/CBNPs/GCE was used as a non-platinum electrocatalyst for electrocatalytic oxidation of methanol in alkaline media. The obtained results show the efficient electrocatalytic activity of the NiNPs/MOFs/CBNPs/GCE toward the MOR with high anodic peak current density (Jpa = 34.8 mA cm−2) compared with the other prepared electrocatalysts; MOFs/CCE, NiNPs/CCE, MOFs/CBNPs/GCE, NiNPs/CBNPs/GCE, and NiNPs/MOFs/CCE, due to the synergistic effect of nanocomposite components; NiNPs, MOFs and CBNPs. The prepared electrocatalyst; NiNPs/MOFs/CBNPs/GCE, not only shows a high electrochemically active surface area (ECSA = 2.15 cm2) but also has long-term durability in MOR. In general, it can be said the NiNPs/MOFs/CBNPs/GCE is a promising candidate for application in DMFC.

Effect of Cathode Rotation Speed on Mechanical Properties of Abrasive-Assisted Copper Electroforming with High Anode Current Density

Effect of Cathode Rotation Speed on Mechanical Properties of Abrasive-Assisted Copper Electroforming with High Anode Current Density

Indirect charge transfer of holes via surface states in ZnO nanowires for photoelectrocatalytic applications

In this work, ZnO nanowires with high aspect ratio were obtained by fast and simple electrochemical anodization. Morphological, structural and photoelectrochemical characteristics of the synthesized ZnO nanowires were evaluated by using different techniques: field emission scanning electron microscopy, atomic force microscopy, high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–VIS spectroscopy, Mott-Schottky analysis and photoelectrochemical impedance spectroscopy. The synthesized ZnO nanowires presented high roughness and high crystallinity. Besides, surface defects were identified in the sample. The value of the donor density (ND) was in the order of 1019 cm−3 in the dark and 1020 cm−3 under illumination. In addition, the ZnO nanowires presented good photosensibility, with a photocurrent density response 85 times higher than a ZnO compact layer, and lower resistance to charge transfer. The charge transfer processes taking place at the ZnO/electrolyte interface were studied, since these processes strongly influence the photoelectrocatalytic efficiency of the material. According to the results, the charge transfer of holes in the synthesized ZnO nanowires occurs indirectly via surface states. In this regard, surface states may be an important feature for photoelectrocatalytic applications since they could provide lower onset voltages and higher anodic current densities.

Urea Oxidation Electrocatalysis on Nickel Hydroxide: The Role of Disorder

The urea oxidation reaction (UOR) is an important challenge in electrocatalysis, in the context of electrolyzers, fuel cells, medical sensing, and bio-waste treatment. The leading electrocatalysts for the UOR are nickel hydroxide surfaces, operating by the Botte mechanism: NiII(OH)2 is oxidized to NiIIIOOH, and the latter drives the UOR. However, these materials have several polymorphs, with α- and β-Ni(OH)2, and γ- and β-NiOOH, as described by the Bode diagram. We now report a systematic study of a series of nickel hydroxides, varying gradually from α-rich to β-rich materials. The crystallinity, order, hydration, intercalation, and morphology of these materials have been characterized by XRD, Raman, ATR-FTIR, XPS, and HRSEM and linked to their electrochemical activity. The disordered α phase was found to be superior to the β phase as a UOR electrocatalyst, with an oxidation onset potential of 0.31 V vs. SCE, better reversibility, and higher anodic current densities. Moreover, the perfect match in onset potentials between UOR electrocatalysis and the Ni2+/Ni3+ oxidation was observed for both phases, suggesting that the Botte mechanism is true for both the α-Ni(OH)2/γ-NiOOH couple and the β-Ni(OH)2/β-NiOOH couple. We further characterize the dynamic behavior of these materials (activation and aging), allowing us to propose a unified Botte-Bode diagram of UOR on Ni(OH)2/NiOOH.

Assessment of the Local Mechano-Electrochemical Effect on Pipeline Defects by 2D and 3D Finite Element Models

Local corrosion at a defect on a pipeline was assessed using both 2-dimensional (2D) and 3-dimensional (3D) finite element models under mechano-electrochemical (M-E) interaction. While the M-E interaction increases corrosion activity at the defect, the assessment of M-E interaction would have different results using 2D and 3D models. Compared with the 3D model, the 2D model produces a greater local stress, a higher local plastic strain, a more negative corrosion potential and a higher anodic current density at the defect, and thus, a lower threshold internal pressure causing local yielding. The 3D model is more conservative for corrosion rate prediction of corroded pipelines. A new concept, rAZ (the ratio of the anodic zone length to defect length in the 2D model, or the ratio of the anodic zone area to the defect area in the 3D model), is proposed to define growth mode of the corrosion defect. There is a smaller rAZ produced in 2D model. At specific internal pressures, the 2D model predicts an ellipsoidal defect center area experiencing accelerated corrosion and potentially resulting in pipeline leaking.

How microstructure affects localized corrosion resistance of stir zone of the AA2198-T8 alloy after friction stir welding

In this study, the microstructure and corrosion resistance of the stir zone (SZ) of the AA2198-T8 Al-Cu-Li alloy welded by friction stir welding (FSW) were investigated by microscopy, immersion tests and electrochemical techniques such as measurements of open circuit potential variation with time, and scanning vibrating electrode technique (SVET) measurements. A low chloride-containing solution (0.005 mol L−1 NaCl) was employed in the corrosion studies and severe localized corrosion (SLC) was observed in the SZ related to intergranular attack. The results were compared to those of the non-affected areas by FSW, also known as base metal (BM). In the BM, SLC was found and the type of attack related to it was intragranular. In both zones, BM and SZ, SLC was due to precipitates of high electrochemical activity, specifically T1 (Al2CuLi) phase in the BM, whereas TB (Al7Cu4Li) / T2 (Al6CuLi3) in the SZ. Scanning vibrating electrode technique (SVET) analysis was very useful in the study of SLC in the AA2198-T8 alloy showing the development of high anodic current densities at the mouth of the SLC sites.

Urea oxidation electrocatalysis on nickel hydroxide: the role of disorder

The urea oxidation reaction (UOR) is an important challenge in electrocatalysis, in the context of electrolyzers, fuel cells, medical sensing, and bio-waste treatment. The leading electrocatalysts for the UOR are nickel hydroxide surfaces, operating by the Botte mechanism: NiII(OH)2 is oxidized to NiIIIOOH, and the latter drives the UOR. However, these materials have several polymorphs, with α- and β-Ni(OH)2, and γ- and β-NiOOH, as described by the Bode diagram. We now report a systematic study of a series of nickel hydroxides, varying gradually from α-rich to β-rich materials. The crystallinity, order, hydration, intercalation, and morphology of these materials have been characterized by XRD, Raman, ATR-FTIR, XPS, and HRSEM and linked to their electrochemical activity. The disordered α phase was found to be superior to the β phase as a UOR electrocatalyst, with an oxidation onset potential of 0.31 V vs. SCE, better reversibility, and higher anodic current densities. Moreover, the perfect match in onset potentials between UOR electrocatalysis and the Ni2+/Ni3+ oxidation was observed for both phases, suggesting that the Botte mechanism is true for both the α-Ni(OH)2/γ-NiOOH couple and the β-Ni(OH)2/β-NiOOH couple. We further characterize the dynamic behavior of these materials (activation and aging), allowing us to propose a unified Botte-Bode diagram of UOR on Ni(OH)2/NiOOH.

Ultrafine Pd nanocrystals anchored onto single-walled carbon nanohorns: A highly-efficient multifunctional electrocatalyst with ultra-low Pd loading for formic acid and methanol oxidation

Hybrid electrocatalysts made from ultrafine Pd nanoparticles strongly coupled on single-wall carbon nanohorns (Pd/CNH) are prepared via a facile and scalable approach. Benefiting from the unique interconnected open-pore microstructure of CNHs as well as the numerous exposed Pd active sites, such an architectural design can substantially increase the Pd utilization efficiency and thereby reduce the overall dosage of metal Pd. Strikingly, the newly-developed Pd/CNH hybrid with an ultra-low Pd loading amount of 5.0 wt% exhibits high forward anodic peak current densities of up to 1420.4 and 1910.6 mA mg−1 toward formic acid and methanol oxidation, respectively, both of which are significantly superior to those of commercial 20.0 wt% Pd/carbon black catalyst. This study may offer an economic option and a new vision for the development of the next-generation low-cost fuel cell anode catalysts.

Corrosion and Alloy Engineering in Rational Design of High Current Density Electrodes for Efficient Water Splitting

AbstractAlongside rare‐earth metals, Ni, Fe, Co, Cu are some of the critical materials that will be in huge demand thanks to growth in clean‐energy sector. Herein scrap stainless steel wires (SSW) from worn‐out tires are employed as a support material for catalyst integration in the hydrogen evolution reaction (HER). In addition, SSW by corrosion engineering is exercised as an in situ formed freestanding robust electrode for the oxygen evolution reaction (OER). By superficial corrosion of SSW, inherent active species are unmasked in the form of Ni/FeOOH nanocrystallites displaying efficient water oxidation by reaching 500 mA cm−2 at low overpotential (η500) of 287 mV in 1 m KOH. Similarly, cathode scrap SSW with active (alloy) coatings of MoNi4 catalyzes the HER at η‐200 = 77 mV, with a low activation energy (Ea = 16.338 kJ mol−1) and high durability of 150 h. Promisingly, when used in industrial conditions, 5 m KOH, 343 K, these electrodes demonstrate abnormal activity by yielding high anodic and cathodic current density of 1000 mA cm−2 at η = 233 mV and η = 161 mV, respectively. This work may inspire researchers to explore and reutilize high‐demand metals from scrap for addressing critical material shortfalls in clean‐energy technologies.

Nonenzymatic Glucose Sensing Using Ni60Nb40 Nanoglass.

Despite being researched for nearly five decades, chemical application of metallic glass is scarcely explored. Here we show electrochemical nonenzymatic glucose-sensing ability of nickel-niobium (Ni60Nb40) amorphous alloys in alkaline medium. Three different Ni60Nb40 systems with the same elemental composition, but varying microstructures are created following different synthetic routes and tested for their glucose-sensing performance. Among melt-spun ribbon, nanoglass, and amorphous-crystalline nanocomposite materials, nanoglass showed the best performance in terms of high anodic current density, sensitivity (20 mA cm-2 mM-1), limit of detection (100 nM glucose), stability, reproducibility (above 5000 cycles), and sensing accuracy among nonenzymatic glucose sensors involving amorphous alloys. When annealed under vacuum, only the heat-treated nanoglass retained a similar electrochemical-sensing property, while the other materials failed to yield desired results. In nanoglass, a network of glassy interfaces, compared to melt-spun ribbon, is plausibly responsible for the enhanced sensitivity.

Effect of Cathode–Anode distance and electrical resistivity on macrocell corrosion currents and cathodic response in cases of chloride induced corrosion in reinforced concrete structures

When dealing with macrocell corrosion, it is crucial to consider the geometry and size of the structure, including the mobilizable cathode–anode distance, which is the maximum distance where passive reinforcement bars exchange current with corroding active sites. An application of the mobilizable cathode–anode distance is the corrosion of submerged regions of reinforced concrete structures where very high local anodic current densities were reported with no visual manifestation making this type of corrosion very dangerous. One possible explanation for these observations is that active steel (anode) bars in the submerged region could be coupled with a cathodic aerated zone located far away from the anode. This paper aims to study the influence of cathode–anode distance on the macrocell current. Experimental investigations were carried out on a 10 m long reinforced beam consisting of 20 segments of rebars: an anode where corrosion was initiated with chloride diffusion, and 19 identical cathodes. Different electrical connections were made between cathodes and corrosion currents were measured in order to test the impact of the cathode–anode distance on the evolution of corrosion current and the attenuation of the cathodic reaction in relation to the distance between anode and cathode. The experimental campaign was supported by numerical simulations, which confirmed the experimental results and tested the impact of electrical resistivity on the mobilizable cathode–anode distance. By connecting the anode to each cathode alone, it was found that macrocell corrosion current could be provided by cathode bars at large distances from the anode, the distance being dependent on the electrical resistivity of the structure. It was also found that, when all the cathodes were connected to the anode, the closest bar received the highest proportion of the total current, which increased with electrical resistivity, whereas the most distant bars received very limited amounts of current.

Corrosion Localization Analysis in T‐Shape Pipe Junction Based on Multielectrode Current Measurements

The water flow rate and galvanic current distribution in the T‐shape junction of steel pipes were investigated using the multielectrode array approach. The inner surface of polypropylene pipes junction was divided into 15 separate sections, and a steel plate was placed in every section to form a single inner surface. The tap water flow rate varied between 0.28 and 0.57 m/s, and the water distribution in the junction was between 5 : 1 and 1 : 5. The galvanic current flowing through each steel electrode was mapped on the 3D model of the T‐shape junction. Two differential aeration pairs were found with high anodic current densities.

Origin of Mosaic Structure Obtained During the Production of Porous Silicon with Electrochemical Etching

So far, while producing porous silicon (PSi) with anodic etching of silicon in an aqueous solution of hydrofluoric acid, many researchers (including us) have obtained the crack-into-pieces (or mosaic) structure. Most of the authors believed that the cause of this structure is the collapse and the cracking of the porous, especially highly porous, silicon layer which took place during the drying of PSi after fabrication. However, our study showed that the mosaic structure was formed right during the course of silicon anodization at high anodic current density. Furthermore, our study also showed that at high anodic current density the real silicon etching has been replaced by the growth of a silicon oxide layer. This is a layer of another substance that grows on silicon, so when the layer is too thick (which is obtained when the anodic current density is too high and/or the anodization time is too long) it will crack, creating mosaic pieces. When the silicon oxide layer is cracked, the locations around the cracks will be etched more violently than elsewhere, creating trenches. Thus, the mosaic structure with mosaic pieces emerged between the trenches has formed.

Effect of current density on Ni-Mo electrodeposition using EMIM [Br

ABSTRACTThis study was conducted to investigate the current density impact on the Ni-Mo electrodeposit and on its catalytic activity of methanol oxidation in an alkaline solution. For this purpose, Ni-Mo coatings with good electrocatalytic properties were achieved by electrodeposition in the modified Watts bath containing 1-ethyl-3-methyl imidazolium bromide (EMIM [Br]) ionic liquid. The results showed that a 1–6 A dm−2 increase in the current density could decline the Mo content in the Ni-Mo/Ni coatings. The XRD patterns demonstrate that an amorphous coating formed with increasing the current density. Moreover, it was found that the catalytic performance of Ni-Mo coatings was significantly enhanced in the presence of methanol. Based on the obtained results, the Ni-Mo coating obtained at the current density of 3.5 A dm−2 and in the presence of EMIM [Br] showed a higher anodic current density, lower onset oxidation potential, and better catalytic performance.

The effect of pH on electrocatalytic properties of electrodeposited Ni–Mo/Ni coating using 1-ethyl-3-methylimidazolium bromide

In this research, Ni–Mo/Ni coating was deposited by electrodeposition in the modified watts bath containing 1-Ethyl-3-Methylimidazolium Bromide (EMIM [Br]) ionic liquid, followed by studying the effects of pH on the phase formation, morphology, particle size and electrocatalytic properties of Ni–Mo/Ni alloy coating for methanol oxidation reaction (MOR). It was found that by increasing the pH value, Mo content in the structure increases and leading to the conversion of its crystalline structure to an amorphous structure and also reduction of crystallite size. The electrocatalytic results of Ni–Mo/Ni coatings showed that the catalytic activity in the presence of methanol is considerably increased. Also, investigation of the coatings in different pH values in the presence of ionic liquid showed a high anodic current density (15.38 mA cm−2) and low onset oxidation potential (0.35 V) at pH 7, suggesting a high catalytic activity at this pH value.

Comparative, real-time in situ monitoring of galvanic corrosion in Mg-Mg2Ca and Mg-MgZn2 couples in Hank’s solution

The purpose of this study is to comparatively investigate on intermetallic compounds Mg2Ca and MgZn2 in galvanic corrosion of magnesium alloy by using real-time in situ monitoring techniques. The results indicated Mg2Ca functioned as an anode with higher anodic current density, higher Mg2+ concentration and higher pH values than the Mg cathode, while MgZn2 worked as a cathode with a cathodic current density, lower Mg2+ concentration and higher pH value than the anodic Mg. The results also suggested a corrosion forming mechanism involving solubility product constant (Ksp) in which Zn-based corrosion products were easier to form than their Mg counterparts.

Polyaniline-decorated honeycomb-like structured macroporous carbon composite as an anode modifier for enhanced bioelectricity generation

The design of high-performance anodes for bioelectricity generation remains a challenge in microbial fuel cells (MFCs). In the present work, we found that sodium citrate-derived carbon (SC) with a honeycomb-like macroporous structure could be prepared by a facile pyrolysis method. Then, a novel electrode fabricated by in-situ polymerization of polyaniline (PANI) nanoparticles on the SC-loaded carbon paper (CP), named PANI@SC-CP electrode, was used as the anode in electrochemical cells (ECs); this configuration resulted in much higher anodic current density than that of the control CP electrode. This improvement was attributed to the higher biocapacity resulting from the large Brunauer-Emmett-Teller (BET) surface area of the SC, the outstanding hydrophilicity of PANI, and the increased extracellular electron transfer efficiency owing to the good conductivity and the excellent electrochemical activity of the PANI@SC-CP electrode as well as the enhanced interaction between the electroactive microbes and the electrode triggered by the combination of PANI and SC. The excellent performance of the PANI@SC-CP anode for bioelectricity generation was also demonstrated in MFCs inoculated with a pure or mixed culture.

Crystalline nickel boride nanoparticle agglomerates for enhanced electrocatalytic methanol oxidation

In this paper, crystalline Ni3B nanoparticle agglomerates have been successfully prepared via dry-powder annealing of the solution-produced amorphous nickel boride. The electron microscopy (EM) images indicate that the Ni3B nanomaterial is composed of numerous nano-sized particles with a diameter ranging from 100 to 200 nm. The electrocatalytic characteristics of nickel boride in an alkaline medium were observed by cyclic voltammetry (CV) and chronoamperomerty (CA). Compared to the amorphous nickel boride/Ni foam (ANB/NF), the crystalline Ni3B/Ni foam (CNB/NF) electrode exhibits a higher catalytic performance with low initial oxidation potential of 0.35 V and a high anodic oxidation current density of 62 A g−1 at 0.55 V in a 6 M KOH solution with 0.5 M methanol. And the CNB/NF electrode shows good long-term cycling stability and the catalytic current of methanol retains 87% of the initial value after 1000 time cycles. The CNB/NF electrode should be a promising candidate for alkaline direct methanol fuel cells (DMFCs).

Electrochemical recycling of nickel-cobalt-containing tungsten alloys

The potentiodynamic method of linear scanning voltamperometry and chronopotentiometry have been used to investigate the electrochemical dissolution of VNZhK alloy (wt.%: W 90, Ni 7,2, Fe 1,8, Co 1), VNZh alloy (wt.%: W 90, Ni 7, Fe 3), as well as their components in alkaline-ammonium solutions. The high anode current density of tungsten (~700 mA/cm2), the passivity of iron and the similarity of nickel and cobalt anode behavior in the studied electrolytes were revealed. A higher electrochemical activity of VNZhK alloy has been established as compared with VNZh alloy, it is related with a decrease in the iron content in the alloy. Using the example of VNZh alloy, the possibility of electrochemical processing of tungsten heavy alloys with a degree of tungsten extraction into solution of more than 99% has been shown.

Surface effect of platinum catalyst-decorated mesoporous carbon support using the dissolution of zinc oxide for methanol oxidation

Due to their excellent chemical stability, as well as low operating temperature, high energy density, and environment-friendliness, carbon supports are a prospective candidate for platinum (Pt) nanocatalysts in direct methanol fuel cells (DMFCs). However, numerous efforts to achieve the high efficiency for the energy conversion by carbon supports have faced considerable challenges owing to an inefficient utilization of the inside region, leading to the low electrochemical performance. Thus, in the present study, we propose an advanced surface technology for the mesoporous structure. The obtained Pt nanocatalyst-decorated mesoporous carbon nanofiber support offers a high anodic current density of 732 mA mgPt−1, and an excellent catalytic stability as compared to the commercial Pt/C (20 wt% Pt on Vulcan carbon, De Nora S.P.A.) and Pt/CNF. Due to these characteristics, this advanced carbon support provides several, benefits such as the well-dispersed Pt nanocatalysts on the surface, as well as achieves a superb catalytic stability. In sum, the advanced carbon support is a promising candidate to improve the electrochemical performance of DMFCs.