Real Surface Area Research Articles

Electrodeposition of Cu 3D structures suitable for CO2 reduction

Porous Cu foam electrodes, suitable for cathodic CO2 reduction, were deposited in an acidic sulphate solution with different additives to obtain structures with a high real surface area and an adequate mechanical stability. The influence of the electrodeposition time and solution composition on the porosity parameters, microstructure and stiffness of Cu 3D structures was evaluated. Neither ammonium acetate nor polyethylene glycol were found to be effective additives to the Cu sulphate electrolyte to achieve the main objectives. Only the presence of Cl– ions in the deposition solution resulted in a threefold increase in the real surface area and the achievement of a sufficient mechanical stability of the Cu 3D structure. The latter effect is related to the specific influence of Cl– ions during the electrodeposition process on the microstructural characteristics, such as the size of micropores in the walls of holes and crystallite aggregates that form dendritic branches. These structural changes, in contrast to the Cu samples deposited in a solution without additives, resulted in larger real surface areas, while the denser structures deposited in the presence of Cl– ions ensured the mechanical stability of the 3D structure.

Methanol electrooxidation performance of nickel-modified polyaniline thin films for direct methanol fuel cells

A metal–organic composite thin film composed of polyaniline (PANI) and Ni was prepared and characterized for methanol electrooxidation reaction. First, PANI thin films were electrodeposited on a fluorine-doped tin oxide (FTO) coated glass support in an aqueous acidic solution. Subsequently, the polymer film was modified with Ni particles (FTO/PANI-Ni) by chronoamperometric (CA) technique. The composite film was characterized by structural, morphological and electrocatalytic analyses. X-ray diffraction (XRD) results confirmed the crystallization of Ni according to the cubic structure. Scanning electron microscopy (SEM) images showed that the Ni nanoparticles were uniformly dispersed on the PANI surface. The electrocatalytic performance of the FTO/PANI-Ni composite electrode for the methanol electrooxidation reaction was investigated in 0.5 M KOH solution containing methanol using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. The effects of temperature and methanol concentration on the methanol electrooxidation performance were also studied. The modified composite catalyst exhibited an electrochemically active surface area of 0.5235 cm2. The presence of Ni nanoparticles on the polymer surface promoted the adsorption of methanol molecules and facilitated the oxidation process, leading to higher current densities and better overall performance. The maximum current density was 14 mA cm-2 and the electrode maintain 68 % of its initial activity even after 200 cycles, indicating that the FTO/PANI-Ni electrode exhibited good stability. The high methanol oxidation performance of the composite electrode was associated with large real surface area, a possible synergistic effect between the polymer moleucles and Ni particles as well as high intrinsic activity of Ni for this process.

Thermally stimulated desorption from the surface of black aluminum layers prepared by PVD methods

Black aluminum is characterized by a highly granular structure and porous surface - i.e. the real surface area is several times larger than its geometric projection to the substrate. In addition, it is a metal with good surface gas sorption capacity and structural stability up to temperatures T ∼500 °C.The surface exchange interactions between the ambient environment and thin layers of black aluminum prepared by different methods are described. These properties are convenient for materials that are suitable for the fabrication of active layers of chemiresistors. The layers were prepared by magnetron sputtering at room temperature and liquid nitrogen temperature, and evaporation with different compositions and gas flow rates. In this work, the process of thermally stimulated desorption was measured using mass spectrometry. The calculation of the activation energy Eact for the release of individual desorbing atoms, or radicals, from the surface of black aluminum was performed. Knowing of the temperature and the number of particles released by desorption allows us to get an idea of the number of defects and the functionalized structure of the surface layer.

Cadmium oxide nanoparticles doped with nickel and silver: Photocatalytic activity for environmental remediation

In this work, we used a co-precipitation approach to create CdO nanoparticles that were co-doped with nickel (Ni) and silver (Ag). X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were employed to assess the structural attributes of the nanoparticles that were synthesized. Co-doping with Ni and Ag resulted in a steady rise in nanoparticle crystallite size, increasing from 20.97 nm to 32.16 nm. Following the co-doping procedure, FESEM pictures demonstrated a morphological shift from tiny, rock-like formations in pure CdO to bigger rock-like structures. Energy-dispersive X-ray spectroscopy (EDX) was utilised to explore the compositional characteristics of Ni and Ag-doped CdO nanoparticles. The existence of particles’ agglomerations was observed, which may have limited the real surface area available for gas adsorption and resulted in smaller apparent pore sizes in the Brunauer-Emmett-Teller (BET) investigation. Diffused Reflectance Spectroscopy (DRS) revealed a decline in the band gap from 2.45eV to 2.30eV, which was most likely caused by structural changes caused by cadmium ion replacement or the occupancy of interstitial spaces within the lattice by nickel and silver ions. The chemical and electronic states of the atoms were assessed using X-ray photoelectron spectroscopy (XPS), which examined the formation of defects in the form of oxygen vacancies, which contributed to accelerated photocatalytic performance. The deterioration of Crystal Violet (CV) dye during sunlight exposure utilising co-doped CdO nanoparticles vs pristine CdO is being evaluated in the evaluation of photocatalytic activity. Notably, co-doped nanoparticles improved photocatalytic activity significantly, with CV degradation reaching up to 95 % within 180 min of exposure. The potential of Ni and Ag impregnated CdO nanoparticles as effective photocatalysts for environmental remediation applications is highlighted in this study.

Effect of Electrochemical Surface Oxidation on Intrinsic Activity Towards the Hydrogen Evolution Reaction of Ultra-Smooth Nanocrystalline Ni Thin Films

Green hydrogen has emerged as a leading contender in the pursuit of a sustainable energy transition, driving the need for optimized catalysts in hydrogen production. Therefore, considerable effort is taken to replace the highly active, yet expensive Pt-group metals with non-noble alternatives such as Ni. Understanding the hydrogen evolution reaction (HER) mechanism on well-performing Ni surfaces is essential for gaining fundamental knowledge and implementing this in practical applications. While high surface area structures are typically designed for enhanced efficiency, there is limited research available on the fundamental aspects of thin films and smooth surfaces, which are crucial for benchmarking intrinsic catalytic activity and elucidating catalytic mechanisms. To address this gap, we perform a combined microstructural and electrochemical evaluation of smooth Ni thin film electrodes to analyze HER in alkaline media.This study aimed to evaluate the intrinsic catalytic properties of nanocrystalline Ni thin films and the effect of electrochemical oxidation on the catalytic behavior, while precisely monitoring the evolution of the film surface state and roughness. In addition to experimental work, Density Functional Theory (DFT) calculations and Kinetic Monte Carlo (KMC) simulations are used to understand HER on oxide-modified Ni surfaces and the role of different elementary processes involved in the HER mechanism.Nanocrystalline low-roughness Ni electrodes for HER were produced via magnetron sputter deposition to minimize the difference between geometrical and electrochemical surface area. This means we find intrinsic material properties directly, bypassing the need for additional measurements for real surface area determination. The analysis of catalyst activities towards HER as well as the oxidation process [1] was performed via cyclic voltammetry, using a three-electrode setup. Within the conducted studies, we can report a significant lowering of the overpotential for HER upon in-situ oxidation of the electrodes due to the existence of NiO, and Ni(OH)2 on the Ni catalyst surface [2], leading also to a limitation of the deactivation processes. Further analysis including topography evaluation (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) in combination with selected area diffraction (SAED) of the as-deposited and oxidized electrodes confirmed that the observed effect can be assigned to the availability of oxides on the surface assuredly (Figure 1). Additionally, theoretical calculations and simulations (DFT, KMC) support the experimental data and derived theories.In conclusion, the beneficial effect of NiO and Ni(OH)2 presence on Ni surfaces was examined and successfully proven by a combination of electrochemical measurements, material characterization, theoretical calculations, and a careful experimental design that minimizes the influence of interfering factors, such as surface roughness.

Roughness Factors of Electrodeposited Nanostructured Copper Foams

Copper-based electrocatalytic materials play a critical role in various electrocatalytic processes, including the electroreduction of carbon dioxide and nitrate. Three-dimensional nanostructured electrodes are particularly advantageous for electrocatalytic applications due to their large surface area, which facilitates charge transfer and mass transport. However, the real surface area (RSA) of electrocatalysts is a crucial parameter that is often overlooked in experimental studies of high-surface-area copper electrodes. In this study, we investigate the roughness factors of electrodeposited copper foams with varying thicknesses and morphologies, obtained using the hydrogen bubble dynamic template technique. Underpotential deposition (UPD) of metal adatoms is one of the most reliable methods for estimating the RSA of highly dispersed catalysts. We aim to illustrate the applicability of UPD of lead for the determination of the RSA of copper deposits with hierarchical porosity. To find the appropriate experimental conditions that allow for efficient minimization of the limitations related to the slow diffusion of lead ions in the pores of the material and background currents of the reduction of traces of oxygen, we explore the effect of lead ion concentration, stirring rate, scan rate, monolayer deposition time and solution pH on the accuracy of RSA estimates. Under the optimized measurement conditions, Pb UPD allowed to estimate roughness factors as high as 400 for 100 µm thick foams, which translates into a specific surface area of ~6 m2·g−1. The proposed measurement protocol may be further applied to estimate the RSA of copper deposits with similar or higher roughness.

Efficiency of nanostructured CuxCo3-xO4 and NixCu1-xCo2O4 electrodes as electrocatalysts for the oxygen evolution reaction–revisited

Binary and ternary cobalt-based spinel oxides have been shown to possess enhanced electrocatalytic activity and stability towards the oxygen evolution reaction (OER), however their performance is inconsistent. In this work, copper and nickel-copper substituted cobalt spinel oxides, CuxCo3-xO4 (x = 0, 0.25, 0.5, 0.75 and 1) and NixCu1-xCo2O4 (x = 0.25, 0.5, 0.75, 0.9 and 1), were prepared by the thermal decomposition method to re-examine their properties. We used several physical and chemical characterization methods to understand their behavior. The formation of spinel structure was confirmed by X-ray diffraction analysis, however, CuxCo3-xO4 remains monophasic only up to x = 0.75. CuCo2O4 was found to contain an additional CuO phase. The lattice parameters were determined as a function of the composition and found to increase with increased Cu and Ni content in the cobalt spinel lattice, which supports Cu and Ni incorporation in the spinel structure. For CuxCo3-xO4 electrodes, the lattice parameter gradually increased when cobalt is replaced by copper in the composition. NixCu1-xCo2O4 lattice parameters are higher than those of CuxCo3-xO4 but do not display a particular trend with replacement of Cu by Ni. The XPS analysis indicates the existence of various chemical species on the surface of the electrodes with a significant amount of NiO being detected on the surface of Ni-containing samples. The core-level spectra of all metal cations indicate the presence of mixed-valence states in the spinel structure. The roughness factor was determined by measuring the double layer capacitance of the electrodes using cyclic voltammetry and the data obtained was verified by performing electrochemical impedance spectroscopy (EIS) in a region of low faradaic current. The incorporation of Cu and Ni significantly increased the surface area of cobalt oxide. The current density obtained from cyclic voltammetry (CV) data is reported as a function of the geometric and the real surface areas for each sample, which revealed that Co3O4 possesses the highest current density than other Cu or Cu and Ni-containing cobalt spinel oxides towards OER when corrected for differences in surface area. However, the addition of Cu could be viewed as beneficial as it provides a lower onset potential for OER and results in a relatively high current density compared to Co3O4. NixCu1-xCo2O4 materials have a similar current density per unit geometric area, however, when corrected for real surface area these electrodes display lower catalytic activity for OER than CuxCo3-xO4 (x = 0 to 1). The presence of a significant surface NiO species may have affected the catalytic activity of Ni-containing samples. The data will be discussed in the context of variable material performance found in the literature.

Pulsed laser deposition grown La0.3Ca0.7Fe0.7Cr0.3O3-δ thin films on yttria-stabilized zirconia substrates for fundamental electrochemical energy conversion studies

La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr) perovskites, normally deposited as a powder-based ink to form porous electrode layers, have been shown to be exceptional catalysts for the electrochemical splitting of CO2 to form CO at one electrode and O2 at the other during electrolysis in solid oxide cells, while also being highly active and stable under fuel cell conditions. This work constitutes the first report of thin film deposition of LCFCr via pulsed laser deposition on a 001-oriented yttria-stabilized zirconia substrate, used to simulate the ionically conducting electrolyte in operating cells. The primary goal of this work was to determine fundamental LCFCr properties and performance metrics without complications from morphology effects. Scanning Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy analysis confirmed that oriented, dense, uniform, and smooth films with a thickness of ca. 25 nm and a RMS surface roughness of 0.2 nm are grown at 700 °C from a stoichiometric LCFCr target, while containing all the components of LCFCr in their expected oxidation states. These thin films have allowed the determination of the oxidation states of the redox active species on the electrode surface. Moreover, the preliminary electrochemical response of the LCFCr thin films in an air environment is shown to mimic the trends observed in more common highly porous LCFCr electrodes, thus arguing for a similar reaction mechanism and kinetics per real surface area.

Improving the Electrocatalytic Performance for the Hydrogen Evolution Reaction in the Electrodeposited Ni-Based Matrix by Incorporating WS2 Nanoparticles

Ni based alloys and composites may constitute an alternative to noble metal as a catalyst for the hydrogen evolution reaction (HER) during the water electrolysis. The aim of the present study was to evaluate the electrocatalytic activity of the electrodeposited Ni-WS2 and Ni–Mo–WS2 composites. The effect of the addition of WS2 nanoparticles on the structure, surface morphology and surface composition of Ni and Ni–Mo metallic matrix was thoroughly examined. The obtained results were used to explain the catalytic performance and the HER mechanism of the studied composites. It was found that the incorporation of the WS2 nanoparticles increased the electrocatalytic activity of the Ni and Ni–Mo matrix. The highest electrocatalytic activity was found for the Ni–Mo–WS2 electrode. This was, firstly, a consequence of the quasi-amorphous structure of the composite, which increased the real surface area of the electrode. On the other hand, the intrinsic catalytic activity was enhanced by the outer oxide layer rich in Mo oxides formed on the surface of the composite electrode. The presented research is an important contribution to the design of the non-precious composite electrodes for the HER.

Effects of processing conditions and fine powder loading on real and electroactive surface areas of porous nickel manufactured by lost carbonate sintering

ABSTRACT The effects of five key processing parameters on the real and electroactive surface areas of porous nickel samples produced by the Lost Carbonate Sintering (LCS) process have been investigated systematically. The specific real and electroactive surface areas of the LCS porous Ni samples are 500–1600 cm−1 and 80–115 cm−1. Pore size, compacting pressure and sintering temperature have no significant effect on the surface areas. Porosity has no effect on the gravimetric real surface area, but a higher porosity leads to a lower volumetric real surface area and a higher electroactive surface area. Metal particle size has a huge effect on the surface areas of the LCS porous metal. An intermediate amount of fine Ni powder results in the highest real surface area, approximately 70% higher than the samples produced with coarse Ni powder. Samples produced with fine Ni powder can increase the electroactive surface area by up to 100%.

Ambiguities and best practices in the determination of active sites and real surface area of monometallic electrocatalytic interfaces

Determining the number of electrocatalytically accessible sites (ECAS) and real surface area (RSA) for any given electrocatalyst precisely is important in energy conversion electrocatalysis as these are directly used in the determination of intrinsic activity markers. For monometallic electrocatalysts and electrocatalysts of just one type of active site, there believed to be ways of making precise determination of ECAS and RSA using underpotential deposition (UPD), stripping, and redox-charge integration employing transient voltammetric sweeping techniques. This transient nature of sweeping techniques makes the determination of ECAS and RSA relatively less reliable. This study is directed at examining the effects of scan rate in the determination of ECAS and RSA taking Ni(OH)2/CC and Pt wire as model catalytic electrodes. The results suggest that the scan rate and the determined ECAS and RSA values are inversely related and the lowest possible scan rate set experiment was witnessed to give the highest possible ECAS or RSA values with LSV/CV.

Air purifiers, comparison between real and declared surface for use: fake it or make it?

Abstract Introduction Air pollution has been recognized as one of the major risk factors for the global burden of disease. In modern society, most exposure occurs indoors, and air quality may be improved with air purifiers utilizing various cleaning techniques. This analysis aims to evaluate whether recommended room surface in which to use these devices as declared by producers is actually in line with their real effective area of activity. Methods A review of devices for the purification of the air was carried out between January-April 2022. Four different types of air purifiers were considered based on the adopted technologies: I) HEPA filters and UV lamps; II) only with HEPA filters; III) only UV lamps and IV) those using other technologies. For each group, based on the CADR (Clean Air Delivery Rate) provided by the producers, the optimal real surface area of the room to use the device was calculated, referring to the standard EN779:2012. This value was compared with the recommended area of the room declared by the producers. Descriptive statistics and Wilcoxon matched pair test used for comparisons. The significance level was set at p < 0.05. Results The analysis was carried out on 252 devices; I) 52 had HEPA filters + UV lamps, with a recommended mean room area of 40 m2 (IQR 49.75), II) 142 devices had only HEPA filters with 52.5 m2 (IQR 46.75), III) 27 devices only UV lamps, 40 m2 (IQR 105), IV) 31 devices with other technologies, 54 m2 (IQR 84.2). As required by EN779:2012, the effective area of activity was calculated using CADR x 0.075: the medians of the 4 groups were I) 12 m2 (IQR 16.5), II) 15.83 m2 (IQR 26.4), III) 4.5 m2 (IQR 22.5), IV) 7.5 m2 (IQR 21.53), respectively. Comparing declared and calculated CADR values, all the groups showed significant differences (p < 0.05). Conclusions Results show that recommended surfaces derived from CADR declared by producers largely overestimate the real volume of the room that devices can purify, whatever the technology used. Key messages • There’s no correspondence between recommended area of room to be sanitized indicated by producers of air purifiers and area that they are actually able to sanitize, which is significantly lower. • It is necessary to be aware of the difference between data indicated by producers and real data, in order to purchase a device that actually corresponds to dimensional needs of the environment itself.

PEMFC Platinum-Based Catalysts Recycling Using an Electrochemical Process

Hydrogen is one of the most promising energy carriers. Currently, the most used technology to produce electricity from hydrogen, particularly for green mobility, is the technology based on the use of Proton Exchange Membrane Fuel Cells (PEMFC). Platinum, pure or alloyed with another element, remains essential in the design of efficient catalysts either for anode or cathode catalytic layer in PEMFC. This metal is rare and expensive hence recycling it becomes an important issue for the hydrogen sector development.Chemical ways to recover platinum from PEMFC have been already studied 1-2 based on Pt leaching using either a mix of HCl/HNO3 or HCl/H2O2. In our project, we investigate an electrochemical process to leach platinum contained in aged Pt based catalysts to further resynthesize catalysts from the recovered Pt salts. The electrodissolution of platinum becomes significant with the oxidation of the metal (around 1.1 V vs RHE) but particularly when the oxidized platinum is reduced (around 0.7 V vs RHE) 3. Moreover, the dissolution is enhanced when a complexing agent as chloride anion is introduced 4. The idea of our process is to study the impact of different protocol of steps between high potential (to oxidize platinum) and low potential (to reduce platinum oxide). The improvement of the process is linked to the upper and lower potential values, the number of steps and the nature of the electrolyte and the complexing agent. Our main parameter to monitor the dissolution is the changes in electrochemical real surface area (ECSA) associated to transmission electron microscopy (TEM) images of the catalyst at different stages of the protocol as illustrated in Figure 1.In terms of methodology a model study on fresh commercial Pt/C catalyst has been first performed to determinate the optimal conditions of Pt dissolution followed by the application of the protocol on membrane electrode assemblies (MEA) aged in real conditions. 1 L. Duclos, L. Svecova, V. Laforest, G. Mandil, et P.-X. Thivel, « Process development and optimization for platinum recovery from PEM fuel cell catalyst », Hydrometallurgy, vol. 160, p. 79-89, mars 2016, doi: 10.1016/j.hydromet.2015.12.013. 2 L. Duclos, M. Lupsea, G. Mandil, L. Svecova, P.-X. Thivel, et V. Laforest, « Environmental assessment of proton exchange membrane fuel cell platinum catalyst recycling », J. Clean. Prod., vol. 142, p. 2618-2628, janv. 2017, doi: 10.1016/j.jclepro.2016.10.197. 3 S. Cherevko, A. R. Zeradjanin, G. P. Keeley, et K. J. J. Mayrhofer, « A Comparative Study on Gold and Platinum Dissolution in Acidic and Alkaline Media », J. Electrochem. Soc., vol. 161, n° 12, p. H822-H830, 2014, doi: 10.1149/2.0881412jes. 4 S. Geiger, S. Cherevko, et K. J. J. Mayrhofer, « Dissolution of Platinum in Presence of Chloride Traces », Electrochimica Acta, vol. 179, p. 24-31, oct. 2015, doi: 10.1016/j.electacta.2015.03.059. Figure 1

Pt Nanoelectrodes Sealed in Quartz Capillaries Modified with Underpotential‐Deposited Bismuth for Formic Acid Electrooxidation

AbstractPlatinum disk nano‐ and micro‐electrodes with radii in the range 40 nm–12.5 μm were fabricated using quartz capillaries and the laser‐puller assisted approach. The hydrogen underpotential deposition (H‐UPD), performed in a 0.5 M H2SO4 aqueous solution, revealed that the nanoelectrodes, with radii of 160 nm and less, displayed extraordinarily large surface areas, which in terms of roughness factors (RFs, i. e., the ratio of the real surface areas to the geometric surface areas) were in the range 1030–3600. This finding was attributed to diffusion of adsorbed species at the Pt/quartz interface along portions of the Pt wires sealed within the glass. RFs between 2 and 3 were instead found at the microelectrodes. Similar results were also obtained with underpotential‐deposited metallic bismuth. In this case, diffusion of Bi adatoms onto the Pt surface was hindered to some extent, providing a RF value of 172. Bi‐modified Pt nano‐ and micro‐electrodes were employed to study the electrooxidation of HCOOH, which is of interest in the field of fuel cells. It was found that the nanoelectrode displayed higher activity towards the electrooxidation of HCOOH and tolerance to CO poisoning, compared to the microelectrode.

One-step synthesis of the hydrophobic conical Co-Fe structures-the comparison of their active areas and electrocatalytic properties

Enhancement of the surface of the catalyst is desirable in the interest of mass transport maximizing. However, without a well-defined method of determination of its active surface, catalyst deposited with different conditions cannot be accurately compared. In this work, Co-Fe alloy cones were synthesized from the electrolyte containing ammonium chloride as a crystal modifier. It controls the direction of the deposit growth, and consequently, develops the active surface area. Moreover, the influence of the direction of the applied magnetic field on the ferromagnetic Co-Fe alloy was investigated. It affected noticeably the morphology and composition of layers and therefore, the catalytic activity of the samples in the Hydrogen Evolution Reaction (HER). Linear Sweep Voltammetry (LSV) measurements were used to test the catalytic activity in 1 M NaOH electrolyte. The expected development of the real active surface area was determined using two different methods: Brunauer-Emmett-Teller (BET) and Helmholtz Double-Layer Capacitance (DLC). Results show that no specific value of the sample surface multiplication can be found based on these methods. All conical structures were hydrophobic.

Hydrogen evolution reaction activity and stability of sintered porous Ni-Cu-Ti-La2O3 cathodes in a wide pH range

Finding a low-cost, efficient, stable, and workable electrode for the production of hydrogen based on the hydrogen evolution reaction (HER) is particularly critical. At present, the use of Pt/C electrodes is under development, but the expensive cost hinders its wide application in the HER field. Herein, a novel porous Ni-Cu-Ti-La 2 O 3 cathode with a porosity of 29.07% was proved to be an excellent substitute for the HER, which was fabricated by vacuum sintering based on powder metallurgy. The hydrogen evolution efficiency is superior to that of commercial 20% Pt/C under pH = 14.1 condition (2.67 mol/L KOH). The HER activity is also close to commercial 20% Pt/C under pH = 0.1 (1 mol/L HCl) and pH = 8.1 (3.34% simulated seawater) conditions and exceeds it after reaching a high potential. Meanwhile, it can achieve good HER stability within 48 h and maintain its HER activity after 1000 continuous cycle electrolysis. • The porous Ni–Cu-Ti-La 2 O 3 cathodes were sintered through powder metallurgy. • The cathodes exhibited excellent HER activity and stability in a wide pH range. • The HER activity of the cathodes is superior to that of 20% Pt/C in 2.67 mol/L KOH. • The La 2 O 3 and La phases greatly increased the real surface area of the cathodes.

Electrochemical characterization and influencing factor analysis of the real surface area of lamellar Ni3Si electrode

To reflect the real contact state, we characterize the real surface area of lamellar Ni3Si electrodes by the potentiostatic step method, and analyze its influencing factors. The theoretical surface areas of lamellar Ni3Si are calculated through mathematical methods, and reasons for the difference between the real and theoretical surface area are explained. The theoretical surface area of Ni3Si electrode is inversely proportional to lamellar spacing, and proportional to corrosion depth. The increase in lamellar spacing facilitates material exchange, but decreases the lamellae number. Ni3Si electrodes with a lamellar spacing less than 6.4 μm observed a smaller real surface area than theoretical surface area. Variation of real surface area with the corrosion depth reflects the competition between the resident gas and the rough inner surface. When the corrosion depth is 49.6 μm, the real surface area is 3.225 cm2 and is 31% less than its theoretical surface area, which is due to the hindering effect of the resident gas. Whereas, when the corrosion depth is larger than 49.6 μm, the real surface area sharply increases and becomes larger than the theoretical surface area, because the roughness inner-surface of the Ni3Si electrode becomes the dominant factor. The real surface area of lamellar Ni3Si electrode is controllable and can be adjusted by changing the structural parameters. It will undoubtedly play a positive role in the precise control of electrochemical measurements and reactions. Hopefully, this paper can enrich people's cognition of lamellar Ni3Si and provide an exercisable characterization method for porous materials.

A discussion on the order of magnitude of corrosion current density in reinforcements of concrete structures and its link with cross-section loss of reinforcement

This paper deals with the determination of the corrosion current density in chloride-induced corrosion in reinforced concrete structures. Because the corrosion of steel bars is generally localized, calculations of the densities of corrosion current need to take the real surface areas of anodic zones into account. Nowadays, in the lab or on site, the calculation of densities of corrosion are based on arbitrary steel surface areas, which merge anodic and cathodic zones. As a result, the order of magnitude of corrosion current density is not correct; it is underestimated. A second aspect of the paper is the relationship between corrosion current density and the prediction of service life in RC structure when including a part of the propagation phase. The consequences of the corrosion current density on mechanical properties such as corrosion-induced cracking or load-bearing capacity must consider that anodic areas grow both laterally and in-depth.

A flexible and disposable electrochemical sensor for the evaluation of arsenic levels: A new and efficient method for the batch fabrication of chemically modified electrodes

In this study, a novel flexible and disposable electrochemical sensor was fabricated through the straightforward laser-induced synthesis of catalytic Au nanoparticles (AuNPs)@LIG composite for the square wave stripping voltammetry (SWASV) determination of arsenic in soil. In this process, polyimide and a metal precursor (PI-MP) were transformed to three-dimensional porous LIG and AuNPs through the graphitization, photoreduction and thermal reduction of laser ablation. To our knowledge, this is the first time that laser-induced PI-MP was employed to fabricate chemically modified electrodes on a large scale for arsenic determination. X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometer (EDX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and N2 adsorption isotherm were used to characterize the morphological and physical properties of the materials, which demonstrated the successful synthesis of AuNPs@LIG nanocomposite. Additionally, the mechanism of AuNPs@LIG synthesis by laser induction was also investigated, and the deposition potential and the deposition time for the SWASV determination of arsenic were also optimized. The electrochemical sensor fabricated using the proposed method shows satisfactory sensitivity, stability and reliability and exhibits a good linear relationship over concentrations ranging from 0 to 40 μg/L, with a low determination limit of 0.18 μg/L. Furthermore, the obtained AuNPs@LIG surface exhibited good conductivity with a charge transfer resistance (Rct) of 73.85 Ω and a large real surface area of 807.28 mm2. Finally, several real soil samples were analyzed using the prepared sensor with a satisfactory result, which verified the feasibility of this sensor. The results show that the method for chemically modified electrode fabrication proposed in this paper has good commercial potential for the batch manufacturing of electrochemical sensors.

Photobioanodes Based on Nanoimprinted Electrodes and Immobilized Chloroplasts

AbstractAs the global energy demand continues to increase, the interest in photosynthetic energy conversion is growing accordingly. Chloroplasts, photosynthetic organelles present in plants and algae, are attractive candidates for construction of bio solar cells; however, they have been less studied because of their complex membrane system, which restricts electrochemical communication with an electrode surface. Nevertheless, in this work photobioanodes based on planar and nanoimprinted gold substrates modified with chloroplasts were designed and evaluated. Apparently, nanoimprint lithography contributed to higher photocurrent densities, not only owing to the enlarged real surface area, but also due to boosting electrochemical communication between the photosynthetic organelles and the electrode. Combining chloroplast‐modified nanoimprinted gold electrodes with a capacitive part made of a planar gold substrate, coated with a conductive polymer, resulted in a dual‐feature photobioanode providing a lower open‐circuit potential, i. e., −0.11 V vs. Ag|AgCl|KClsat, and an enhanced capacitance of ca. 37 F m−2 upon illumination of 400 W m−2.