Heterogeneous Surface Morphology Research Articles

Magnetized algae-silica hybrid from Porphyridium sp. biomass with Fe3O4 particle and its application as adsorbent for the removal of methylene blue from aqueous solution

Algae-silica hybrid material from biomass Porphyridium sp. (AS) has been modified by coating Fe3O4 particles (MPs) via a sol-gel process using tetraethyl orthosilicate (TEOS) to produce algae-silica-Fe3O4 (AS-MPs). The AS-MPs produced were applied as adsorbent for the adsorption of methylene blue (MB). Identification of functional groups was performed by infrared spectrometer (IR) indicating that in AS-MPs there were active organic group derived from Porphyridium sp., silanol, and siloxane. Diffraction pattern of the AS-MPs material analyzed by X-ray diffraction (XRD) showed that the material has peak with higher intensity at 2θ = 30.04 and 35.52o. Analyst results using a particle size analyzer (PSA) showed that the average particle size distribution of the AS-MPs material was 1.40 µm. In addition the results of the analysis using Scanning Electron Microscopy (SEM), material of AS-MPs has a more heterogeneous surface morphology. The models of MB adsorption by AS and AS-MPs tend to follow the pseudo second-order kinetics model and Freundlich adsorption isotherm. The adsorption of MB solution by AS-MPs produces rate constants (k2) of 0.003 g/mg·min and adsorption capacity (qm) of 96.927 mg/g under the experiment conditions of dose of adsorbent 2.5 mg/L, interaction pH of 6, contact time of 60 min, and temperature of 27 °C. The AS-MPs material obtained from the results of this study can be used as an effective adsorbent because it can remove MB dyestuff in solution, it is chemically stable in acidic and neutral media, and it can be used repeatedly

Degradations in the surface wettability and gas permeability characteristics of proton exchange membrane fuel cell electrodes under freeze-thaw cycles: Effects of ionomer type

Current state-of-the-art proton exchange membrane (PEM) fuel cell electrodes are typically comprised of either short-side-chain (SSC) or long-side-chain (LSC) ionomers, owing to their proven success in the electrode performance and durability under regular cell operation. However, the electrodes based on these two prominent ionomers have not been sufficiently investigated under sub-freezing conditions. In this study, the impact of ionomer type on the degradations of the surface wettability and gas permeability characteristics has been investigated for PEM fuel cell electrodes under freeze-thaw (F-T) cycles between 30 °C and −40 °C. The electrodes comprised of either SSC or LSC ionomers are manufactured with different catalyst loadings. It is found that the F-T cycles induce severe degradations in the electrodes, and the resulting surface morphologies differ greatly, depending on the ionomer type and catalyst loading. For a given catalyst loading, the SSC electrodes degrade more heavily than the LSC ones. Further, independent of the ionomer type, the high catalyst loading electrodes tend to degrade slower than their low catalyst loading counterparts. The SSC catalyst layers peel off from the electrodes virtually completely with the microporous layer largely degraded, inducing a highly corroded and heterogeneous surface morphology. The LSC electrodes experience relatively less degradations, thus the resulting surface morphologies are less corroded and more homogeneous. For all the electrodes, the morphological degradations cause a substantial increase in the gas permeability coefficients, but a decrease in the static contact angles. These increments and decrements correlate well with the severity of the surface degradations, and they are rapid and more substantial for the SSC electrodes.

Adsorption of As (III) and As (V) from aqueous solution by modified Cassia fistula (golden shower) biochar

The biosorption of two Arsenic (As) species [As (III) and As (V)] from aqueous solution onto activated biochar derived from Cassia fistula, belonging to Fabaceae family was studied. SEM/EDX characterization of the adsorbent showed an irregular, porous, and heterogeneous surface morphology with calcium and iron available for As binding. FTIR also showed the presence of groups responsible for As adsorption. Batch adsorption experiments were conducted to determine the optimum conditions for As adsorption to the biomass with optimum adsorbent dose, ambient temperature, initial concentration of As, pH, and stirring rate. Under optimized conditions, the maximum removal percentage was 78.1% [uptake capacity (qe) = 0.78 mg/g] for As (III) and 84.8% [uptake capacity (qe) = 0.42 mg/g] for As (V). The Freundlich isotherm model, characteristic of multilayer binding, fit the data best with R2 values of 0.92 for As (III) and 0.96 for As (V). Fitting of the data to the Dubinin–Radushkevich model indicated physisorption, while the kinetics study suggested a pseudo-second-order reaction. Thermodynamic parameters indicated adsorption was spontaneous. In aqueous solutions, phosphate hindered As removal more than the any other ions. Regeneration studies showed a 23.0% and 21.1% recovery for arsenite and arsenate, respectively, indicating limited leaching under both acidic and alkaline conditions. The absorptive capacity of C. fistula biomass for arsenic removal was compared with a number of other reported biosorbents and was found to be considerably efficient.

Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 < d < 20 nm in size are applied on InGaN/GaN multiple quantum well structures with surface morphology less nonuniform than that of ZnO films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.

Effect of surface heterogeneity on phosphorus adsorption onto mineral particles: experiments and modeling

Adsorptive interaction at the solid-water interface plays an important role in the fate and behavior of phosphorus (P) in rivers and lakes and the resulting eutrophication. This study aims to investigate the contributions of heterogeneous morphology to P adsorption onto mineral particles. The dominant minerals in Yellow River sediment, quartz, k-feldspar, and calcite are investigated with adsorption experiments and microscopic examinations. Taylor expansion is applied to quantitatively characterize the heterogeneous surface morphology. The results reveal that locally concave or convex micro-morphology characterized by the second derivative term of the Taylor expansion, F 2, can be related to adsorption capacity due to its effect on surface-charge density and distribution. The distribution of adsorbed P as a function of F 2 was determined for selected particles composed of each of the pure minerals and was fit to a Weibull distribution. Each mineral was characterized by F 2a , the weighted average value of F 2, and Weibull distribution factors, and correlated with sorption isotherms. The developed relationships were used to accurately predict adsorption onto individual particles as well as pure mineral samples. Mineral particles have complex surface morphology, which affects the interface P adsorption. Micro-morphological characterization of F 2 and F 2a can be used to predict adsorption onto the pure minerals, and this study provides physical basis for predicting adsorption on sediment particles composed of these minerals.

Evaluation of Physicochemical and Antifungal Properties of Polylactic Acid–Thermoplastic Starch–Chitosan Biocomposites

ABSTRACTBiocomposites of polylactic acid, thermoplastic starch, chitosan powder, and chitosan lyophilized powder were prepared using an extrusion process. The color, thermal, structural, mechanical, morphology, and antimicrobial properties were evaluated. The addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder) produced significant changes in color and heterogeneous surface morphology of the polylactic acid biocomposites. The thermal, mechanical, and morphometric properties of the material showed changes with the addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder). The biocomposites formulated with chitosan powder and chitosan lyophilized powder showed antifungal activity when evaluating this property. The biocomposites produced could be used in packaging applications.

Water-based functionalization of mesoporous siliceous materials, Part 1: Morphology and stability of grafted 3-aminopropyltriethoxysilane

Surface modification of mesoporous biogenic silica (rice husk ash) by aqueous and ethanol-based 3-aminopropyltriethoxysilane (APTES) grafting solutions has been investigated using 29Si NMR, ESI-MS, TGA, surface-sensitive NH2 titration, and DFT method. Prior to grafting, a rapid formation of ladder-like aminosilane oligomers has been observed in both solvents limiting the grafting time for the mostly desired formation of a monomolecular organosilane layer to few minutes. An excess of water yielded a long-term stable equilibrium between the oligomerized APTES species within the grafting solution promising a reproducible surface modification. After curing at 120 °C, washing studies showed that these oligomeric aminosilane clusters have been successfully grafted but yielding a heterogeneous surface morphology with even pore blocking rather than a dense, uniform aminosilane monolayer.In addition, the optimized structures of three different grafting modes between APTES and a silica cluster model were obtained by DFT calculations. The results indicated that bond lengths and angles of the different grafting modes reveal no substantial structural distortions. Nevertheless, the ladder-like grafting mode is given preferential consideration because the DFT results are in accordance with the ESI-MS and 29Si NMR findings.

Removal of naproxen from aqueous environment using porous sugarcane bagasse: impact of ionic strength, hardness and surfactant

We investigated the impact of ionic strength, hardness and surfactant on the removal of the widely used drug naproxen (NAP) onto the developed porous sugarcane bagasse (PSB). The experiments demonstrated that increases in ionic strength, surfactant and hardness impacted on the removal of NAP from aqueous phase. The surface of the developed materials showed very high (52 %) carbon content and low (2.3 %) moisture content. The presence of hydroxyl and carboxylate groups might be responsible for the removal of NAP, as confirmed by Fourier transform infrared (FTIR) spectroscopic study. The developed material showed relatively higher surface area of 669.76 m2 g−1, and pore volume of 1.15 cm3 g−1 with average particle size of 37.5 µm, justifying its utility for the adsorption process. The developed material also showed heterogeneous surface morphology and graphite-like pattern. The mechanism of adsorption was explained based on spectroscopic analysis. The computed thermodynamics parameters (ΔH° = −22.03 kJ mol−1, ΔS° = −54.53 J mol−1 K−1 and ΔG° = − 5.50 kJ mol−1) confirmed the exothermic and spontaneous nature of the adsorption process. Experiments were also conducted to optimize the operating parameters for maximum possible removal of NAP from aquatic environment. Regeneration of spent adsorbent was carried out using microwave irradiation, achieving ~83.11 % desorption. The energy recovered from the loaded NAP in terms of higher heating value was 14.15 MJ kg−1, further enhancing its utilization. The low cost of PSB (USD 19.49) also justifies its utilization for wastewater treatment from the economic perspective.

Controlled synthesis of ZnO particles on the surface of natural cellulosic fibers: effect of concentration, heating and sonication

We report on the use of fique natural fibers as solid matrices for the deposition of zinc oxide (ZnO). Fique fibers, native to Colombia, are composed of cellulose (63–70 %) and have a heterogeneous surface morphology with high oxygen density that facilitates metal oxide nanoparticle growth and stabilization. Fique fiber–ZnO biocomposites were synthesized by a co-precipitation method using ZnSO4 as precursor, NaOH for hydroxide formation and thermal/ultrasound energy to promote Zn(OH)2/Zn(OH) 4 2− decomposition and ZnO formation. The biocomposite was characterized using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy with attenuated total reflectance, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The synthesis of ZnO nanoparticles has been widely reported on inorganic substrates and soft natural fibers; however studies on how experimental parameters affect ZnO features on heterogeneous phase reactions are scarce, as well as the use of hard complex cellulosic fibers as solid supports for its growth. We observed that [OH−]/[Zn2+] ratios, heating or sonication time wield a strong influence on the amount, shape, size and distribution of ZnO crystals on the fique fibers; hence confirming the potential of hard natural fibers as surface active materials for novel biocomposites synthesis. We believe these materials, where the hard fiber robustness and the transition metal oxide catalytic properties are synergistically combined, could be promising functional alternatives that will favor a widespread nanoparticle usage for environmental applications such as wastewater treatment processes.

Lignocellulosic-derived modified agricultural waste: Development, characterisation and implementation in sequestering pyridine from aqueous solutions

The development and characterisation of modified agricultural waste (MAW) by H3PO4 activation is addressed in this study for sequestering pyridine from aqueous solutions. The adsorbent is characterised by carbon, hydrogen and nitrogen content of 55.53%, 3.28% and 0.98% respectively. The adsorbent also shows acidic (carboxylic, lactonic, phenolic groups) and basic carbon surface functionalities, functional groups viz. hydroxyl, carboxylic acid and bounded water molecules, BET surface area of 1254.67m2g−1, heterogeneous surface morphology and graphite like XRD patterns. Adsorption of pyridine is executed to evaluate the adsorptive uptake in batch (qe=107.18mgg−1) as well as in column system (qe=140.94mgg−1). The adsorption process followed the pseudo-second-order kinetics with the Langmuir isotherm best representing the equilibrium adsorption data. The thermodynamic parameters (ΔHo=9.39kJmol−1, ΔGo=−5.99kJmol−1, ΔSo=50.76JK−1mol−1) confirm the endothermic and spontaneous nature of the adsorption process with increase in randomness at solid/solution interface. The adsorption mechanism is governed by electrostatic and π–π dispersive interactions as well as by a two stage diffusion phenomena. Thermally regenerated spent MAW exhibited better adsorption efficiency for five adsorption–desorption cycles than chemically regenerated. The low-cost of MAW (USD 10.714 per kg) and favourable adsorption parameters justifies its use in the adsorptive removal of pyridine.

Thermal and Dynamic Investigations on Brake Pad Composites Produced with Lignin-Phenol-Formaldehyde Resin

Brake pads are composite materials which have been constantly improved by new materials that increase the quality and reduce the non-renewable raw materials. The goal of this work is to study the behavior of brake pads produced with replacement of phenol-formaldehyde resin by lignin up to 40% weight ratio. The Krauss method of characterization and SEM analysis were employed. The results showed an average friction coefficient approximately to μm=0.4 and a heterogeneous surface morphology. The satisfactory results are compatible with the current friction materials.

Adaptive Selective Learning for automatic identification of sub-kilometer craters

Counting craters is a fundamental task of planetary science, because it provides the only tool for measuring relative ages of planetary surfaces. However, advances in surveying craters present in data gathered by planetary probes have not kept up with advances in data collection. It becomes extremely challenging to automatically count a very large number of small, sub-kilometer size craters in a deluge of high resolution planetary images. In this paper, we combine active learning with semi-supervised learning to build an adaptive learning system to automatically detect craters from high resolution panchromatic planetary images. We propose an Adaptive Selective Algorithm to iteratively enrich an original small training set, using unlabeled test set without additional human labeling effort, to detect craters from a large volume of images. We propose three strategies to improve detection accuracy by integrating classification with exploration on unlabeled samples. The Majority Vote Strategy is used to automatically obtain class labels by exploiting unlabeled samples. The De-Mixed Strategy is used on instance filtering to obtain reliable samples. The Active Stability Strategy is used to obtain an appropriate class distribution in the constructed training set by detecting unstable classes. By using those three strategies, we actively select test instances from test images into an existing small initial training set while rebuilding the classifier in the mean time. Our proposed algorithms are empirically evaluated on a large high resolution Martian image, exhibiting a heavily cratered Martian terrain characterized by heterogeneous surface morphology. The experimental results demonstrate that the proposed approach achieves a higher accuracy than other existing approaches to a large extent.

Shellac‐polyamidoamine: Design of a new polymeric carrier material for controlled release application

AbstractThe development of a pH sensitive, biodegradable polymer from the combination of Shellac (a natural polymer secreted by lac insect) and polyamidoamine (PAA) (a synthetic polymer) yielded a new biocompatible polymer Shellac‐PAA in a photopolymerization process. Scanning electron micrograph of Shellac‐PAA shows an interesting heterogeneous surface morphology supported with observation of two different melting temperatures obtained from differential scanning calorimetric measurement. The equilibrium swelling properties of the polymeric material was studied as a function of pH and time in buffer solutions similar to that of gastric and intestinal fluids. The controlled release kinetics of a model colon specific drug 5‐aminosalicylic acid showed Fickian diffusion behavior. The new polymer is biocompatible, biodegradable and, hence, projected as a new kind of polymer with improved properties, which can be a potential candidate for controlled release of therapeutic agents in colon specific diseases. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Flexible Memristors Fabricated through Sol-Gel Hydrolysis

Memristors were fabricated on flexible polyethylene terephthalate substrates consisting of an oxide film generated through hydrolysis of a spun-on sol-gel. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, and electron energy loss spectroscopy measurements indicated that the oxide films were amorphous TiO2 with a significant fraction of organic material, causing a heterogeneous surface morphology. Despite the morphology and the organic material, these memristors exhibit switching similar to "traditional" memristors. Also, current-voltage (I-V) measurements suggest that this switching was not due to the electric field in the memristors. Additionally, thermal imaging measurements and I-V measurements performed after sectioning the memristors suggest that conduction occurred via localized conduction pathways. Capacitance-frequency and conductance-frequency measurements indicate an additional dielectric loss mechanism was present prior to switching to the higher current state. This loss mechanism is attributed to dipoles present in the organic components of the oxide films from the original sol-gel.

Optical and spectroscopic characterization of germanium selenide glass films

A previews study of germanium selenide glass films by scanning electron microscopy and atomic force microscopy revealed a heterogeneous surface morphology consisting of granular regions ∼15–50 nm in size, which cause high optical losses. The present work was performed in order to further characterize such materials using spectroscopic ellipsometry, infrared (IR) and Raman spectroscopies. Chalcogenide glass films with GeSe 2, Ge 28Sb 12Se 60 and GeSe compositions have been deposited on single crystal silicon and silica glass substrates by vacuum thermal evaporation. The film thickness and the optical constants were obtained from spectroscopic ellipsometry using the Tauc-Lorenz dispersion formula. A model was derived for the film structure, which included a roughness layer at the surface. This top layer was found to have a thickness of ∼5–15 nm, of the order of the size of the granular regions previously reported. The optical bandgap of the samples increased with increasing selenium content, while the refractive index decreased. Despite a previous report of large scale phase separation in bulk Ge 26Sb 14Se 60 glass, the fundamental IR and Raman spectra obtained in the present work did not provide any clear evidence for such phase separation which could be associated with the heterogeneous nanostructure observed at the surface of the films.

Nanografting versus Solution Self-Assembly of α,ω-Alkanedithiols on Au(111) Investigated by AFM

The solution self-assembly of alpha,omega-alkanedithiols onto Au(111) was investigated using atomic force microscopy (AFM). A heterogeneous surface morphology is apparent for 1,8-octanedithiol and for 1,9-nonanedithiol self-assembled monolayers (SAMs) prepared by solution immersion as compared to methyl-terminated n-alkanethiols. Local views from AFM images reveal a layer of mixed molecular orientations for alpha,omega-alkanedithiols, which evidence surface structures with heights corresponding to both lying-down and standing-up orientations. For dithiol SAMs prepared by solution self-assembly, the majority of alpha,omega-alkanedithiol molecules chemisorb with both thiol end groups bound to the Au(111) surface with the backbone of the alkane chain aligned parallel to the surface. However, AFM images disclose that there are also islands of standing molecules scattered throughout the surface. To measure the thickness of alpha,omega-alkanedithiol SAMs with angstrom sensitivity, methyl-terminated n-alkanethiols with known dimensions were used as molecular rulers. Under conditions of spatially constrained self-assembly, nanopatterns of alpha,omega-alkanedithiols written by nanografting formed monolayers with heights corresponding to an upright configuration.

Atomic Force Microscopy Measurement of Heterogeneity in Bacterial Surface Hydrophobicity

The structure and physicochemical properties of microbial surfaces at the molecular level determine their adhesion to surfaces and interfaces. Here, we report the use of atomic force microscopy (AFM) to explore the morphology of soft, living cells in aqueous buffer, to map bacterial surface heterogeneities, and to directly correlate the results in the AFM force-distance curves to the macroscopic properties of the microbial surfaces. The surfaces of two bacterial species, Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c, showing different macroscopic surface hydrophobicity were probed with chemically functionalized AFM tips, terminating in hydrophobic and hydrophilic groups. All force measurements were obtained in contact mode and made on a location of the bacterium selected from the alternating current mode image. AFM imaging revealed morphological details of the microbial-surface ultrastructures with about 20 nm resolution. The heterogeneous surface morphology was directly correlated with differences in adhesion forces as revealed by retraction force curves and also with the presence of external structures, either pili or capsules, as confirmed by transmission electron microscopy. The AFM force curves for both bacterial species showed differences in the interactions of extracellular structures with hydrophilic and hydrophobic tips. A. venetianus RAG-1 showed an irregular pattern with multiple adhesion peaks suggesting the presence of biopolymers with different lengths on its surface. R. erythropolis 20S-E1-c exhibited long-range attraction forces and single rupture events suggesting a more hydrophobic and smoother surface. The adhesion force measurements indicated a patchy surface distribution of interaction forces for both bacterial species, with the highest forces grouped at one pole of the cell for R. erythropolis 20S-E1-c and a random distribution of adhesion forces in the case of A. venetianus RAG-1. The magnitude of the adhesion forces was proportional to the three-phase contact angle between hexadecane and water on the bacterial surfaces.

Selective Protein Adsorption on a Phase-Separated Solvent-Cast Polymer Blend

Polymer-based biomedical devices are growing increasingly sophisticated as compositions evolve toward copolymers and blends in order to satisfy complex design criteria. Such polymers afford opportunities for both micro- and macrophase separation at nano- and micro-length scales and raise questions concerning the role of heterogeneous surface morphology on protein adsorption. Adsorbed protein layers play a critical role in mediating the interaction of cells with polymer surfaces, and both understanding and controlling protein adsorption is assuming greater significance in the development of surfaces with enhanced physiological compatibility. Here we study the short-time adsorption of ferritin, a model protein highly resistant to denaturation and easily imaged in the transmission electron microscope (TEM), onto a phase-separated homopolymer blend of polycaprolactone (PCL) and a polycarbonate derived from desaminotyrosyl-tyrosine dodecyl ester (PDTD). At physiological pH, ferritin selectively adsorbs onto the PDTD phase at a surface density approximately three times greater than that on the PCL phase. By decreasing the pH below ferritin's isoelectric point so its average charge becomes positive, the selective adsorption disappears and the surface density of adsorbed ferritin becomes independent of the phase separation. We attribute the selectivity to the electrostatic repulsion between ferritin and hydrolytically charged PCL, both of which will have a net negative charge at physiological pH. To perform these experiments, we solvent-cast ultrathin polymer films onto dissolvable salt substrates, and we characterize the morphology by TEM imaging and quantitative spatially resolved electron energy-loss spectroscopy (EELS). We find that the film morphology depends strongly on such processing-related variables as the solvent evaporation rate and the nature of the surface in contact with the polymer film during casting. The adsorption of ferritin depends on whether the film is phase-separated as well as to which surface of the film the protein solution is exposed, and these findings suggest that seemingly small variations in polymer processing that influence both the bulk and surface morphology can have a profound effect on the short-time protein adsorption.

Influence of heterogeneous surface morphology on analytical signal formation in total reflection x‐ray fluorescence analysis

AbstractThe fundamentals of the influence of heterogeneous surface morphology on the analytical signal formation in total reflection x‐ray fluorescence (TXRF) analysis were developed. The dependence of x‐ray fluorescence line intensity on mechanisms of new phase nucleation and growth on a foreign low‐density substrate (reflector) was considered theoretically. The approaches were tested during the study of surfaces of disc glass–ceramic carbon electrodes electrochemically modified by metal deposition and co‐deposition from aqueous solutions. It was shown that TXRF could be effectively applied for the identification of nucleation and growth mechanisms of metal and alloy thin films. Copyright © 2002 John Wiley &amp; Sons, Ltd.

An electrochemical impedance study on the kinetics and mechanism of the hydrogen evolution reaction on nickel molybdenite electrodes

Electrodeposited Ni NiMoS 2 electrodes have shown good electrocatalytic activity towards the hydrogen evolution reaction as well satisfactory long-term operational performance. The hydrogen evolution reaction on these electrodes, which in previous investigations using steady-state polarizations, cyclic voltammetry and scanning electron microscopy revealed high surface area and a very heterogeneous surface morphology, has been studied by applying electrochemical impedance spectroscopy (EIS). The kinetics and mechanism of the hydrogen evolution reaction (HER) on electrodeposited Ni NiMoS 2 electrodes have been investigated in the frequency range 5 mHz ⩽ f ⩽ 10 kHz. A detailed dynamic system analysis is presented taking into account the contributions of Tafel-Volmer-Heyrovsky reaction steps as well as the absorption and diffusion of hydrogen atoms into the electrode material. For comparison results obtained for the HER on electrodeposited Ni electrodes are also discussed.