Cathodic Charging Research Articles

In-situ observation of martensitic transformation in an interstitial metastable high-entropy alloy during cathodic hydrogen charging

We show for the first time that a critical amount of dissolved hydrogen can induce a phase transformation from γ-austenite to ε-martensite in an interstitial metastable high-entropy alloy. This is demonstrated by in-situ hydrogen charging in combination with nanoindentation and scanning probe microscopy, plus further electron channeling contrast imaging, X-ray diffraction, and transmission Kikuchi diffraction techniques. The transformed martensites appear as bands on the surface along γ-{111} habit planes, leading to an irreversible increase of hardness. The hydrogen-induced internal stress together with the intrinsic hydrogen effects are proposed to be responsible for the martensitic transformation upon hydrogen charging.

Evaluation of properties in steel with boride coatings under hydrogen

In this study present the benefit of boride coating on surface of ASTM A-36 steel and the evaluation of the properties of the hard coatings under hydrogen permeation. The ASTM A-36 steel was surface hardened by diffusion boron atoms at temperature at 950 °C for 3, 5, and 7 h using the dehydrated boron paste-pack method. The hard coatings obtained on surface A-36 steel were examined using scanning electron microscopy combined with energy dispersive spectrometry and X-ray diffraction. In addition, the hydrogen was introduce into samples with hard coating through cathodic charging applying a current density of 50 mA/cm2 by 0.5 M sulfuric acid solution kept at a room temperature. Three-point bending and instrument nanoindentation were evaluated on sample borided before and after hydrogen charged.Microstructural characterization revealed bilayer (FeB + Fe2B) coatings with saw-tooth morphology and the thicknes values of FeB and Fe2B were in range of 25.30 to 45.3 μm and 77.09 to 187.10 μm, respectively. After hydrogen charged, the microstructure delayed the diffusion of hydrogen, reducing the formation of cracks by increasing the FeB and Fe2B coatings. However. the hardness of the samples tends to increase while the elastic modulus decrease. As well as the static load by bending test decrease due to steel ASTM A-36‑hydrogen interaction.

High-performance Nanocrystal Platinum on Hierarchical Microelectrode for Biochemical Sensing.

A high-performance hierarchical microelectrode array was reported, which significantly enlarged the surface area and reduced edge effect of the unevenly distributed electric field, using novel nanocrystal platinum (Pt) surface modification and hierarchical topologies. A hierarchical three-dimensional (3D) nanostructured Pt was introduced on the surface of microelectrodes (diameter Φ=10 pm, and seed pad Φ=200 μm) to reduce the impedance by ~91.2% down to 2.63 kn at 1kHz, and increase the cathodic charge storage capacity (CSCc) by ~60 times up to 217.9 mC.cm-2 compared with that of bare Pt substrate, demonstrating superior electrochemical performances to the traditional modified electrodes. In addition, the hierarchical microelectrodes exhibited great stability and linearity for glucose sensing with a detection limit of ~1.5 μM, which showed potential applications for neural interface and biochemical sensing.

Sequential run of the PEO process with various pulsed bipolar current waveforms

Oxide coatings were produced on a 2024 aluminium alloy using a pulsed bipolar current plasma electrolytic oxidation (PEO) process in an alkaline electrolyte. The use of sequences including various current waveforms during the same treatment was investigated, mainly by applying various combinations of two different anodic to cathodic charge quantity ratio (RCQ = 0.9 and 6.0). The morphology of the produced PEO coatings was observed using scanning electron microscopy while the behaviour of the micro-discharges was characterized in real time with the process using plasma diagnostic techniques. Compared with conventional treatments conducted in a single sequence, results evidenced that the thickness and the compactness of the PEO coating are enhanced by switching from a high to a low RCQ value in the course of the process. In contrast, reverse sequenced treatments leads to a significant deterioration of the produced PEO coating. A possible explanation exposed in the present study consists in considering the main role played by the mechanism of charge accumulation at the electrolyte/oxide interface on the micro-discharges behaviour with respect to the coating morphology and the applied charge quantity ratio. Finally, by establishing a relationship between process, physical and material quantities, this study demonstrate that the use of sequenced treatments open opportunities for a better energetic management of the PEO process.

A Comparative Study of the Role of Hydrogen on Degradation of the Mechanical Properties of API X60, X60SS, and X70 Pipeline Steels

Three grades of high strength pipeline steel (API X60, X60SS, and X70) are subjected to cathodic hydrogen charging to determine the susceptibility of each steel grade to hydrogen‐induced cracking (HIC). The specimens are subjected to tensile stress until failure to generate stress‐strain, ductility, and toughness data. The fractured specimens are analyzed using a scanning electron microscope equipped with an EDS detector to determine crack initiation sites for the investigated grades of steel. The expectation that the X60SS steel grade will perform better than other grades is not met, instead it is found that under the cathodic hydrogen charging condition, the X60SS is more susceptible than the other two steel grades with respect to loss of toughness, ductility, and ultimate tensile strength. The presence of Ca‐Al‐based inclusions is the most common along the fracture surfaces. Therefore, these inclusions also act as fairly strong trapping sites that under plastically strained conditions, they can result in fisheye features which severely impact the mechanical properties of the steel specimens.

Preferential corrosion of coherent twin boundaries in pure nickel under cathodic charging

We describe an investigation of microstructure in pure nickel (Ni) after cathodic charging in an aqueous electrolyte. Intergranular corrosion occurs on the sample surface and takes the form of long trenches along coherent twin boundaries (CTBs): sites that have often been considered especially resistant to corrosion. Integrating electron backscatter diffraction and x-ray computed tomography, we show that the trenches are formed by the growth and eventual overlap of isolated conical cavities, which, in turn, are aligned with $\ensuremath{\langle}110\ensuremath{\rangle}$-type directions within CTB planes. The $\ensuremath{\langle}110\ensuremath{\rangle}$-type orientation is consistent with cavity initiation at high-energy, symmetric incoherent twin boundary facets within CTB planes. Our observations show that, far from being always corrosion resistant, CTBs are especially susceptible to intergranular corrosion under some conditions.

A Proposal for the Application of Failure Assessment Diagrams to Subcritical Hydrogen Induced Cracking Propagation Processes

In this work, an optimization proposal for a model based on the definition of regions for crack propagation by means of the micromechanical comparison by SEM images and its application to failure assessment diagrams (FADs) is presented. It consists in three approaches. (1) The definition of the crack propagation initiation in the elastic-plastic range. (2) A slight modification of the zones in which the FAD is divided for hydrogen induced cracking (HIC) conditions. (3) The introduction of a simple correction for the definition of the Kr coordinate of the FAD to take into account the fracture toughness reduction caused by an aggressive environment, instead of using a fracture parameter obtained from a test in air. For the experimental work, four medium and high strength steels exposed to a cathodic charge and cathodic protection environments were employed, studying two different loading rates in each case, and testing C(T) samples under slow rates in the environment. The study was completed with a subsequent fractographic analysis by SEM. A good degree of fulfilment was appreciated in both materials and environmental conditions, showing the validity of the predictions supplied by the FAD optimization model proposal, which constitutes an advance in the accuracy of the FAD predictive model.

Effect of Hydrogen Embrittlement on the Mechanical and Electrochemical Properties of Carbon Steel API 5L X65 in a CO2-Saturated 3.5 Wt.% NaCl Solution

The effect of hydrogen charging of carbon steel API 5L X65 (UNS K03014) used in natural gas pipelines was investigated. Metal specimens were cathodically charged at potentials below Ecorr at 40°C in CO2-saturated 3.5 wt.% NaCl solution, pH 4 for 24 hours prior to carrying out potentiodynamic polarization and tensile tests. Electrochemical experiments were used to calculate corrosion rates and elucidate active, active-passive, and passive regions. Furthermore, fracture and fatigue of the alloy was determined at 1 × 10−6 s−1 strain rate. Surface characterization of the fractured and corroded samples was conducted using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results from hydrogen embrittlement-induced specimens were compared to a parallel study of uncharged specimens to understand the effect of hydrogen cathodic charging on carbon steel API 5L X65.

XPS Analysis of the Oxide Films Formed on Non-Charged and Hydrogen-Charged 316L SS in Deaerated High Temperature Water

Austenitic stainless steel components have been used in pressurized water reactors (PWRs) coolants. These austenitic stainless steels may absorb hydrogen from either the dissociation of dissolved hydrogen in PWR primary water or the corrosion processes at the steel surfaces during the immersion in PWR primary water. It is necessary to investigate the effect of hydrogen in alloys on the oxidation and resultant environmental degradation processes in high temperature water environments. In the present study, the oxide films formed in deaerated PWR primary water at 300℃on a cold worked 316L (316LCW) stainless steel with or without prior hydrogen-charging were characterized. Hydrogen-charging of 316LCW was performed by cathodic charging in sulfuric acid solution containing thiourea at room temperature. Prior to the immersion tests, the Immersion tests were performed in a 2-L Ti-autoclave with solution deaerated by purging N2 gas before heating to test temperature. The oxide films formed on 316LCW and hydrogen-charged 316L CW (316LCW-H) specimens after exposure to deaerated PWR primary water at 300 oC for168 h were observed. The XPS depth profiles of the oxide films formed on 316LCW and 316LCW-H specimens after exposed to simulated PWR primary water are compared. The thickness of the oxide film was estimated from the half height of oxygen concentration and the sputtering rate (0.1 nm/s), for determining the thickness of the oxide film that was about 180 nm on 316LCW and about 250 nm on 316LCW-H. The oxide films formed on both 316LCW and 316LCW-H were enriched in Fe and Ni in the outer layer, and enriched in Cr in the inner part of the oxide film. The Cr content in the inner oxide layer formed on 316LCW-H specimen was lower than that on 316LCW specimen. Figure 1

Ultra Micro Neural Stimulation and Recording Electrodes

With recent interest in increasing selectivity and reducing foreign body reaction to neural implants by using small-scale indwelling electrode arrays, the necessity of using ultramicroelectrodes (UME) in the implant design is inevitable. UMEs have been widely used as sensors for detecting biological elements such as neurotransmitters and oxygen in living tissue. Thus, their behavior in vitro under similar experimental conditions has been well investigated by performing electrochemical experiments such as cyclic voltammetry and chronoamperometry. However, the behavior of UMEs under neural stimulation and recording conditions has not been well characterized. In this study we have investigated the behavior of UMEs in cyclic voltammetry, electrochemical impedance spectroscopy, chronopotentiometry, and chronoamperometry experiments in phosphate buffered saline (PBS) electrolyte. Comparisons are made between macro, micro, and ultra micro platinum electrode behavior in PBS with ionic reactive species, hydrogen and hydroxyl ions, in galvanostatic and potentiostatic experiments. As migration is also a charge transfer mechanisms besides diffusion in electrochemical cells with ionic reactive species, the effect of hemispherical diffusion on the total current flux in such conditions has been evaluated by means of finite element analysis. A transient two-dimensional axisymmetric finite element model is developed to solve the Poisson-Nernst-Planck equation (Equations (1-2)) using COMSOL Multiphysics software. It has been assumed that the ionic flux is due to migration and diffusion and there is no convection flux. where V is the electric potential, ε the permittivity of the electrolyte, e the electron charge, ci the ionic concentration of ion i, Ni the flux of ion i, Di the diffusion coefficient of ion I, R the Boltzmann constant, T the temperature, zi the balance of ion i, umi the mobility of ion I, F the Faraday constant. Butler-Volmer equation (Equation 3) was assigned to the electrode-electrolyte interface to represent the interfacial reactions. where iloc is the local charge transfer current density, i0 the exchange current density, cr is the concentration of reduced species, co the concentration of oxidized species, crb the bulk concentration of reduced species, cob bulk concentration of oxidized species, η the overpotential, ac the cathodic transfer coefficient. Gouy-Chapman-Stern model was used to simulate the electric double layer. Based on the Gouy-Chapman-Stern model the electric double layer is the capacitance of the Stern and Gouy-Chapman layers in series (Equations (4-5)). Where CH is the Stern layer capacitance, CGc the Gouy-Chapman layer capacitance, εr the relative permittivity of the electrolyte, ε0 the electric permittivity of free space,λD the Debye length, e the elementary charge, UT the thermal voltage, c0 the concentration of ions in the bulk. Cyclic voltammetry experiments were performed in PBS electrolyte purged with Argon gas with a scan rate of 50 mV/s. Charge storage capacity of a 10 mm diameter UME, 100 mm diameter microelectrode, and 1.6 mm diameter macroelectrode platinum electrodes (Bioanalytical Systems) in PBS electrolyte were compared. Upon 99% decrease in geometric surface area, the increase in cathodic and anodic charge storage capacities are 82% and 140% from microelectrode to UME, while these increases are only 16% and 11% from macro to microelectrode, respectively. Figure 1

A simple one-step hydrothermal synthesis of cobalt[sbnd]nickel selenide/graphene nanohybrid as an advanced platinum free counter electrode for dye sensitized solar cell

A nanohybrid comprises of cobalt-nickel selenide (Co0.50Ni0.50Se) nanoparticles dispersed on graphene nanosheets (GN) has been synthesized by a simple one-step hydrothermal method to use as a counter electrode for dye sensitized solar cell (DSSC). The structural changes and the corresponding electrocatalytic properties in terms of cathodic peak current density and charge transfer resistance at the electrode/electrolyte interface for Co0.5Ni0.5Se/GN nanohybrid with respect to the mass ratio between Co0.5Ni0.5Se nanoparticles and graphene nanosheets have been investigated. Co0.5Ni0.5Se/GN0.50 exhibits higher electrocatalytic activity and lower charge transfer resistance than other Co0.5Ni0.5Se/GN nanohybrids and std. platinum (Pt) counter electrodes. Finally, the DSSC fabricated with Co0.5Ni0.5Se/GN0.50 as the counter electrode delivered photo-conversion efficiency (PCE) of 9.42%, which is higher than that of DSSC fabricated with Co0.5Ni0.5Se (7.59%) and std. Pt (7.68%) counter electrodes. This improved electrochemical performance and higher PCE incited by the synergistic effect of Co and Ni in Co0.5Ni0.5Se nanoparticles, as well as Co0.5Ni0.5Se and graphene, could make Co0.5Ni0.5Se/GN0.50 nanohybrid as a promising low-cost Pt-free counter electrode for DSSC.

Electricity generation from paddy soil for powering an electronic timer and an analysis of active exoelectrogenic bacteria

In farmlands, most electronic devices have no connection to a power source and have to work on batteries. To explore paddy soil as an in situ power source, herein, we in the present study constructed sediment microbial fuel cells (SMFCs) in paddy soil. An open circuit voltage of 1.596 V and a maximum power density of 29.42 mWm−2 were obtained by serially connecting three SMFCs. Electrochemical impedance spectroscopy showed that the internal resistance which comprised ohmic resistance and anodic and cathodic charge transfer resistance was approximately 400 Ω for each of the three individual SMFCs. We used the serially connected SMFCs to power an electronic timer through a 1 F capacitor. The SMFCs had powered the timer for 80 h until the potential of the SMFCs dropped below 0.936 V. Then, RNA was extracted from anode samples and 16S rRNA was sequenced following reverse transcription. The results showed that the relative abundance of active exoelectrogenic bacteria-associated genera on the anode was 13.03%, 27.78%, and 16.17% for the three SMFCs with Geobacter and Anaeromyxobacter being the dominant genera. Our findings provide the possibility of powering electronic devices in the field by using soil as a power source.

CNT bundle-based thin intracochlear electrode array.

It is known that the insertion of the intracochlear electrode is critical procedure because the damage around cochlear structures can deteriorate hearing restoration. To reduce the trauma during the electrode insertion surgery, we developed a thin and flexible intracochlear electrode array constructed with carbon nanotube (CNT) bundles. Each CNT bundle was used for an individual electrode channel after coated with parylene C for insulation. By encapsulating eight CNT bundles with silicone elastomer, an 8-channel intracochlear electrode array was fabricated. The mechanical and electrochemical characteristics were assessed to evaluate the flexibility and feasibility of the electrode as a stimulation electrode. The functionality of the electrode was confirmed by electrically evoked auditory brainstem responses (eABR) recorded from a rat. The proposed electrode has a thickness of 135μm at the apex and 395μm at the base. It was demonstrated that the CNT bundle-based electrodes require 6-fold the lower insertion force than metal wire-based electrodes. The electrode impedance and the cathodic charge storage capacitance (CSCc) were 2.70 kΩ ∠-20.4° at 1kHz and - 708 mC/cm2, respectively. The eABR waves III and V were observed when stimulation current is greater than 50μA. A thin and flexible CNT bundle-based intracochlear electrode array was successfully developed. The feasibility of the proposed electrode was shown in terms of mechanical and electrochemical characteristics. A proposed CNT bundle-based intracochlear electrode may reduce the risk of trauma during electrode insertion surgery.

Activated carbon-supported multi-doped graphene as high-efficient catalyst to modify air cathode in microbial fuel cells

It is difficult to apply microbial fuel cells (MFCs) basing on activated carbon air cathode in practical application because of the low efficiency of oxygen reduction reaction. Thus, exploring high-efficient catalyst to improve the cathode performance is of emergent significance. Herein, we synthesize an activated carbon-supported FeAgN multi-doped graphene as the air cathode catalyst in MFCs via a simple preparation and calcination of FeAg prussian blue analogues. As proved, the designed catalyst contributes to the decrease of the cathode's diffusion resistance and charge transfer resistance; meanwhile it immensely promotes the kinetics towards ORR by accelerating the migration of electron from the encapsulated bimetals to the surrounding carbon structure, indicating that the deposit of multi-doped graphene catalyst reinforces the cathode's conductivity and expedites the electron transfer process. The output power performances indicate that a highest maximum power density reaches up to 1956.45 mW m−2, which is 7 times higher than that of the control, foreboding the catalyst's potential application in MFCs.

Multi-labeled electrochemical sensor for cost-efficient detection of single nucleotide substitutions in folded nucleic acids

Analysis of single nucleotide substitutions (SNS) in nucleic acids is the basis for the diagnosis of drug-resistant pathogens as well as human genetic disorders among a broad range of other applications. However, SNS are often inaccessible for the analysis by hybridization probe due to the location in double stranded regions of folded single stranded DNA or RNA analytes. Here we introduce an electrochemical sensor that is able to analyze SNS in folded nucleic acids. The electrochemical sensor takes advantage of a universal electrode-bound hairpin (UTH). It relies on the recognition of targeted nucleic acids by analyte-specific adaptor strands R and L that also hybridize with UTH. Strand L can bind several methylene blue (MeB)-probes thus placing MeB groups close to the electrode surface, which enables cathodic charge transfer. We demonstrated that the same UTH-functionalized electrode and MeB-probe can be used to analyze DNA analytes with different sequences. The sensor is highly selective toward SNS even at room temperature and can be regenerated for next round by rinse with water. The ability of the sensor to analyze SNS within secondary structure folded DNA was demonstrated. The sensing system is capable of detecting SNS in bacterial DNA, useful to differentiate drug-resistant from drug-susceptible mycobacterium tuberculosis. The proposed platform uniquely combines high SNS selectivity with ability to analyze potentially any DNA or RNA sequence including those folded in stable structures, therefore, creates a basis for a cost efficient electrochemical sensing of nucleic acids applicable both in medical diagnostics and environmental monitoring of microorganisms.

Characterization of hydrogenated niobium interlayer and its application in TiAl/Ti2AlNb diffusion bonding

Hydrogenation of niobium foil was achieved by cathodic charging and its application as the interlayer facilitates a sound joint of TiAl/Ti2AlNb. The microstructure and mechanical properties of hydrogenated niobium were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nano-indentation and thermogravimetry (TG) analysis. It is demonstrated that the plasticity of the surface of niobium interlayer is improved and dislocation density in niobium crystal lattice increases significantly, owing to the process of niobium interlayer hydrogenation and subsequent dehydrogenation. To investigate the effect of the hydrogenation of the niobium interlayer on the TiAl/Ti2AlNb diffusion bonding joint, the pure niobium foil was also applied as the interlayer for comparison. The effect of the bonding parameters on the interfacial microstructure evolution and mechanical properties of the joints were systematically analyzed by SEM coupled with an energy-dispersive spectroscopy (EDS) and shear test. The typical microstructure of the joint is found to be TiAl/B2 phase/Nb/δ phase/β phase/Ti2AlNb. With the increase of the hydrogen content, bonding temperature, holding time and bonding pressure, the bonding defects decreased and the thickness of the diffusion layer increased correspondingly. The shear strength of joint reached 258.9 MPa at 950 °C for 40 min under a pressure of 5 MPa with the hydrogenated niobium interlayer of 1.0 wt% hydrogen content.

Characterization of tetrodes coated with Au nanoparticles (AuNPs) and PEDOT and their application to thalamic neural signal detection in vivo

Tetrodes, consisting of four twisted micro-wires can simultaneously record the number of neurons in the brain. To improve the quality of neuronal activity detection, the tetrode tips should be modified to increase the surface area and lower the impedance properties. In this study, tetrode tips were modified by the electrodeposition of Au nanoparticles (AuNPs) and dextran (Dex) doped poly (3,4-ethylenedioxythiophene) (PEDOT). The electrochemical properties were measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A decrease in the impedance value from 4.3 MΩ to 13 kΩ at 1 kHz was achieved by the modified tetrodes. The cathodic charge storage capacity (CSCC) of AuNPs-PEDOT deposited tetrodes was 4.5 mC/cm2, as determined by CV measurements. The tetrodes that were electroplated with AuNPs and PEDOT exhibited an increased surface area, which reduced the tetrode impedance. In vivo recording in the ventral posterior medial (VPM) nucleus of the thalamus was performed to investigate the single-unit activity in normal rats. To evaluate the recording performance of modified tetrodes, spontaneous spike signals were recorded. The values of the L-ratio, isolation distance and signal-to-noise(SNR) confirmed that electroplating the tetrode surface with AuNPs and PEDOT improved the recording performance, and these parameters could be used to effectively quantify the spikes of each cluster.

Detailed mechanisms of hydrogen charging and hydrogen stress cracking of steel in liquid ammonia storage

When the unprecedented environmental cracking of steel in liquid ammonia was collectively studied, its undisputable “anodic character” was taken as the signature of astress corrosion crackingmechanism, which is effectively the case in aqueous corrosion. Conversely, when the metallurgical precautions proved to be the same as in sour service, this strongly suggested ahydrogen stress crackingmechanism. In aqueous corrosion, however, this can only occur by cathodic hydrogen charging at low potential, and for 50 years, this basic contradiction could never be overcome. Actually, it occurs that the liquid ammonia solvent (NH3) is 50% richer in hydrogen than the water solvent (OH2), so that hydrogen gas can also be produced by a partial oxidisation into ½ N2 + H2. This therefore induces a theoretical possibility of an “anodic” hydrogen charging, or more exactly a protonic cathodic reaction only running at high potential on passive iron in oxygen contaminated ammonia. And once the detrimental potential is achieved through appropriate combinations of oxygen and water traces, the charging process becomes an autonomous oxidation-reduction at the steel surface NH3 → ½ N2 + H2 + (H+ + e−)steel. In Part II (Jean-Louis Crolet,Matériaux & Techniques107, 402, 2019), this new assumption will be successfully confronted to all the factual data from both field and laboratory experience.

Cathodic electrolytic hydrogen charging into Type 316L stainless steel weld

Cathodic electrolytic hydrogen charging into Type 316L stainless steel weld

Reduction Charge Smaller than the Deposited One in Cathodic Stripping Voltammograms of AgCl

A silver electrode was anodized in lowly concentrated potassium chloride solution almost under the steady state to generate a deposit of silver chloride on the electrode, and the deposit was cathodically stripped by linear potential scan to evaluate the reduction charge. Then the oxidation charge was larger than the reduction one. Since the equality was valid for long term chronocoulometry at the double potential step, the inequality is not due to any irreversibility of electrode reactions, but can be attributed to the process of the cathodic potential scan. A reason for the inequality is the negative charge of the capacitance involved in the electrode reaction, which has been observed in simple, dissolved redox species like a ferrocenyl derivative. The negative capacitive currents are conspicuous for high concentrations of redox species on the electrode because they result from the orientation of the dipoles of the redox species coupled with counterion, of which direction is opposite to that of the solvent dipoles. If a silver chloride film was thin enough to be regarded as a monolayer, we found that half of the cathodic stripping charge should be lost by the negative capacitance.