Galvanic Cell Research Articles

Graphene-Dominated Hybrid Coatings with Highly Compacted Structure on Stainless Steel Bipolar Plates.

Highly conductive corrosion protection coatings are necessary for metallic bipolar plates (BPs) of the proton-exchange membrane fuel cell. Graphene coatings have the potential of protecting metal substrates from corrosion without obscuring their excellent electrical conductivity. The electron transfer in the coatings facilitates the formation of galvanic cells, so the challenge is to block the mass transfer of the corrosion process. Here, we constructed highly compacted hybrid coatings with aligned water-dispersible graphene layers. The water-dispersible graphene (SG) held an electrical conductivity of >270 S cm-1 while providing an unprecedented dispersibility, which can be redispersed from filter cake with a concentration of 120 mg mL-1 or even dry state. The cohesion of the hybrid coatings was attributed to the interaction between highly aligned SG layers and the heterointerface between SG and polydopamine (PDA), as proven by the molecular dynamics simulations. The hybrid coatings presented a corrosion current density of 0.023 μA cm-2 and an interfacial contact resistance of 9.94 mΩ cm2, which meets the requirements of corrosion protection and electron transfer for the coatings on metallic BPs. The water-based fabrication method of the graphene-dominated hybrid coatings was a promising alternative of the vacuum-based deposition method for industrial production.

Poly(l-lactic acid)/polypyrrole(ATP)/magnesium composites for controlled drug release based on a galvanic cell

Taking drug orally is the most common method to treat chronic disease because it is less expensive and more convenient. However, the drug delivered by this route may be destroyed or cannot maintain the proper concentration to treat disease. This study develops poly(l-lactic acid)/polypyrrole(ATP)/magnesium (PLLA/PPy(ATP)/Mg) composite which is employed as a drug release system based on a galvanic cell. The PLLA/PPy(ATP)/Mg composite is synthesized by chemical polymerization which is efficient to prepare and suitable for large-scale production. The ATP release experiment indicates the system can release drug without electrical stimulation and the drug release rate can be controlled by adjusting the amount of Mg particles in a suitable range. The co-culture experiment with MC3T3-E1 cells reveals the composite membrane has little cytotoxicity. The present PLLA/PPy(ATP)/Mg composite possesses good conductivity, mechanical properties, biocompatibility and stability so that it can be applied in medical field in the future.

Influence of Different Heat Treatment Temperatures on the Microstructure and Corrosion Behaviour of Dual-Phase EN8 Steel in 0.5 M Sulphuric Acid Solution

Dual-phase steels provide an excellent combination of strength and ductility, as well as improved energy absorption and anti-corrosion protection properties. This research aims at evaluating the microstructure and corrosion behaviour of EN8 steel under different heat treatment temperatures in 0.5 M sulphuric acid solution (H2SO4) using the EIS, potentiodynamic polarization, and gravimetric method (weight-loss method). Austenitizing is performed at 973 K, 1023 K, 1063 K, and 1173 K for 2 h followed by quenching in water to form a ferrite–martensite (F–M) dual-phase structure. From the results, it is seen that the corrosion rate increased with different heat treatment conditions depending on the change in the phase when immersed in 0.5 M H2SO4 at the temperature of 303 K, 313 K, 323 K, and 333 K. This work investigates the energy of activation, enthalpy, and entropy of activation. For dual-phase steel containing ferrite and martensite, the corrosion behaviour depends on the amount of martensite and ferrite. As the austenitization temperature increases from 1023 to 1173 K, the amount of martensite increases. This is reflected in the increase of micro galvanic corrosion cells in the region between the ferrite and martensite phases, which acts as active corrosion centres. The normalized specimen showed greater corrosion resistance compared to the water-quenched specimen at 1173 K. This is due to the presence of lower carbon content for normalized dual-phase steel containing ferrite–pearlite phase than the ferrite–martensite phase present in specimen austenitized at 1173 K. Surface characterization and XRD confirmed the corrosion behaviour of the specimens under investigation.

Analysis of Tafel polarization scans of Magnesium-Steel galvanic couple under different corrosive environments at various temperatures

It is an attributed fact that magnesium, in normal conditions, behaves as active or anodic material and steel as a noble or cathodic material in a galvanic cell. In the current study, various experiments have been conducted to investigate the electrochemical behavior of magnesium and mild steel galvanic couples in tap water and 0.1M NaHCO3 corrosive environments at different temperatures (40 ℃ to 80 ℃). The potentiodynamic results have confirmed that in tap water, magnesium acts as an anode as it corrodes itself and protects steel surfaces under the influence of galvanic action at selected temperatures. However, magnesium became passive under 0.1M NaHCO3 making steel anodic, which deteriorates aggressively at higher temperatures in 0.1M NaHCO3. The polarity reversal phenomenon was also observed in the magnesium-steel couple when exposed to this environment. The microstructural examination has shown that passivation occurred due to the formation of an oxide layer that grew towards the steel side in the galvanic couple as the temperature increased. Thus, the study revealed that the magnesium would be more damaging to steel in a NaHCO3 environment if utilized in the temperature range of 60 ℃to 80 ℃.

Computational design of Mg alloys with minimal galvanic corrosion

Formation of galvanic cells between constituent phases is largely responsible for corrosion in Mg-based alloys. We develop a methodology to calculate the electrochemical potentials of intermetallic compounds and alloys using a simple model based on the Born-Haber cycle. Calculated electrochemical potentials are used to predict and control the formation of galvanic cells and minimize corrosion. We demonstrate the applicability of our model by minimizing galvanic corrosion in Mg-3wt%Sr-xZn alloy by tailoring the Zn composition. The methodology proposed in this work is applicable for any general alloy system and will facilitate efficient design of corrosion resistant alloys.

Acid mine drainage (AMD) treatment using galvanic electrochemical system Al–Cu

ABSTRACT Acid mine drainage was evaluated using a galvanic (GV) electrochemical system, Al–Cu (anode/cathode), based on a 32 factorial design. The factors analyzed were anodic area/volume ratios (A/V) of 0.037, 0.072, and 0.112 cm2/cm3, and treatment time from 0.25–8 h, and analyses were performed in duplicate with 11 degrees of freedom. The response variables were the total dissolved solids and concentrations of As, Cu, Co, Cr, Pb, Fe, Ni, and . The pH, electrical conductivity, and temperature were monitored during the process. Significant differences between treatments were determined by analysis of variance with Tukey’s test (p < 0.05) using Statgraphics Centurion XVI.I software. The results showed that a greater electrode surface, A/V ratio, and treatment time improved pollutant removal. The spontaneous reactions generated by the galvanic cell, through the current that flows owing to the potential difference between the Al and Cu electrodes, allows the removal of heavy metals, arsenic, and by coagulation and precipitation mechanisms. The removal efficiencies achieved were Cu (99.1%), As (76.6%), Ni (80.2%), Pb (83.6%), Cr (100%), Fe (93.71%), and 92.9% for sulfates. The X-ray diffraction and Raman analyses of the solid fraction indicated that cuprite was formed with a purity of 96%, and the recovery of Cu by the GV system may be a viable option for mining companies.

STATE AND PROSPECTS OF HANDLING METAL-CONTAINING HOUSEHOLD WASTE

The basic data on the volume of the formation of household (municipal) metal-containing waste, in particular, aluminum cans for drinks, cans, waste electrical and electronic equipment, electrical power sources (batteries and galvanic cells), as well as lighting lamps. The main methods of handling the indicated waste are considered and their critical analysis is presented. Particular attention is paid to the recycling and disposal of common waste such as waste electrical and electronic equipment, chemical sources of electrical current, and lighting lamps. Taking into account the rapid growth in the consumption of electrical and electronic products, it is shown that now there is a tendency not so much to improve the methods of disposal of the corresponding waste, but to ensure the production of more durable goods that provide for the possibility of their repair. A gradual transition from the 3R strategy (Reuse, Reduce, Recycle) to the 10R strategy (Refuse, Rethink, Reconsider, Reuse, Repair, Refurbish, Remanufacture, Repurpose, Recycle, Recover) is proposed. At the same time, the development of effective technologies for extracting not only traditional iron, aluminum, copper and their alloys from metal-containing household waste is not removed from the agenda, but also more scarce metals, including rare earth and heavy metals, as well as platinum group metals, which will allow significantly reduce the man-made load on the environment. Bibl. 69, Table 1.

Influence of processing and microstructure on the corrosion behavior of ultrafine grained Al 5083 alloy

Ultrafine grained (UFG) material has received significant research interest due to its combination of strength and toughness when compared with its coarse-grained counterpart. In the present investigation, a distinct UFG microstructure of Al 5083 alloy fabricated through cryorolling (CR), CR followed by warm rolling (WR), and CR followed by short annealing (SA) have been subjected to salt immersion, polarization, and intergranular corrosion tests in 3.5% NaCl solution. A salt immersion test revealed that UFG structures have resistance to pitting corrosion for all conditions when compared to their coarse-grained counterpart. The presence of coarse intermetallic second phase particles leads to the formation of micro galvanic cells with matrix resulting in highly localized pitting corrosion in the solution treated (ST) material, whereas crystallographic pits along the lateral direction have been observed in deformed material. The lower values of corrosion current density ( icorr = 3.640 and 3.910 μA/cm2) were observed for CR and WR conditions, respectively, than ST samples ( icorr = 8.140 μA/cm2) were attributed to the presence of a higher volume fraction of low angle grain boundaries along with a high density of dislocations. SA after CR has slightly increased the corrosion current ( icorr = 3.8 μA/cm2) values thereby shifting the corrosion potentials to a noble direction.

Effect of carbonaceous reinforcements on anticorrosive and magnetic properties of Ni-Cu based composite coatings prepared by pulsed electrodeposition

Magnetic and anticorrosive properties of Ni-Cu alloy-based composite coatings prepared by pulsed electrodeposition reinforced with CNT (Ni-Cu-CNT), graphene (Ni-Cu-G), and diamond (Ni-Cu-D) have been assessed in the current work. The corrosion behavior of the composite coatings was evaluated in a 3.5% NaCl corrosive medium. Linear polarization test performed within ±10 mV with respect to open circuit potential (OCP) unveiled that graphene added coatings exhibited maximum polarization resistance (~13.1 kΩcm2) followed by the Ni-Cu-D (~9.1 kΩcm2), the Ni-Cu-CNT (~8.3 kΩcm2), and the Ni-Cu with a minimum resistance of ~4.2 kΩcm2. Electrochemical impedance spectroscopy tests performed with a signal perturbation of ±10 mV with respect to OCP and frequency sweep from 105 Hz to 10−2 Hz elicited maximum film resistance of ~32 kΩ cm2 for the Ni-Cu-G coating, which could be attributed to the high area to volume ratio, α ~134/m, of graphene nanoflakes inducing strong particle-matrix interaction and to the formation of micro galvanic cell between the graphene particles and the Ni-Cu matrix where the surface was covered predominantly with graphene, eventually lowering the corrosion rate to 5.91 MPY. For Ni-Cu-D coating, the uniform dispersion of diamond particles prohibits localized corrosion. In contrast, agglomeration of CNTs in Ni-Cu-CNT causes ~50% reduction in corrosion resistance compared to diamond reinforced coating. However, corrosion resistance of CNT grafted coating was around 2.5 times higher than Ni-Cu (~4.2 kΩcm2), which can be imputed to the filling of the pores, cracks, and crevices by CNT fibers. The hysteresis loops of Ni-Cu composite coatings traced by a vibrating sample magnetometer indicated that CNT incorporation enhanced the magnetic saturation to ~1.89 Am2/kg from ~0.84 Am2/kg (Ni-Cu) and maximum coercivity of ~110 Oe (~78.91 Oe for Ni-Cu). However, graphene and diamond addition has negligible effect on the magnetic properties of the coated systems. The enhanced anticorrosive and magnetic properties of proposed coating designs consisting of Ni-Cu matrix with carbonaceous reinforcements impart multifunctionality to the system. The marine industry can successfully adopt the proposed coating systems to protect propellers shafts, ship hulls, and specialty sensors.

Removal of phosphate from wastewater by Fe-C micro-electrolysis: application of a novel integrated Fe/C aggregate

ABSTRACT To overcome the drawbacks of typical Fe-C micro-electrolysis in wastewater treatment, we developed a new electrolysis material, integrated Fe/C aggregate (FCA) made from Fe0 and carbon powder, and used it for phosphate removal from wastewater. Results show that the free iron ions could quickly react with and form an iron phosphate precipitate in phosphate-containing wastewater. The release rate of iron ions was extremely rapid in the first 10 h, indicating that Fe-C microscopic galvanic cells formed on the aggregate surface. Acid conditions are beneficial for accelerating the Fe-C micro-electrolysis reaction and enhancing the iron ion release capacity and phosphate removal capacity. In batch experiments, the maximum phosphate removal capacity of FCA was found to be 10.84 mg P/g. The phosphate removal behaviour of FCA can be well described by the Langmuir isotherm model and the pseudo-second-order kinetic model. SEM and XPS investigations also revealed that phosphates were absorbed by ferrous or ferric hydroxide and generated Fe-P precipitate, which adhered to the surface of FCA throughout the phosphate removal process. Because of its low cost and outstanding performance, the FCA aggregate has a high potential for P removal in wastewater treatment.

The spontaneity of chemical reactions: challenges with handling the concept and its implications

Abstract The spontaneity concept plays crucial roles in the description of chemical reactions and entails a variety of implications, including the determination of the difference between galvanic and electrolytic cells. Students experience challenges with handling the concept and its implications within chemistry contexts. Everyday-life examples do not provide immediate evidence of chemistry-related spontaneity, and some features may be misinterpreted. The ΔG &lt; 0 spontaneity criterion does not have an everyday-life correspondence and mostly remains abstract. Tendencies to equate exothermic or fast with spontaneous appear frequently. Using the spontaneity or non-spontaneity concepts in the interpretation of observed simple electrochemical phenomena may pose difficulties. The challenges are greatly enhanced by two diffuse contextual features: tendency to rote learning and inadequate language-mastery, with the latter being a major cause of the former and generally hindering conceptual understanding. The paper highlights the main difficulties diagnosed within an action research approach, documenting them with a sufficiently ample selection of illustrative examples. The ways in which diagnoses are utilised as guidelines for in-class interventions aimed at addressing identified challenges are delineated and discussed. The integration of chemistry-concepts analysis and language-analysis is viewed as the most powerful instrument to address identified difficulties in real time.

Enhanced corrosion resistance of 17-4 PH stainless steel fabricated by laser powder bed fusion in H2SO4 solution

The purpose of this study is to examine the microstructure and corrosion performance of martensitic stainless steel 17-4 PH produced by laser powder bed fusion (LPBF) and its corresponding rod specimen in sulfuric acid. Based on a microstructural analysis, the LPBF alloy contained melt pools with an ultrafine cellular structure and uniform distribution of elements, including Nb. The LPBF process significantly improved the corrosion resistance of the 17-4 PH stainless steel alloy in sulfuric acid. The alloy manufactured by LPBF had a charge transfer resistance of at least 7 times that of the Rod counterpart and a corrosion current density that was 4 times lower than Rod. The homogeneous distribution of elements during the solidification process improved the electrochemical performance of LPBF 17-4 PH stainless steel due to the development of gentle galvanic cells compared to Rod one.

Magnesium galvanic cells produce hydrogen and modulate the tumor microenvironment to inhibit cancer growth

Hydrogen can be used as an anti-cancer treatment. However, the continuous generation of H2 molecules within the tumor is challenging. Magnesium (Mg) and its alloys have been extensively used in the clinic as implantable metals. Here we develop, by decorating platinum on the surface of Mg rods, a Mg-based galvanic cell (MgG), which allows the continuous generation of H2 in an aqueous environment due to galvanic-cell-accelerated water etching of Mg. By implanting MgG rods into a tumor, H2 molecules can be generated within the tumor, which induces mitochondrial dysfunction and intracellular redox homeostasis destruction. Meanwhile, the Mg(OH)2 residue can neutralize the acidic tumor microenvironment (TME). Such MgG rods with the micro-galvanic cell structure enable hydrogen therapy to inhibit the growth of tumors, including murine tumor models, patient-derived xenografts (PDX), as well as VX2 tumors in rabbits. Our research suggests that the galvanic cells for hydrogen therapy based on implantable metals may be a safe and effective cancer treatment.

The Influence of Shot Peening and Artificially Ageing Aluminium Alloy 7075 on Corrosion Behaviour.

This paper investigates the corrosion of shot peened AA7075 aluminium alloys aged at different temperatures. The surface integrity of the hardened layer was evaluated with SEM, EDS, differential scanning calorimetry, hardness, and roughness measurements, and in the end also with corrosion resistance tests. The research results indicated that there were significant differences in precipitates distribution between aluminium alloys artificially aged at different temperatures. As the ageing temperature increases, the microhardness decreases, which influences the final roughness condition of the surface layer after shot peening. The results of potentiodynamic polarisation tests indicate that shot peening enables shifting the pitting potential to positive values, which ensures slightly higher corrosion resistance. SEM images confirmed the dissolution of the aluminium matrix near the separated iron-rich phases of the Alx form (Fe, Mn) by the action of galvanic cells.

Use of Dyes As Photosensitizer in Photo Galvanic Cell for Conversion and Storage of Solar Energy

Abstract: The impact of photogalvanic cells containing the best combination of dyes, reductants, and surfactants was studied. The photosensitizers employed in this research were Methyl Orange-Glucose-Cetyl Trimethyl Ammonium Bromide, Thymole Blue-Glucose-Cetyl Trimethyl Ammonium Bromide, Victoria Blue-Glucose-Cetyl Trimethyl Ammonium Bromide, and Methyl Orange-EDTA-Cetyl Trimethyl Ammonium Bromide. Cell efficiency also has been reported to be significantly higher. The device has a conservation efficiency of 0.55 to 1.01 percent and can be used in the dark for 32 to 68 minutes. Various factors which influence solar energy conversion efficiency are also evaluated and accounted for.Key words: Potentials at power point, Photosensitizers, Rates of generation, Reductants, Fill Factors, surfactants, Power consumption, Charging time.GOAL 7: Affordable and Clean Energy

Bio-electrochemical production of hydrogen and electricity from organic waste: preliminary assessment

This study investigated the performance of a novel integrated bio-electrochemical system for synergistic hydrogen production from a process combining a dark fermentation reactor and a galvanic cell. The operating principle of the system is based on the electrochemical conversion of protons released upon dissociation of the acid metabolites of the biological process and is mediated by the electron flow from the galvanic cell, coupling biochemical and electrochemical hydrogen production. Accordingly, the galvanic compartment also generates electricity. Four different experimental setups were designed to provide a preliminary assessment of the integrated bio-electrochemical process and identify the optimal configuration for further tests. Subsequently, dark fermentation of cheese whey was implemented both in a stand-alone biochemical reactor and in the integrated bio-electrochemical process. The integrated system achieved a hydrogen yield in the range 75.5–78.8 N LH2/kg TOC, showing a 3 times improvement over the biochemical process.Graphical abstract

Simulations of the Electrochemical Oxidation of Pt Nanoparticles of Various Shapes

The activity and stability of a platinum nanoparticle (NP) are not only affected by its size but additionally depend on its shape. To this end, simulations can identify structure–property relationships to make a priori decisions on the most promising structures. While the activity is routinely probed by electronic structure calculations on simplified surface models, modeling the stability of NP model systems in electrochemical reactions is challenging due to the long time scale of relevant processes such as oxidation beyond the point of reversibility. In this work, a routine for simulating electrocatalyst stability is presented. The procedure is referred to as GREG after its main ingredients─a grand-canonical simulation approach using reactive force fields to model electrochemical reactions as a function of the galvanic cell potential. The GREG routine is applied to study the oxidation of 3 nm octahedral, cubic, dodecahedral, cuboctahedral, spherical, and tetrahexahedral platinum NPs. The oxidation process is analyzed using adsorption isobars as well as interaction energy heat maps that provide the basis for constructing electrochemical phase diagrams. Onset potentials for surface oxidation increase in the sequence cube ≈ dodecahedron ≤ octahedron ≤ tetrahexahedron < sphere < cuboctahedron, establishing a relationship between the oxidation behavior and the surface facet structure. The electrochemical results are rationalized using structural and electronic analyses.

Microstructure, corrosion behavior, and biocompatibility of Ti-6Al-4 V alloy fabricated by LPBF and EBM techniques

This study aims to investigate the microstructure and electrochemical behavior of the laser powder bed fusion (LPBF-) and electron beam melting (EBM-) manufactured Ti-6Al-4 V alloy in the Ringer′s solution. The microstructure of the LPBF-fabricated part contained the acicular α’ martensite phase, while the EBM-fabricated part possessed a combination of α and β phases. The formation of two phases in the EBM sample can be related to the lower thermal tension and higher temperature of the table during the fabrication process. Electrochemical studies have revealed that the better corrosion performance of the LPBF-manufactured alloy was mainly due to the formation of local galvanic cells in the EBM-manufactured Ti-6Al-4 V alloy. Corrosion current densities of the LPBF- and EBM-manufactured alloys after 100 h of immersion were 0.36 and 0.87 µA cm−2, respectively. MTT assay was performed using MG-63 cells to assess the biocompatibility of the manufactured samples. The results showed that the cells had good adhesion and durability on the samples. Though, both samples could be regarded as good candidates for implant applications, but the LPBF-manufactured part showed a higher resistance corrosion and is then more suitable for implant alloys.

A composite Fe–C/layered double oxides (Fe–C/LDO) carrier fabrication and application for enhanced removal of nitrate and phosphate from polluted water with a low carbon/nitrogen ratio

In this study, a multifunctional biofilm carrier (Fe–C/LDO) integrating Fe–C micro-electrolysis with Mg–Al layered double oxides (LDO) was developed and applied in a biofilter aimed to remove nitrogen and phosphorus simultaneously from slightly polluted water with a low carbon/nitrogen (C/N) ratio. Four types of carriers were prepared under different conditions and their performance in nitrate reduction and phosphorus removal were compared. Results showed that the composite Fe–C/LDO carrier prepared with polyethylene glycol as the pore-forming agent demonstrated the highest nitrate reduction rate and phosphorate adsorption capacity (2.09 mg PO43--P·g−1). A biofilter packed with the Fe–C/LDO carrier was investigated under heterotrophic conditions (C/N = 4.13) and complete autotrophic conditions (C/N = 0) during a long-term operation. Good removal of NH4+-N (96–98%), TN (92–96%) and PO43--P (50–58%) were achieved in the biofilter under both heterotrophic and autotrophic conditions. High throughput pyrosequencing analysis revealed that a large population of autotrophic denitrifying bacteria Thiobacillus and Thioalkalispira were enriched in the biofilm. Metagenomic analysis was performed to analyze functional genes related to nitrogen metabolism and carbon cycle, and it confirmed the presence of a whole denitrification and Calvin-Benson-Bassham carbon fixation pathway in biofilm. Finally, the possible mechanisms for nitrogen and phosphorus removal in the biofilter were proposed. The Fe–C/LDO carrier not only enriched abundant autotrophic denitrifying bacteria, but also provided numerous Fe–C galvanic cells for nitrate reduction through micro-electrolysis. In addition, the Mg–Al LDO in combination with iron hydroxides generated during micro-electrolysis may contribute greatly to phosphorus removal. Biofilter packed with the multifunctional Fe–C/LDO carrier could be a promising technology for simultaneous nitrogen and phosphorus removal from slightly polluted water.

An Ion Selective Electrode Based on Ti3C2 Solid‐state Transduction for Rapid Detection of Lead Ion Concentration in Aqueous Solution

Conduction layer plays an important role in ion-selective electrodes (ISEs) with solid-state transduction. Herein, a lead ISE was prepared with Ti3C2 as the conductive layer, which has less water film and good anti-interference ability to O2, CO2 and light. Concentration of lead ions can be quickly determined by detecting the electromotive force of the galvanic cell. In 10−3–10−7 M, the Nernst slope is found to be 28.3±1.02 mV/decade. And the detection limit is 4.4×10−8 M (n=3). It indicates that Ti3C2 is suitable for the conductive layer in solid ISEs.