Potentiostatic Polarization Tests Research Articles

Corrosion resistance and conductivity of CrN, CrAlN, and CrTiN coatings applied to bipolar plates for proton exchange membrane fuel cells

In order to improve the corrosion resistance and conductivity of 316L stainless steel bipolar plates used for proton exchange membrane fuel cells, three Cr-containing nitride coatings were deposited on 316L stainless steel by multiarc ion plating. First, the microstructure, composition, and contact angle of the three coatings were systematically investigated. Then, electrochemical impedance spectroscopy, potentiodynamic polarization, potentiostatic polarization (PSP), and interfacial contact resistance (ICR) of the three coatings were also fully examined. The results revealed that CrN coating has the highest contact angle of 98.26°, indicating its superior hydrophobicity. Additionally, CrN coating performed the best corrosion resistance with the highest corrosion potential of 0.31 V, the lowest corrosion current density of 2.28 × 10−7 A cm−2, and the largest resistance. Furthermore, CrN coating showed the lowest current density during PSP tests and the smallest ICR value after corrosion. The superior corrosion resistance of CrN coating is mainly attributed to its decreased pore density caused by vacancylike defects and its uniform structure. This article provided evidence for the potential application of CrN coating to bipolar plates.

Corrosion behavior of multi-layer friction surfaced structure from dissimilar aluminum alloys

Friction surfacing (FS) is a solid-state coating technology for metallic materials, where the deposition of a consumable material on a substrate is enabled via friction and plastic deformation. The deposited layer material commonly presents a significantly refined microstructure, where corrosion could be an issue due to this grain refinement within the layer deposited, possibly creating micro galvanic pairs. The present work investigates the corrosion behavior of the FS deposited material as well as stud base material and substrate using cyclic polarization tests and open circuit potential (OCP) monitoring. Comparing the FS deposited material and the respective consumable stud base material (both AA5083), the grain size is correlated with the results from the corrosion tests, where the deposited material shows more equiaxed and refined grains in comparison to the stud base material. The cyclic potentiostatic polarization tests showed that the stud base material is more resistant to pitting nucleation presenting smaller pits and a lower amount of pits compared to deposited material and substrate. As a complement to OCP test, the stud base material is also more stable on a chloride solution compared to the substrate and the deposited material.

A novel carbon coating by electrochemical deposition in deep eutectic solvent with the assistance of ammonium chloride for stainless steel bipolar plates

In this work, pulse electrodeposition method was proposed to directly deposit amorphous carbon coating (ACC) onto 316L stainless steel substrate in choline chloride-ethylene glycol deep eutectic solvent (DES) mixed with ammonium chloride (NH4Cl) to fabricate bipolar plates. The obtained dense ACC has a thickness of ∼400 nm. Potentiodynamic and potentiostatic polarization tests demonstrated that the corrosion current density of ACC coated 316L steel was of the order of 10−7 A cm−2 in the simulated proton exchange membrane fuel cells (PEMFC) working environment, and the self-corrosion potential of the coating positively shifted by 0.4V, indicating a significant improvement on corrosion resistance of the coated steel plate due to excellent electrochemical stability of ACC. The Rockwell C indentation test showed that the as-obtained ACC was strongly bonded to the substrate and also had high in-plane strength. Further numerical simulation and comparison experiments showed that C was chemically bonded with Fe in the substrate, which was boosted by the assistance of NH4Cl. The intact and strong bonding between ACC and the substrate is highly helpful to improve corrosion resistance. The success in coating stainless steel plate with ACC by pulse electrodeposition method provides a promising alternation for coating of proton exchange membrane electrolyzer cell (PEMEC) and PEMFC metal bipolar plates.

Effect of magnetron sputtering C-doped CrN film on the conductivity and corrosion resistance of 304 stainless steel bipolar plates

Using a high-power impulse and direct current (DC) magnetron sputtering approach, C-doped CrN films with various C-target pulse frequencies are created on the surface of SS 304. The microstructure, corrosion resistance and conductivity of the films are examined. With the decreases of C-target pulse frequency, the roughness of the CrCN films decreases and the density increases. The results of XPS and TEM analyses demonstrate that C atoms are either present in CrN lattice as interstitial atoms or precipitate at grain boundaries to form amorphous carbon, which facilitates the increase of film density and conductivity. In the potentiodynamic tests, the CrCN-1000 Hz film exhibits the lowest corrosion current density 0.54 μA/cm2 at 0.6 V vs. Ag/AgCl potential. The values of icorr and Ecorr are 0.11 μA/cm2 and 0.427 V, respectively. Furthermore, the CrCN-1000 Hz film has the lowest interface contact resistance (ICR) under a compaction force of 140 N/cm2 after potentiostatic polarization test, indicating that C doping is beneficial to improve the corrosion resistance and conductivity of CrN film.

Investigating Pitting Behavior of Stainless-Steel for Canister in Vertical Position Using Electrochemical Acceleration Test

Stainless steel is renowned for its corrosion resistance and is widely used in constructing canisters for nuclear waste containment. These canisters are designed to endure burial in soil for over a century, making it crucial to study the long-term corrosion behavior of SS in this specific context. However, analysis of the corrosion behavior of SS is challenging due to its slow corrosion rate. Therefore, electrochemical acceleration methods are essential in studying the corrosion behavior of SS. This research employs the potentiostatic polarization test to comprehensively analyze SS pitting corrosion. The study focuses on vertically-positioned SS specimens, simulating canister conditions. Advanced microscopy techniques and simulation aid in understanding anolyte, pit depth, and pit shape behavior. Through this, the pitting propagation process of SS could be divided into four stages. Key outcomes of this study include models for absolute depth during propagation and the formation of secondary pitting. Comparative analysis with immersion tests reveals insights crucial for industrial installations safety and longevity.

Improved corrosion resistance and interfacial conductivity of a-C/(Ti:C)/Ti nano-thin film for 316L stainless steel bipolar plates

To enhance corrosion resistance and electrical conductivity of metallic bipolar plates for proton exchange membrane fuel cells (PEMFCs), the film containing amorphous carbon (a-C) outer layer, titanium carbon compound (Ti:C) transition layer and titanium (Ti) seed layer has been deposited on the surface of 316L stainless steel (316L SS) by multi-arc ion plating method. Dense and uniform a-C/(Ti:C)/Ti nano-thin film is relatively hydrophobic and approximately 300 nm thick, presenting a clear multilayer structure. The interfacial contact resistance of 316L SS is effectively reduced from 124.97 mΩ·cm2 to 3.97 mΩ·cm2 at 1.4 MPa after modification. Electrochemical corrosion tests are investigated in the simulated cathodic PEMFCs environment (0.5 M H2SO4 and 2 ppm HF at 70 ℃ bubbled with air). Potentiodynamic polarization results reveal that the corrosion potential of a-C/(Ti:C)/Ti film modified sample is 0.23 V (vs. Ag/AgCl) and the corrosion current density is only 0.14 μA·cm−2. The durability of the a-C/(Ti:C)/Ti film was assessed by conducting potentiostatic polarization tests at various applied potentials. After 4 h potential of 0.6 V and 0.8 V (vs. Ag/AgCl) holding tests, the current densities of the modified 316L SS have stabilized at 0.076 μA·cm−2 and 0.098 μA·cm−2, respectively.

Electrochemical performance of metal nitride coated titanium bipolar plate for proton exchange membrane water electrolyser

In order to improve corrosion resistance and electric conductivity of titanium bipolar plate (BPP) for proton exchange membrane water electrolyser (PEMWE), three different metal nitride (i.e.Ta/TaN, Cr/CrN and Nb/NbN) coated titanium bipolar plates are prepared by magnetron sputtering. The coated BPP is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM), and their electrochemical performance is assessed by electrochemical corrosion tests including open circuit voltage (OCP), potentiodynamic and potentiostatic polarization tests in the simulated PEMWE anode environment. It is revealed that the surface roughness of titanium substrates is decreased after coating, implicating the reduced interfacial contact resistance (ICR). Potentiodynamic and potentiostatic tests demonstrate that Ta/TaN and Nb/NbN coatings can significantly improve the corrosion resistance of titanium bipolar plate. The corrosion current density of coated substrate is reduced by approximately 67 % upon coating with Ta/TaN and Nb/NbN under the simulated PEMWE anode environment. However, the ICR of Ta/TaN coating is the lowest (3.9 mΩ × cm2), which is reduced by 74 % compared with pristine titanium substrate (14.9 mΩ × cm2). Hence, the Ta/TaN coated BPP is tested in single electrolytic cell and demonstrates significantly improved electrolysis efficiency.

On the selective corrosion mechanism of LPBF-produced AlSi10Mg: Potentiostatic polarization effects

Additive manufacturing technologies are quickly gaining success in several industries. However, a complete understating of how the unique macro- and microstructures obtainable influence the corrosion behavior is still far from being achieved. In this work, potentiodynamic and potentiostatic polarization tests were performed in an aerated chloride solution on laser powder bed fusion (LPBF)-produced AlSi10Mg specimens, built adopting different baseplate temperatures. Potentiodynamic polarization tests evidenced two separate breakdown potentials. The first was associated with the initiation of corrosion localized at the edge of the melt pool, while the second with the break of the passive film of the matrix. This phenomenon highlighted that potentiodynamic curves can overestimate the critical potentials required to trigger the selective corrosion. Potentiostatic polarization tests were performed at an intermediate potential value with respect to the ones highlighted in the previous test. All the specimens achieved the dissolution of the passive layer after a certain immersion time. This period was lower for the specimens built using higher baseplate temperatures, due to the coarsening of the microstructure and disruption of the Si-rich network. A similar behavior was encountered by the heat-treated samples. These required significantly less time to trigger corrosion, due to the complete disappearance of the melt pool macrostructure and formation of Si particles.

Antibiofilm activity of electrochemically activated water (ECAW) in the control of Salmonella Heidelberg biofilms on industrial surfaces.

Owing to its antimicrobial activity, electrochemically activated water (ECAW) is a potential alternative to chemical disinfectants for eliminating foodborne pathogens, including Salmonella Heidelberg, from food processing facilities. However, their antibiofilm activity remains unclear. This study aimed to evaluate the antibiofilm activity of ECAW against S. Heidelberg biofilms formed on stainless steel and polyethylene and to determine its corrosive capacity. ECAW (200ppm) and a broad-spectrum disinfectant (0.2%) were tested for their antibiofilm activity against S. Heidelberg at 25°C and 37°C after 10 and 20min of contact with stainless steel and polyethylene. Potentiostatic polarization tests were performed to compare the corrosive capacity of both compounds. Both compounds were effective in removing S. Heidelberg biofilms. Bacterial counts were significantly lower with ECAW than with disinfectantin polyethylene, regardless the time of contact. The time of contact and the surface significantly influenced the bacterial counts of S. Heidelberg. Temperature was not an important factor affecting the antibiofilm activities of the compounds. ECAW was less corrosive than the disinfectant. ECAW demonstrated a similar or even superior effect in the control of S. Heidelberg biofilms, when compared to disinfectants, reducing bacterial counts by up to 5 log10 CFU cm-2. The corrosion of stainless steel with ECAW was similar to that of commercial disinfectants. This technology is a possible alternative for controlling S. Heidelberg in the food production chain.

Improvement in Corrosion Resistance and Interfacial Contact Resistance Properties of 316L Stainless Steel by Coating with Cr, Ti Co-Doped Amorphous Carbon Films in the Environment of the PEMFCs.

In order to obtain films with high corrosion resistance and excellent interfacial contact resistance (ICR) on 316L stainless steel used for bipolar plates in proton-exchange membrane fuel cells (PEMFCs), Cr, Ti co-doped amorphous carbon films were prepared on 316L stainless steel. The preparation method for the coating was magnetron sputtering. The doping amount of the Ti element was controlled by a Cr target and a Ti target current. The change in the structure and properties of the coating after the change from Cr single-element doping to Cr and Ti co-doping was studied. The change rule of the structure and properties of the coating from Cr single-element doping to Cr and Ti co-doping was studied. An increase in the Ti content led to a decreased grain boundary, a flatter surface, and a higher sp2-hybridized carbon content. TiC and CrC nanocrystals were formed in the amorphous carbon structure together. The amorphous carbon films doped with Cr and Ti simultaneously achieved a low ICR and high corrosion resistance compared with single-Cr-doped amorphous carbon. The enhanced corrosion resistance was attributed to the decreasing grain boundary, the formation of the TiC crystal structure, and the smaller grain size. The best performance was obtained at a Ti target current of 2A. Compared with bare 316L stainless steel, the corrosion resistance of Cr, Ti co-doped amorphous carbon (Icorr = 5.7 × 10-8 A/cm2, Ti-2 sample) was greatly improved. Because Ti doping increased the content of sp2-hybridized carbon in the coating, the contact resistance of the coating decreased. Moreover, the interfacial contact resistance was 3.1 mΩ·cm2 in the Ti-2 sample, much lower than that of bare 316L stainless steel. After the potentiostatic polarization test, the coating still had excellent conductivity.

Passivation and pH-Induced Precipitation during Anodic Polarization of Steel in Aluminate Electrolytes as a Precondition for Plasma Electrolytic Oxidation

Potentiodynamic and potentiostatic polarization tests in the potential range between open circuit potential (OCP) − 0.1 V and OCP + 4 V were carried out in aluminate–phosphate electrolytes with an aluminate concentration of 0.2 mol/L and varying phosphates contents between 0 and 0.1 mol/L. The pH was adjusted between 11.5 and 12.0 due to phosphate and optional KOH addition. A high-strength, dual-phase steel, which is relevant for lightweight construction, served as the substrate material. The layer microstructure was investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase analyses. We found that iron hydroxides or oxides are initially formed independently of the electrolyte composition at low potentials. At around 1 V vs. standard hydrogen electrode (SHE), the current density suddenly increases as a result of oxygen evolution, which causes a significant reduction in the pH value. Precipitation leads to the formation of porous layers with thicknesses of 10 µm to 20 µm. In the case of a pure aluminate solution, the layer mainly consists of amorphous alumina. When adding phosphate to the electrolyte, the layer additionally contains the hydrous phosphate evansite. At the highest phosphate content in the electrolyte, the highest P content and the most pronounced crack network were observed.

Novel hybrid coating of TiN and carbon with improved corrosion resistance for bipolar plates of PEM water electrolysis

Surface modification of Ti based bipolar plates (BPs) could be an effective solution to prevent the formation of low-conductive oxide film, promote the corrosion resistance and electronic conductivity as well. In this work, a novel hybrid coating composed of nano-sized TiN and carbonaceous phases (TiN–C) was successfully established on a Ti substrate via a combined electrophoretic deposition and thermal treatment process. Various physiochemical characterizations revealed that the coating was uniform, and the formation of the nano-sized TiN and carbonaceous composites reduced the interfacial contact resistance significantly. The potentiodynamic and potentiostatic polarization tests indicated that the hybrid coating TiN–C prepared at 400 °C had a corrosion current density of only 1.41 μA cm−2, which was an order of magnitude lower than that (36.02 μA cm−2) of the bare Ti. Furthermore, the as-prepared coating showed excellent durability in both the simulated PEMWE environment and the PEMWE cell under polarization at 1.7 V for more than 300 h.

Electrochemical behaviour of AISI 201 austenitic stainless steel in 0.5 M H2SO4

ABSTRACT In the present investigation, the electrochemical behavior and the semiconducting properties of the passive film formed on AISI 201 austenitic stainless steel has been studied using different electrochemical analysis techniques. The passivity of the steel was evaluated by potentiodynamic and potentiostatic polarisation, and electrochemical impedance spectroscopy. Additionally, the Mott–Schottky analysis considering the point defect model was used for determining the semiconducting behavior of the film formed at different applied potentials. The potentiodynamic polarisation curve indicated that AISI 201 austenitic stainless steel exhibits a passivation property in the potential range of −0.2–0.8 V. The average steady-state current density was calculated by conducting a series of potentiostatic polarisation tests at the selected film-forming potentials. The passive films formed on the surface of metals are mainly made up of metallic oxides and hydroxides, which are envisaged as semiconductors. The Mott–Schottky analysis showed that the passive film exhibits n-type behavior. Based on the point defect model, it was deduced that the primary defects in the passive film formed on AISI 201 steel are metal interstitials and oxygen vacancies. The p-type behavior was not observed, indicating that the concentration of the cation vacancies is not significant in the passive film.

Pitting corrosion resistance of additive manufactured alloy 718 in alkaline brines at elevated temperatures

AbstractThe feasibility of additive manufacturing (AM) to produce industrial components, also for the oil and gas industry, has been demonstrated in the past. Therefore, current research efforts focus on demonstrating the reliability of AM materials subjected to demanding service conditions. In this regard, special attention has been paid to its corrosion resistance in harsh environments as one of the most critical properties in these applications. The beneficial combination of high strength, excellent thermal stability, and outstanding corrosion resistance makes alloy 718 (UNS N07718) the most used wrought and AM nickel alloy in the oil and gas industry. Wrought 718 has an extensive record of field performance in demanding oil and gas applications including directional drilling tools that undergo extreme mechanical loads in corrosive drilling fluids. On the other hand, limited data regarding the corrosion behavior of AM718 in typical drilling environments has been collected so far. In this research work, the pitting susceptibility of selective laser melted alloy 718 in simulated drilling environments has been studied. Open circuit potential measurements as well as cyclic potentiodynamic and potentiostatic polarization tests were used to characterize the pitting corrosion resistance of AM718 in alkaline brines at elevated temperatures. In addition, microstructural particularities in alloy 718 were investigated to explain the observed differences in the electrochemical behaviors.

Modification and durability of carbon paper gas diffusion layer in proton exchange membrane fuel cell

To solve the durability problem caused by carbon corrosion in the porous carbon paper gas diffusion layer (GDL) of proton exchange membrane fuel cell (PEMFC), a Cr7C3 ceramic coating on porous carbon paper by molten salt method was prepared. The obtained Cr7C3 coating is dense and shows good adherent with the carbon paper. Based on the corrosion resistance testes, it is concluded that the Cr7C3 coated carbon paper can keep high chemical stability in the long-time acid immersion accelerated corrosion tests and simulated cathodic proton exchange membrane fuel cells environment. The carbon paper with Cr7C3 coating shows a small current density with a value of about 1.1 × 10−5 A cm−2 in the potentiostatic polarization test under 1 M H2SO4 + 2 ppm HF at 70 °C and1.4 VSCE for 72 h. Meanwhile, the resistivity of carbon paper with Cr7C3 coating prepared is 30% lower than that of pure carbon paper, and the conductivity is 1.5 times that of pure carbon paper.

A corrosion mechanism of NbC/α-C:H films for metallic bipolar plates in proton exchange membrane fuel cell cathode based on percolation model

A series of NbC/α-C:H films were prepared through arc ion plating for the protection of metallic bipolar plates in proton exchange membrane fuel cells (PEMFCs). Phase characterizations show that NbC grains were randomly embedded into the α-C:H matrix and their size and content increased with the decreasing of C2H2 flow rate. Results from the kelvin probe force microscope (KPFM) and conductive atomic force microscope (CAFM) presented a uniform surface potential distribution but significant local conductivity differences. DFT calculations and potentiostatic polarization tests indicated that dissolution of NbC grains were preferred in PEMFC cathode environment due to preferential adsorption of corrosive media. On the basis of theoretical calculations and experimental results, a corrosion mechanism was presented based on percolation model to better understand the corrosion process of NbC/α-C:H films in PEMFC cathode.

Nanometric CrN/CrAlN and CrN/ZrN multilayer physical vapor deposited coatings on 316L stainless steel as bipolar plate for proton exchange membrane fuel cells

Nanometric CrN/ZrN and CrN/CrAlN multilayer coatings were deposited on 316L stainless steel as metallic bipolar plates (BPs) for proton exchange membrane fuel cells (PEMFCs) by the cathodic arc evaporation-physical vapor deposition technique. The coatings were evaluated using X-ray diffraction, field emission scanning electron microscopy, surface roughness determination, and water droplet contact angle measurement. In order to study the electrochemical behavior of the coatings, potentiodynamic polarization and electrochemical impedance spectroscopy examinations were conducted at the simulated cathodic PEMFC media (0.5 M H2SO4 purging O2, 70°C). Also, the interfacial contact resistance (ICR) of the coated and uncoated 316L BPs was evaluated in different compaction forces before and after the potentiostatic polarization test. The current density at 0.644 V vs. Ag/AgCl of 0.16 and 0.76 μA cm−2 was recorded for CrN/ZrN and CrN/CrAlN, respectively. Moreover, it was found that after the potentiostatic polarization tests, the ICR values of the 316L BPs were decreased from 276 to 8.3 and 9.4 mΩ cm2 by the deposition of the CrN/ZrN and CrN/CrAlN coatings, respectively. The enhancement in the ICR and corrosion behavior of both CrN/ZrN and CrN/CrAlN multilayer coatings indicated that these coatings can be potentially suitable for PEMFCs application, according to the United States Department of Energy's targets.

Effect of Sealing Treatments on Erosion–Corrosion of a Fe-Based Amorphous Metallic Coating in 3.5 wt.% NaCl Solution with 2 wt.% Sand

In this study, a Fe-based amorphous metallic coating (AMC) was sealed with three sealants, i.e., stearic acid, aluminum phosphate and cerium salt, respectively. Two types of electrochemical tests, namely the ex situ electrochemical impedance spectroscopy test and the in situ potentiostatic polarization test, were conducted to evaluate the erosion–corrosion resistance of as-sprayed and as-sealed AMCs. The results show that the aluminum phosphate–sealed AMC exhibits the best erosion–corrosion resistance with the higher critical flow velocity compared with the as-sprayed AMC, which is attributed to the deep penetration of aluminum phosphate and high hardness of the sealed layer. In contrast, the sealants of stearic acid and cerium salt are easily removed by sand particle impacting, deteriorating their erosion–corrosion resistance.

Nanocrystalline TaCN coated titanium bipolar plate dedicated to proton exchange membrane fuel cell

To promote the corrosion resistance and surface conductivity of metal bipolar plates (BP) in proton exchange membrane fuel cells (PEMFC), a TaCN nanoceramic coating with TaN and TaC dual phase structures was engineered onto a commercially pure titanium substrate employing the double cathode glow discharge plasma (DCGDP) technique. The as-prepared TaCN coating was well-adhered to the substrate with a thickness of ∼16.5 μm. The coating exhibited a microstructure comprising equiaxed grains with an average size of ∼10.3 nm. The electrochemical behavior of the TaCN coating was evaluated in a simulated PEMFC environment containing various HF concentrations. Open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization, and Mott-Schottky tests showed that the addition of HF enhanced the corrosion rate of both the Ti substrate and the TaCN coating. Nevertheless, the TaCN coating exhibited improved corrosion potential, lower corrosion current density and larger resistance than that of Ti for all HF concentrations. The Hilbert-Huang and corrosion morphology analysis indicated that the TaCN coating maintained a passive state with increasing HF concentration. First-principle calculations investigated the adsorption capacity of the F− ions on the passive film on the TaCN coating. Furthermore, the TaCN coating possesses desirable interfacial contact resistance (ICR) (about 10 mΩ cm2 under a compressive force of 140 N cm−2) and outstanding hydrophobicity (92.9° ± 2°). Overall, the TaCN coating, which can deliver appreciable enhancement relative to the performance of titanium, represents an extremely competitive candidate as a protective coating for bipolar plates.

The performance research of TaC modified 316L bipolar plate for proton exchange membrane fuel cell

The corrosion resistance and conductive property are two crucial factors affecting the performance of bipolar plates in proton exchange membrane fuel cell (PEMFC). In this research, a TaC coating is deposited on a 316L bipolar plate through plasma surface modification technology. The electrochemical property of bare 316L and TaC modified bipolar plate has been studied in a simulated PEMFC operation environment. The electrochemical analysis indicates that the performance of bipolar plate has been significantly improved due to the effective effect of TaC modified coating. An obviously decreased corrosion current density is represented by TaC modified bipolar plate and the corrosion potential is more positive in a simulated electrolyte environment. A satisfactory water contact angle of 80.5° is obtained to be beneficial to the water management of PEMFC after surface modification. Furthermore, the TaC-316L bipolar plate presents a minor interfacial contact resistance (ICR) and maintains a favourable result after the potentiostatic polarization test.