Increase In Open Circuit Potential Research Articles

Influence of Moisture on the Electrochemical Performance of Prelithiated Graphite/SiOx Composite Anodes for Li-Ion Batteries

Prelithiation is widely recognized as a promising technology to enable the use of high capacity anode active materials such as silicon. Numerous prelithiation techniques have been proposed over the years, with a handful successfully undergoing pilot scale testing. Nevertheless, new challenges arise when moving from optimizing single processes to integrating them into the process chain. A major concern is the stability of prelithiated electrodes against moisture. In this study, we investigate the influence of industrially-relevant moisture levels on the electrochemical performance of prelithiated graphite/SiOx composite anodes in 3-electrode half- and full-cells. We identify several indicators of electrode degradation such as an increase in open circuit potential, a decrease in graphite lithiation potential, and changes in specific charge/discharge capacity. The underlying degradation mechanisms are examined using electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, which show increased solid electrolyte interphase (SEI)-related interfacial resistances but no clear evidence of SEI degradation. Based on the experimental results, we define a process window for the stability of the investigated electrodes as a function of dew point and exposure time. Our results indicate an encouragingly high stability at dew points up to −40 °C for a realistic exposure time of 1 h.

Utilizing transparent and conductive SnO2 as electron mediator to enhance the photocatalytic performance of Z-scheme Si-SnO2-TiOx

Z-scheme photocatalysts, with strong redox ability, have a great potential for pollutants degradation. However, it is challenging to construct efficient Z-scheme photocatalysts because of their poor interfacial charge separation. Herein, by employing transparent and conductive SnO2 as electron mediator to pass light through and promote interfacial charge transportation, a novel Z-scheme photocatalyst Si-SnO2-TiOx (1 < x < 2) was constructed. The Z-scheme photocatalyst displayed an order of magnitude higher photocurrent density and a 4-fold increase in open-circuit potential compared to those of Si. Moreover, the onset potential shifted negatively for approximately 2.2 V. Benefiting from these advantages, this Z-scheme Si-SnO2-TiOx exhibited efficient photocatalytic performance toward phenol degradation and mineralization. 75% of the phenol was degraded without bias potential and 70% of the TOC was removed during phenol degradation. Other typical pollutants such as bisphenol A and atrazine could also be degraded without bias potential. Introducing a transparent and conductive electron mediator to construct Z-scheme photocatalyst gives a new sight to the improvement of photocatalytic performance in Z scheme.

Influence of dissolved oxygen content on the bacteria‐induced ennoblement of stainless steels in seawater and its consequence on the localized corrosion risk

AbstractThe ennoblement of stainless steel (e.g., the increase of open circuit potential [OCP]) is associated with bacterial colonization. This increases the risk of localized corrosion as the critical pitting/crevice potential can be overcome, especially for lower grade stainless steel. In this study, we assessed the influence of dissolved oxygen content (DOC) on the crevice corrosion of duplex and super duplex stainless steels. In addition, we used DNA amplicon sequencing to identify the bacteria most likely associated with the ennoblement. Above approximately 100 parts per billion (ppb) of dissolved oxygen, the ennoblement of OCP was observed leading to an increased risk of localized corrosion. Below approximately 100 ppb of dissolved oxygen, no ennoblement occurred and the risk of localized corrosion was reduced. We identified certain hydrocarbon‐degrading bacteria whose presence correlated with the ennoblement of super duplex stainless steel at saturated DOC. The role of these bacteria is not clear yet, but their distribution indicates a possible involvement in stainless steel ennoblement in seawater.

Characterization of adsorption of 5-carboxy-3-amino-1,2,4-triazole towards copper corrosion prevention in neutral media

Adsorption behavior of 5-carboxy-3-amino-1,2,4-triazole (COOH-ATA) on copper in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical polarization methods show significant suppression of the anodic and cathodic currents on the polarization curves in the presence of COOH-ATA. Chronopotential diagrams show increase of open circuit potential during adsorption. Ellipsometric studies has allowed to estimate the free energy of adsorption. X-ray photoelectron spectroscopy was applied to examine the surface composition after COOH-ATA adsorption from the inhibitor solution. Spectra analysis shows oxidation of copper to Cu+ and Cu2+ with surface complex formation. Protective properties in humid air and salt fog chamber of such layer are discussed.

Corrosion Inhibition of Cold-rolled Low Carbon Steel with Pulse Fiber Laser Ablation in Water

This study aims at the use of a fiber laser for modifying the surface properties of cold-rolled low carbon steel via a pulse laser ablation technique in water. The effect on the corrosion behavior of the fiber laser-treated metal surface was investigated in NaCl and HCl environments. Electrochemical tests showed significant improvement in the corrosion resistance of the laser-treated sample in NaCl, with an increase in open-circuit potential (OCP) from − 0.65 to − 0.60 V and an inhibition efficiency of 89.22% as obtained from the impedance study. Such improvement was less significant in an acidic environment. Lower corrosion rates of 20.9 mpy and 5.819 × 103 mpy were obtained for the laser-treated samples in neutral and acidic electrolytes, respectively, than the corrosion rates obtained for the as-received samples (33.2 mpy and 11.98 × 103 mpy). Morphological analysis indicated a passive film built by spherical grains of regular size on the metal surface after laser treatment. The corrosion inhibition effects in NaCl were evident by the nonexistence of the common corrosion products of lepidocrocite and crystalline structures that were seen on as-received samples; only polyhedral crystals with micrograins grown on them were seen covering the laser-treated surface. Therefore, the laser treatment using a fiber laser source improved the corrosion resistance of cold-rolled low carbon steel.

Non-Platinum Group Catalysts to Improve Performance of a Membraneless Microbial Fuel Cell

Over the last couple decades, microbial fuel cells (MFCs) have become a technology of interest for renewable energy production and waste treatment/reclamation. MFCs are flexible with fuel and, for this reason, have garnered interest as biosensors, unit operations in advanced wastewater treatment, and alternative power sources. MFCs oxidize organic matter at the anode where microbes perform anaerobic respiration to convert organic matter into simpler compounds (such as carbon dioxide, methane, etc.); however, the anode electrode serves as the final electron acceptor [1, 2]. The electrons produced at the anode are used at the cathode in oxygen reduction reaction (ORR), a reaction that requires the presence of a catalyst. The system design for MFCs can vary to meet different applications [3], but one of the more popular designs is a membrane less, single chamber, air cathode microbial fuel cell [4], which has the anode submerged in an oxygen-less, nutrient solution and has an air-exposed cathode. Although promising in concept, MFCs have very low power density, making them cost inefficient. A major performance limitation in MFCs has been identified in the cathode. Overall efficiency and power density a strongly influenced by cathode design and catalyst selection for the ORR [4, 5]. Previous modeling efforts have suggested oxygen crossover to the anode, oxygen diffusion to the ORR catalyst, and the catalyst used are major factors for low power density [6-8]. In this work, improved MFC performance is demonstrated using non-platinum group catalyst material. The novel catalyst was benchmarked against a platinum group catalyst. Using the novel non-platinum catalyst results in a modest increase in open circuit potential, and a significant increase in maximum current density and power density. In addition, we have investigated the influence of non-platinum catalyst loading on the overall performance. The novel catalysts used in this work demonstrated stability over months of operation. This suggests that the non-platinum group catalyst used in this work is more efficient than platinum group catalyst, improving the cell performance while simultaneously enabling lower cost. References Jr, L.B.W., C.H. Shaw, and J.F. Castner, Bioelectrochemical fuel cells. Enzyme and Microbial Technology, 1982. 4(3): p. 6.Kim, H.J., et al., A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens. Enzyme and Microbial Technology, 2002. 30(2): p. 8.He, Z., S.D. Minteer, and L.T. Angenent, Electricity Generation from Artificial Wastewater Using an Upflow Microbial Fuel Cell. Environmental Science and Technology, 2006. 39: p. 6.Liu, H. and B.E. Logan, Electricity Generation Using an Air-Cathode Single Chamber Microbial Fuel Cell in the Presence and Absence of a Proton Exchange Membrane. Environmental Science and Technology, 2004. 38: p. 6.Rismani-Yazdi, H., et al., Cathodic limitations in microbial fuel cells: An overview. Journal of Power Sources, 2008. 180: p. 12.Ou, S., et al., Full cell simulation and the evaluation of the buffer system on air-cathode microbial fuel cell. Journal of Power Sources, 2017. 347: p. 11.Ou, S., et al., Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition. Journal of Power Sources, 2016. 328: p. 12.Ou, S., et al., Multi-variable mathematical models for the air-cathode microbial fuel cell system. Journal of Power Sources, 2016. 314: p. 9. Figure 1

Characterization of the microstructure and corrosion performance of Ce-alloyed Nd-Fe-B magnets

Expensive rare-earth elements used in neodymium-iron-boron permanent magnets can be partly replaced by a more abundant cerium without significantly compromising the magnetic properties. In this study, we investigated the effects that cerium addition has on the corrosion resistance of Nd-Fe-B magnets. The cerium-alloyed magnet grade was compared to two Ce-free magnet materials, a standard-grade Nd-Fe-B and a Co-alloyed magnet grade, with respect to microstructure and corrosion behaviour. The microstructure of the magnets was characterized by scanning electron microscopy, with the location of Ce being of primary interest. The magnets were exposed to electrochemical measurements and accelerated corrosion tests. Although the amount of the corrosion-sensitive grain-boundary phase was higher in the Ce-alloyed magnets than in the other two magnet grades, the overall corrosion behaviour was in many ways comparable to that of the Co-alloyed grade magnet, e.g., showing a slight increase in open circuit potential as compared to the standard grade magnet. In accelerated tests, corrosion of the Fe-rich phase was equal to the other magnet grades. Pulverization of the Ce-alloyed magnet was not detected during the accelerated tests, similarly to the Co-alloyed grade.

Response of duplex Cr(N)/S and Cr(C)/S coatings on 316L stainless steel to tribocorrosion in 0.89% NaCl solution under plastic contact conditions

Two duplex coatings, Cr(N)/S and Cr(C)/S, were deposited on 316 L stainless steel by magnetron sputtering. The effectiveness of these duplex coatings in improving the tribocorrosion behavior of medical alloys under elastic contact conditions has been demonstrated in a recent publication. The present work focused on the response of these duplex coatings to tribocorrosion under plastic contact conditions. Tribocorrosion tests were conducted in 0.89% NaCl solution at 37°C at an initial contact pressure of 740 MPa and under unidirectional sliding conditions for sliding duration up to 24 h. The results showed that during sliding in the corrosive solution, the duplex coatings were plastically deformed into the substrate to a depth about 1 μm. The Cr(C)/S duplex coating had sufficient ductility to accommodate the deformation without cracking, such that it was worn through gradually, leading to the gradual increase in open circuit potential (OCP) and coefficient of friction (COF). On the other hand, the Cr(N)/S duplex coating suffered from cracking at all tested potentials, leading to coating blistering after prolonged sliding at OCP and stable pit formation in the substrate beneath the coating at applied anodic potentials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1503-1513, 2017.

Ammonia Decomposition at Titanium Oxide Nanotube Photosensitive Anode

Kinetic behavior of ammonia decomposition at titanium dioxide nanotube photosensitive anode was studied. Ammonia was dissolved into water to form solutions with difference concentrations. The ammonia concentration ranges from 0.025 wt% to 10 wt%. Time-dependent open-circuit potential was measured to examine the photochemical response of the cell. The ammonia decomposition behavior was confirmed by measuring the decrease in pH values of the solutions. In addition, the kinetic behavior of ammonia decomposition was characterized under the actions of both ultra violet light irradiation and polarization. The current density values at the titanium dioxide nanotube anode during anodic polarization and UV light irradiation tests were used to compare the ammonia decomposition rates associated with photon excitation and polarization. The double–layer capacitance was estimated as high as 35 F/m indicating the excellent charge storing capability of Original Research Article Gan et al.; ACRI, 3(4): 1-12, 2016; Article no. ACRI.25848 2 the nanotube photosensitive anode. The effect of ammonia concentration on the open-circuit potential was also observed. In the lower ammonia concentration range, the change in the open circuit potential increase with the increasing in the ammonia concentration. Interestingly, in the higher concentration range from 2.5 wt% to 10 wt%, the change in the open circuit potential reveals a reversed trend.

Low Alloy X100 Pipeline Steel Corrosion and Passivation Behavior in Bicarbonate-Based Solutions of pH 6.7 to 8.9 with Groundwater Anions: An Electrochemical Study

This research investigates the fundamental corrosion and passivation processes occurring on API-X100 pipeline steels before, during, and after passive layer formation in bicarbonate-based simulated soil solutions of pH 6.7 to 8.9. Free corrosion potentials decrease exponentially with bicarbonate (and pH), owing to increased water and bicarbonate reduction in more alkaline conditions and the coupled iron oxidation reaction. Active corrosion rates at potentials slightly above open circuit potential increase with bicarbonate, until a concentration of 1.68 g L−1 sodium bicarbonate (plus dilute amounts of chlorides/sulfate) at which first signs of film formation appear. Thereon, increased bicarbonate concentration generally decreases current densities and resists ferrous-oxide product formations due to improved iron carbonate formation conditions precipitating more durable passive layers. Potentiodynamic polarization in the anodic regime reveals varying electrochemical processes involving interactions between hydroxide, carbonate, and oxide complexes with ferrous, with diverse pH and potential dependencies. The products of corrosion reactions were investigated by scanning electron microscopy, X-ray diffraction, and/or X-ray photoelectron spectroscopy.

Kinetics Study on O2 Adsorption and OHad Desorption at Pt(111), Its Implication to Oxygen Reduction Reaction Kinetics

Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction (ORR) at Pt(111) electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V (vs. RHE) with the exchange current density of ca. 50 mA/cm2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kinetic- or kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed (&amp;gt;800 r/min) and slow potential scan rate (&amp;lt;100 mV/s). The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt(111) the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad+H++e ⇌H2O.

Dual-cell reduction and group effect in an internal microelectrolysis reactor

To address some of the fundamental questions regarding the functions of cathodes and anodes (e.g., iron and granular active carbon) and what happens when numerous particles (microscopic galvanic cells) are combined in the widely used and efficient wastewater treatment of an internal microelectrolysis (IME) reactor, we employed a specifically designed dual-cell IME reactor with single-couple electrodes and a narrow cell IME reactor with multi-couple electrodes. The simultaneous removal of 6.36mgL−1 and 2.93mgL−1 of 2,4-dichlorophenol within 30min from the graphite cathode and the iron anode cells, respectively, was observed in the dual-cell reactor. The innovative concept behind this phenomenon is that the anode, which is generally believed to be oxidative, could probably be reductive in an IME reactor. Thus, it is important to understand the unique performance of IME reactors. The group effect, which provides a 45% increase of open-circuit potential with just two additional electrode couples in aqueous solution, was tested and verified in a multi-couple electrode reactor. It suggests a complex potential distribution in the IME reactor and that compounds even with high redox potential could possibly be reduced, which was generally believed to be difficult to accomplish.

Liquid Tin-Lead Anode Solid Oxide Fuel Cell Fueled by Coal

Liquid tin-lead alloy, liquid bismuth, and liquid tin-lead-bismuth alloy were investigated as potential anodes for a solid oxide fuel cell powered directly by coal. Power generation from direct oxidation of solid coal was demonstrated with a good stability only in the case when liquid tin-lead anode was used. The tests were carried out at 900 °C under ambient pressure. The open circuit potentials of the SOFC with tin-lead and bismuth anodes operated under nitrogen were compared, and those values were found to correspond to the metal-metal oxide redox potentials for tin and bismuth, respectively. When the SOFCs were fueled by hydrogen, only the tin-lead anode showed a direct electrochemical reaction between hydrogen and oxygen. When 60-mesh coal powder was fed to the liquid tin-lead anode, SOFC showed increase in open circuit potential and generated power from direct electrochemical oxidation of coal.

Effect of High-Intensity Pulsed Ion Beam Irradiation on the Electrochemical Corrosion Behavior of AZ31 Magnesium Alloy

HIPIB irradiation experiment is carried out at a specific ion current density of 1.1 J/cm2 with shot number from one to ten in order to explore the effect of shot number on electrochemical corrosion behavior of magnesium alloy. Surface morphologies, microstructure and corrosion resistance of the irradiated samples are examined by scanning electron microscopy (SEM), transmission electron microscope (TEM) and potentiodynamic polarization technique, respectively. It is found that HIPIB irradiation leads to the increase in open circuit potential, corrosion potential and breakdown potential, and the decrease in the corrosion current density and the corrosion rate as compared to the original sample. The improved corrosion resistance is mainly attributed to the grain refinement and surface purification induced by HIPIB irradiation.

A Mechanism of Improvement in the Corrosion Resistance of Ferritic Stainless Steels by Cu Addition

A mechanism of improvement in the corrosion resistance of ferritic stainless steels by Cu addition was studied by field exposure tests, XPS analysis of passive films and electrochemical evaluation.Corrosion area ratio after a 1-month field exposure test was the smallest with 0.4%Cu addition among 21%Cr–0~2.0%Cu stainless steels, and chromium concentration of the passive films was higher with the Cu-bearing stainless steels than the Cu-free stainless steel. After an 18-month field exposure test, chromium concentration of the passive films of high Cr and Cu bearing stainless steels was higher than that of low Cr and Cu bearing stainless steels. This result suggested an existence of a synergistic effect between Cr and Cu.Cu in ferritic stainless steels accelerates cathodic reaction and reduces anodic reaction when the steels dissolve in the active potential region. Therefore, Cu in the steels increases the open circuit potential at the passivation stage, and the increase of open circuit potential promotes the enrichment of chromium concentration of passive films on the Cu-bearing ferritic stainless steels. The cycle of dissolution and passivation strengthens the passive films on the Cu-bearing stainless steels.On the other hand, the 1-month field exposure test revealed corrosion area ratio of stainless steels bearing more than 1% Cu was larger than that of a 0.4%Cu-bearing stainless steel. Stainless steels containing more than 1% Cu contain ε-Cu in matrix. It is considered that precipitation of ε-Cu deteriorate the corrosion resistance of these stainless steels.

CdSe electrodeposition on anodic, barrier or porous Ti oxides. A sensitization effect

A variety of oxide layers, from passive amorphous TiOx of few nanometer thicknesses to micrometer-thick porous with different anatase to rutile ratios, were prepared by potentiostatic or galvanostatic anodization of Ti metal in H2SO4 and HF/H3PO4 solutions and used as substrates for electrodeposition of cadmium selenide from acidic selenite baths. The substrate and CdSe microstructures were investigated by X-ray diffraction and electron microscopy techniques. Barrier TiOx and heterogeneously structured oxide substrates induced growth of zinc blend/wurtzite CdSe, whereas highly ordered porous titanium dioxide (TiO2) accommodated growth of (10.0) oriented hexagonal CdSe thin layers. Pulsed potential plating was employed to control pore-filling during electrodeposition of CdSe. Photoelectrochemical evaluation of the produced electrodes in polysulfide cell under green light illumination implied a TiO2 sensitization effect in the case of CdSe/(porous TiO2)/Ti system, as evidenced by a negative shift in flat band potential and an increase in open circuit potential. The sensitization effect was observed even with CdSe deposited by a single potential pulse signifying the importance of contacting the TiO2 surface to the electrolytic solution via a very thin layer of CdSe.

Development of YDB/GDC Composite Electrolyte For Low-Temperature Solid Oxide Fuel Cells

A bilayered yttria-doped bismuth (YDB) and gadolinia-doped ceria (GDC) composite electrolyte has been developed using painting/screen printing method. SOFC fabricated from the composite electrolyte showed 70∼100 mV increase in open-circuit potential at 500°C, depending on the thickness ratio of YDB layer to GDC substrate, as compared to that from a single GDC layer. Moreover, under fuel cell operation condition, YDB/GDC composite electrolyte demonstrated higher specific conductivity than single GDC layer electrolyte at 600°C. These results showed the YDB/GDC composite electrolyte as a promising candidate for electrolyte for low temperature solid oxide fuel cells.

Impact of biological factors on the ennoblement of stainless steel in Baltic seawater

Open circuit potentials of stainless steels increased when immersed in the Baltic Sea. The ennoblement potential was +200 mVsce in 40 to 50 days when sea water temperature was below 52°C and +300–400 mVsce within <40 days at around 102°C. Ennoblement occurred in a laboratory ecosystem at 232°C in 20 to 30 days, and at 262°C in <20 days, but no ennoblement occurred at A322°C within 40 days. By the time the ennoblement was complete, compact microcolonies covered 1–10% of the steel surface. Nutrient enrichment of Baltic Sea water by twofold above the natural levels increased microbial growth but attenuated open circuit potential increase of the stainless steels. Exposure of the ennobled stainless steels to similar levels of nutrients did not reverse the already developed open circuit potentials. Attenuation of the ennobling response of the stainless steels by increases of temperature and eutrophication suggests a role for microorganisms which is crucial for the electrochemical behaviour of steels in brackish Baltic Sea water. Journal of Industrial Microbiology & Biotechnology (2000) 24, 410–420.

Raman and Electrochemical Probes of the Dissolution Kinetics of Tungsten in Hydrogen Peroxide

The interaction of tungsten with hydrogen peroxide was studied by Raman spectroscopy and electrochemical measurements. We found that W catalyzes the decomposition of peroxide into its ion, while the native oxide of W becomes increasingly hydrated and soluble. The decay of the peroxide concentration upon immersion of W is consistent with a model of 1-D diffusion to the W surface followed by a surface reaction with a heterogeneous rate constant of 3 × 10-5 cm/s. This model can also be used to explain the decrease of the H2O2 solution pH and the increase in open circuit potential of W that occurs while W is immersed in H2O2.

Developments in photoelectrochemistry: light-addressable photoelectrochemical cyanide sensors

The photopotential of several semiconductors when immersed in solution and illuminated respond to the concentration of specific ions in solution. Trends observed for alkaline ferrocyanide electrolytes in contact with illuminated CdSe and CdTe comprise a substantial negative shift of flat-band cyanide potential V fb and an increase in open circuit potential V oc with increasing concentration. Based on this increase in V oc, a one-dimensional light-addressable photoelectrochemical (LAP) sensing configuration capable of probing five distinct 2 mm 2 regions along a 1 mm × 10 mm surface area of a single n-CdSe detector is demonstrated for cyanide analysis. This permits a single sensing LAP element which can be externally illuminated in different regions to provide both spatial and temporal information on the analyte concentration. Spatial sensing is achieved without sensor movement and with fewer electrical contacts as compared with a conventional array scheme. In solution, the photopotential has a linear response to cyanide of 120 mV × log[KCN].