Negative Potential Shift Research Articles

Effect of Cu2+ on the corrosion behavior and mechanism of Al-2 %Zn coatings in 3.5 % NaCl solution

• Effect of the reduction of Cu 2+ on the corrosion behavior and mechanism of Al-2%Zn coating in NaCl solutions was reported. • Impact of reduction reaction of more Cu 2+ is more pronounced, resulting in a negative shift in corrosion potential and a decrease in cathodic Tafel slope. • General corrosion morphology changes to localized as the concentration of Cu 2+ increases to 110 μg/L. • The corrosion products film plays a shielding effect when the concentration of Cu 2+ is below 50 μg/L. A layer of Al-2%Zn coating was sprayed on 5083 aluminum alloy substrate. The effect of Cu 2+ on the corrosion behavior and mechanism of the coating in 3.5 wt.% NaCl solution was investigated using electrochemical techniques and surface analysis. The experimental results show that when the concentration of Cu 2+ is lower than 50 μg/L, an inductive semicircle appears in the electrochemical impedance spectrum at the beginning of immersion. When Cu 2+ concentration is 110 μg/L, no inductive semicircle was detected, indicating that the degradation process was promoted in the presence of Cl - . XPS and EDS analysis shows that Cu are formed in the corrosion process. With the increase of Cu 2+ concentration, the reduction of Cu 2+ to Cu gradually plays an important role in the cathodic reaction, while the reduction of oxygen is relatively weak, leading to the reduction of the cathodic slope and the negative shift of the mixed potential. The corrosion products film on the surface will cover the corrosion pits and plays a shielding effect due to the active dissolution of the coating. When the concentration of Cu 2+ exceeds 50 μg/L, this effect disappears and the surface morphology changes to obvious local corrosion morphology, including flaking and cracking.

Corrosion of X65 steel by Pseudomonas sp. in planktonic and sessile states and inhibition effect of cathodic polarization

In harsh marine environment, corrosion is a serious problem, among which microbiologically influenced corrosion is particularly common and complex. This work studied corrosion of X65 steel by planktonic and sessile iron oxidizing bacteria (IOB), i.e. Pseudomonas sp. isolated from coastal water of Qingdao, and inhibition effect of cathodic polarization. Results demonstrate that both the planktonic and sessile IOB caused the corrosion of X65 steel by promoting the oxidation of ferrous ions, but the contribution of sessile cells was far greater than that of planktonic cells. Cathodic polarization kills sessile cells on the metal surface and prevent attachment of IOB. With a negative shift of the cathodic potential, the inhibition effect was enhanced. Cathodic polarization altered interface properties of X65 steel, affecting adhesion and corrosion process of IOB cells. However, when X65 steel was sufficiently polarized to −1050 mV vs. SCE, IOB produced more extracellular polymeric substances to resist stimulation by an external electric field. Therefore, cathodic polarization could not completely remove sessile IOB cells, and pitting corrosion existed on the metal surface.

Study on inhibition effect and mechanism of sodium humate in hematite reverse flotation

The inhibitor can improve the hydrophilicity of minerals and prevent minerals from interacting with collectors. It plays an important role in the reverse cation flotation of iron ore, and it has become the focus of current research to find efficient, environmental friendly and cheap inhibitors. Sodium humate (NaHA) is a product extracted from weathered Lignite by means of biodegradation and organic decomposition. In this study, this new inhibitor NaHA was used to separate hematite and quartz. The results of micro-flotation showed that an appropriate concentration of NaHA could selectively inhibit hematite and realize the effective separation of quartz and hematite. Zeta potential and adsorption measurement results showed that after treatment by NaHA, the negative shift of zeta potential of hematite was more obvious, and could prevent the further adsorption of dodecylamine (DDA). The adsorption capacity of NaHA on hematite surface was much greater than that on quartz surface. FTIR results showed that there was chemisorption of NaHA on the surface of hematite but no on the quartz. XPS analysis again confirmed that NaHA may adsorb on the surface of hematite through coordination with surface iron.

Correlation between Redox Potential and Solvation Structure in Biphasic Electrolytes for Li Metal Batteries.

The activity of lithium ions in electrolytes depends on their solvation structures. However, the understanding of changes in Li+ activity is still elusive in terms of interactions between lithium ions and solvent molecules. Herein, the chelating effect of lithium ion by forming [Li(15C5)]+ gives rise to a decrease in Li+ activity, leading to the negative potential shift of Li metal anode. Moreover, weakly solvating lithium ions in ionic liquids, such as [Li(TFSI)2 ]- (TFSI = bis(trifluoromethanesulfonyl)imide),increase in Li+ activity, resulting in the positive potential shift of LiFePO4 cathode. This allows the development of innovative high energy density Li metal batteries, such as 3.8V class Li | LiFePO4 cells, along with introducing stable biphasic electrolytes. In addition, correlation between Li+ activity, cell potential shift, and Li+ solvation structure is investigated by comparing solvated Li+ ions with carbonate solvents, chelated Li+ ions with cyclic and linear ethers, and weakly solvating Li+ ions in ionic liquids. These findings elucidate a broader understanding of the complex origin of Li+ activity and provide an opportunity to achieve high energy density lithium metal batteries.

The Effect of Surface-Abundant Hydrogen Bonding on the Electrolyte Reduction for the Stable SEI in Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) have been attracted world-wide attention as an ideal anode because of its extra-high theoretical capacity (3860 mAh g-1) and low electrode potential (-3.04 V vs S.H.E.). However, the dendritic growth of Li and low Coulombic efficiency (CE) are still hindering their practical uses [1]. To date, numerous methods such as construction of artificial solid electrolyte layer (ASEI) [2], adoption of 3D current collector [3], and tuning of the electrolyte composition [4] have been proposed to prevent Li dendrite growth and increase the CE. Among them, introducing functional additives is one of the most efficient approaches for practical application considering its cost-effectiveness. Until now, various functional additives were introduced to form stable and robust SEI layer in LMBs [4]. Among them, lithium nitrate (LiNO3) is considered as the most efficient electrolyte additive, ensuring high coulombic efficiency (CE) as well as long lifespan of LMBs. When LiNO3 is dissolved in the electrolyte, NO3 - anions are mainly reduced to form inorganic species such as Li3N, which has a high ionic conductivity and mechanical strength. As such species contribute to the construction of the robust and ionic-conductive SEI layer, and hence the reduction of NO3 - is important for stable Li cycling. In this regard, many researchers have focused on increasing reduction of NO3 - by using high-concentration LiNO3 [4], or adding solubilizer to increase more NO3 - in the electrolyte [5]. However, those remedies are still insufficient because most of them increase the viscosity of electrolyte leading to low kinetics, hence a novel and more efficient way to increase NO3 - reduction is needed for practical application.On the other hand, recent researches have reported that the preferential reduction of specific anions is possible by regulation of inner Helmholtz plane (IHP) structure [6]. For instance, Huang et al. reported that intermolecular force between PF6 - anions and surface adsorbent tris(trimethylsilyl) borate could derive in PF6 --abundant IHP, successfully resulted in LiF-rich SEI layer to increase the stability of LMA [6]. Inspired by those works, we expected that NO3 --derived SEI layer would be achieved by using surface adsorbent showing strong intermolecular interaction with NO3 -.In this context, we introduce the adoption of thiourea (TU) as a catalytic additive for the LiNO3 reduction during the SEI formation. Due to its unique molecular structure, addition of TU could induce NO3 - derived SEI layer. Firstly, TU could adsorb onto metallic surface by its S atom. Meanwhile, thiourea could form hydrogen bonding with NO3 - anion by its N-H bonds [7]. Hence in the presence of TU, we suggest that NO3 --abundant electrode surface would be achieved by interaction between TU-NO3 -, resulting in Li3N-rich SEI layer.The adsorption behavior of TU on the Cu electrode was investigated by potential of zero charge (PZC) measurement (Figure 1(a)). As the TU concentration increases, PZC decreases, indicating more surface coverage by TU. Figure 1(b) shows 1H NMR spectra of electrolytes with different components. Upshift displacement of N-H bond of TU were detected after addition of DME and LiTFSI, indicating that intramolecular H-bond of TU were weakened. By contrast, downshift displacement appeared when LiNO3 was added, which means NO3 - would form strong hydrogen bonding with TU. Furthermore, linear scanning voltammetry (LSV) curves at different concentration of TU were measured to investigate the effect of TU on electrolyte reduction (Figure 1(c)). The distinct peaks at 1.6 V and 1.3 V in the cell with 5 wt% LiNO3 indicate reduction of LiNO3 and LiTFSI, respectively. Interestingly, in the presence of TU, negative potential shift and increased current of those redox peaks were shown, indicating that the TU significantly increases the LiNO3 reduction.Importantly, from the XPS analysis, it was found that more abundant Li3N components are in the ASEI layer with TU than that without TU, implying that TU accelerates the reduction of LiNO3 (Figure 2(a-b)). As a result, Li|Cu@ASEI with TU shows better cyclability and higher average CE of 96.44% during 80 cycles compared to Li|Cu@NSEI and Li|Cu@ASEI w/o TU (Figure 3). In addition, morphological and chemical investigation on the favorable ASEI layers assisted by TU, and its electrochemical performance in LMBs will be discussed in this presentation.[1] Cheng et al, Chem. Rev, 117, 10403, 2017.[2] Lopez Jeffrey, et al. JACS 140.37 (2018): 11735-11744.[3] Yang Chun-Peng et al. Nature communications 6.1 (2015): 1-9.[4] Kang et al. Journal of Power Sources 490 (2021): 229504.[5] Zhang et al. Advanced Materials 32.24 (2020): 2001740.[6] Huang et al. Angewandte Chemie. 60.35 (2021): 19232-19240.[7] Nishizawa et al. Tetrahedron letters 36.36 (1995): 6483-6486. Figure 1

Localized Environment Enriched with Hydrogen Sulfide for Inducing Sulfide Stress Cracking on Type-430 Stainless Steel

Exposure tests to hydrogen sulfide environments are frequently used to evaluate hydrogen sulfide stress corrosion cracking (SSC) in steel. However, there are many safety restrictions in handling hydrogen sulfide, and the maintenance of the facilities is very costly. To improve this situation, an electrochemical measurement method that can be used even in laboratories to simulate hydrogen sulfide stress corrosion tests easily. Specifically, a safe hydrogen sulfide corrosion test method was developed using a local hydrogen sulfide concentration environment near the steel surface.A local acidic environment of pH 3-4 was induced by constant potential anodic polarization of a platinum electrode below 2 VSHE in an aqueous sodium sulfide solution. Exposure of the carbon steel surface to a local acidic environment resulted in the formation of iron sulfides such as FeS and FeS2 on the surface, accompanied by a negative shift of the carbon steel electrode potential and an increase in the microelectrode current. Local acidification of a potentiostatically polarized type-430 steel surface confirmed the existence of a critical potential at which the steel surface begins to depassivate and actively dissolve. It was suggested that the substitution of iron oxide for iron sulfide in a hydrogen sulfide environment determines the sulfidation of the steel surface. Using this method, furthermore, the formation of cracks was successfully induced on the surface of type-430 steel under tensile stress loading.

Temperature Dependence of the Alkaline Oxygen Evolution Reaction Catalyzed By Amorphous/Crystalline Ni-Co Oxides

As the installation of renewable energy power generation systems such as solar and wind power increases, efficient energy storage devices are needed to overcome the problem of fluctuations in the availability of electrical energy. In particular, water splitting by electrolysis to produce storable hydrogen and oxygen appears to be one of the most promising approaches for large-scale energy storage. However, the efficiency of water electrolysis is greatly restricted due to the high overpotential required for the anodic oxygen evolution reaction (OER). Therefore, effective catalysts are needed to accelerate the reaction, reduce overvoltage, and increase energy conversion efficiency. Among various OER catalysts, nickel-cobalt oxides have received enormous attention due to their low cost and high OER activity in alkaline electrolyte. A better understanding of the OER kinetics is essential for accurate activity/durability predictions and the development of next generation OER catalysts. In this work, we synthesized a series of Ni-Co oxides with tunable amorphous/crystalline surface structures, with particular emphasis on the temperature dependence of the OER catalysis, as a way to elucidate the catalytic reactions, from both experimental and theoretical perspectives.The Ni-Co oxide was synthesized by the flame oxide-synthesis method.1 The as-prepared sample was treated in an oxidizing atmosphere (20% O2/N2) at elevated temperatures (from room temperature to 300 °C) without changing the Ni-Co-O atomic composition. Based on the measured composition and treatment temperature, the obtained three catalysts were denoted as Ni0.8Co0.2O-RT, Ni0.8Co0.2O-100, and Ni0.8Co0.2O-300. The OER activities were evaluated in 1 M KOH at 20 to 80 oC by use of the rotating disk electrode (RDE) technique.2 It was found that the increase in O2-treatment temperature led to increased structural order or crystallization of the oxide phase, i.e., crystallinity Ni0.8Co0.2O-RT < Ni0.8Co0.2O-100 < Ni0.8Co0.2O-300, as confirmed by XRD measurement. Figure 1a showed that the Ni-Co oxide materials presenting an amorphous or poorly crystalline oxide phase showed higher activity than their crystalline counterparts, which was correlated with a negative shift in the oxyhydroxide formation peak potential (inset of Figure 1a). The OER activation energy, extracted from temperature dependence of OER currents, also decreased with decreasing the crystalline oxide phases (Figure 1b). Thus, efficient OER was demonstrated to be associated with facilitated formation of oxyhydroxide species during electrochemical anodization. We proposed, based on density functional theory calculations, that the amorphous or disordered structure of the oxide top surface layers renders the surface geometry energetically favorable for the crucial step O + OH → OOH, which significantly accelerates the OER activity.This work was partially supported by funds for the JSPS KAKENHI (20H02839), and the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.[1] K. Kakinuma, M. Uchida, T. Kamino, H. Uchida, and M. Watanabe, Electrochim. Acta, 56, 2881 (2011).[2] G. Shi, T. Tano, D. A. Tryk, A. Iiyama, M. Uchida, and K. Kakinuma, ACS Catal., 11 , 5222 (2021). Figure 1

Multifunctional double active layers formed with electrochemically controlled nanoparticle dispersion for resistive switching memory arrays

Expanding resistive random-access memory (RRAM) from a single device to an array requires a selector to suppress the sneak path and an external device to control the compliance current. Thus, a unique crossbar array that can be independently driven through the novel design of a multilayer RRAM structure with intelligently controlled Cu2O consisting of nanoparticles embedded in the amorphous matrix (ANPs) is proposed. The ANPs–Cu2O active layers are prepared by electrodeposition, and the negative shift of the deposition potential induces a higher density and smaller size of the nanoparticles. The ANPs–Cu2O films show different set voltages and extremely uniform reset voltages, and thus a functional double active layer (DAL) structure consisting of two ANPs–Cu2O layers with different set voltages is proposed. The electrochemically fabricated VCu-controlled DALs effectively protected the reverse current from the self-rectifying characteristics of a large forward/reverse current ratio, thus realizing selector-less RRAMs. In addition, the soft-breakdown showing filament formation in the upper layer reveals the saturation current step acting as a self-compliance current without the assistance of transistors. Finally, a 4 × 4 crossbar DAL RRAM array with transistor-less self-rectification is demonstrated, which shows excellent memory performance and endurance without interfering with adjacent cells.

Sand impingements on cathodic protection of marine carbon steel in natural sea water

ABSTRACT In this work, the influence of sand impingements on cathodic protection (CP) of marine carbon steel in natural sea water was studied in comparison with the CP performances in static and flowing sea water without sand particles. Results show that the propagation of local active anodic dissolution at the steel inclusions could be totally inhibited by providing sufficient cathodic current in the sea water free of sand particles. However, the local ‘CP shielding’, potential fluctuation and sand impingements would enhance the anodic dissolution at inclusions, thus leading to the occurrence of erosion-corrosion under CP. The negative shift of the CP potential could not retard the propagation of erosion-corrosion pits under sand impingements. The synergy of erosion and corrosion might result in long-term failure of local CP.

Electrochemical Sensing Platform Based on Functionalized Multi-Walled Carbon Nanotubes and Metal Oxide for the Detection and Degradation Studies of Orange II Dye.

Textile industry effluents are heavily contaminated with dyes. The discharge of these toxic dyes into waterbodies poses a serious threat to aquatic flora and fauna. The ultimate entrance of these toxins from thereon into the food chain affects the primary and secondary consumers. Therefore, the adoption of a sustainable solution for protection against the detrimental effects associated with adulterated water is an immediate need of the hour. To address the severity of the issue, the present work aims to design an electrochemical sensing platform by modifying the glassy carbon electrode (GCE) with zinc oxide nanoparticles and amino group-functionalized multi-walled carbon nanotubes (NH2-fMWCNTs) for the detection of Orange II, which is a toxic azo dye. Zinc oxide nanoparticles facilitate electron transfer between the transducer and the analyte. While, the positively charged NH2-fMWCNTs in acidic medium help in preconcentration of negatively charged analyte molecules at the electrode/electrolyte interface. The modification of the GCE catalyzed the oxidation of Orange II, as evidenced by the negative shift of the oxidation potential and enhancement in peak current intensity. Square wave voltammetry was used to optimize various experimental conditions, such as the supporting electrolyte, pH of the electrolyte, deposition potential, and deposition time for the best performance of the designed sensor. Under the optimized conditions, the detection limit and quantification of the designed sensor were found to be 0.57 and 1.92 nM, respectively. The catalytic degradation studies of Orange II was shown to be facilitated by titanium dioxide, which acted as a photocatalyst. The addition of hydrogen peroxide further promoted the extent and rate of degradation of dye. The breakdown of Orange II was probed by the designed sensing platform electrochemically and also by UV–visible spectroscopy. The dye degraded up to 92% by following pseudo-first-order kinetics.

Thermally Driven Structural Order of Oligo(Ethylene Glycol)-Terminated Alkanethiol Monolayers on Au(111) Prepared by Vapor Deposition.

To probe the effects of deposition temperature on the formation and structural order of self-assembled monolayers (SAMs) on Au(111) prepared by vapor deposition of 2-(2-methoxyethoxy)ethanethiol (CH3O(CH2)2O(CH2)2SH, EG2) for 24 h, we examined the surface structure and electrochemical behavior of the resulting EG2 SAMs using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM observations clearly revealed that EG2 SAMs vapor-deposited on Au(111) at 298 K were composed of a disordered phase on the entire Au surface, whereas those formed at 323 K showed improved structural order, showing a mixed phase of ordered and disordered phases. Moreover, at 348 K, uniform and highly ordered EG2 SAMs on Au(111) were formed with a (2 × 3√3) packing structure. CV measurements showed sharp reductive desorption (RD) peaks at −0.818, −0.861, and −0.880 V for EG2 SAM-modified Au electrodes formed at 298, 323, and 348 K, respectively. More negative potential shifts of RD peaks with increasing deposition temperature are attributed to an increase in van der Waals interactions between EG2 molecular backbones resulting from the improved structural quality of EG2 SAMs. Our results obtained herein provide new insights into the formation and thermally driven structural order of oligo(ethylene glycol)-terminated SAMs vapor-deposited on Au(111).

The role of thiosulfate and sulfite in gold thiosulfate electrowinning process: An electrochemical view

In this study, electrochemical and analytical techniques are employed to explore the effect of thiosulfate, sulfite, and a mixture of thiosulfate-sulfite in the electrolyte on the gold electrowinning process. The open circuit potential (OCP) analysis showed negative potential shifts from − 0.02 V (in the electrolyte containing Au-TS (E1)) to − 0.21 V, − 0.33 V, and − 0.42 V in the presence of thiosulfate oversupply (electrolyte E2), sulfite (electrolyte E3), and thiosulfate-sulfite mixture (electrolyte E4). The linear sweep voltammetry (LSV) results exhibited − 0.4 V potential shift by the addition of sulfite to the gold-thiosulfate electrolyte, attributing to the formation of Au(S2O3)(SO3)25- as the most stable gold complex. Based on chronoamperometry (CA) and atomic absorption spectrometer (AAS) results, sulfite could control the kinetics and thermodynamics of gold reduction reactions by minimizing undesired cathodic side reactions such as thiosulfate decomposition or water reduction, resulting in purer gold deposition, elimination of colloidal sulfur, and a more efficient EW process. The presence of thiosulfate accelerated the kinetics of the gold reduction reaction. However, adding sulfite to the electrolyte stabilized the kinetic about 10 times faster. SEM and EDS analysis depicted the morphological changes in the deposited gold layer from different electrolytes during CA, showing that thiosulfate oversupply results in the formation of a greater number of smaller grains by accelerating the nucleation process, while sulfite addition led to the formation of a smoother and more uniform gold layer on the cathode surface.

A novel synergy of Co/La co-doped porous BiVO4 photoanodes with enhanced photoelectrochemical solar water splitting performance

This work discussed a straightforward approach to manufacture Co-, La-, and Co/La-doped BiVO4 nanoporous films. The effect of doping in the photoelectrochemical (PEC) water splitting performance was evaluated through PEC test and the strong electronic correlation of the framework in the density functional theory (DFT) calculation was taken into account. It was shown that replacing Bi atoms with Co would decrease the bandgap of BiVO4, but doping with La shifted the bandgap from indirect to direct and resulted in the negative shift of onset potential. Furthermore, doping Co and La ions into BiVO4 also introduced deep levels into the BiVO4 bandgap. After the optimization of the mole ration of Co to La, the (0.7/0.3)Co/La:BiVO4 photoanode achieved a high photocurrent density of 3.65 mA cm−2 under the simulated solar irradiation with a bias of 1.23 VRHE, resulting in an H2/O2 production rate of 57.6/25.8 μmol cm−2 h−1. More importantly, without any co-catalysts and hole scavengers, the photoanode presented a favorable stability during 16 h test. The enhanced PEC performance was mainly due to improved visible light absorption and carrier separation ability. Both the experimental and theoretical demonstrations proved that the dual-element doping strategy shed light on designing efficient and stable photoelectrodes for solar energy conversion.

Green synthesis of zinc sulfide nanoparticles-organic heterocyclic polyol system as eco-friendly anti corrosion and anti-bacterial corrosion inhibitor for steel in acidic environment

ABSTRACT Green synthesis, characterization and evaluation of nanoscale zinc sulfide (ZnS) by precipitation chemical method. The zinc sulfide nanoparticles were prepared by chemical precipitation method using heterocyclic polyvinyl alcohol, PVA as a sensitizer. The prepared heterocyclic compounds system ZnS nanoparticles, PVA, EG were used as anti-bacterial corrosion towards sulfate-reducing bacteria (SRB) and anti-corrosion for carbon steel substrate in sulfuric acid and hydrogen sulfide bacterial corrosive environment using chemical, analytical, and electrochemical techniques. Effect of adding PVA, and ethylene glycol, EG to ZnS nanoparticles were studied. Effect of ZnS nanoparticles concentrations and the reaction temperature on the corrosion inhibition efficiency were studied. The inhibition due to adsorption of nanoparticles on steel surface, the adsorption agree well with Langmuir isotherm with suggested chemical adsorption mechanism. Potentiodynamic polarization (PD) and Electrochemical impedance spectroscopy (EIS) data explain that the used inhibitor is mixed-type and improves polarization resistance and inhibition performance by adhering to metal/electrolyte interface. The cathodic and anodic reactions are delayed when inhibitor molecules are added to an aggressive medium, which results in a negative shift in the open circuit potential. Addition of both PVA, and EG as organic polyol materials enhance the adsorption and inhibition properties of zinc sulfide nanoparticles on steel surface.

An FTIR Study of the Electrooxidation of C2 and C3 Alcohols on Carbon‐Supported PdxRhy in Alkaline Medium**

AbstractWe have investigated the promoting effect of Rh addition to Pd‐based materials in the electrooxidation of ethanol and glycerol. Physicochemical characterizations (XRD, EDX, TEM, and XPS) of the PdxRhy/C materials, prepared by bromide anion exchange (BAE), showed that the experimental bimetallic compositions were close to the targeted ones. PdxRhy/C particle sizes ranged from 2.2 to 3.8 nm. The ethanol oxidation reaction (EOR) on the PdxRhy/C catalysts yielded four times larger carbonate (CO32−) amount. As for the glycerol oxidation reaction (GOR), the onset potential on the Pd50Rh50/C catalyst occurred at lower potentials. Chromatographic analysis combined with in situ Fourier transform infrared (FTIR) spectroscopy showed that GOR on the Pd50Rh50/C catalyst selectively and quantitatively produced glycerate and tartronate. The outstanding ability of the Pd50Rh50/C catalyst toward EOR and GOR was correlated to the electronic effect expressed by a negative potential shift (200 mV) and the 47 % alloying degree in the Pd50Rh50/C structure.

Electrochemical behavior and electrodeposition of Fe-Co-Ni thin films in choline chloride/urea deep eutectic solvent

Fe-Co-Ni coating, a vital type of transition metal alloy, shows great potential in the field of hydrogen storage and magnetic materials. In this study, Fe-Co-Ni coatings were prepared on Cu substrates from a deep eutectic solution of choline chloride/2Urea (ChCl/2Urea) DES by electrodeposition. The effects of deposition potential on the morphology, chemical composition, crystal structure, corrosion resistance and magnetic properties of nanostructured Fe-Co-Ni coatings were investigated. The results revealed that the reduction process of Fe-Co-Ni alloy on the Cu electrode in ChCl/2Urea DES was irreversible three-dimensional instantaneous nucleation, which was controlled by diffusion. The surface morphology, microstructure, compose and crystallite size of the Fe-Ni-Co alloy were related to the deposition potential. The Fe content of the electrodeposited alloys showed a maximum of 48.17 at% at the applied potential of −1.3 V and a positive correlation was observed between the Fe content and electrodeposition potential in the investigated potential range. The nickel-rich coatings were obtained at high potential and iron-rich coatings were obtained at low potential. The less roughness, more compact grain and uniform flat Fe-Co-Ni coatings were prepared under a more negative potential. The Fe-Co-Ni coatings were composed of face-centered cube (fcc, NiFe) and body-centered cube crystals (bcc, FeCo). With the negative shift of deposition potential, the structure of Fe-Co-Ni coatings grew preferentially toward FeCo(110) and FeCo(211) crystal surfaces. The Fe-Co-Ni coatings prepared from ChCl/2Urea DES at different deposition potentials showed good corrosion resistance. Fe-Co-Ni coating that is produced at the deposition potential of −1.2 V, exhibited a more positive corrosion potential and obvious magnetic anisotropy.

Low-temperature hydrogenation of nanodiamond as a strategy to fabricate sp3-hybridized nanocarbon as a high-performance persulfate activator

This study presents the first instance of the application of hydrogenated nanodiamonds (H-NDs) for persulfate activation and the associated organic degradation. Surface hydrogenation at 600 ℃, confirmed by the increased surface density of the C-H moiety in XPS and FT-IR spectra, produced H-NDs that outperformed graphitized NDs (prepared via annealing at 1000 ℃) in terms of organic degradation and persulfate utilization efficiency. Hydrogenation improved the electrical conductivity of NDs; however, it was not accompanied by an increase in the sp2 carbon content − in contrast to energy-intensive ND graphitization − resulting from sp3-to-sp2 carbon transformation. In addition to the enhanced electron-transfer mediating activity, evidenced by the negative shift of the open circuit potential and current generation, isothermal titration calorimetry measurements indicated a significantly higher binding affinity of H-ND toward persulfate compared with that of graphitized ND. Multiple empirical results confirmed the progress of electron-transfer mediation as a major activation pathway.

Bi Doped Sb2S3 Thin Film Synthesized by a Two-Step Approach with Enhanced Photoelectrochemical Water Splitting Performance

Photoelectrochemical water splitting (PEC) is believed as a promising approach to address the energy and environmental crisis. Here, we adopted a simple two-step method to synthesize bare Sb2S3 film, and then employed a Bi element doping strategy to improve the PEC performance of obtained bare Sb2S3. The obtained Bi-Sb2S3 exhibited an increased photocurrent density, 2.8 mA cm−2 at 1.23 VRHE and a negative shift of onset potential, compared to bare Sb2S3. The enhancement in PEC performance of Bi-Sb2S3 could be attributed to the expanded light absorption range, increased electron carrier concentration and improved charge transfer ability.

Mo-doped BiVO4 modified with NH2-MIL-88B(Fe) cocatalyst overlayer for enhanced photoelectrochemical water oxidation

The photoelectrochemical (PEC) performance of BiVO4 is limited by poor charge separation and slow surface water oxidation kinetics. Herein, an simple and effective caffeic acid-assisted solvothermal method was developed to grow Fe-based metal–organic framework (NH2-MIL-88B(Fe)) overlayer onto the Mo-doped BiVO4 for efficient PEC water oxidation. The synergistic role of Fe-MOF cocatalyst and Mo dopant resulted in a 3.5-fold photocurrent density (1.46 mA cm−2) increase in comparison with bare BiVO4 (0.46 mA cm−2) at 1.23 V [vs. reversible hydrogen electrode (RHE)] and showed an obviously negative shift of the onset potential (200 mV). The enhanced PEC performance can be attributed to the improved charge separation and injection efficiency with Mo doping and Fe-MOF coating, the introduction of Fe-MOF also increased the utilization of visible-light and served as an efficient electrocatalyst to accelerate the oxygen evolution reaction (OER) kinetics. This work provides a universal strategy for constructing semiconductor/MOFs photoanodes for enhanced photoelectrochemical water splitting.

Effect of test media on the crevice corrosion of stainless steel by sulfate reducing bacteria

The potential for crevice corrosion of UNS30400 stainless steel in the presence of sulfate-reducing bacteria (SRB) was studied in different media. Immersion studies found crevice corrosion to occur in test media supplemented with high chloride levels and SRB present for crevice gaps of ~3 μm. Electrochemical measurements showed high susceptibility to corrosion in this particular medium, demonstrated by a negative shift of open circuit potential, increased corrosion current and the lowest passivity breakdown potential. Overall, the results showed that test media can play a critical role in the crevice corrosion of stainless steel in the presence of SRB.