Phosphate-based Electrolyte Research Articles

Corrosion, Wear, and Antibacterial Behaviors of Hydroxyapatite/MgO Composite PEO Coatings on AZ31 Mg Alloy by Incorporation of TiO2 Nanoparticles

Plasma electrolytic oxidation (PEO) is a promising surface treatment for generating a thick, adherent coating on valve metals using an environmentally friendly alkaline electrolyte. In this study, the PEO method was used to modify the surface of AZ31 Mg alloy. The composite coatings were formed in a phosphate-based electrolyte containing hydroxyapatite nanoparticles (NPs) and different concentrations (1, 2, 3, and 4 g/L) of TiO2 NPs. The results showed that the incorporation of TiO2 NPs in the composite coatings increased the porosity, coating thickness, surface roughness, and surface wettability of the coatings. The corrosion-resistance results of coatings in simulated body fluid (SBF) were tested for up to 72 h and all coatings showed superior corrosion resistance compared to the bare substrate. Among samples containing TiO2, the sample containing 1 g/L TiO2 had the highest inner layer resistance (0.51 kΩ·cm2) and outer resistance (285 kΩ·cm2) and the lowest average friction coefficient (395.5), so it had the best wear and corrosion resistance performance. The antibacterial tests showed that the higher the concentration of TiO2 NPs, the lower the adhesion of bacteria, resulting in enhanced antibacterial properties against S. aureus. The addition of 4 g/L of TiO2 NPs to the electrolyte provided an antibacterial rate of 97.65% for the coating.

Empowering Zn Electrode Current Capability Along Interfacial Stability by Optimizing Intrinsic Safe Organic Electrolytes.

Metallic Zn is one of the most promising anodes, but its practical application has been hindered by dendritic growth and serious interfacial reactions in conventional electrolytes. Herein, ionic liquids are adopted to prepare intrinsically safe electrolytes via combining with TEP or TMP solvents. With this synergy effect, the blends of TEP/TMP with an IL fraction of ≈25 wt% are found to be promising electrolytes, with ionic conductivities comparable to those of standard phosphate-based electrolytes while electrochemical stabilities are considerably improved; over 1000 h at 2.0 mA cm-2 and ≈350 h at 5.0 mA cm-2 with a large areal capacity of 10 mAh cm-2 . The use of functionalized IL turns out to be a key factor in enhancing the Zn2+ transport due to the interaction of Zn2+ ions with IL-zincophilic sites resulting in reduced interfacial resistance between the electrodes and electrolyte upon cycling leading to spongy-like highly porous, homogeneous, and dendrite-free zinc as an anode material.

Guar gum-driven high-energy plasma electrolytic oxidation for concurrent improvements in the electrochemical and catalytic properties of Ti-15 Zr alloy

A hybrid composite layer with optimal chemical stability and catalytic activity was formed on Ti-15 Zr alloy for the first time via high-energy plasma electrolytic oxidation driven by guar gum (GG). Here, the substrate was treated in a phosphate-based electrolyte containing GG (0, 1, 1.5, and 2 g/L), which might act as an electron donor during plasma-assisted electrochemical processes. The ability of GG molecules to form an adsorption layer on the substrate surface through either polar –OH or hetero-oxygen atoms would be responsible for the reduction in the intensity of plasma discharges observed at lower concentrations of GG (1 g/L). However, higher concentrations of GG would act as barriers to the electron avalanche by accumulating at the surface of the barrier passive layer developed on the substrate surface. As a result, the discharges in the 1.5GG and 2GG samples were more potent than those observed in other electrolytes to overcome the electron avalanche obstruction. In addition, the chemical incorporation of ZrO2 into the TiO2 layer would be affected by the GG additive, which would donate electrons to the oxygen bubble, acting as electron acceptors in the electrolyte. The chemical stability of the 1.5GG sample was superior to the other samples as it had the highest values of outer and inner layer resistances (1.79 × 107 and 4.81 × 107 Ω.cm2, respectively). The 1.5 GG sample achieved also a relatively good catalytic activity of 95.97% toward methylene blue. Thus, a multifunctional layer with high chemical stability and high catalytic activity was formed, which would be associated with the presence of rutile and ZrO2 in the coatings, respectively. The obtained results of the oxide layers were very high and comparable to other works.

Computational Investigation of a NASICON-Type Solid Electrolyte Material LiGe2(PO4)3

Phosphate-based electrolyte materials are of great interest in the field of Li-ion batteries due to their rigid structural integrity. LiGe2(PO4)3 is a NASICON-type phosphate material with high thermal and electrochemical stability. Computational simulation techniques were employed to study the defects, diffusion, and dopant properties of LiGe2(PO4)3. Furthermore, the reaction energies for the formation of LiGe2(PO4)3 and the incorporation energies for the insertion of additional Li into this material were calculated. The calculations revealed that the Li Frenkel is the lowest-energy defect. The second most favorable defect is the Ge-P anti-site defect cluster. A low Li migration energy of 0.44 eV implies high Li ionic conductivity. The most favorable isovalent dopants on the Li and Ge sites are Na and Si, respectively. The formation of Li interstitials and oxygen vacancies can be facilitated through the doping of Ga on the Ge site. The doping of Ga slightly enhances the Li ionic conductivity. Li incorporation (up to four Li) is thermodynamically feasible.

Effect of Si3N4/TaC Particles on the Structure and Properties of Microarc Oxidation Coatings on TC4 Alloy

Si3N4/TaC composite MAO coatings were fabricated by microarc oxidation (MAO) on a Ti–6Al–4V (TC4) alloy in a phosphate-based electrolyte containing Si3N4/TaC mixed particles. The influence of the amount of Si3N4/TaC particles on the microstructure, composition, tribological behavior, and corrosion properties of the MAO coatings has been investigated. Morphological research of the MAO coatings was carried out using scanning electron microscopy (SEM), with the surface porosity analyzed by ImageJ software. X-ray diffraction (XRD) was used for the detection of the phase characteristic of the MAO coatings, and an abrasive wear test and electrochemical measurements were conducted in the artificial seawater solution by the ball-on-disc friction tester and the electrochemical workstation, respectively. The results showed that Si3N4/TaC particles could be successfully incorporated into the composite coatings, and the addition of Si3N4/TaC particles greatly reduced the porosity of the coatings, thus improving both tribological and corrosion properties of the composite MAO coatings. The composite MAO coating with the addition of 1 g/L Si3N4 + 0.5 g/L TaC particles showed the best tribological property and the optimum corrosion properties.

In-situ synthesized MgO-based ceramic coatings on a novel Mg–Ca material: Morphological response to the PEO electrolyte

MgO-based ceramic layers were in-situ synthesized on a novel Mg-based substrate via plasma electrolytic oxidation (PEO). The effects of electrolyte composition on the morphology of the layers were investigated through preparing three different ion arrangements, including common silicate-based and phosphate-based electrolytes as well as a modified Ca-containing phosphate-based electrolyte. Characterization methods including scanning electron microscopy and EDS elemental analysis were used to investigate the morphological features of the coatings, at the surfaces and cross-sections. Results indicated that the silicate-based electrolyte yields morphologically inhomogeneous coating with small porosities, while using the phosphate-based electrolytes may result in improved thickness and modified porosities. However, both of the coatings prepared via common electrolytes present Ca-containing heterogeneities, called nuggets. Using the modified phosphate-based electrolyte, it was indicated that the addition of Ca2+ ions not only removes any elemental/morphological heterogeneities in the PEO coating but also provides a ceramic layer with homogenous thickness distribution. However, it was confirmed that the PEO conditions should be changed to obtain the optimum morphological characteristics in coatings synthesized via Ca-contained electrolyte.

Strong ion pairing at the origin of modified Li-cation solvation and improved performances of dual-salt electrolytes

Organic phosphates have been widely used as fire-retardant additives/co-solvents to improve the Li-ion electrolyte safety. However, these solvents show poor compatibility with low potential electrodes and cannot work efficiently as sole solvent at low salt concentration. The utilization of high concentration electrolytes was shown to improve the interfacial properties by altering the solvation structure but the drawbacks are low ionic conductivity, high viscosity, and elevated costs. Herein, a dual-salt phosphate-based electrolyte consisting of medium concentration lithium nitrate (LiNO3) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salts in triethyl phosphate (TEP) is analyzed and found to address the above issues. Benefiting from the strong affinity between NO3− and Li+, the use of LiNO3 is found to perturb the solvation structure, with mixed anion (NO3− and TFSI−) pairing with Li+. The detailed environment of Li+ in dual-salt phosphate-based electrolyte is probed through nuclear magnetic resonance and Raman analysis, corroborated by theoretical calculations. The dual-salt formulation is found to lead to the formation of a LiF–Li3N-LiNxOy-rich solid-electrolyte interphase on Li metal surface. The results and analyses not only allow the assembly of LiNi0·5Co0·2Mn0·3O2||Li cells with significantly improved cycling and low-temperature performances but also shine a light on taming strong polarity phosphate electrolytes with fine solvation interplay.

Role of phosphate, silicate and aluminate in the electrolytes on PEO coating formation and properties of coated Ti6Al4V alloy

A comparison of PEO layers on Ti6Al4V alloy formed in phosphate, aluminate and silicate-based electrolytes respectively, has been made to reveal the influence of the electrolyte composition on the formation process. The phosphate-based electrolyte has been identified as the most promising one as it has the best coating formation efficiency and the lowest breakdown voltage. On the bases of the microstructure and elemental/phase analysis of the different PEO coatings, it could be observed that the PEO coating formed in phosphate-based electrolyte is mainly composed of anatase and rutile. An amorphous phase is dominant in the coating produced in silicate-based electrolyte. Moreover, there are mainly γ-Al2O3, Na2Al2xO3x+1 and TiAl2O5 present in the coating formed in the aluminate-based electrolyte. The coating formation process in silicate- and aluminate-based electrolytes is more dependent on the deposition originating from the electrolytes. All of the coatings have shown noticeable corrosion resistance and good performance in the photocatalytic test as the degradation rates of methyl orange higher than 45 %. Thus, multifunctional PEO coatings on Ti6Al4V alloy are obtained.

Effect of EDTA addition on the biotribological properties of coatings obtained from PEO on the Ti6Al4V alloy in a phosphate-based solution

Coatings were obtained on the Ti6Al4V alloy by Plasma Electrolytic Oxidation (PEO) in a phosphate-based electrolyte with different Ethylenediaminetetraacetic acid (EDTA) concentrations. TiO2 was detected in the coatings in both anatase and rutile phases, with the incorporation of P and Ca into the coating from the electrolyte. A significant change was evidenced for samples anodized with EDTA addition, compared to the sample anodized without EDTA. The thickness was higher for coating obtained with an increased amount of EDTA sample (20.24 μm), compared to the coating anodized without EDTA (13.12 μm). All samples were anodized at galvanostatic conditions, applying a current density of 50 mA cm−2 during 1000s. A higher coating thickness leads to the formation of higher intensity micro-discharges, which promotes the formation of a higher amount of rutile phase, in the coatings with higher EDTA content in the anodizing electrolyte. The friction and wear properties of coatings were analyzed in a ball-on-disk tribometer, under lubricated conditions in simulated body fluid (SBF). The coatings substantially improved the wear behavior of the Ti6Al4V alloy. The coating with a higher amount of EDTA exhibits better tribological performance (6 times better than the substrate (Wear rate: 22.077 × 10−10 Kg/N.m)), due to the higher amount of rutile into the coating, which reduces the wear rate as well as the friction coefficient.

Superior properties and behaviour of coatings produced on nanostructured titanium by PEO coupled with the EPD process

Surface modification of commercially pure Grade 4 coarse-grained titanium (CG-Ti) and nano-grained titanium (n-Ti) by plasma electrolytic oxidation (PEO) and plasma electrolytic oxidation conjugated with electrophoretic deposition (PEO-EPD) processes is reported in the present study. Two different coatings were developed on each CG-Ti and n-Ti in phosphate-based electrolytes without and with the incorporation of hydroxyapatite (HA) nanoparticles. The phase composition, morphology (surface and cross-sectional), corrosion resistance, surface roughness, and scratch-resistance of the fabricated coatings were thoroughly studied and analysed. The L-929 fibroblast cells were used for assessing the in-vitro cell viability. The L-929 cells cultured on PEO-EPD treated CG-Ti, and n-Ti samples exhibited higher cell growth than PEO treated CG-Ti and n-Ti samples. Among all the PEO and PEO-EPD treated samples, the PEO-EPD treated n-Ti sample showed significantly better corrosion resistance (icorr = 8.85 × 10−7 mA cm−2), lower contact angle (40°), and good adhesion strength (Lc = 29 N), demonstrating the importance of the nanostructuring of the titanium substrate for the properties of the coating. The origin of the discovered enhancement in the properties of the modified PEO coating produced on nanostructured titanium was examined and discussed. After soaking in SBF for 14 days, the PEO-EPD treated sample is wholly covered with apatite layer indicating its good bioactivity

PEO processing of AZ91Nd/Al2O3 MMC-the role of alumina fibers

• Al 2 O 3 fibers interrupted the continuity of PEO coating at the interface of coating/substrate. • Al 2 O 3 fibers reactively incorporated in PEO coating through thermal drive reactions. • A MgAl 2 O 4 containing layer was formed in plasma electrolytic oxidation coating near the surface. This work reports the influence of alumina fiber reinforcement of an AZ91Nd MMC (metal matrix composite) on the PEO coating formation process in a sodium phosphate-based electrolyte. By comparison with the pure AZ91Nd, the evolution of alumina fiber during the processing and the characteristics of the resultant PEO coating were investigated. The voltage response as a function of processing time was changed. Lower voltage in the presence of alumina fiber is responsible for the lower coating thickness. The morphology and phase composition of the coatings are also influenced by the incorporation of the fiber. Firstly, the fiber is embedded in the coating and interrupts the continuity of the coating. With increasing processing time, the fiber is found to be reactively incorporated in the coating. The intention to produce a MgAl 2 O 4 containing coating is achieved and it is mainly accumulated near the coating surface. However, due to the low number of fibers, the Al content is overall still low and only near to the fibers the MgAl 2 O 4 spinel phase can form.

Effects of co-incorporated ternary elements on biocorrosion stability, antibacterial efficacy, and cytotoxicity of plasma electrolytic oxidized titanium for implant dentistry

In this study, calcium, phosphorus, and copper co-incorporated titanium oxide (TiO2) layers were prepared on titanium substrates using the plasma electrolytic oxidation process. Thereafter, their features were studied to be used in dental implants. Surface characterization revealed that the addition of calcium and copper ions to the phosphate-based electrolyte led to the development of the ternary elements incorporated TiO2 layer with greater surface homogeneity, roughness, hydrophobicity, and growth rate. As well, electrochemical impedance spectroscopy proved that the placement of the ternary elements caused more compaction of the TiO2 layer by reducing inherent defects. Thus, the corrosion behavior of the TiO2 layer in artificial saliva solution has promoted, which consequently enhanced the corrosion potential by 187 mV and diminished the corrosion current density by one order of magnitude. Antibacterial assessment against Escherichia coli showed that incorporation of copper along with calcium and phosphorus significantly restored the bactericidal activity of the TiO2 layer. Furthermore, the integration, proliferation, and viability of MG-63 osteoblastic cells have considerably improved in the biological response to the calcium, phosphorus, and copper-containing layer.

High-Safety and Dendrite-Free Lithium Metal Batteries Enabled by Building a Stable Interface in a Nonflammable Medium-Concentration Phosphate Electrolyte.

Lithium metal anodes are promising for their high energy density and low working potential. However, high reactivity and dendrite growth of lithium metal lead to serious safety issues. Lithium dendrite may form "dead lithium" or pierce the separator, which will cause low efficiency and short-circuit inside the battery. A nonflammable phosphate-based electrolyte can effectively solve the flammability problem. Also, it shows poor compatibility with lithium metal anodes, resulting in an unstable solid electrolyte interface (SEI), which leads to dendrite growth and poor electrochemical performance. In this study, trimethyl phosphate is used to ensure the safety of lithium metal batteries. By adjusting the concentration of lithium salt and introducing fluoroethylene carbonate, a stable SEI layer is formed on the surface of the lithium metal anode and dendrite growth of the lithium metal anode is inhibited. Lithium metal batteries with a modified electrolyte achieved stable electrochemical plating/stripping, and the full cell has 93.4% capacity left and the coulombic efficiency is nearly 100%. In addition, the modified electrolyte can also enable reversible intercalation and de-intercalation of Li+ in the commercial graphite anode. This work may provide an alternative direction for the development of lithium metal batteries with high safety and high energy density.

Enabling Atomic-Scale Imaging of Sensitive Potassium Metal and Related Solid Electrolyte Interphases Using Ultralow-Dose Cryo-TEM.

Potassium-based solid electrolyte interphases (SEIs) have a much smaller damage threshold than their lithium counterpart; thus, they are significantly more beam sensitive. Here, an ultralow-dose cryogenic transmission electron microscopy (cryo-TEM) technique (≈8 e Å-2 s-1 × 10 s), which enables the atomic-scale chemical imaging of the electron-beam-sensitive potassium metal and SEI in its native state, is adapted. The potassium-based SEI consists of large brackets of diverse inorganic phases (≈hundreds of nanometers) interspersed with amorphous phases, which are different from the tiny nanocrystalline inorganic phases (≈a few nanometers) formed in a lithium-based SEI. Organic phosphate-based electrolyte solvents induce the formation of a thin and stable SEI layer for enhanced cycling performance, while the carbonate ester-based electrolytes result in large quantities of metastable KHCO3 , and K4 CO4 products in the SEI, depleting the potassium reserves in the battery. The findings provide deep insights and guidance in the selection of optimum electrolytes that should be used for potassium batteries.

Structured solid electrolyte interphase enable reversible Li electrodeposition in flame-retardant phosphate-based electrolyte

Tailoring non-flammable phosphate-based electrolytes with high safety and good Li reversibility are in urgent demand for practical lithium metal batteries. However, phosphate-ester exhibits a poor compatibility with active Li surface and the key to solve this challenge is to build a sustainable solid-electrolyte interphase. Herein, dual-layer crystalline/polymeric solid electrolyte interphase (SEI) is designed in phosphate ester/ether mixed electrolyte utilizing lithium difluoro(oxalato)borate (LiDFOB) as main salt. The coordinated ether in Li solvation sheath will be reduced in Li metal surface, forming alkoxides residue in the early cycling stage, which will further react with DFOB− to form an outer Li2O, inner amorphous polyether SEI layer. Consequently, the flame-retardant electrolyte exhibits a low self-extinguishing time of 6.10 s g−1 and a satisfied Li reversibility of 98.31% in NCM/Cu configuration. The coin-type limited-excess Li/LiNi0.8Mn0.1Co0.1O2 (NCM811) full cell with negative to positive electrode capacity ratio (N/P) of 1.92 can cycle for more than 140 cycles. Meanwhile, a pouch cell with ∼0.2 Ah capacity, low N/P ratio of ∼2.22 shows a good capacity retention of 87.9% after 60 cycles without Li exhaustion.

Functionalized and Platinum-Decorated Multi-Layer Oxidized Graphene as a Proton, and Electron Conducting Separator in Solid Acid Fuel Cells

In the present article, electrodes containing a composite of platinum on top of a plasma-oxidized multi-layer graphene film are investigated as model electrodes that combine an exceptional high platinum utilization with high electrode stability. Graphene is thereby acting as a separator between the phosphate-based electrolyte and the platinum catalyst. Electrochemical impedance measurements in humidified hydrogen at 240 °C show area-normalized electrode resistance of 0.06 Ω·cm−2 for a platinum loading of ∼60 µgPt·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. The presented platinum decorated graphene electrodes enable stable operation over 60 h with a non-optimized degradation rate of 0.15% h−1, whereas electrodes with a similar design but without the graphene as separator are prone to a very fast degradation. The presented results propose an efficient way to stabilize solid acid fuel cell electrodes and provide valuable insights about the degradation processes which are essential for further electrode optimization.

One-pot synthesis and microstructure of multi-layered nanospheres via plasma electrolytic oxidation

In the present work, plasma electrolytic oxidation (PEO) is creatively introduced as a novel method to fabricate multi-layered nanospheres. Titanium (Ti) was oxidized in a phosphate-based electrolyte containing ZnO nanoparticles (NPs), which results in the formation of nanospheres on the ceramic coating. The as-fabricated nanosphere is amorphous with a three-layered architecture. The inner layer of the nanosphere contains Zn, Ca and P whereas Cu and P were detected in the medium layer with the outer layer enriched in Cu, O and Ti, which is promising in the field of bio-medical implanted devices. Herein, a novel one-pot synthesis strategy is proposed to fabricate multi-layered nanospheres, which could enlighten the preparation of hierarchical structures in various fields.

Phosphate Electrolyte Design for Highly Reversible Sodium Ion Batteries

Sodium ion battery (NIB) is a very promising technology for the next generation of energy storage systems because of the abundance and low cost of Na in the Earth’s crust. However, the large-scale application of NIBs is still a challenge because of limited cycle life and potential safety concerns. In this regard, electrolyte plays a critical role in both cycle life and safety of NIBs. The battery stability is directly related to the properties of the electrode-electrolyte interphase. Therefore, designing advanced electrolytes with a stable electrode-electrolyte interphase is crucial to develop stable NIBs for their practical applications in large-scale energy storage. In this work, we report a phosphate-based electrolyte for sodium ion batteries with high capacity retention and excellent coulombic efficiency (99.9 %) during long term cycling. The details together with postmortem analysis of the cycled electrode will be discussed at the presentation. The insights obtained in this work can be used to further improve cycling stability and safety of rechargeable batteries.

Multipurpose surface modification of PEO coatings using tricalcium phosphate addition to improve the bedding for apatite compounds

Recently, Mg alloys have found appealing biomedical applications because of properties such as biodegradability and biocompatibility. However, the full potential of Mg alloys has yet to be exploited as implant materials due to insignificant corrosion resistance and inadequate support to contain apatite compounds. This study presents a novel method to prepare and modify plasma electrolytic oxidation (PEO) coatings facilitating the formation of apatite compounds on the surface without compromising corrosion protection. We prepared calcium-phosphate PEO coatings in a phosphate-based electrolyte benefiting from introducing tricalcium phosphate (TCP) salt as an additive. The composition and surface morphology of coatings produced with the addition of 1–4 g/l TCP were studied using EDS, XRD, FT-IR, and FE-SEM. Moreover, coatings’ surface roughness and wettability were evaluated. We investigated the electrochemical behavior of coatings exposed to simulated body fluid (SBF) at four intervals (1 h, 1, 3, and 7 days) using electrochemical impedance spectroscopy (EIS). We realized that the coating produced with 4 g/l TCP addition offers a modified surface supporting the bedding for precipitation of apatite compounds and demonstrating significant corrosion protection.

Phosphate-Based Electrolyte and Pristine Graphite Cathode for a High-Voltage Rechargeable Dual-Ion Magnesium Battery

The pristine graphite cathode and Mg anode magnesium dual-ion battery (MDIB) consists of a noncorrosive and nonvolatile electrolyte, i.e., 0.1 M magnesium trifluoromethanesulfonate (Mg(OTf)2), in a...