Electrochemical Impedance Spectroscopy Results Research Articles

Heterojunction-based and structure-engineered construction of Cs3Bi2Br9/g-C3N4/PDMS photocatalytic flexible s with three-dimensional interpenetrating uniform pores

Using photocatalysts for the degradation of antibiotics in aqueous environments is a highly promising strategy for achieving green and sustainable development. Although significant improvements have been made in photocatalyst reuse, the recycling rate is still unsatisfactory. Herein，we prepared a photocatalyst Cs3Bi2Br9/g-C3N4 and incorporated it into PDMS using a three-dimensional fiber porous structure (PCC) prepared by electrospinning sacrificial templates. This structure served to protect the catalyst without limiting its degradation performance. The photocurrent measurements and electrochemical impedance spectroscopy results are consistent with those of the oxytetracycline hydrochloride (OTC-HCl) removal test. The electron spin resonance results confirmed the formation of •OH and •O2− under visible light irradiation. This way of using the film to protect the catalyst for photocatalytic degradation may open up new possibilities for the remediation of environmental pollution.

Effect of manifold size on PEMFC performance with metal foam flow field

Metal foam flow fields are considered as an alternative to conventional channel/rib flow field in polymer electrolyte membrane fuel cell (PEMFC) because of the advantages of three-dimensional pore structure. In this study, the effect of metal foam flow field with different manifold size on PEMFC performance was investigated, with a 25 cm2 unit cell. Polarization curve and electrochemical impedance spectroscopy results were analyzed to investigate the effects of gas stoichiometry and relative humidity on performance. The mass transfer loss was decreased with reduced manifold size. However, mass transfer loss was increased due to difficulty of water discharge in small manifold case. The metal foam flow field offer advantages in water discharge and mass transfer loss. At 100% relative humidity, performance was improved with increased air stoichiometry for different manifold size. At 25% relative humidity, performance was a little improved with increased air stoichiometry for small manifold case. Regardless of relative humidity, fuel cell performance with metal foam flow field was most improved in case of smallest manifold size based on air stoichiometry due to the high pressure drop.

Double-layered composite coating with enhanced self-healing and anti-corrosion performance based on synergistic effect of l-methionine and vanillin

Nanocontainers loaded with corrosion inhibitors as fillers can endow the organic coating with self-healing abilities. However, the number of nanocontainers that can be added to the coating is limited, and the number of corrosion inhibitors that can be accommodated by the nanocontainers is also limited. These considerably mitigate the anti-corrosion properties of the self-healing coating. Herein, a self-healing double-layered composite coating (MK-VK/EP), l-methionine (L-met)-loaded dendritic silica (KCC-1) nanocontainers modified epoxy coating (EP) as the bottom layer (MK/EP) and vanillin (Van)-loaded KCC-1 modified EP as the top layer (VK/EP), was fabricated on the surface of carbon steel. The results of electrochemical impedance spectroscopy (EIS) show that the low frequency impedance modulus (|Z|0.01Hz) of MK-VK/EP is nearly two orders of magnitude higher than that of MK/EP or VK/EP in 3.5 wt% NaCl solution after 45 days. Furthermore, the self-healing rate (rself-healing) of the scratched MK-VK/EP coating (S-MK-VK/EP) is still much higher than that of the scratched MK/EP or VK/EP in the last two stages of immersion. Meanwhile, there exists no apparent corrosion after 12 h of immersion from the optical image of S-MK-VK/EP. The results show that MK-VK/EP can provide better self-healing corrosion protection performance than the single coating (MK/EP or VK/EP). Hence, the synergistic effect of different corrosion inhibitors can greatly improve anti-corrosion abilities of the coating, which will provide an effective approach for corrosion protection of metal in marine environment.

Enhanced electro-catalytic activity of TNTs/SnO2-Sb electrode through the effect mechanism of TNTs architecture

The TiO2 nanotubes arrays/SnO2-Sb (TNTs/SnO2-Sb) electrode is successfully fabricated using the solvothermal synthesis technique. Various architectures of TNTs are constructed by varying the anodization voltage and time, aiming to investigate their impact on the structural and electrochemical properties of the SnO2-Sb electrode. The anodization voltage is identified as the primary influencing factor on the morphology and surface hydrophilia of TNTs arrays, which is evidenced by scanning electron microscopy (SEM) and contact angle testing. In contrast, the effect of anodization time is relatively small. SEM, X-ray diffraction (XRD), linear sweep voltammograms (LSV), and electrochemical impedance spectroscopy (EIS) results indicate that the morphology and crystal size of the catalytic coating, as well as the oxygen evolution potential of the electrode, are influenced by the pore size of TNTs arrays. The influencing mechanism of enhanced electrochemical activity by adjusting the architecture of TNTs arrays is investigated using X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and hydroxyl radicals (·OH) generation test. The results reveal a higher concentration of oxygen vacancies on the sample with a compact and smaller particle coating, indicating the presence of more adsorbed oxygen species. Consequently, this enhances the generation capacity of active radicals for organic matter degradation. The electrode featuring TNTs arrays with a length of 950 nm and a pore diameter of 100 nm exhibits the most effective remediation of phenol-containing wastewater, achieving approximately 92% ± 4.6% removal after a duration of 2 h.

Bi-Doped and Bi Nanoparticles Loaded CeO2 Derived from Ce-MOF for Photocatalytic Degradation of Formaldehyde Gas and Tetracycline Hydrochloride.

Bi/CeO2 (BC-x) photocatalysts are successfully prepared by solvothermal loading Bi nanoparticles and Bi-doped CeO2 derived by Ce-MOF (Ce-BTC). Formaldehyde gas (HCHO) and tetracycline hydrochloride (HTC) are used to evaluate the photocatalytic activity of the synthesized Bi/CeO2. For BC-1000 photocatalyst, the degradation of HTC by 420nm < λ < 780nm light reaches 91.89% for 90min, and HCHO by 350nm < λ < 780nm light reaches 94.66% for 120min. The photocatalytic cycle experiments prove that BC-1000 has good cyclic stability and repeatability. The results of photoluminescence spectra, fluorescence lifetime, photocurrent response, and electrochemical impedance spectroscopy showed that the SPR (Surface Plasmon Resonance) effect of Bi nanoparticles acted as a bridge and promoted electron transfer and enhanced the response-ability of Bi/CeO2 to visible light. Bi-doping produced more oxygen vacancies to provide adsorption sites for adsorbing oxygen and generated more ·O2 - thus promoting photocatalytic reactions. The mechanism of photocatalytic degradation is analyzed in detail utilizing active free radical capture experiments and electron paramagnetic resonance (EPR) characterization. The experimental results indicate that ·O2 - and h+ active free radicals significantly promote the degradation of pollutants.

Effect of hydrostatic pressure on the anodic dissolution process of X80 steel

Based on the fact that hydrostatic pressure affects chemical potentials of reaction species and the structure evolution of electric double layer (EDL), the authors propose a generalized-BV equation to analyze the anodic dissolution process of X80 steel in deep-sea environment. Combined with the results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the following conclusions can be drawn: hydrostatic pressure can compress the electric double layer non-uniformly. The CHCD (CD: capacitance of diffused layer; CH: capacitance of compact layer) value increases first and then decreases with increasing hydrostatic pressure and reaches its maximum at 15 MPa, which is sure to influence the difference in electrical potential that drives chemical reaction at interface. Ultimately, the anodic dissolution current increases and then decreases with rising hydrostatic pressure at the same anodic polarized potential. Besides, low hydrostatic pressure may contribute to forming a dense corrosion product film and inducing a good inhibiting effect on further dissolution of X80 steel; However, when the hydrostatic pressure exceeds the critical value of 20Mpa, too high anodic dissolution rate along with promoted Cl− adsorption will deteriorate the protection performance of corrosion product film, and exacerbate local corrosion process.

Cardanol‐based polybenzoxazine coatings: Crosslinking structures, hydrophobicity and corrosion protection properties

AbstractTwo bio‐based polybenzoxazine coatings, cardanol/3‐aminopropyltriethoxysilane‐based polybenzoxazine (PC‐aptes) and cardanol/stearylamine‐based polybenzoxazine (PC‐s), were prepared for corrosion protection on mild steel. The structures of polybenzoxazines were characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT‐IR). Due to the presence of long hydrocarbon chains and hydrogen bond networks, the PC‐aptes and PC‐s coatings showed high hydrophobicity, with static water contact angles of 106.0 ± 0.6° and 104.8 ± 1.6°, respectively. It was noted that the silane‐functionalized PC‐aptes coating had a dual‐crosslinked network of polybenzoxazine and polysiloxane, which could effectively inhibit the penetration of corrosive media. The results of electrochemical impedance spectroscopy (EIS) indicated that the PC‐aptes coating with higher crosslinking density exhibited superior corrosion resistance compared to the PC‐s coating.

Understanding of corrosion inhibition behavior of expired isoniazid modified benzothiazole 2-carboxaldehyde at mild steel/0.5 M H2SO4 interface

The corrosion hindering behaviour of (E)-N'-((benzo[d]thiazol-2-yl) methylene) isonicotinohydrazide (BTMIH) was tested on mild steel (MS)/0.5 M H2SO4 interface and established BTMIH as an excellent corrosion retarding agent. Various techniques, viz. electrochemical analyzing, surface studies, contact angle measurement, and gravimetric measurement, have been used to establish the corrosion-resistant behaviour of BTMIH. Thermodynamic and activation parameters obtained from gravimetric studies elucidated the mechanism of corrosion. The increase in charge transfer resistance caused by the presence of BTMIH confirmed its capacitive behaviour. Addition of 7.08 × 10−4 M of BTMIH exhibited 98 % corrosion combating efficiency confirmed by electrochemical impedance spectroscopy (EIS) results. The X-ray photoelectron spectroscopy (XPS) scan confirmed the presence of BTMIH film on the MS surface. The presence of BTMIH in electrolytic solution makes the MS surface hydrophobic towards electrolytic solution as shown by increased contact angle between MS/electrolyte (42.38° with 7.08 × 10−4 M of BTMIH compared to 12.6° with 0.5 M H2SO4). The maximum magnitude of corrosion potential shift (39 mV) established BTMIH as a mixed-type inhibitor.

Experimental and theoretical insights on long-term corrosion protection performance of MXene Nanosheets decorated with graphene quantum dots in epoxy coatings

In this study, MXene nanosheets decorated with zero-dimensional graphene quantum dots and functionalized with 3-aminopropyltriethoxysilane (APTES-MXene@GQDs) are used as a nanofiller in epoxy coatings. The MXene@GQDs and APTES-MXene@GQDs are characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results prove that the GQDs with spherical size (≤ 10 nm) have covered the MXene nanosheets through creating C-O-Ti covalent bonds. The Si-O-C and Ti-O-Si bonds in the APTES-MXene@GQDs indicate that both MXene and GQDs have reacted with the APTES molecules. The results of electrochemical impedance spectroscopy reveal that the low-frequency impedance modulus of epoxy coatings loaded with 0.1 wt% APTES-MXene@GQDs is 4.4 × 109 and 6.4 × 108 Ω.cm2 after 1 day and 7 weeks of immersion in NaCl solution, respectively. Meanwhile, hydrophobic coatings with high adhesion strength are achieved by adding the modified nanofillers. Density Functional Theory calculations emphasize the potential of MXene@GQDs nanohybrids in corrosion protection. The COO covalent bond significantly bolsters stability, making it a strong contender. An efficient electron transfer, as revealed in charge transfer dynamics, reinforces the interactions. The presence of MXene reshapes the electronic landscape, facilitating robust charge transfer processes. Conversely, the systems lacking MXene exhibit less advantageous energy level placement.

Characteristics of low-pressure-plasma-processed NiRu-MOFs/nickel foam for Hydrogen evolution reaction

NiRu bimetallic metal–organic frameworks (NiRu-MOFs) are grown by a simple hydrothermal method on nickel foam (NF) as an the electrocatalyst for the hydrogen evolution reaction. Low-pressure plasmas of pure Ar, 95%Ar + 5%H2, and 95% Ar + 5%O2 are used for the post-treatment of the NiRu-MOFs. NiRu-MOFs-AO with post-plasma treatment with 95%Ar + 5%O2 show the lowest overpotential of 123.3 mV at a current density of 10 mA cm−2 and a Tafel slope of 72.0 mV dec−1 in 1 M KOH electrolyte. Electrochemical impedance spectroscopy results indicate that post-plasma treatment can further reduce the charge transfer resistance. Moreover, the electric double-layer capacitance (Cdl) is calculated based on the cyclic voltammetry results, and the electrocatalyst subjected to 95%Ar + 5%O2 post-plasma treatment shows a 2Cdl value of 3.69 mF/cm2, suggesting a larger electrochemically active surface area after oxygen-containing-plasma treatment.

Design of New Ecofriendly Schiff Base Inhibitors for Carbon Steel Corrosion Protection in Acidic Solutions: Electrochemical, Surface, and Theoretical Studies.

Corrosion poses a significant problem for several industrial sectors, inducing continuous research and development of corrosion inhibitors for use across a wide range of industrial applications. Here, we report the effectiveness of three newly developed Schiff bases derived from amino acids and 4-aminoacetophenone, namely, AIP, AMB, and AImP, as environmentally friendly corrosion inhibitors for Q235 steel in hydrochloric acid using electrochemical and surface analyses, in addition to theoretical techniques. The electrochemical findings of potentiodynamic polarization (PDP) demonstrated that the explored compounds serve as mixed-type inhibitors and can effectively suppress steel corrosion, with maximal protection efficiencies of 93.15, 96.01, and 77.03% in the presence of AIP, AMB, and AImP, respectively, at a concentration of 10 mM. The electrochemical impedance spectroscopy (EIS) and polarization results confirmed the growth of a durable protective barrier on the steel surface in the existence of the inhibitors, which is responsible for decreasing the metallic dissolution. Results were further supported by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-vis, and Fourier transform infrared (FTIR), which ascribed the development of inhibitor-adsorption films on the steel surface. The results of EDS and XPS analyses demonstrated the existence of the distinctive elements of the inhibitors on the metallic surface. Furthermore, density functional theory (DFT) calculations and Monte Carlo (MC) simulations showed the electronic structure of the examined inhibitors and their optimized adsorption configurations on the steel surface, which helped in explaining the anticorrosion mechanism. Finally, the theoretical and experimental findings exhibit a high degree of consistency.

Corrosion Inhibition of Expired Cefazolin Drug on Copper Metal in Dilute Hydrochloric Acid Solution: Practical and Theoretical Approaches.

In this work, we studied the corrosion of Cu metal in 0.5 mol L-1 HCl and the inhibition effect of the expired Cefazolin drug. The inhibition efficiency (IE) of Cefazolin varied according to its concentration in solution. As the Cefazolin concentration increased to 300 ppm, the IE increased to 87% at 298 K and decreased to 78% as the temperature increased to 318 K. The expired drug functioned as a mixed-type inhibitor. The adsorption of the drug on the copper surface followed Temkin's adsorption model. The magnitudes of the standard free energy change (ΔGoads) and adsorption equilibrium constant (Kads) indicated the spontaneous nature and exothermicity of the adsorption process. Energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques showed that the drug molecules were strongly attached to the Cu surface. The electrochemical frequency modulation (EFM), potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS) results were in good agreement with the results of the weight loss (WL) method. The density functional tight-binding (DFTB) and Monte Carlo (MC) simulation results indicated that the expired drug bound to the copper surface through the lone pair of electrons of the heteroatoms as well as the π-electrons of the tetrazole ring. The adsorption energy between the drug and copper metal was -459.38 kJ mol-1.

Electrodeposition of copper on glassy carbon and palladium from choline chloride - ethylene glycol deep eutectic solvent

Electrodeposition of copper from deep eutectic solvents (DES) based on a mixture of choline chloride and ethylene glycol containing CuCl2·2H2O at 50 °C and 80 °C was studied. Electrochemical reduction/oxidation of Cu(II)/Cu(0) on glassy carbon (GC) and palladium (Pd) electrodes was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) emphasizing that this process takes place through two steps, Cu(II) ↔ Cu(I) and Cu(I) ↔ Cu(0). The CV results showed that in chloride-rich DES electrolytes, the increased presence of chloro ligands raises the overpotential required for Cu electrodeposition. The electrochemical impedance spectroscopy (EIS) results indicate simultaneous electrodeposition of Cu and electrosorption of large cations on electrodeposited Cu on both GC and Pd substrates. Scanning electron microscopy (SEM) results showed that Cu grains of approximately 1 μm were obtained by electrodeposition of Cu on both Pd and GC, whereby better coverage by electrodeposited Cu was obtained on Pd than on GC. Cu electrodeposited on Pd was relatively uniform and smooth, but porous, while Cu electrodeposited on GC was dispersed in small agglomerates. Energy-dispersive X-ray spectroscopy (EDS) of Cu electrodeposited on Pd detected the dominant presence of Cu with the possibility of the formation of CuPd alloy. The presence of CuPd alloy face-centred cubic structures is confirmed by X-ray diffraction (XRD) along with metallic Cu.

Protective and Flame-Retardant Bifunctional Epoxy-Based Nanocomposite Coating by Intercomponent Synergy between Modified CaAl-LDH and rGO.

Extensive utilization in various settings poses extra requirements of coatings beyond just anticorrosion properties. Herein, 8-hydroxyquinoline (8-HQ) intercalated CaAl-based layered double hydroxide (CaAl-8HQ-LDH) was loaded on reduced GO (rGO) through a one-pot hydrothermal reaction, which was employed as the nanofiller endowing the epoxy (EP/CaAl-8HQ LDH@rGO) with excellent flame-retardancy while ensuring efficient protection for mild steel. Results of electrochemical impedance spectroscopy (EIS) demonstrated the durability of the EP/CaAl-8HQ LDH@rGO-coated specimen, with the impedance at the lowest frequency (|Z|0.01Hz) maintained as 1.84 × 1010 Ω cm2 after 120 days of immersion in a 3.5 wt % NaCl solution. Even for the scratched EP/CaAl-8HQ LDH@rGO system, only a slight decline in |Z|0.01Hz was observed during 180 h of exposure to the NaCl solution, indicating a self-healing feature supported by salt spray tests. UL-94 burning tests revealed the V-0 rating for EP/CaAl-8HQ LDH@rGO with improved thermostability. Strong physical barrier from two-dimensional rGO and the release of 8-HQ from LDH interlayers accounted for the anticorrosive and self-healing properties. However, O2-concentration dilution and charring-layer promotion governed the flame-retardant behavior of the nanocomposite coating. The intercomponent synergy of nanofillers achieved in this work may provide a useful reference for designing multifunctional coatings.

An investigation to enhance the performance of molten carbonate-direct coal/carbon fuel cells through improvements in anode layouts and the compositions of carbonate electrolyte

Two anode configurations are systematically tested in composite electrolytes of molten carbonate with Cs2CO3 at various temperatures using different carbon fuels, including bituminous coal, bituminous coal char, carbon black, and graphite powder. The results of electrochemical impedance spectroscopy show that electrolytes composed of (Li-K)2CO3 62:38 doped with 20 wt% Cs2CO3 and utilizing graphite powder as a fuel exhibit reduced ohmic and charge transfer resistance. This can be attributed to the decreased surface tension, which enhances the gas solubility of the reactants within the electrolytic matrix. The analysis of particle size distribution through laser diffraction reveals that the graphite specimen has the smallest mean particle size, resulting in an enhanced rate of electrochemical oxidation. The ultimate and proximate analysis indicates that graphite powder has a lower moisture and ash ratio along with a significantly higher fixed carbon content compared to other carbon fuels. Therefore, the obtained V-j &P-j curves in Anode 1 illustrate that graphite powder yields the highest current density and power density of 903 mA/cm2 and 172 mW/cm2, respectively, at an operating temperature of 680 °C under the laboratory conditions. These values surpass those reported in the existing literature. In contrast, Anode 2 exhibits low performance, due to ash particles regime-controlled at the lower part of the chamber during the coal pyrolysis. Based on results, we suggest that graphite powder is the promising fuel candidate for MC-DCFC to achieve the higher performance.

Highly catalytic reduced graphene oxide decorated Cu2S counter electrode boosting quantum dot–sensitized solar cell performance

This paper shows the outcomes of making and planning quantum dot solar cells with cathode electrodes made from a nanocomposite of rGO and Cu2S. The hydrothermal method is used to make this stuff into a powder, which is then mixed with polyethylene glycol and polyvinylpyrrolidone to make a paste coating that is then printed onto an FTO substrate that is conductive. Cu2S, rGO, and rGO@Cu2S nanocomposite electrodes, with the initial mass of graphene oxide varying at 8 mg, 12 mg, and 16 mg. The composition and structure of the films were determined using EDX mapping, XRD, Raman spectroscopy, and FTIR spectra, confirming that they were successfully fabricated. In addition, the results showed that the surface of the film is very porous, making it suitable for electrode fabrication. The results of measuring the PCE show that the efficiency has been effectively improved. The efficiency of the rGO counter electrodes is increased as compared to the Cu2S counter electrodes. The device has the highest efficiency of 5.665%, VOC = 0.48V, JSC = 22.776 mA cm−2, and FF = 0.518 for the 12 mg-rGO@Cu2S counter electrode. This result shows that the support of the graphene network helps the Cu2S nanoparticles be distributed more evenly when Cu2S material is directly coated on the FTO. Besides, the graphene network also helps to make the electrons transition to the polysulfide more flexible, which is proven through cyclic voltammetry and electrochemical impedance spectroscopy results.

Effect of Graphene on Corrosion Resistance of Low Zinc Epoxy Coatings Applied to Low-Carbon Steel

To reduce the consumption of zinc resources, it is necessary to reduce the zinc powder content of epoxy zinc-rich coatings. However, the reduced zinc powder content tends to reduce the degree of connectivity in the layer, which leads to a reduction in the corrosion resistance of the coating. The effective zinc powder content was also reduced. Therefore, it is important to increase the connection capacity of the zinc powder in the coating while reducing the amount of zinc powder. In this paper, an epoxy coating with low zinc content is prepared by using flake zinc powder instead of spherical zinc powder. It also uses graphene to connect zinc powder in the coating to increase the electrical conductivity of the zinc powder in the coating. This results in an increase in the protection of the coating determined, although the cathodic protection of the coating was not prolonged by the results of open-circuit potential and electrochemical impedance spectroscopy. In addition, when the zinc powder in the coating is cleanly consumed, the complex nature of corrosion product formed with graphene can increase the barrier resistance of the coating thereby increasing the corrosion resistance.

In English

The improvement of the electrochemical characteristics of lithium-manganese spinel LiMn2O4 is one of the most important tasks for researchers in the field of lithium-ion batteries. Graphene materials can have a positive effect on the functional characteristics of LiMn2O4-based composite electrodes due to their unique properties. Therefore, the composite electrodes based on spinel LiMn2O4 with commercial samples of graphene nanoplatelets were investigated. Structural, morphological and surface characteristics of LiMn2O4 and graphene samples studied using X-ray diffraction, scanning electron microscopy and nitrogen adsorption–desorption methods. Electrochemical test of the composite electrodes was performed in CR2016 coin cells with lithium metal anode. It is shown that the nature of LiMn2O4 is the main factor that determines electrochemical behavior of composite electrodes in terms of their cycling stability and rate capability. At the same time, the influence of graphene type within one spinel is relatively small, but the presence of graphene is important to ensure the required level of conductivity of the electrode structure. Despite the lower initial specific capacity, the composites with LiMn2O4 sample synthesized by a citric acid-aided route demonstrate better cycling stability and higher maximum discharge currents up to 40 C compared to composites based on LiMn2O4 synthesized by a solid-state method. The electrochemical characteristics obtained are in good agreement with the results of electrochemical impedance spectroscopy.

Electrochemical Behavior of Mg and Zn-Substituted HA Composite Coating on Titanium Produced By Plasma Electrolytic Oxidation

The aim of this study is to develop a long-term corrosion-resistant, antibacterial, and bioactive TiO2/hydroxyapatite (HA) coating using a one-step plasma electrolytic oxidation (PEO) method. Magnesium and zinc-substituted HA particles were synthesized and utilized to create a composite coating that is corrosion-resistant, bioactive, and antibacterial. Prior to their use in the coating, the synthesized particles were characterized by XRD and FESEM. The results of polarization and electrochemical impedance spectroscopy (EIS) tests showed a significant increase in corrosion resistance. Moreover, the EIS results indicated an improvement in corrosion behavior after 168h, which was attributed to the formation of apatite in simulated body fluid (SBF). Additionally, a significant improvement in the bioactivity and antibacterial activity of the composite coatings was observed. Hence, the use of Mg, Zn-doped HA/TiO2 composite coatings could be a promising approach for developing bio-corrosion-resistant coatings for titanium biomaterials.Keywords: Plasma electrolytic oxidation, Hydroxyapatite, Corrosion, Electrochemical impedance spectroscopy, Biomaterials

Investigation of Aliovalent Substitution in the Solid Sodium Ion Electrolyte Na2ZrCl6

The research community is working hard on the development of solid-state batteries (SSB) as an alternative to commercialized lithium-ion batteries, due to their higher energy density and enhanced safety. One of the core research areas of SSBs is the solid-state electrolyte (SE), which should fit the demand for high ionic conductivity and electrochemical stability at the same time. Recently, halide SEs have emerged because they are mechanochemical processable, similar to sulfidic SEs, but halide SEs exhibit excellent electrochemical oxidation stability compared to sulfidic SEs [1,2].However, the relatively low ionic conductivity at room temperature still hinders the application of halide SE in SSBs. Aliovalent substitution is a very widely used method to improve the ionic conductivity of SEs [3,4]. We are also motivated by the application of earth-abundance elements to reduce raw material costs.Recently, significant focus has been gained by Zr-based compounds such as Na2ZrCl6. We investigate here such compounds, focusing on elemental substitutions to gain increased ionic conductivity and on gaining insight into the influence of synthesis on SE crystal structure and electrochemical properties.In our work, different amounts of elemental substitutions are investigated, and the related materials are synthesized at different temperatures. In particular, the influence of a series of subsequent heating temperatures on the structure of the binary system is studied through XRD diffraction analysis and further refinement. The Ionic diffusion paths are also estimated through the band valence sum approach, in order to validate the electrochemical impedance spectroscopy (EIS) results.In summary, we report our early results on the development of novel solid electrolytes for Na-based solid-state batteries.REFERENCES[1] Kwak, H.; Lyoo, J.; Park, J.; Han, Y.; Asakura, R.; Remhof, A.; Battaglia, C.; Kim, H.; Hong, S.-T.; Jung, Y. S. Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries. Energy Storage Mater. 2021, 37, 47−54.[2] Tong Zhao, Alexander N. Sobolev, Roman Schlem, Bianca Helm, Marvin A. Kraft and Wolfgang G. Zeier. Synthesis-Controlled Cation Solubility in Solid Sodium Ion Conductors Na2+xZr1 - xInxCl6. ACS Appl. Energy Mater. 2023, XXXX, XXX, XXX-XXX.[3] Schlem, R.; Banik, A.; Eckardt, M.; Zobel, M.; Zeier, W. G. Na3-xEr1-xZrxCl6-A Halide-Based Fast Sodium-Ion Conductor with Vacancy-Driven Ionic Transport. ACS Appl. Energy Mater. 2020, 3, 10164−10173.[4] Wu, E. A.; Banerjee, S.; Tang, H.; Richardson, P. M.; Doux, J.M.; Qi, J.; Zhu, Z.; Grenier, A.;Li, Y.; Zhao, E.; Deysher, G.; Sebti, E.;Nguyen, H.; Stephens, R.; Verbist, G.; Chapman, K. W.; Clement, R.J.; Banerjee, A.; Meng, Y. S.; Ong, S. P. A stable cathode-solid electrolyte composite for high-voltage, long-cycle-life solid-state sodium-ion batteries. Nat. Commun. 2021, 12, 1256.