Cdl Values Research Articles

Exploration and tuning of Al2O3/Mo composite for enhancement of anti-corrosion and tribological characteristics in zinc phosphate conversion coatings

Recently, phosphate conversion coatings have been modified by transition/non-transition metal oxide with distinguished characteristic features such as corrosion resistance, wear resistance, lubrication and adhesion. The present paper explores the development of Al2O3/Mo composite incorporated zinc phosphate coatings on galvanized steel for achieving higher corrosion-resistant characteristics with an added advantage of tribological performance. Incorporation of Mo leads to the phase transformation from γ to α-Al2O3, which ensures the subsequent crystallization of alumina particles by the anisotropic grain growth of Mo content. Particle size, elemental composition and morphology of the Al2O3/Mo composite are tuned for retaining the stable crystalline alpha phase of the composite. The optimum concentration of the tuned content of Al2O3/Mo composite in the phosphating solution can effectively perform as an active nucleating source for the establishment of more compact, homogeneous and dense zinc phosphate crystal growth and coverage in the galvanized steel surface by significantly reducing the activation energy during the phosphating process. The resultant composite phosphate coating ensures the formation of a large quantity of crystalline hopeite rich phase compared to other coatings, which effectively acts as an insulator during the electrochemical reaction by imparting a corrosion-resistant barrier between the substrate and corrosive media. Uniform distribution of composite particles at the grain boundaries and at the bulk grain composition is also achieved. Lower average surface roughness (Sa), root mean square surface roughness (Sq), maximum height (St), surface skewness (Ssk) and higher surface kurtosis (Sku) values are acquired for better anti-corrosion properties with excellent tribological performance. The higher Rp and Rct values with lower Cdl and corrosion rate values of the tuned composition of Al2O3/Mo composite based zinc phosphate coating confirms the better porosity and thereby enhances the corrosion-resistant performance due to the sealing action of the composite.

Study on Oxygen Evolution Reaction Performance of Jarosite/C Composites.

In the electrolysis of water process, hydrogen is produced and the anodic oxygen evolution reaction (OER) dominates the reaction rate of the entire process. Currently, OER catalysts mostly consist of noble metal (NM) catalysts, which cannot be applied in industries due to the high price. It is of great importance to developing low-cost catalysts materials as NM materials substitution. In this work, jarosite (AFe3(SO4)2(OH)6, A = K+, Na+, NH4+, H3O+) was synthesized by a one-step method, and its OER catalytic performance was studied using catalytic slurry (the weight ratios of jarosite and conductive carbon black are 2:1, 1:1 and 1:2). Microstructures and functional groups of synthesized material were analyzed using XRD, SEM, FI-IR, etc. The OER catalytic performance of (NH4)Fe3(SO4)2(OH)6/conductive carbon black were examined by LSV, Tafel, EIS, ECSA, etc. The study found that the OER has the best catalytic performance when the weight ratio of (NH4)Fe3(SO4)2(OH)6 to conductive carbon black is 2:1. It requires only 376 mV overpotential to generate current densities of 10 mA cm−2 with a small Tafel slope (82.42 mV dec−1) and large Cdl value (26.17 mF cm−2).

NIR Photothermal-Enhanced Electrocatalytic and Photoelectrocatalytic Hydrogen Evolution by Polyaniline/SnS2 Nanocomposites

A series of polyaniline (PANI)-decorated SnS2 nanoplates (PANI/SnS2) were produced via a hydrothermal method followed by a liquid–solid mixing. The PANI/SnS2 nanocomposites were composed of amorphous PANI and hexagonal-phase SnS2 nanoplates. Infrared thermal images revealed that PANI had an excellent near-infrared (NIR)-induced photothermal effect. Overall, the PANI/SnS2 nanocomposites showed better NIR-enhanced electrocatalytic and photoelectrocatalytic hydrogen evolution activity than bare SnS2 nanoplates. The optimized 4% PANI/SnS2 (which contained 4 wt % PANI) displayed the largest electrochemical double-layer capacitance (Cdl) value (0.85 mF cm–2) and the lowest Tafel slope of 66 mV dec–1 in 0.5 M H2SO4 under NIR irradiation. It was investigated and confirmed that the photothermal effect and the synergistic effects between SnS2 and PANI heterostructure played important roles in promoting electrocatalytic and photoelectrocatalytic hydrogen evolution processes.

Polyvinylpyrrolidone-assisted novel copper antimony sulfide nanorods for highly efficient hydrogen evolution reaction

Transition metal dichalcogenides have been the most attractive material in hydrogen evolution reaction due to their advantages such as being cost-effective, earth-abundant, excellent conductivity, etc. In this study, PVP-assisted CuSbS2 nanorods were produced via hydrothermal technique. In XRD spectra, high intense peak at 28.34, 28.64, 29.54 and 29.80° clearly divulged CuSbS2 phase. The synthesized products Raman spectra also confirmed the existence of pure orthorhombic phase CuSbS2. The surface morphology of CuSbS2 has been studied by scanning electron spectroscopy, which displayed the 1D nanorod morphology and it is further confirmed by the TEM images. The elemental composition of the synthesized products is also characterized by the EDX mapping and EDX spectra, which shows the homogenous distribution of elements such as Cu, Sb and S in proper atomic percentage of 27.16, 21.06 and 51.78 respectively. Compared to the excess amount of PVP assisted CuSbS2, optimum amount of PVP assisted CuSbS2 exhibited 40.37 m2/g elevated surface area. The required over potential for 0.5 g PVP-CuSbS2 is only the 177 mV to attain 10 mA/cm2. Moreover, Tafel value of 0.5 g PVP-CuSbS2 (187 mV/dec) was smaller than pure (241 mV/dec) and 1.0 g PVP-CuSbS2 (219 mV/dec). The estimated turnover frequency (TOF) also showed that 0.5 g PVP-CuSbS2 has high intrinsic activity and exhibited excellent durability with 90.6% retention in long-term i-t test. Moreover, the catalytic activity of 0.5 g PVP-CuSbS2 was also high, which exhibited the Cdl and ECSA value of 115.3 mF/cm2 and 5.76 cm2 respectively. Therefore, the ternary metal chalcogenide revealed capable superior stability for hydrogen evolution reactions.

Binary Mixture of t(3)-Methyl-r(2),c(6)-diphenyl-piperidin-4-one and Gum Exudates of Astragalus genus as an Green Soldier for Dissolution Control of Mild Steel in HCl

The corrosion inhibitive behaviour of t(3)-Methyl-r(2),c(6)-diphenyl-piperidin-4-one (3MDPP) and gum exudates of Astragalus genus (GTP) on mild steel in 1 N HCl were studied using weight loss measurements for 1 h immersion period at 303-323 K. The corrosion rate of mild steel directly varies with temperature whereas it varies inversely with concentration. The synergistic influence of different concen-trations of GTP on 3MDPP was analyzed at 303-323 K using weight loss technique. The icorr, Ecorr, Rct and Cdl values were obtained for 3MDPP, GTP and the mixture of GTP and 3MDPP (binary mixture). The calculated values of Ea, ΔH*, ΔS* and ΔG°ads suggests the physical adsorption mechanism and it obeys Langmuir isotherm. The synergistic influence of GTP on 3MDPP is clear from the synergistic parameter value (> 1).

Uticaj tiouree na otpornost na koroziju mekog čelika uronjenog u simulirani rastvor betonskih pora

The corrosion resistance of mild steel in simulated concrete pore solution (SCPS) in the absence and presence of thiourea has been investigated by polarization study and AC impedance spectra. Polarisation study reveals that thiourea system functions as anodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. When mild steel is used as rebar, thiourea may be mixed with concrete. Thus the mild steel will be protected from corrosion. The protective film consists of iron-thiourea complex formed on metal surface. In the presence of thiourea the linear polarisation resistance increases, corrosion current decreases, charge transfer resistance (Rt) increases, impedance increases, phase angle increases and double layer capacitance (Cdl) value decreases. This formulation may find application in concrete technology.

Inhibicija korozije cevovoda od legure L 80, koji nosi simuliranu vodu iz bunara, ćilibarnom kiselinom

Simulated oil well water (SOWW) is conceded out by pipelines made of several alloys, for instance mild steel L80. These alloys may simulated oil well water undergo corrosion owing to presence of various aggressive ions present in SOWW. To prevent this several inhibitors have been used. Inhibition of corrosion of L80 alloy pipeline carrying simulated oil well water by succinic acid has been evaluated by electrochemical studies such as polarization study and AC impedance spectra (EIS). Polarisation study reveals that in the presence of inhibitor linear polarization resistance increases and corrosion current decreases. AC impedance spectra reveal that in presence of succinic acid, RT value increases, impedance value increases, phase angle increases and Cdl value decreases. The present study reveals that when succinic acid is added to simulated oil well water, the corrosion resistance of L80 alloy increases. It implies that succinic acid may be added to simulated oil well water flowing through pipe line made of L80 alloy.

Direct design of cage-like bimetallic NiFe hydroxides with regulated electron structure to boost the kinetic activity of oxygen evolution reaction

The key to inhibiting agglomeration of bimetallic nanocatalysts and increasing their efficiency of oxygen evolution reaction (OER) highlights the necessity to design hollow porous structures in water electrolysis. Herein, the well-regulated NiFe bimetallic nanocages have been directly synthesized through the coordinated etching and precipitation (CEP) route, and then employed as advanced electrode materials in OER. Density functional theory (DFT) calculations disclosed that the synergistic effect between Fe and Ni significantly regulated the electron density and enhanced the conductivity. Significantly, the high catalytic activity of NiFe nanocages arises from the strong interactions between Fe and Ni along with rapid electron transfer, and the favorable structure with abundant porosity and large surface area. When employed as OER electrocatalysts, the electrode based on Ni2Fe1 nanocages exhibited a low overpotential of 280 mV at 10 mA·cm−2 combined with a low Tafel slop of 55.3 mV·dec−1 and large Cdl (double layers capacitance) value of 2.33 mF·cm−2. In summary, it is promising to directly design hollow porous structures based on bimetallic hydroxide to boost the OER performance.

Protective effect of Toddalia asatica leaf extract on Mild steel in 1.0N HCl

A study has been made on the Novel corrosion inhibitor on mild steel in 1.0N HCl. Commonly deterioration of steel is caused due to various environmental and other chemical factors. It is unavoidable but protectable using inhibition methods. Here the usual inhibitor is replaced by green inhibitors to evade toxicity, easy availability, and to minimize the waste. This work seeks out to analyze the dried leaves of Todalia Asiatica as an inhibitor on mild steel in 1.0N HCl. The anticorrosive effectiveness of this inhibitor is studied by using non- electrochemical and electrochemical techniques. Non -electrochemical studies such as the effect of time (87.6%) and temperature (93.0%) at optimum concentration show the maximum inhibition efficiency of the inhibitor due to the formation of an inhibited layer by the inhibitor on the metal surface. Langmuir isotherm most closely fits into the info data obtained suggesting the physical adsorption between the extract and the mild steel substrate. Electrochemical such as potentiodynamic polarization studies proved that extract of Todalia Asiatica dried leaves is a cathodic type of inhibitor and 85.12% inhibition efficiency provided by the inhibitor. Charge Transfer Resistance (Rct) value increased and also Double-layer capacitance (Cdl) value decreases by EIS studies. The observed inhibitor efficiency at optimum inhibitor concentration is 84.05%. Surface and corrosion product Analysis (EDX/FTIR) was carried out to determine the corrosion-inhibitive properties of the samples.

Corrosion Inhibition Using Harmal Leaf Extract as an Eco-Friendly Corrosion Inhibitor.

Extract of natural plants is one of the most important metallic corrosion inhibitors. They are readily available, nontoxic, environmentally friendly, biodegradable, highly efficient, and renewable. The present project focuses on the corrosion inhibition effects of Peganum Harmala leaf extract. The equivalent circuit with two time constants with film and charge transfer components gave the best fitting of impedance data. Extraction of active species by sonication proved to be an effective new method to extract the inhibitors. High percent inhibition efficacy IE% of 98% for 283.4 ppm solutions was attained using impedance spectroscopy EIS measurements. The values of charge transfer Rct increases while the double layer capacitance Cdl values decrease with increasing Harmal extract concentration. This indicates the formation of protective film. The polarization curves show that the Harmal extract acts as a cathodic-type inhibitor. It is found that the adsorption of Harmal molecules onto the steel surface followed Langmuir isotherm. Fourier-transform infrared spectroscopy FTIR was used to determine the electron-rich functional groups in Harmal extract, which contribute to corrosion inhibition effect. Scanning electron microscopy SEM measurement of a steel surface clearly proves the anticorrosion effect of Harmal leaves.

Facile preparation of sugarcane bagasse-derived carbon supported MoS2 nanosheets for hydrogen evolution reaction

Increasingly, future energy conversion systems highly demands non-noble metal catalysts with high activity and low cost for hydrogen evolution reaction (HER). This paper reports the use of waste sugarcane bagasse (SCB)-derived biomass carbon (SCBC) to synthesize carbon-supported molybdenum disulfide (MoS2) nanosheets for HER activity. The MoS2 nanosheets are uniformly loaded on the SCBC and show a vertical growth trend. Together, a synergistic effect was produced that impacted HER activity. The obtained MoS2/SCBC 2:1 showed admirable HER electrochemical activity, with a minimum overpotential of 142 mV at 10 mA cm−2, Tafel slope of 71 mV·dec-1 and Cdl value of 65.26 mF cm−2. The MoS2/SCBC 2:1 catalyst also exhibited high stability under acidic conditions. In conclusion, a non-noble metal electrocatalyst with low-cost and high-activity for HER from biomass waste has been provided for energy conversion system.

Carbon wrapped bimetallic NiCo nanospheres toward excellent HER and OER performance

The development of highly efficient and low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) dual-functional catalysts is one of the key issues in the energy conversion system of water splitting. In this work, the carbon wrapped bimetallic NiCo nanospheres were prepared via a simple annealing process. Furthermore, the effect of different molar ratio of Ni:Co on the electrocatalytic properties of the obtained samples were investigated. Among these obtained catalysts, sample (with the molar ratio of Ni:Co was 1:2) exhibited the best electrocatalytic performance both for HER and OER. Electrochemical analysis showed that the overpotentials were only 105 and 330 mV for HER and OER to reach a catalytic current density of 10 mA cm−2, respectively. The corresponding Cdl (electric double-layer capacitance) value can reach up to 17.1 mF cm−2. What is more, the I-t-tests were carried out to prove its superior long-term catalytic durability. It was demonstrated that the excellent properties of HER and OER can be attributed to the large Cdl of the sample, the optimized molar ratio of NiCo alloy as well as the improved stability and electron transfer efficiency via carbon coating. The schematic diagrams have been provided to better understand the possible formation process and electrocatalytic mechanism. In brief, this work could provide a feasible and simple route for the design of bimetallic-based electrode materials toward superior HER and OER performance.

Enhanced electrocatalytic oxygen evolution reaction kinetics using dual-phase engineering of self-supported hierarchical NiCoV(OH)x nanowire arrays

Transition multi-metal components with high oxidation states can expedite the slow oxygen evolution reaction (OER) kinetics owing to their high intrinsic catalytic activity. Herein, we propose dual-phase engineering of self-supported hierarchical trimetallic NiCoV double hydroxides (NiCoV(OH)x) nanowire arrays for enhanced electrocatalytic OER activity via increased surface reaction sites and charge transfer. X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy analyses are performed to demonstrate the chemical composition and structural features of the synthesized electrocatalysts.Self-supported NiCoV(OH)x shows better OER catalytic performance with an overpotential of ~ 320 mV at a current density of 50 mA/cm2 and Tafel slope (~114 mV/dec) in 1 M KOH electrolyte medium. Furthermore, NiCoV(OH)x exhibits a smaller charge transfer resistance (Rct; ~ 0.63 Ω) and a larger Cdl value (~77 mF/cm2) than NiCo(OH)x (~1.22 Ω, 53 mF/cm2) and NiV(OH)x (~1.86 Ω, 46 mF/cm2), suggesting faster electrocatalytic kinetics. NiCoV(OH)x displays remarkable electrochemical stability at a high current density of 50 mA/cm2 for 10 h without significant changes in the OER activity. Owing to its greater abundance of catalytic active sites, high conductivity, faster charge transfer kinetics, and close contact with the electrolyte, NiCoV(OH)x exhibits superior electrocatalytic performance and stability toward the OER.

Mo-incorporated three-dimensional hierarchical ternary nickel-cobalt-molybdenum layer double hydroxide for high-efficiency water splitting

Flowers-like 3D hierarchical ternary NiCoMo-layered double hydroxide (NiCoMo-LDH) spheres have been fabricated in substrate-free route via a one-pot hydrothermal method and utilized as efficient electrocatalysts for the OER and HER. The well-structured 3D hierarchical flowers were composed of numerous two-dimensional nanosheets, which inherently possess considerable electrochemical active sites, thereby enhancing catalytic activity. NiMo and CoMo binary LDHs, with similar morphology, were also prepared to illustrate the efficiency of the ternary LDH. The results indicate higher electrocatalytic activity for the ternary LDH as compared to binary LDHs under alkaline conditions. The NiCoMo-LDH required an overpotential as low as 202 and 93 mV to deliver a constant anodic and cathodic current density of 10 mA cm−2 for the OER and HER, respectively. Furthermore, the NiCoMo-LDH exhibited remarkable HER activity, affording a low overpotential of 198 mV at a current density of −100 mA cm−2. Moreover, it could offer a stable current density of 10 mA cm−2 for overall water splitting at 1.62 V in 1 M KOH with long-term stability for 20 h. The double-layer capacitance (Cdl) value indicated that the NiCoMo-LDH significantly influenced interface conductivity and the electrochemical active surface area. The ternary NiCoMo-LDH electrode yielded low Tafel slope values of 54 and 51 mVdec−1 for the OER and HER. Owing to the efficient incorporation of Ni, Co, and Mo in a layered structure, synergetic effect, and high electrochemical surface area, the NiCoMo-LDH exhibited remarkable electrocatalytic activity. Such eco-friendly ternary LDHs can be used in rechargeable metal–air batteries for industrial applications.

Graphene oxide supported transition metal mixed oxide nanourchins onto bimetallic phosphide coatings as high performance hydrogen evolution electrodes in alkaline media

Recently, electrocatalyst with high reactivity and stability towards hydrogen evolution reactions are necessary for large scale high purity hydrogen production to resist upcoming energy crisis. The transition metal mixed oxide based HER electrocatalyst are promising candidates for hydrogen generation in renewable energy field due to their low-cost nature, ease of commercialization and green nature. Herein, graphene oxide supported MnO2-TiO2 nanourchins synthesized by thermal decomposition technique was incorporated to bimetallic phosphide ENCP coatings by electroless plating technique. During alkaline hydrogen evolution, the incorporation of composite onto bimetallic phosphide causes a drastic decreases in overpotential value to 190 mV dec−1 and respective Tafel slope value to 45 mV dec−1. The studies reveals that the modified electrode follows Volmer–Heyrovsky mechanism. The lower Rct of 140.8 Ω and a high Cdl value obtained from Nyquist plot of modified electrodes ensures the fastest electron transfer kinetics and confirms its more facile electrocatalytic nature towards hydrogen evolution. Also, a high value for exchange current density of modified electrode authenticate its superior HER performance. The modified electrodes was durable, long term stable, economically viable and performance was consistent over a wide span of time during alkaline hydrogen evolution reaction. The enhanced performance of modified electrode can be ascribed to the intermetallic synergetic effect arises within ENCP matrix and MnO2-TiO2 nanourchins. These conclusions lead to innovative insights on future perspective for the development and tuning of novel electrocatalysts with enhanced electrochemical performance for hydrogen evolution reaction.

Importance of Time‐Dependent Wetting Behavior of Gas‐Diffusion Electrodes for Reactivity Determination

AbstractTin foil and SnOx/C gas‐diffusions electrodes (GDEs) were investigated via electrochemical impedance spectroscopy (EIS) to extract the differential double‐layer capacitance (Cdl) as a measure of the wetted surface area. Time‐dependent Cdl values revealed an immediate stationary wetting for tin foil electrodes while a distinct increase of Cdl – which becomes stationary with time – was observed for GDEs. The time‐dependent wetting behavior of the GDEs was substantiated by physical post‐mortem characterization. Since the wetted surface area determines the number of reachable active sites the performance of GDEs should be normalized to the wetted surface area for evaluation of reactivity.

Corrosion Inhibitive Properties of 5-(4-Aminophenyl)-1,3,4-oxadiazole-2-thiol and 5-(4-Methylphenyl)-1,3,4-oxadiazole-2-thiol on Mild Steel in 1.0 M HCl Solution

The corrosion inhibition consequence of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol (APOT) and 5-(4-methylphenyl)-1,3,4-oxadiazole-2-thiol (MPOT) were accomplished by employing weight loss measurement, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization measurement and scanning electron microscope (SEM). An impact of immersion time 12.0 h and different temperatures (298, 308 and 318 K) with solution of 1.0 M HCl, which include various concentration of inhibitor at the corrosion of mild steel were designed. Weight loss measurement showed that with enhancing the concentration of these studied inhibitors the percentage inhibition efficiency (IE%) enhances, but corrosion rate (CR) diminishes while reverse condition in case of temperatures change. The electrochemical impedance spectroscopy examine pointed out that the charge transfer resistance (Rct) values enhances and consequently the double layer capacitance (Cdl) values diminishes with rising each inhibitor concentration in 1.0 M HCl and also there is a formation of adsorption coating at the metal surface. Polarization measurement showed that both APOT and MPOT perform as mixed type corrosion inhibitors. Furthermore, the adsorption behaviour on surface of mild steel for each studied inhibitor results the Langmuir adsorption isotherm. Surface conduct of mild steel also designed through the SEM and energy dispersive X-ray (EDX) analysis and concludes that there is evolution of inhibitive film of APOT and MPOT on the surface of mild steel.

Inception of Co3O4 as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co0.85Se/Co9Se8 Network.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s-1) compared to Co0.85Se/Co9Se8 (0.0102 s-1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the Cdl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender Cdl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

Corrosion Resistance of Bis-Silane-Modified Epoxy Coatings on an Al-Zn-Mg-Cu Alloy

A bis-silane prepolymer-modified epoxy coating was applied to an Al-Zn-Mg-Cu alloy to improve corrosion protection. The bis-silane prepolymer was synthesized from tetraethoxysilane and γ-glycidoxypropyl trimethoxysilane. To study the mechanism of protection failure by the silane–epoxy hybrid coating and to determine an appropriate coating for protection, various coatings with different silane prepolymer contents were developed. The corrosion behavior of the coatings was studied by electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. In comparison with silane monomer-modified epoxy coatings, the bis-silane-modified epoxy coating had lower coating capacitance (Cc), higher charge transfer resistance (Rdl) and lower double-layer capacitance (Cdl) during long immersion times, indicating a higher resistance to water permeation and stronger protection against substrate corrosion. The lowest Cc and Cdl values were obtained by mixing epoxy and the bis-silane prepolymer at a ratio of 1:1.

One-pot synthesis of pure phase molybdenum carbide (Mo2C and MoC) nanoparticles for hydrogen evolution reaction

Herein, we report the one-step synthesis of pure phase molybdenum carbide (Mo2C and MoC) nanoparticles via the in-situ carburization reduction route without using any reducing agent. The X-ray diffraction (XRD) results confirm the formation of pure phase Mo2C and MoC at 800 °C for 8 h and 15 h respectively. The as-synthesized powders have been investigated for hydrogen production and energy storage applications. The pure phase Mo2C shows high performance towards the hydrogen evolution reaction (HER) with a Tafel slope of 129.7 mV dec−1 however, MoC exhibits a low activity towards HER with a Tafel slope of 266 mV dec−1. Both the phases show high stability up to 5000 cyclic voltammetry (CV) cycles in the potential range of 0–0.4 V. In the case of MoC, the specific capacitance increases during the initial 2000 CV cycles which may be attributed to the electrode activation during the CV test. The Mo2C powder shows a double layer capacitance (Cdl) value of 2.47 mF cm−2 and a specific capacitance of 2.24 mF g−1. The MoC phase shows a higher Cdl value of 8.99 mF cm−2 and a specific capacitance of 8.17 mF g−1.