Effects Of Electrolyte pH Research Articles

Characterization and electrodeposition mechanism of Ni–Mo coatings from self-regulating electrolyte

Electrochemical Ni–Mo coatings were obtained on a low-carbon steel substrate using a stable, environmentally safe, self-regulating electrolyte containing 0.2 M NiCl2, 0.3 M Na3C6H5O7, and SrMoO4 (saturated). The effects of electrolyte pH, temperature, deposition current density, and hydrodynamic conditions on chemical composition and morphology of the coatings were studied. It was established that the addition of ammonia to the electrolyte contributes to the deposition of a more uniform, globular, nonporous coatings morphology. The effect of ammonia on the formation mechanism of coatings was substantiated. The stages of deposition and the limiting stage of the formation of Ni–Mo coatings from citrate-ammonia electrolytes, which involves the chemical reduction of molybdenum oxide (IV) to molybdenum, were determined using cyclic voltammetry.

Effects of electrolyte pH on oxygen reduction properties using a cobalt porphyrin-coated carbon composite

Understanding the pH-dependent mechanism of metalloporphyrin-based composite electrocatalystic oxygen reduction reactions (ORRs) can provide the basis for rational porphyrin molecular design. Tunable ORR properties of a cobalt porphyrin-based composite catalyst aFP-TCoP/C is accomplished by adjusting the electrolyte pH values spanning from 0.7 to 13.7. The composite performs the best ORR reactivity in the pH13.7 electrolyte, exhibiting the most positive characterized potentials (the ORR reduction potential EORR of 0.76 V and the half-wave potential E1/2 of 0.80 V) and the smallest Tafel slope of 43.1 mV dec−1. Whilst the sample with the pH3.7 electrolyte displays quite negative reduction potentials and a large Tafel slope, it exhibits an electron transfer number of 3.84, which indicates a nearly 4-electron transfer selectivity. The findings provide a practical protocol for regulating the catalytic reactivity and selectivity of ORRs by adjusting the components of electrolytes.

Effects of Electrolyte pH on the Electrodeposition of Nickel on Zincated Aluminium Surfaces

A nickel coating was successfully deposited on zincated aluminium by electrodeposition. A detailed study was made on the effect of the pH of electrolytes containing 0.1 M nickel sulphate (NiSO4) by cyclic voltammetry (CV). A constant potential of -0.8 V (pH 2), -1.1 V (pH 6) and -1.5V (pH 10) was chosen from different regions of each CV for the deposition of nickel using chronoamperometry (CA). The surface morphology, chemical composition and crystallographic structure of the nickel coating were investigated by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDAX) and X-ray diffraction (XRD), respectively. The adhesion strength of the nickel coating was analysed using  Scotch® tape. It was found that the nucleation potential for nickel deposition on zincated aluminium increased with increasing electrolyte pH. Notably, pH 2 produced the highest current during the deposition of nickel as compared to pH 6 and pH 10, due to the simultaneous hydrogen evolution reaction (HER). Because of HER, a lot of pits were present on the zincated aluminium surface and only a few nickel particles were formed, as shown in FESEM images. Meanwhile, deposition using a pH 6 solution (without HER)  produced an almost fully-covered nickel coating with uniform nodular morphology. However, when the pH 10 solution was used, the coating morphology appeared as cauliflower-like agglomerates with less surface coverage. EDAX analysis showed that the nickel coating deposited at pH 6 had the highest nickel content with 73.63 wt%. XRD analysis indicated that all nickel deposits had a cubic crystalline structure. Nickel deposited with the pH 6 solution was the most well-adhered coating. Thus, electrolyte pH has a strong influence on the deposition of nickel on a zincated aluminium surface.  

Effects of Electrolyte pH on the Electrodeposition of Nickel on Zincated Aluminium Surfaces

Effects of Electrolyte pH on the Electrodeposition of Nickel on Zincated Aluminium Surfaces

Effect of Dimethylglyoxime on Cobalt Bottom-up Filling

Copper (Cu) damascene processes have been used to produce back end of line (BEOL) interconnect structures1. As the critical dimension of BEOL structures approaches the electron mean free path of Cu or below, the copper resistivity exponentially increases, posing significant challenges on scaling. Metals with shorter electron mean free path, for example cobalt (Co), have been explored as the alternative material to replace Cu in the finest metal levels2.Cu electrodeposition for trench filling has been extensively investigated. The use of multi-component additive packages leads to void-free filling and the deposition process is explained with the synergistic interaction between the so called suppressor and accelerator3, 4. However, since the standard potential of Co2+/Co is more negative than that of H+/H2, hydrogen evolution reaction (HER) is inevitable during Co deposition, which may pose additional challenges on Co void-free filling. Defect-free filling of Co has been reported in fine features using a single derivative of mercapto-benzimidazole, which suppresses Co deposition but breaks down upon the metal deposition and additive incorporation5. Co filling in extremely fine structures has also been reported6, 7 and HER has been shown to play an important role in such processes8, 9, creating a contrast in current efficiency, and thus in deposition rates, between the feature bottom and field regions. However, proprietary chemistries were used in such studies and no chemical information is available. In our previous study, additives with a conjugated pair of oxime groups such as dimethylglyoxime (DMG) not only strongly suppress Co deposition, and the suppression breaks down upon the reduction and incorporation of adsorbed Co-dioxime chelates10, but also catalyze HER11 and have the potential in tailoring the Faraday efficiency. In this talk, the effects of electrolyte pH, concentration of DMG, current density and agitation will be systematically discussed in a context of current efficiency. A mechanism is proposed to explain the Co bottom-up filling using DMG.Figure 1 (a) shows the cyclic voltammograms of Co deposition in presence of different DMG concentrations. It is clear to see that the suppression effect becomes stronger as more DMG is added into the electrolyte. Moreover, the suppression breaks down at a negative potential and a hysteresis is resulted, potentially enabling different deposition rates between field and feature. Figure 1 (b) shows the effect of agitation on Co deposition, where such hysteresis loops gradually shift toward more negative potentials as the rotation rate increases, in a similar way as the DMG concentration increases. Figure 1 (c) shows the current efficiency of Co thin film deposition at different DMG concentration and different rotation rates. For example, 200 ppm DMG at 215 rpm was used to emulate Co deposition in the field region and 25 ppm DMG at 29 rpm to mimic the situation at the bottom of a feature with an aspect ratio of about 1:3. The significant difference in Co deposition rates at a low current density of 4 mA/cm2 leads to a successful void-free Co filling in the trench shown in Figure 1(d). References P. C. Andricacos, C. Uzoh, J. O. Dukovic, J. Horkans, and H. Deligianni, IBM Journal of Research and Development 42, 567 (1998).D. Gall, Journal of Applied Physics 119, 085101 (2016).T. Moffat, D. Wheeler, W. Huber, and D. Josell, Electrochemical and Solid-State Letters 4, C26 (2001).T. P. Moffat, J. Bonevich, W. Huber, A. Stanishevsky, D. Kelly, G. Stafford, and D. Josell, Journal of The Electrochemical Society 147, 4524 (2000).C. H. Lee, J. E. Bonevich, J. E. Davies, and T. P. Moffat, Journal of The Electrochemical Society 156, D301 (2009).F. Wafula, J. Wu, S. Branagan, H. Suzuki, A. Gracias, and J. van Eisden, in Electrolytic Cobalt Fill of Sub-5 nm Node Interconnect Features, 2018 (IEEE), p. 123.J. Wu, F. Wafula, S. Branagan, H. Suzuki, and J. van Eisden, Journal of The Electrochemical Society 166, D3136 (2019).M. A. Rigsby, L. J. Brogan, N. V. Doubina, Y. Liu, E. C. Opocensky, T. A. Spurlin, J. Zhou, and J. D. Reid, ECS Transactions 80, 767 (2017).M. A. Rigsby, L. J. Brogan, N. V. Doubina, Y. Liu, E. C. Opocensky, T. A. Spurlin, J. Zhou, and J. D. Reid, Journal of The Electrochemical Society 166, D3167 (2019).T. Lyons and Q. Huang, Electrochimica Acta 245, 309 (2017).Y. Hu and Q. Huang, Journal of The Electrochemical Society 166, D3175 (2019). Figure 1

Effects of Electrolyte pH on the Electro-Osmotic Characteristics in Anthracite.

Accelerating the drainage of water in coal reservoirs can significantly improve the extraction efficiency of coalbed methane (CBM). The movement of water with different pH values in anthracite was tested and analyzed. The results showed that the electro-osmotic flow velocity increased first and then slightly decreased with the increase of time up to 120 h. The electro-osmotic flow was markedly strengthened under a strong acid (pH 2) or strong alkaline (pH 13) environment, and the direction of electro-osmosis was reversed at a pH of 3–4. The changes in zeta potential, surface groups, and minerals in anthracite were tested to analyze the mechanism of electro-osmotic characteristics. The results obtained from this work will provide a basis for the process of drainage and depressurization during the CBM extraction.

Pulse electroplating of Ni-W-P coating and its anti-corrosion performance

Abstract Ni-W-P coatings were electrodeposited on copper substrates by pulse electroplating. Effects of electrolyte pH (1-3), temperature (40–80 °C), average current density (1–7 A/dm2) and pulse frequency (200–1000 Hz) on deposition rate, structure and corrosion resistance performance of Ni-W-P coatings were studied by single factor method. Surface morphology, crystallographic structure and composition of Ni-W-P coatings were investigated by means of scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy, respectively. Corrosion resistance performances of Ni-W-P coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution (mass fraction) and soil-containing solution. It was found that the pulse electroplated Ni-W-P coatings have superior corrosion resistance performance and the electroplating parameters significantly affect the structure and corrosion resistance performance of Ni-W-P coatings. The optimized parameters of pulse electroplating Ni-W-P coatings were as follows: pH 2.0, temperature 60 °C, average current density 4 A/dm2, and pulse frequency 600 Hz. The Ni-W-P coating prepared under the optimized parameters has superior corrosion resistance (276.8 kΩ) and compact surface without any noticeable defect.

Preparation of N-Type Cuprous Oxide Films via Electrodeposition Method and their Photoelectrochemical Activities

The n-type Cu2O films were deposited on ITO substrate by three-electrode electrochemical deposition method in a CuSO4-lactic acid electrolyte. The effects of electrolyte pH, bath temperature, and annealing treatment on films’ conductivity and their photoelectrochemical activity were investigated by X-ray diffraction (XRD), photocurrent (I-t) and mott-schottky (M-S) plots. The results show that the n-type Cu2O could be electrodeposited at electrolyte pH of 8.5, 9 and 10, and the electrolyte temperature did not change the films’ conductivity. The highest n-type photocurrent density of 0.014 mA /cm2 and carrier concentration of 2.3×1019 cm-3 was obtained when the electrolyte pH was 8.5 and the bath temperature was 60°C. With increasing annealing temperature from 150°C to 400°C, the photocurrent density and carrier concentration of n-type Cu2O thin films correspondingly increased, indicating that heat treatment is helpful to improve the photoelectrochemical activity.

Effect of pH, Surfactant, and Heat Treatment on Morphology, Structure, and Hardness of Electrodeposited Co-P Coatings

Nano-crystalline and amorphous Co-P coatings were deposited on plain carbon steel substrates by using direct current. Effects of electrolyte pH on morphology, current efficiency, phosphorus content, hardness, and preferred orientation of the nano-crystalline coatings were investigated. Moreover, the effects of heat treatment on microstructure and hardness of the nano-crystalline and the amorphous coatings were studied. The results showed that, phosphorus content and hardness of the nano-crystalline coatings were decreased by increasing of the pH, in spite of a current efficiency enhancement to as much as 98%. Grain size and preferred orientation were also changed from 13 to 31 nm and from mostly [002] to [100] by increasing the pH from 1 to 4, respectively. Smoother coatings and higher current efficiencies were obtained by the addition of 1 g/L sodium dodecyl sulfate (SDS) to the bath. Highest hardness of the nano-crystalline and the amorphous coatings was about 600 and 750 HV, which increased and reached 760 and 1090 HV after heat treatment, respectively.

Effects of electrolyte pH on morphologies and mechanical properties of α-Al2O3/Ni composite coatings and role of zeta potentials in co-deposition process

Zeta potential of α-Al2O3 particles in electrolytes was measured and used to describe the electrical properties of nano-particles. α-Al2O3 reinforced composite coatings were prepared from electrolytes respectively from pH5, 6, 7, 8, 9 and 10 by electro-brush plating. Morphologies of the six coatings were observed in a scanning electron microscope (SEM). Some bright dots were found in the coatings prepared at pH5, 6 and 7, while no dots were found in the coatings prepared at pH8, 9 and 10. To investigate the differences, energy dispersive spectroscopy (EDS) was performed to determine the composition of bright dots in the coatings. And it was found that the bright dots were α-Al2O3 depositing in the coatings. The result indicated that α-Al2O3 particles with positive zeta potentials deposit in a different way from particles with negative zeta potentials. A new co-deposition process of nano-particles and metallic ions was introduced from the perspective of nano-particle electrical behaviors. In general, the higher the absolute value of zeta potential is, the more the nano-particles will deposit in the coatings, and the better performance the coatings will have in micro-hardness and wear resistance because of the lower size of grains. But more negative zeta potential will prevent nano-particles from depositing.

Design of a new hypoxanthine biosensor: xanthine oxidase modified carbon film and multi-walled carbon nanotube/carbon film electrodes

A new and simple-to-prepare hypoxanthine biosensor has been developed using xanthine oxidase (XOD) immobilised on carbon electrode surfaces. XOD was immobilised by glutaraldehyde cross-linking on carbon film (CF) electrodes and on carbon nanotube (CNT) modified CF (CNT/CF). A comparison of the performance of the two configurations was carried out by the current response using amperometry at fixed potential; the best characteristics being exhibited by XOD/CNT/CF modified electrodes. The effects of electrolyte pH and applied potential were evaluated, and a proposal is made for the enzyme mechanism of action involving competition between regeneration of flavin adenine dinucleotide and reduction of hydrogen peroxide. Under optimised conditions, the determination of hypoxanthine was carried out at -0.2 V vs. a saturated calomel electrode (SCE) with a detection limit of 0.75 μM on electrodes with CNT and at -0.3 V vs. SCE with a detection limit of 0.77 μM on electrodes without CNT. The applicability of the biosensor was verified by performing an interference study, reproducibility and stability were investigated, and hypoxanthine was successfully determined in sardine and shrimp samples.

Effects of electrolyte ph on the electrochemical behavior of Fe-based bulk metallic glass

The effects of electrolyte pH on the electrochemical behavior of Fe-based bulk metallic glass with a composition of Fe68.8C7.0Si3.5B5P9.6Cr2.1Mo2.0Al2.0 were investigated at an ambient temperature. The results indicate that corrosion behavior is strongly dependent on the pH values. The corrosion current densities and capacitance values decrease with an increase in pH values in acidic electrolytes, while the opposite tendencies are obtained in alkaline electrolytes. While the corrosion product of the outer layer in low pH conditions is an amorphous structure, crystalline ferric oxide is obtained in the electrolyte with pH=14. The electrochemical behavior is discussed on the basis of the results of electrochemical and microstructural analysis.

Metal loaded WO3 particles for comparative studies of photocatalysis and electrolysis solar hydrogen production

Striving for new solar hydrogen fuel, the water oxidation reaction based on photocatalyst suspension and photoelectrochemical (PEC) cell are currently the most important research for sustainable energy. Here, the effects of electrolyte pH, crystallinity and grain size of tungsten trioxide (WO3) particles on photoconductivity are studied. Subsequently, a simple hydrothermal route was employed to synthesize Cs loaded WO3 (Cs-WO3) particles to further improve the photochemical reactivity. The photoanodes and photocatalyst based on the Cs-WO3 reveals a different photoreactivity performance in the PEC and photocatalyst suspension systems. This important fundamental insight can assist in optimization of WO3 particles photocatalyst and photoanode for future hybrid photocatalysis–electrolysis water splitting system. Based on the high photocatalytic capability demonstrated in this study, surface modified WO3 particles are proven to be a promising candidate for efficient water-splitting catalyst.

Effects of electrolyte pH and composition on the ethanol electro-oxidation reaction

The electrochemical oxidation of ethanol has been studied on platinum and gold electrodes by a combination of electrochemical and spectroscopic techniques in electrolytes of varying pH and composition, the latter primarily determined by the buffering anions. It was found that the activity of reaction increases significantly when the pH of the electrolyte is higher than 10. Furthermore, the results indicate that the selectivity of the reaction depends strongly on the nature of the electrolyte, and, to a smaller extent, on the electrolyte pH. In particular, carbon–carbon bond breaking, which is necessary to achieve full oxidation, could only be observed on platinum in the absence of strongly adsorbing anions. Based on these findings, a tentative general mechanism is suggested and discussed.

Microfluidic Reactor for the Electrochemical Reduction of Carbon Dioxide: The Effect of pH

This article reports the development and characterization of a microfluidic reactor for the electrochemical reduction of carbon dioxide. The use of gas diffusion electrodes enables better control of the three-phase interface where the reactions take place. Furthermore, the versatility of the microfluidic reactor enables rapid evaluation of catalysts under different operating conditions. Several catalysts as well as the effects of electrolyte pH on reactor efficiency for reduction of CO2 to formic acid were tested. Operating at acidic pH resulted in a significant increase in performance: faradaic and energetic efficiencies of 89 and 45%, respectively, and current density of 100 mA/cm 2

Effects of electrolyte pH and temperature on dielectric properties of anodic oxide films formed on niobium

The effects of electrolyte pH and temperature on the structure and properties of anodic oxide films formed on niobium in phosphoric acid solution with the addition of NH 4OH for pH adjustment have been investigated. The film thickness formed at the same voltage slightly increased with increasing pH and significantly increased with increasing electrolyte temperature. The capacitance of the film was independent of electrolyte pH in an acid region, while it notably increased with increasing pH in an alkaline region. The relative permittivity of the film changed 43.7–80.5 when the electrolyte pH was increased from 1.6 to 10. The incorporation depth and content of phosphorus in the film were markedly suppressed at pH 10, and nitrogen was found to penetrate into a depth of 70%. Furthermore, the apparent transport number of Nb 5+ ion decreased from 0.26 to 0.02 by a pH increase from 1.6 to 10. The notable changes in structure and dielectric properties of the anodic niobia film formed in the alkaline region would primarily be caused by the different incorporation behavior of electrolyte species such as phosphorous and nitrogen.

Separation of structurally related synthetic peptides by capillary zone electrophoresis

The separation of two different sets of synthetic peptides has been investigated by high-performance capillary zone electrophoresis utilising naked, fused silica capillaries. The effects of electrolyte pH, buffer concentration, capillary length and electric field strength on the separation efficiency and selectivity were systematically varied, with the highest resolution achieved with buffer electrolytes of low pH and relatively high ionic strength. Under optimised separation conditions utilising the “short end injection” separation approach with negative electric field polarity, a series of eight structurally-related synthetic peptides were baseline resolved within 4 min without addition of any modifier of the background electrolyte with separation efficiencies in the vicinity of 600 000 theoretical plates/m. Further significant enhancement of separation efficiencies could be achieved by taking advantage of the “long end injection” approach with positive electric field polarity. The outcome of these experimental variations parallels the “sweeping” effect that has been observed in the capillary electrochromatographic and micellar electrokinetic separations of polar molecules and permits rapid resolution of peptides with focusing effects. In addition, small changes in the electrolyte buffer pH and concentration were found to have a significant impact on the selectivity of synthetic peptides of similar intrinsic charge. These observations indicate that multi-modal separation mechanisms operated under these conditions with the unmodified fused silica capillaries. This study, moreover, documents additional examples of peptide-specific multi-zoning behaviour in the high-performance capillary zone electrophoretic separation of synthetic peptides.

Cartilage electromechanics—I. Electrokinetic transduction and the effects of electrolyte pH and ionic strength

Articular cartilage contains a high fixed charge density under physiological conditions associated primarily with the ionized proteoglycan molecules of the extracellular matrix. Oscillatory compression of cartilage using physiological loads produces electrical potentials that have been shown previously to be the result of an electrokinetic (streaming) transduction mechanism. We have now observed two additional electromechanical phenomena not previously seen in cartilage or other soft tissues: ‘streaming current’ and ‘current-generated stress’. Sinusoidal mechanical compression induced a sinusoidal streaming current density through cartilage disks when the Ag AgCl electrodes that were used to compress the cartilage were shorted together externally. Conversely, a sinusoidal current density applied to the tissue generated a sinusoidal mechanical stress within the tissue. Both these phenomena were found to be consisten with the same electrokinetic transduction mechanism responsible for the streaming potential. Changes in the measured streaming potential response that resulted from modification of bath ionic strength and pH have provided additional insights into the molecular origins of these transduction processes. Finally, we have now observed streaming potentials in living cartilage maintained in organ culture, as well as in previously frozen tissue.

Effects of electrolyte pH upon the structure of fine cobalt powders

It is shown that the changes observed in the structure of fine cobalt powders are closely related to the degree of cathode polarization and the solution pH.