Effects of Incorporating TiO₂ Aggregates on the Growth, Anticorrosion, and Antibacterial Properties of Electrodeposited Multifunctional Coatings Based on Sn-Ni Materials

Abstract

Multifunctional coatings based on Sn-Ni materials with and without titanium oxide nanoparticles (TiO₂NPs) incorporation were prepared using the electrochemical deposition technique at 70 °C. TiO₂NPs were dispersed in the electrolyte bath, and their influence on the surface texture, crystalline phase, and properties was investigated. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray microanalysis (EDX) were used to characterize the prepared coatings. The formation mechanism of the deposited coatings has been demonstrated to be consistent with the electrochemical behavior of instantaneous growth, and the three-dimensional growth is controlled by diffusion phenomena. The anticorrosion effectiveness of the coatings was assessed using potentiodynamic polarization curves and electrochemical impedance spectroscopy in an artificial sweat medium, while the bactericidal activity of the composite coatings (the ability to induce cell death) was evaluated in accordance with the ISO 27447:2019 test. The influence of TiO₂NPs at a low concentration of 1 g/L on the composition, structure, and properties of the deposited coatings was demonstrated. Particular attention was paid to the relationship between the anticorrosive and bactericidal properties of the coatings and their structure composition and wetting properties. The synergistic effect of chemical composition and surface-wetting properties has been demonstrated to enhance the anticorrosive and bactericidal properties of the prepared coatings.

1. Introduction

In recent years, there has been a growing demand for multifunctional coatings that combine physical, biological, chemical, and mechanical properties, such as increased hardness, decorative appearance, corrosion resistance, hydrophobicity, and antibacterial properties. Indeed, the changing conditions in which coatings are used require them to be multifunctional to meet the challenges and demands of their environment. Various approaches have been developed to produce coatings with numerous properties, making them multifunctional. Among these approaches, those that combine different chemical elements and controlled nanostructuring of the surface have proven to be very effective in producing multifunctional coatings. Alloys produced by electrochemical deposition have demonstrated their ability to exhibit multiple properties, which can lead to the multifunctional nature of certain coatings and their widespread use in industry.

Metallic coatings have evolved considerably in recent centuries, from single-layer coatings to multi-layer-gradient and micro-stack coatings and from alloy coatings to composite coatings. The most common alloys used in coatings are nickel-based—notably nickel–tin—which offer a wide range of properties such as corrosion, wear, and abrasion resistance. To date, protective metals and alloys such as Zn [1], Ni-based alloys [2], Al-based alloys [3], Ti [4], Hf [5], Cr [6], and Cu [7] have been investigated for various applications, particularly for metals that are prone to corrosion.

The combination of chemical elements in an alloy represents an effective strategy for creating synergies between the properties of these elements. This approach can result in the enhancement of existing properties or the emergence of new ones [8,9,10]. The study and development of alloys of different metals, as well as their shaping into layers, represent a significant area of research within the field of materials science.

Coatings with anticorrosive, superhydrophobic, and antibacterial properties [11,12,13,14] are currently in demand for certain surfaces that require constant disinfection, such as door handles, handrails, lift buttons, etc. The antibacterial properties and aesthetic appeal of Cu-based electrochemical coatings have been extensively documented in the scientific literature [15,16,17,18]. TiO₂ is another material that has been extensively documented in the scientific literature for its photocatalytic and antibacterial properties in metal coatings [19,20,21]. The synthesis method and preparation conditions often determine many of the characteristics and properties of TiO₂ nanoparticles, such as size, morphology, crystalline phase, degree of agglomeration, etc. [22,23,24,25]. TiO₂ has been used as an inert phase in composite coatings based on Cu [15,16], Zn [26,27], Ni [28,29,30,31,32], and alloys [33,34,35,36,37] to impart photocatalytic and antibacterial properties. The impact of ultrasonic treatment on the electrodeposition of Cu-Sn-TiO₂NP nanocomposite coatings with enhanced antibacterial properties has been the subject of extensive research in the literature [15]. The effect of ultrasonic treatment and current loading on microstructure, quantitative and qualitative composition, distribution of TiO₂NP aggregates, and antibacterial properties against E. coli bacteria was demonstrated. Furthermore, a comparative study was conducted to examine the impact of mechanical agitation and ultrasound on the characteristics of the nanocomposite coatings produced.

Electrochemically produced Sn-Ni-based alloy coatings are widely used in metal finishing and microelectronics [38,39,40,41,42,43,44,45,46,47,48,49]. They prevent allergic skin reactions and corrosion in artificial environments [43] and can replace nickel electroplating on the skin of clothing fasteners. They can also replace chromium in the decorative and lighting industries [40]. This alloy combines physical and chemical properties that allow it to be widely used in industry. These include increased corrosion resistance, improved hardness, high wear resistance, and many other properties [38,39,40,41,42,43,44,45,46,47,48,49]. Various electrolytes have been used to deposit Sn-Ni alloys, including fluoride–chloride [34,36], pyrophosphate [39,41], sulphuric acid [42], glyconat [42], and others. Various studies have reported the influence of the kinetic parameters of Sn-Ni alloy deposition on its physicochemical and mechanical properties [40,41,42,43,44,45,46,47,48,49] as well as on composite coatings with TiO₂ NPs of different phase compositions [33,34,35,36]. Visible and photoactive Sn-Ni-TiO₂NP coatings incorporating carbon-doped particles and N- and S-doped TiO₂NPs (N, S-TiO₂NPs) have been reported in the literature [34]. It has been reported that the optimum parameters for obtaining the best co-deposition rates of carbon and doped TiO₂NPs are a low current density of 0.01 A/cm² and a concentration of 30 g/L under DC conditions. The highest co-deposition percentage of 3.25 wt% was obtained in the case of incorporation of N, S-TiO₂NPs. TiO₂ NPs synthesized by direct oxidation of titanium are reported in the literature [35,36] to have yielded a mixture of two TiO₂ polymorphs, anatase and rutile, with particle sizes between 30 and 50 nm. The effect of the TiO₂NP aggregate content on the physicochemical and biocidal properties of Sn-Ni coatings has been demonstrated [36].

The present work aimed to study the kinetics of electrochemical deposition of Sn-Ni-TiO₂NP composite coatings, as well as the effect of the incorporation of TiO₂NPs synthesized by the hydrothermal method on their properties. The mechanism of coating formation was also investigated. Furthermore, the corrosion resistance and antibacterial properties of Sn-Ni-TiO₂NP coatings were investigated in an artificial sweat environment. The relationships between the properties of the coatings and their structure, composition, and surface roughness were demonstrated. These results allow us to evaluate the use of these coatings for public applications such as door handles, turnstiles, lift buttons, etc.

2. Materials and Methods

The Sn-Ni alloy coating was deposited using a fluoride–chloride electrolyte, with the ionic strength of the solution compensated by sodium chloride. The compositions of the solutions used are provided in

Table 1. Composition of different electrolytes used for coatings deposition: Electrolyte 1 for Ni-Sn coating deposition, Electrolyte 2 for Sn coating deposition, and Electrolyte 3 for Ni coating deposition.

Component	Concentration, mol/L
	Electrolyte 1	Electrolyte 2	Electrolyte 3
SnCl2·2H2O	0.22 ± 0.02	0.22 ± 0.02	–
NiCl2·6H2O	1.05 ± 0.02	–	1.05 ± 0.02
NH4F	1.35 ± 0.14	1.35 ± 0.05	1.35 ± 0.05
NaCl	–	3.19 ± 0.03	0.67 ± 0.03

.

Electrolytes were prepared using double-distilled water and analytical grade NiCl₂·6H₂O, SnCl₂·2H₂.

The reagents were purchased from Belreachim, Minsk, Belarus. NH₄F, NaCl, and HCl compounds were also purchased from Belreachim. After mixing all the electrolyte components, the pH of the electrolyte was adjusted with 0.1 M HCl, and 1 g/L of TiO₂NPs—synthesized according to the procedure described in [25]—was added to the electrolyte composition. The electrolysis was carried out at a temperature of 70 °C, pH of 3, a current density of 0.01 A/cm², with continuous stirring using a magnetic stirrer, and the anode material consisted of nickel and tin. The anode was enclosed in fabric sheaths (polypropylene fabric (KS–34) chlorine) to avoid contamination of the electrolyte by sludge. Copper was used as the cathode material.

The kinetics of the coating deposition was studied by chronovoltammetry and chronoamperometry using an Autolab PGSTAT 302N (Ecochemie, The Netherlands) potentiostat and a three-electrode configuration consisting of a saturated silver chloride electrode as the reference electrode and a platinum electrode as the counter-electrode.

The most commonly used model to describe the electrocrystallization process is that of Scharifker and Hills (SH) [35]. This model is used to determine the type of nucleation by analyzing the rising parts of the chronoamperograms before the nuclei diffusion zones overlap. Depending on the slope of these parts of the chronoamperogram, two types of nucleation can be identified: instantaneous and progressive. Instantaneous nucleation corresponds to the situation where all the nucleation sites on the surface are immediately activated by the applied potential. Furthermore, the number of nuclei remains globally unchanged during the growth process.

In the case of progressive nucleation, the number of nuclei increases progressively with deposition time. Equations (1) and (2) describe progressive and instantaneous nucleation, respectively, in the electroplating process [50]:

$${\left({\displaystyle \frac{i}{i_{max}}}\right)}^2={\displaystyle \frac{1.9542}{\frac{t}{t_{max}}}}{\left\{1-exp\left[-1.2564{\displaystyle \frac{t}{t_{max}}}\right]\right\}}^2·instanneous$$

(1)

$${\left({\displaystyle \frac{i}{i_{max}}}\right)}^2={\displaystyle \frac{1.2254}{\frac{t}{t_{max}}}}{\left\{1-exp{\left[-2.3367{\displaystyle \frac{t}{t_{max}}}\right]}^2\right\}}^2·progressive$$

(2)

where i_max is the maximum current from a current transient at a corresponding time, denoted by t_max.

The phase composition of the coatings was determined by X-ray diffraction (XRD) analysis using a Bruker D8 Advance AXS diffractometer, Ettlingen, Germany. X-ray scanning was performed at a rate of 1° s⁻¹ using CuKα radiation. The position of the maxima of the analyzed peaks was measured with an accuracy of ±0.05°.

The Raman spectra were measured at room temperature using a U1000 Raman microscope-spectrometer (Renishaw, Wotton-under-Edge, UK), and laser radiation with a wavelength of 532 nm (power: 5 mW on the sample). Registration was carried out with a spectral resolution of 1 cm⁻¹.

The prepared coatings’ surface morphology was studied by scanning electron microscopy (SEM) using a JEOL JSM-5610 LV microscope, Tokyo, Japan, while their elemental composition was determined by energy dispersive X-ray (EDX) microanalysis using a JED-2201 EDX (JEOL, Tokyo, Japan).

Corrosion tests were carried out in an artificial sweat medium, the composition of which is shown in

Table 2. The composition of artificial sweat electrolyte.

Compounds	Sodium Chloride (NaCl)	Ammonium Chloride (NH4Cl)	Urea ((NH2)2CO)	Acetic Acid (CH3COOH)	L-Lactic Acid (C3H6O3)
Concentration, g/L	20.0	17.5	5.0	2.5	15.0

.

Polarization curves were recorded at a sweep rate of 1 mV/s, 20 min after the working electrode was immersed in the artificial sweat solution to establish a steady-state potential. Corrosion currents were calculated from the intersection of the straight Tafel sections of the cathode and anode curves. Impedance spectra were recorded in the frequency range from 10 kHz to 0.01 Hz with an AC voltage amplitude of 10 mV. The impedance frequency spectra were recorded 20 min after the sample was kept in the test solution. The data obtained were processed using Nova 2.1 and ZView 3.2c software.

Test cultures of the health indicators bacteria Escherichia coli (ATCC 8739) and Staphylococcus aureus (ATCC 6538) were used to assess the antibacterial properties of the coatings. The antibacterial tests of the composite coatings were conducted according to the standard test method ISO 27447:2019 [51] described in the literature [35]. The evaluation of the bactericidal activity of the composite coatings in terms of their ability to induce cell death was assessed using the reduction factor (RF), which was determined using the following Equation (3):

FR = log(K₁/K₂)

(3)

where K₁ is the concentration of viable cells in the nutrient medium with the coating examined without UV irradiation (CFU/cm³); K₂ is the concentration of viable cells in the nutrient medium with the coating examined after UV irradiation (CFU/cm³).

3. Results and Discussion

The synthesis and formation mechanism of TiO₂NP aggregates has been described in previous works [25]. In the present work, the hydrothermal synthesis temperature was set at 170 °C, and at the end of the synthesis, washing, and annealing processes, a white powder was obtained. The FEGSEM characterization of the TiO₂NP aggregate powders shows a morphology in the form of porous spherical aggregates of several particles (insert Figure 1a). The size of the aggregates varies from 50 to 200 nm (Figure 1).

The crystal structure and phase of the prepared TiO₂NP aggregate powder were analyzed by X-ray diffraction. The XRD patterns obtained are shown in Figure 1b and revealed a crystal structure with peaks characteristic of the anatase phase of TiO₂NP aggregates (JCPDS No. 89-4921). This indicates that the powder is crystallized and of high purity.

The synthesized TiO₂NP aggregates were added to the fluoride–chloride electrolyte for the deposition of the Sn-Ni alloy as well as Ni and Sn monolayers, at a concentration of 1 g/L, as described in the Materials and Methods Section. To understand the properties of the Sn-Ni alloy coating, a comparison was made with those of the Sn and Ni coatings. The electrochemical properties of the electrodeposited Sn, Ni, and Sn-Ni alloy composite coatings were studied (Figure 2) with and without the addition of TiO₂NP aggregates to the electrolyte. The electrodeposition of Sn from a fluoride–chloride electrolyte with ionic strength compensation using NaCl proceeds toward potentials more negative than −0.44 V and more positive than −0.34 V for Ni. For the Sn-Ni alloy, the cathodic polarization curve shifts toward the more positive potentials by approximately −0.28 V, indicating a depolarization effect. The introduction of TiO₂NP aggregates into the electrolyte has virtually no effect on the evolution of the cathodic polarization curves of the coating deposition processes.

To further identify the polarization characteristics accompanying electrochemical deposition reactions, the activation energy for various partial processes has been calculated (Figure 3).

A comparison of the activation energies of Sn and Sn-TiO₂NPs shows that in the same potential range between −0.4 and −0.44 V, the activation energies decrease uniformly. At potentials between −0.45 and −0.55 V, the variation in the activation energy as a function of potential exhibits a slight shift in the activation energy maximum, which can be attributed to the limitations imposed by the diffusion process in the case of the deposition of Sn and Sn-TiO₂ NPs. This finding is in accordance with the results previously documented in the literature [34]. In the case of the Sn-Ni alloy coatings, a more pronounced activation energy peak is observed at −0.35 V. By comparing the dependence of the activation energy on the deposition potentials of the Sn-Ni alloy and the Sn-Ni-TiO₂NP composite, it can be concluded that the ions are discharged together in the form of intermetallic compounds, and similar results have been reported in the literature [34].

The nucleation mechanism of Sn-Ni electrodeposition was investigated using the chronoamperometry technique and potentiostatic current–time transient curves at varying potentials. The results are presented in Figure 4a. The current demonstrates a peak in the potential range between −230 mV and −410 mV, which can be attributed to the formation and growth of the crystalline nuclei. Subsequently, it exhibits a gradual decrease due to electron transfer, ultimately reaching a plateau at the end stage as a result of the growth of the alloy nuclei. This shows the typical characteristic of a diffusion-controlled electrochemical nucleation process with three-dimensional nucleus growth and can be characterized by Cottrell’s equation, which is expressed in Equation (4) as follows [29]:

$$i={\displaystyle \frac{n·F·A·D^{\frac{1}{2}}·c_0}{{\pi }^{\frac{1}{2}}·t^{\frac{1}{2}}}}$$

(4)

where i is the current through the electrolyte; n is the number of electrons involved; F is Faraday’s constant; A is the working area of the electrode; D is the diffusion coefficient; C₀ is the concentration of the species in the bulk; and, t is the time. The diffusion coefficient is an important kinetic parameter used to estimate the effect of additives on the electrodeposition of Sn-Ni and can be determined from the slope of the chronoamperogram of i versus t^1/2 according to Cottrell’s equation (Equation (4)).

It has been observed that as the potential shifts toward more electronegative values down to −410 mV, the time taken to reach the maximum current on the chronoamperograms increases (Figure 4a).

A comparison of some other parameters—such as the maximum value of the transient current (i_m) and the time to reach it (t_m) for the electrodeposited alloy at different applied potentials—is shown in Figure 4b. It can be seen that when the potential is more negative, the value of i_m is higher and the value of t_m is greater. A comparison of the curves obtained at different potentials with the theoretical instantaneous and progressive curves of the SH model is shown in Figure 4b. This comparison shows that the experimental curves are closer to an instantaneous nucleation model; therefore, the electrodeposition of Sn-Ni follows an instantaneous nucleation mechanism and the three-dimensional growth is controlled by the diffusion process [39]. In addition, the deposition potential slightly affects the Sn-Ni nucleation mechanism. However, Figure 4b shows that when t > t_m, the experimental curves deviate from the theoretical instantaneous nucleation behavior due to proton reduction during Sn-Ni electrodeposition. This can occur during the electrodeposition of metal ions in aqueous solutions, as observed in previous work [41].

The SEM and EDX characterizations in Figure 5 show that within 2 s of electrolysis at a potential of 0.32 V, the nuclei begin to coalesce to form a continuous film, while the Ni content of the alloy formed has almost twice the Sn content. This could be an indication of the predominance of Ni deposition in the early stages of electrolysis.

3.1. Influence of Current Density on Cathode Current Efficiency

In complex electrolytes, the variation in cathodic current yield is due to the process characteristics of the electrode surface. The evolution of the cathodic current yield as a function of the applied current density for a TiO₂NP-based alloy and composite coatings at a concentration of 1 g/L is shown in Figure 6.

It was found that as the current density increased from 0.5 to 4 A/dm², the cathodic current efficiency for the Sn-Ni alloy decreased from 99.8% to 53.9%. With the introduction of TiO₂NPs into the electrolyte composition, an approximately linear dependence of current efficiency on current density was observed. For a composite coating with TiO₂NPs, the current efficiency is much higher at high current densities, which may be due to an increase in electrolyte diffusion and a significant change in the composition of the coating phase. To confirm the latter hypothesis, the crystal phase and elemental composition of the Sn-Ni alloy coatings at different current densities were investigated and the X-ray diffraction results are shown in Figure 7.

Figure 7 shows that an increase in current density to 2.5 A/dm² is accompanied by a significant change in the phase composition of the coatings. It is also interesting to note that the Ni₄Sn intermetallic compound did not form at current densities above 2.5 A/dm², whereas a Sn peak was observed for coatings deposited at current densities of 1.5 A/dm² and 2 A/dm². It should be noted in Figure 8 that the Sn and Ni contents of the alloy also increase slightly with current. At current densities of 2 A/dm² and above, the Ni and Sn contents in the coating tend toward a 50/50 ratio.

Increasing the cathodic current density slightly affects the structure of the coatings and also leads to changes in the Sn/Ni ratio. The maximum Ni content in the alloy composition is observed at a current density of 2 A/dm² and amounts to 50.2 wt%, the minimum content is observed at a current density of 1.5 A/dm² and amounts to 46.06 wt%. These results show that an increase in cathodic current density induces Ni and Sn deposition in equivalent proportions. Another hypothesis to explain the behavior of chemical composition as a function of current density is the increase in the specific surface area of the electrode. Under the influence of the electric field resulting from the applied electrodeposition potential, TiO₂NPs covered with ionic adsorbates migrate toward the cathode surface where they are adsorbed. As a result, the positively charged particles adsorbed on the cathode surface increase the active surface area and provide more nucleation sites for Ni²⁺ ion reduction [50].

3.2. The Influence of TiO₂NP Concentration on the Structure and Composition of Deposited Coatings Based on Sn-Ni Alloy

The introduction of TiO₂NPs into the electrolyte also contributes to a change in the composition of the coating phase.

The XRD results in Figure 9 show the presence of Cu in the structure of the Sn coatings. This may be due to the diffusion of Sn into the Cu substrate structure and the formation of intermetallic compounds. TiO₂NP peaks are absent from the diffraction pattern, which can be explained by the relatively low concentration of TiO₂ in the composition of the electrolytes used to prepare the coatings. Figure 10 shows the diffractograms of the Sn-Ni alloy and the Sn-Ni-TiO₂NP alloy-based composite coating.

The XRD results in Figure 10 show that the Sn-Ni alloy is formed by several unstable intermetallic compounds such as NiSn, NiSn₂, Ni₃Sn₂, and Ni₄Sn. When TiO₂NPs are introduced into the electrolyte, the intensity of the main NiSn metastable peak changes. This can be explained by a slight change in the Sn content associated with a change in its solubility. The structure of the prepared coatings was also studied by SEM and the results are shown in Figure 11.

The introduction of TiO₂NPs into the electrolyte leads to changes in the texture of the prepared coatings. It has been shown that in the case of Sn-TiO₂NPs deposition, more pronounced facet structures are observed compared to Sn deposition (Figure 11a,b). The Sn-TiO₂NP coating is inhomogeneous with the local formation of large Sn-TiO₂NPs about 20 µm larger than the Sn grains (Figure 11a) and larger than the size of the TiO₂NP aggregates (Figure 1). This may be due to hinderances of the Sn coating deposition when large TiO₂NP aggregates are deposited on the substrate surface as well as the rapid diffusion of Sn into the Cu substrate with the formation of new intermetallic compounds. In the case of Ni, when the TiO₂NPs are introduced into the electrolyte, the deposit has a uniform texture with fewer pores (Figure 11d). The Sn-Ni alloy coating is characterized by the formation of small spheroidal crystallites (Figure 11e). When TiO₂NPs are introduced into the electrolyte composition during the deposition of the Sn-Ni alloy, an increase in the size of the spheroids on the surface is observed, reaching diameters of the order of 10 μm larger than the size of the TiO₂NPs aggregates (Figure 1a), which is the signature of local inclusion of TiO₂NPs in the coating (Figure 11f). The elemental and phase compositions of the prepared alloys and coatings are given in

Table 3. Composition of different prepared coatings based on Sn, Ni, and Sn-Ni alloy with and without TiO₂NPs.

Coating	Element	Composition, wt.%
1	2	3
Sn	Sn	100
Sn TiO2NPs	Sn	38.38
	Cu	60.47
	TiO2	0.73
Ni	Ni	100
Ni TiO2NPs	Ni	99.87
	TiO2	0.13
Sn-Ni	Sn	51.69
	Ni	48.31
Sn-Ni TiO2NPs	Sn	55.78
	Ni	44.22
	TiO2	0

.

For single-metal coatings, deposited metal content reaches 100%. In the case of Sn-TiO₂NPs, the coating is characterized by an irregular structure and the intercrystallite contains Cu (Figure 11d). In addition, it has been shown that when TiO₂NPs at a concentration of 1 g/L are introduced into the Sn and Ni deposition electrolytes with ionic strength compensation, the TiO₂NPs are incorporated into the Sn and Ni coatings with a composition limit of 0.73 and 0.13 wt%, respectively. For the Sn-Ni alloy coating, the Sn and Ni contents are 51–56 wt% and 48 wt%, respectively. In the case of the composite alloy coating, TiO₂NPs are not detected in the coating composition. This may be due to their highly inhomogeneous inclusion in the coating composition in the form of agglomerates of TiO₂NP aggregates. As the EDX analysis did not reveal the presence of TiO₂NPs in the coating, an XRF analysis was carried out for confirmation (

Table 4. Elemental content of indicated coatings.

Coating	Element	Composition, wt%
Sn-Ni	Ni	32.31
	Sn	67.66
	Cl	0.03
Sn-Ni TiO2NPs (1 g/L)	Ni	46.19
	Sn	53.77
	Cl	0.04
	Ti	-
Sn-Ni-TiO2NPs (2 g/L)	Ni	37.26
	Sn	62.59
	Cl	0.03
	Ti	0.12

).

Table 4 shows that Ti was not detected in the Sn-Ni TiO₂NP-based coating at a TiO₂NP concentration of 1 g/L in the electrolyte. However, by increasing the TiO₂NP concentration to 2 g/L in the electrolyte, the Ti content in the coating increases to 0.12 wt%, a signature that TiO₂NPs have been incorporated into a Sn-Ni TiO₂NP-based coating. To further investigate the presence of TiO₂NPs in the Sn-Ni TiO₂NP coating, Raman experiments were carried out and the spectra are shown in Figure 12. Analysis of these spectra provided an estimate of the TiO₂NP content.

In the Raman spectra corresponding to Sn-Ni alloy-based composite coatings with the presence of TiO₂NPs in the deposition electrolyte, peaks were observed in the region of 150, 395, 512, and 634 cm⁻¹ (Figure 12c,e), which are characteristic of TiO₂NPs (Figure 12a). This confirms the inclusion of TiO₂NPs in the composition of Sn-Ni alloy-based composite coatings and that the embedded TiO₂NPs increase with the concentration of TiO₂NPs in the electrolyte. In addition, these results show that Raman measurements are more sensitive to the presence of TiO₂NPs in Sn-Ni alloy-based composite coatings at concentrations lower than 1 g/L.

Furthermore, the introduction of TiO₂NPs into the composition of the deposition electrolyte for Sn, Ni, and Sn-Ni coatings was observed to have an ambiguous effect on the surface roughness of the prepatterned coatings (Figure S1).

With the introduction of TiO₂NPs into the deposition electrolyte composition, Sn and Ni coatings become rougher. However, for a Sn-Ni alloy-based composite coating, the microroughness decreases slightly. This can be explained by the uniform incorporation of TiO₂NPs into the alloy phase deposited over the entire surface as well as the absence of TiO₂NP agglomeration in the deposition electrolyte.

Table 5. The main indicators of the microroughness of the surface of different prepared coatings.

Coating	Ra, µm	Rz, µm	Rmax, µm
Sn	1.14	5.24	7.89
Sn-TiO2NPs	3.54	13.11	20.73
Ni	0.21	1.04	1.37
Ni-TiO2NPs	0.58	3.05	3.94
Sn-Ni	0.41	2.02	3.45
Sn-Ni-TiO2NPs	0.34	1.66	2.97

shows the surface microroughness for the different coatings studied.

It was found that by introducing 1 g/L of TiO₂NPs in the composition of the electrolyte for the deposition of Sn and Ni (with compensation of the ionic strength by a NaCl solution), the various parameters quantifying microroughness (R_a, R_max, and R_z) increased by almost three times. In the case of composite coatings based on Sn-Ni-TiO₂NPs alloys, the opposite effect was observed, i.e., a decrease in roughness. The dependence of the microroughness of Sn-Ni coatings on the deposition current density was also investigated and the results are shown in Figure 13.

The roughness results shown in Figure 13a indicate that maximum values of R_a, R_z, and R_max were obtained at a current density of 2 A/dm² while minimum values were observed at a current density of 3 A/dm². The irregular dependence of microroughness on current density may be related to a significant change in phase composition and degradation of coatings deposited at current densities above 3 A/dm². In the case of TiO₂NP-based composite coatings, the evolution of microroughness was studied at current densities of 1 and 4 A/dm², and the results are shown in Figure 13b. It can be observed that an increase in the current density of Sn-Ni-TiO₂NP coatings leads to an increase in the roughness parameters R_a, R_max, and R_z by a factor of 2 to 3. These results are in good agreement with those obtained from the SEM characterization. The textures observed from the SEM characterization show an increase in the size of spheroids on the surface, which is a signature of the local inclusion of TiO₂NPs in the coating.

Surface roughness is a characteristic that has a major influence on the properties of the coating, particularly its optical and wetting properties. The physical interaction of a liquid with the surface of a solid or other liquid determines the wetting properties of that surface, and the degree of wetting is characterized by the wetting contact angle, θ, which is the angle formed by the plane tangent to the interfacial surfaces binding the wetting liquid, with the vertex of the angle lying on the line of separation of the three phases. Depending on this angle, a distinction is made between hydrophilic (θ < 90°) and hydrophobic (θ > 90°) surfaces. The value of the contact angle (θ), excluding the effect of gravity, depends solely on the molecular properties of the solid surface and the phases in contact with it. Figure 14 shows a diagram of the effect of current density on the wetting angles of Sn-Ni alloy coatings.

In Figure 14a, the results show that the variation in contact angle is inversely proportional to the variation in surface roughness. For coatings with the lowest roughness, obtained at a current density of 2.5 A/dm², the maximum value of the wetting angle was observed to be 78° ± 1.2. For Sn-Ni alloy-based coatings with higher roughness, obtained at a current density of 2 A/dm², the wetting contact angle reached minimum values of around 61° ± 1.3°. Furthermore, the introduction of TiO₂NPs into the composition of the deposition electrolyte of Sn, Ni, and Sn-Ni-based coatings contributes to a modification of the wetting contact angle (Figure 14b).

As well as affecting surface roughness, the introduction of TiO₂NPs also contributes to changes in the composition and structure of the coatings. TiO₂NPs introduced into the electrolyte composition for the deposition of Sn-based coatings result in a 1.4-fold decrease in contact angle. For Ni and Sn-Ni alloy coatings, the introduction of TiO₂NPs into the electrolyte composition increases the contact angle by 2 and 1.1 times, respectively. The dependence of the Sn-Ni alloy wetting contact angle on the microroughness of the coatings studied was determined. The optimum current density of 1/dm² was used to obtain a wetting contact angle of about 65 ± 1.2°. The dependence of the TiO₂NPs incorporation on the contact angles of the prepared coatings was evaluated. It was found that the introduction of 1 g/L TiO₂NPs into the composition of the Sn-Ni alloy deposition electrolyte imparts hydrophobic properties to the surface.

3.3. Corrosion Properties

Since these coatings can modify objects in massive contact with human skin, evaluation of their corrosion resistance in artificial sweat was carried out using electrochemical impedance spectroscopy. The impedance spectra in an artificial sweat medium (pH = 7) are shown in Figure 15.

From the Nyquist and Bode diagrams in Figure 15, it is clear that in the absence of TiO₂NPs in the composition of Sn coatings, higher resistance values are observed. The charge transfer resistance (low-frequency region) of Sn coatings is 1.40 × 10⁴ Ω·cm², however, with the introduction of TiO₂NPs, the resistance decreases to 7.90 × 10³ Ω·cm² (Table 5). An opposite behavior was observed with the introduction of TiO₂NPs into the electrolyte composition for Ni deposition; an increase in the charge transfer resistance of the coating from 8.3 × 10³ to 2.10 × 10⁴ Ω·cm² was observed. In the case of Sn-Ni alloy-based coatings, with the introduction of TiO₂NPs, charge transfer resistance decreases from 4.25 × 10⁴ to 3.7 × 10⁴ Ω·cm². The impedance spectra were analyzed using the equivalent circuit shown in the insert of Figure 15a. The parameters obtained from the simulation of the impedance spectra using the equivalent circuit are shown in

Table 6. Parameters of the equivalent circuits of the impedance spectra for coatings Sn, Ni, Ni–Sn, Sn-TiO₂NPs, Ni-TiO₂NPs, and Sn-Ni TiO₂NPs obtained in an artificial sweat medium.

Coating	Rs (Ω cm2)	R1 (Ω cm2)	Y1 (Ω−2 cm−2sn)	n1	R2 (Ω cm2)	Y2 (Ω−2 cm−2sn)	n2
Sn	18.74	11,300	1.53 × 10−5	0.8	3000	5.93 × 10−4	0.5
Sn-TiO2NPs	5.03	7450	5.03 × 10−5	0.78	1000	4.43 × 10−4	0.15
Ni	12.53	6277	1.9 × 10−4	0.8	832.9	1.77 × 10−5	0.79
Ni-TiO2NPs	13.57	19,277	7.93 × 10−5	0.7	3833	5.16 × 10−5	0.89
Sn-Ni	11.5	33,053	4.98 × 10−5	0.91	9896	7.96 × 10−5	0.62
Sn-Ni-TiO2NPs	18.04	25,067	3.65 × 10−5	0.79	8891	5.13 × 10−5	0.51

.

Introducing TiO₂NPs into the electrolytes when depositing Sn and Sn-Ni coatings reduces the charge transfer resistance at the interface, whereas, for Ni coatings, the introduction of 1 g/L of TiO₂NPs into the electrolyte composition doubles the charge transfer resistance. For all the coatings studied, the introduction of TiO₂NPs into the deposition electrolyte composition results in a slight decrease in the exponent n1 of the CPE1 element, with values between 0.7 and 0.91, indicating the capacitive nature of the element.

To further assess the anticorrosion properties of the prepared coatings, the potentiodynamic polarization technique was used, and the results are shown in Figure 16. The results were analyzed using the Tafel equation to determine the corrosion current and potential (

Table 7. Electrochemical parameters of corrosion of the studied samples.

Coating	Icorr (A/cm2)	Ecorr (V)	aa (V)	ba (V)	|ac| (V)	|bc| (V)
Sn	1.36 × 10−4	−0.42	0.20	0.06	0.64	0.06
Sn-TiO2NPs	1.17 × 10−4	−0.35	0.21	0.04	0.46	0.03
Ni	4.84 × 10−5	0.13	0.23	0.02	0.03	0.04
Ni-TiO2NPs	4.87 × 10−5	0.17	0.39	0.05	0.10	0.06
Sn-Ni	1.82 × 10−4	0.08	0.36	0.08	0.16	0.06
Sn-Ni-TiO2NPs	2.63 × 10−5	−0.2	0.06	0.03	0.67	0.10

).

The introduction of TiO₂NPs into the deposition electrolyte of the Sn-based coating induces a shift in corrosion potential (E_corr) by 70 mV towards the electropositive region, from E_corr (Sn) = −0.42 V to E_corr (Sn-TiO₂NPs) = −0.35 V, whereas this shift is only about 40 mV in the case of a Ni coating. The E_corr increased from 0.14 V for the Ni coating to 0.18 V for the Ni-TiO₂NP coating. In the latter case, corrosion current densities (I_corr) are 4.84 × 10⁻⁶ A/cm² and 4.87 × 10⁻⁵ A/cm², respectively. Figure 16c shows that in the case of the Sn-Ni alloy coating, the introduction of TiO₂NPs into the electrolyte during deposition of the Sn-Ni alloy coating induces a shift in the E_corr by 300 mV towards the electronegative region, from 0.09 V (Sn-Ni) to −0.21 V (Sn-Ni-TiO₂NPs); the corresponding I_corr are 1.82 × 10⁻⁴ A/cm² and 2.63 × 10⁻⁵ A/cm², respectively. The results of the main corrosion process parameters in an artificial sweat environment with a pH of 7 are presented in Table 7.

The E_corr of Sn- or Ni-based coatings changes insignificantly with the introduction of TiO₂NPs into the electrolyte composition, while in the case of Sn-Ni-based coatings, the corrosion current decreases 6.9-fold. The results of electrochemical impedance spectroscopy of the coatings in a 3% NaCl solution are shown in Figure 17. It can be seen that the Nyquist diagrams obtained for all the coatings studied in the NaCl medium are characterized by a capacitive semicircle in the high- and mid-frequency regions.

In the case of Ni-based coatings, it can be seen in Figure 17a,b that the introduction of TiO₂NPs into the deposition electrolyte induces a higher increase in charge transfer resistance from 1.80 × 10⁴ to 4.0 × 10⁴ Ω·cm², whereas, the Bode diagrams (Figure 17d) show a slight increase in charge transfer resistance from 1.10 × 10⁴ to 1.20 × 10⁴ Ω·cm², in the case of Sn-based coatings with embedded TiO₂NPs (low-frequency region). For Sn-Ni alloy-based coatings (Figure 17e,f), the introduction of TiO₂NPs into the deposition electrolyte induces the charge transfer resistance, which decreases from 1.20 × 10⁵ to 9.0 × 10⁴ Ω cm². The parameters obtained from the equivalent circuit analysis of the impedance spectra are shown in

Table 8. Parameters of equivalent circuits used to analyze the impedance spectra of different prepared coatings (Sn, Ni, Sn-Ni, Sn-TiO₂NPs, Ni-TiO₂NPs, and Sn-Ni-TiO₂NPs) in solution 3% NaCl.

Coating	Rs, (Ω cm2)	R1, (Ω cm2)	Y1, (Ω−2 cm−2sn)	n1	R2, (Ω cm2)	Y2, Ω−2 (cm−2sn)	n2
Sn	7.89	10,188	3.6 × 10−5	0.61	1465	1.7 × 10−6	0.77
Sn-TiO2NPs	11.89	11,324	3.3 × 10−5	0.82	1024	5.15 × 10−5	0.86
Ni	11.62	21,679	1.95 × 10−4	0.76	1918	1.24 × 10−5	0.33
Ni-TiO2NPs	13.42	44,679	6.95 × 10−5	0.74	4118	1.42 × 10−5	0.43
Sn-Ni	11.98	145,600	3.91 × 10−5	0.8	18,286	5.57 × 10−5	0.64
Sn-Ni-TiO2NPs	12.58	75,240	3.7 × 10−5	0.82	30,001	8.99 × 10−5	0.78

.

The introduction of TiO₂NPs into the electrolytes for the deposition of Ni and Sn coatings increases the resistance to charge transfer at the interface. For a Sn-NiTiO₂NP composite coating with 1 g/L TiO₂NPs in the electrolyte composition, the charge transfer resistance indicators decrease by a factor of two. For Ni coatings, the introduction of TiO₂NPs into the composition of the deposition electrolyte decreases the exponent n of the CPE₁ element slightly but for Sn-TiO₂NPs and Sn-Ni-TiO₂NPs this exponent increases. The n₁ index is in the range of 0.61 to 0.82, which indicates the presence of defects in the coating.

The results of potentiodynamic polarization curves are presented in Figure 18 for the different prepared coatings. Based on these results, the corrosion currents and the corrosion initiation potential were calculated.

Analysis of the potentiodynamic polarization curves showed that the corrosion potential of the Sn-based coating (Figure 18a) is −0.22 V and that the introduction of TiO₂NPs into the deposition electrolyte composition resulted in a 110 mV shift in potential towards the electronegative region, reaching a value of −0.33 V. It can also be observed that the corrosion current density is 1.03 × 10⁻⁴ A/cm² and 6.48 × 10⁻⁵ A/cm² for Sn and Sn-TiO₂NPs coatings, respectively. In the case of Ni coatings, it was observed that the corrosion potential is 0.05 V, but when TiO₂NPs are introduced into the deposition electrolyte, the corrosion initiation potential shifts by 230 mV towards the electronegative region and reaches a value of −0.18 V. The corrosion current densities corresponding to the Ni- and Ni-TiO₂NP-based coatings are 2.39 × 10⁻⁵ A/cm² and 2.18 × 10⁻⁵ A/cm², respectively (Figure 18b). Figure 18c shows that TiO₂NPs introduced into the Sn-Ni alloy deposition electrolyte shift the corrosion initiation potential by 100 mV toward the electropositive potentials, from 0.08 V to −0.02 V. Furthermore, the corrosion currents are 1.01 × 10⁻⁴ A/cm² and 9.94 × 10⁻⁶ A/cm² for Sn-Ni and Sn-Ni-TiO₂NPs, respectively. The main parameters characterizing the corrosion process are shown in

Table 9. Electrochemical Tafel parameters of the studied coatings in a solution of 3% NaCl.

Coating	Icorr, A/cm2	Ecorr, V	aa, B	ba, B	|ak|, B	|bk|, B
Sn	1.03 × 10−4	−0.22	0.048	0.066	0.606	0.098
Sn-TiO2	6.48 × 10−5	−0.33	0.145	0.112	0.601	0.066
Ni	2.39 × 10−5	0.05	0.483	0.095	0.792	0.181
Ni-TiO2	2.18 × 10−5	−0.18	0.025	0.032	0.378	0.044
Sn-Ni	1.01 × 10−5	−0.02	0.18	0.04	0.298	0.056
Sn-Ni-TiO2	9.95 × 10−6	0.08	0.33	0.051	0.329	0.081

.

The introduction of TiO₂NPs into the deposition electrolyte compositions of all coatings was accompanied by a more or less pronounced decrease in corrosion current. The corrosion currents of Sn-Ni alloy and Ni-based coatings do not change significantly with TiO₂NPs in the deposition electrolyte composition. In the case of Sn coatings, the corrosion current density decreases by a factor of 1.6.

According to these results, obtained both in an artificial sweat medium and a 3% NaCl solution, the different coatings prepared show different trends in terms of anticorrosion properties when TiO₂NPs are added to the deposition electrolyte. Indeed, TiO₂NPs incorporated in Sn, Ni, and Sn-Ni coatings modify their anticorrosion properties, which can be explained by their surface-wetting properties and their chemical composition. As shown by SEM surface characterization, the surface texture changes with the introduction of TiO₂NPs, which consequently influences their roughness and wetting properties. It is well known in the literature that a surface with an increased contact angle reduces the area of contact with the liquid on its surface, which can lead to a reduction in the surface area in contact with the aggressive medium and therefore its corrosion [52,53]. Bearing this in mind, the results obtained can be explained as follows.

In the case of the Sn coating, the decrease in corrosion resistance can be explained by the decrease in the contact angle and, therefore, an increase in the surface area exposed to corrosion processes. Furthermore, the increase in corrosion resistance of the Ni-based coating after the incorporation of TiO₂NPs is due to the synergistic effect between the increase in contact angle—and therefore minimization of the contact surface with the aggressive solution—and the anticorrosive property of the chemical element Ni. In the case of the Sn-Ni-based coating, it was observed that the corrosion resistance decreased after the introduction of TiO₂NPs, despite a relatively high contact angle compared to the other coatings and the presence of the chemical element Ni. This can be explained by the appearance of porosity in the coating after the incorporation of TiO₂NPs, which can facilitate the penetration of the aggressive solution through the coating, reaching a maximum surface area susceptible to being corroded.

Antibacterial properties are strongly recommended for surfaces in public areas that come into contact with human skin. TiO₂NPs are materials with high photocatalytic properties and, when used in coatings, impart antibacterial properties. The antibacterial properties of the coatings prepared in this work have been investigated and are presented in

Table 10. The antibacterial activity of samples, evaluated using the St. aureus ATCC 6538 test.

Sample	Concentration of Bacterial Cells C (CFU/mL)		Reduction Factors (RF)
	Under UV Irradiation	Without UV Irradiation
Sn-Ni (control)	3.3 × 103	1.4 × 106	2.6
Sn-Ni-TiO2NPs	2.0 × 101	5.0 × 105	4.4
Ni	7.0 × 101	1.3 × 106	4.3
Ni-TiO2NPs	4.0 × 101	9.9 × 105	4.4
Sn	3.0 × 101	4.4 × 105	4.1
Sn-TiO2NPs	2.0 × 101	1.1 × 106	4.7
Sn-Ni-TiO2NPs (Degussa)	8.0 × 101	1.6 × 105	3.3

.

According to the antibacterial test presented in Table 10, the prepared coatings show bactericidal activity with an RF parameter > 2; in addition, the coatings show that under UV light they can reduce the concentration of microorganisms by 4 to 5 orders of magnitude. Furthermore, the antibacterial activity of Sn-based coatings is due to the presence of copper with antibacterial properties in the coating composition as Sn has no antibacterial properties. Figure S2 shows the antibacterial properties of the coatings studied with the St. aureus disease bacterium test.

Experiments have shown that for all coatings, the introduction of TiO₂NPs into the composition of the deposition electrolytes, and consequently into the coatings, leads to an enhancement of the antibacterial properties with and without UV radiation.

Table 11. The antibacterial activity of samples, evaluated using E. coli ATTC 8739 tests.

Sample	Concentration of Bacterial Cells C, CFU/mL		Reduction Factors (RF)
	Under UV Irradiation	Without UV Irradiation
Sn-Ni (control)	5.4 × 103	3.9 × 105	1.9
Sn-Ni-TiO2	3.4 × 102	9.0 × 104	3.4
Ni	3.6 × 102	1.5 × 105	2.6
Ni-TiO2	6.0 × 101	2.5 × 105	3.6
Sn	1.9 × 102	4.6 × 104	2.3
Sn-TiO2	1.6 × 103	5.9 × 105	2.6
Sn-Ni-TiO2 (Degussa)	8.0 × 101	2.5 × 105	3.4

shows that the introduction of TiO₂NPs (1 g/L) into the deposition electrolyte for the deposition of Sn, Ni, and Sn-Ni coatings leads to an increase in the antibacterial properties under UV radiation in the presence of E. coli ATTC 8739 strains but with a lower efficiency than those observed using the St. John’s strains. Electrochemical composite coatings with TiO₂NPs were shown to have the best biocidal properties against Gram-positive and Gram-negative strains. They can be widely used on objects that are accessible to humans in public environments.

To assess the antibacterial properties of a solid surface, several factors must be taken into account, such as the properties of the surface in terms of hydrophobicity, roughness, and chemical composition as well as the bacterial species. The proliferation of bacteria on a solid surface is affected by the configuration and roughness of the surface, which has a strong influence on the adhesion of bacteria to the solid surface and their viability. Bacterial attachment to solid surfaces is considered to be the first step in bacterial growth and proliferation. It has been widely demonstrated that poor bacterial adhesion to a solid surface leads to bacterial death. Therefore, weakening bacterial adhesion is considered one of the indirect approaches to prevent bacterial proliferation. Surface patterning and roughness can increase the hydrophobic character of the surface, causing bacteria to repel and weakly adhere to the solid surface, leading to their death.

A further method of preventing bacterial proliferation, which is regarded as a direct approach, is to regulate the chemical composition of the surface. The metallic surface of nanoparticles (NPs) such as Zn, Al, Ni, Zr, Ce, Mg, and TiO₂ have antibacterial properties [54,55,56,57,58,59]. In particular, the photoelectrochemical and photocatalytic properties of TiO₂ nanoparticles [59,60] have been shown to enable them to generate electron-hole pairs that can react with water or oxygen to produce reactive oxygen species (ROS) such as superoxide anions, hydrogen peroxide, and hydroxyl radicals. The latter species can penetrate bacterial cell walls and cause cell death by disrupting cell function [61,62,63,64,65,66,67]. Several studies in the literature have reported that TiO₂NPs have strong antibacterial and antifungal activity against many Gram-positive bacteria such as Staphylococcus aureus and Gram-negative bacteria such as Escherichia coli [68,69].

In addition, Ni nanocrystals have been reported to have antibacterial activity against Gram-positive/negative bacteria and bacterial spores such as Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Although the mechanism of the antibacterial effect of Ni nanocrystals is not yet fully understood, it has been reported that during the interaction between the Ni surface and bacteria, Ni²⁺ leaching has been detected, which penetrates the bacterial membrane and generates reactive oxygen species, leading to disruption of its function and bacterial death [70]. In the case of the Sn surface, it has been reported to exhibit weak antibacterial activity when exposed to Staphylococcus aureus (S. aureus) or Escherichia coli (E. coli) bacteria [71].

To understand the antibacterial test results of the coating prepared with and without TiO₂NPs, it is necessary to consider the synergistic effect of the two factors influencing the antibacterial activity of the solid surface mentioned above. There is a synergistic effect between the weakening of the bacteria adhesion due to the hydrophobicity of the surface on the one hand and the antibacterial properties of the chemical elements of the solid surface on the other. In the case of Sn with low antibacterial activity, the observed result could be explained by the hydrophobicity of the surface leading to weak adhesion of the bacteria and their death at a later stage. The incorporation of TiO₂NPs into the Sn coating results in a decrease in contact angle from 89° to 63° and an increase in bacterial adhesion to the surface; however, the antibacterial activity of the TiO₂NPs effectively compensates for this effect, thereby explaining the relatively minor change in FR from 2.3 to 2.6.

For Ni and Sn-Ni coatings, the strong increase in FR after incorporation of TiO₂NPs could be explained by the synergistic effect of the antibacterial properties of Ni and TiO₂NPs rather than by the low adhesion of bacteria to the surface. The Ni coating exhibits hydrophilic properties (a contact angle of 32°), which facilitate bacterial adhesion. However, the extensive contact area between the bacteria and the Ni hydrophilic surface ensures the coating’s antibacterial efficacy. Furthermore, the integration of TiO₂ NPs into the Sn-Ni coating leads to a negligible alteration in the contact angle (Figure 15), suggesting that the bacterial adhesion strength remains comparable. The observed antibacterial activity is primarily attributed to the synergistic effect of Ni and TiO₂ NPs.

The results demonstrate that Sn, Ni, and TiO₂NPs are crucial for the development of coatings with enhanced anticorrosion and antibacterial properties. The Sn-Ni-TiO₂ coating exhibits an effective antibacterial activity (RF 3.4) and anticorrosion performance, characterized by a more positive Ecorr (0.08 V), a lower current density (9.95 × 10⁻⁶ A/cm²), and a higher charge transfer resistance (25,067 Ω·cm²).

A comparative analysis of our Ni-Sn-based coatings, prepared with the incorporation of low concentrations of TiO₂ NP aggregates (1 g/L)—with similar coatings identified in the existing literature [35,36]—has revealed that the performance of the current coatings is highly promising, exhibiting significant resistance to corrosion in an artificial sweating environment and to bacterial proliferation.

4. Conclusions

It has been demonstrated that the mechanism by which deposited coatings form is consistent with the electrochemical behavior of instantaneous growth, and the three-dimensional growth is controlled by ion diffusion. Furthermore, it was observed that the introduction of TiO₂NPs did not affect the potentiodynamic polarization curves but significantly modified the phase composition and structure of the coatings formed. Additionally, the deposition current density of the alloy was found to influence the coating yield, elemental and phase composition, and wetting properties of the coatings studied.

In coatings deposited at a current density of 0.5 to 1.5 A/dm², Sn is the predominant element in the coating composition, representing up to 55% by weight. The anticorrosion properties of Sn-Ni alloy-based coatings were investigated in an artificial sweat medium. The incorporation of TiO₂NPs at a concentration of 1 g/L into the deposition electrolyte resulted in a notable reduction in the initial current density, which demonstrates the efficacy of these nanoparticles in their contribution to corrosion inhibition.

The introduction of TiO₂NPs into the composition of deposition electrolytes has been demonstrated to enhance the biocidal properties of the resulting coatings, both with and without UV radiation. This makes them suitable for use on objects in public settings that frequently come into contact with people.

The combined effect of chemical composition and surface roughness has been demonstrated to enhance the anticorrosive and bactericidal properties of the prepared coatings.