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Article

Ultrasonic Enhancement of Tin Dissolution in NaOH/H2O2 System: Electrochemical and Passivation Modulation

by
Dongbin Wang
1,2,
Mingge Fu
1,2,
Tian Wang
1,2,
Wenlong Miao
1,2,
Liuxin Xiang
1,2,
Thiquynhxuan Le
1,2,* and
Libo Zhang
1,2,*
1
State Key Laboratory of Complex Non-Ferrous Metal Resources Clean Utilization, School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
2
School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
*
Authors to whom correspondence should be addressed.
Metals 2025, 15(9), 1016; https://doi.org/10.3390/met15091016
Submission received: 3 August 2025 / Revised: 3 September 2025 / Accepted: 10 September 2025 / Published: 12 September 2025
(This article belongs to the Special Issue Preparation of Metal Compounds—from Fundamental Mechanisms to Circular Economy Applications)
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Abstract

In the alkaline process for sodium stannate preparation, the oxidative dissolution of tin in the NaOH-H2O2 system originates from a spontaneous electrochemical reaction. This study elucidates the mechanism of ultrasound-enhanced tin dissolution in NaOH/H2O2 solutions from an electrochemical perspective, with particular emphasis on the tripartite regulatory effects of ultrasound on mass transfer, passivation suppression, and reaction pathway modulation. Electrochemical analysis indicates that ultrasound enhances mass transfer by disrupting the diffusion boundary layer, delays passivation, accelerates the exfoliation of the passive layer, and generates hydroxyl radicals that lower cathodic activation barriers. Under the action of 30 W ultrasound, the apparent diffusion coefficient of the solution increases and the passivation process of the tin sheet is delayed (the oxidation peak potential shift changes from −0.76 V to −0.70 V). After the passive layer is exfoliated by ultrasound, the charge transfer resistance decreases by 85.8% (from 8.09 ± 0.01 Ω to 1.15 ± 0.01 Ω). Ultrasound effectively overcomes the kinetic limitations imposed by the passivation layer through a triple synergistic mechanism involving mass transfer enhancement, passivation inhibition, and -OH path regulation.

Graphical Abstract

1. Introduction

Sodium stannate, as a key raw material in alkaline tin plating, exerts a critical influence on the development of flame retardant materials, catalysis, and the field of new materials [1,2,3,4]. The market demand for sodium stannate exhibits an upward trend in accordance with the continuous expansion of downstream applications and technological advancements. In industrial production, the alkaline dissolution method, which uses high-purity tin, NaOH and the oxidant H2O2, is the mainstream production process of sodium stannate, primarily due to its operational simplicity and low energy consumption [3,5,6]. The core of this method lies in the oxidative dissolution of tin in the NaOH-H2O2 system, which is inherently a spontaneous electrochemical process. Currently, this process is generally carried out at elevated temperatures (60–80 °C) to overcome kinetic limitations; however, this leads to significant decomposition of hydrogen peroxide, high energy consumption, and increased operational costs. Lowering the temperature markedly reduces the dissolution rate, hindering practical application. Besides, this process is limited by low oxidation efficiency and mass transfer constraints caused by passivation, resulting in difficulties in effectively improving the sodium stannate production efficiency [7,8].
To enhance the oxidative dissolution efficiency, it is crucial to gain a comprehensive understanding of the electrochemical behavior and corrosion characteristics of tin in alkaline media. Studies [9,10] demonstrate that tin undergoes a two-step oxidation process Sn(0) → Sn(II) → Sn(IV) in NaOH medium, leading to the formation of oxide layers that induce two distinct passivation processes. Initial passivation is characterized by the formation of a thin Sn(OH)2 film, which partially dehydrates to form a SnO film. As the oxidation potential further increases, a continuous and dense Sn(OH)4 film forms, leading to stable passivation through the formation of SnO2 [9,11]. Electrochemical measurements indicate [12,13] that oscillations in the constant-current polarization curves occur within the Sn/Sn(OH)2 and Sn(OH)2/Sn(OH)4 potential ranges [12,13]. These passivation layers directly restrict the oxidative dissolution of tin, with the dense passivation layers at high oxidation potentials blocking the transfer of solvent water molecules and OH− ions to the metal interface [14]. Therefore, the key to improving the oxidative dissolution efficiency of tin requires either suppressing the formation of passivation layers or converting them into soluble species, while simultaneously enhancing oxidative dissolution capability.
Regarding enhancement approaches, ultrasound demonstrates remarkable advantages, which is a form of mechanical wave with frequencies above 20 kHz [15]. When propagating through liquid media, ultrasound generates unique physical and chemical effects, most notably cavitation, which induces extreme transient local conditions within collapsing cavities, including high temperature, high pressure, and high-speed micro jet [15,16]. These conditions enhance mass transfer, activate surface active sites, and improve reaction rates in wet metallurgy processes, particularly in disrupting passivation layers and facilitating redox reactions [17,18]. Current studies have reported the enhancing effects of ultrasound on tin oxidative dissolution processes [19,20]. For instance, Liu et al. [7] demonstrated that ultrasound significantly improves tin leaching efficiency from tin plates while simultaneously reducing leaching potential and enhancing process kinetics. Similarly, Liu et al. [21] reported that ultrasound diminished the self-corrosion potential and mitigated anodic passivation for lead-tin alloys in nitric acid systems. Our previous work [5] developed a novel ultrasound-assisted tin oxidative dissolution process that achieved 99.3% tin dissolution efficiency at room temperature, representing a 28% improvement over conventional methods. This technology reduced the reaction temperature by 30 °C, decreased sodium hydroxide consumption by 33.3%, and saved 15% of hydrogen peroxide while maintaining the same tin dissolution efficiency, thereby further confirming the remarkable enhancement effect of ultrasound on tin oxidative dissolution. However, existing research has primarily focused on focuses on macroscopic performance, such as dissolution efficiency, surface morphology, and oxidation potential changes. While the fundamental understanding of interfacial electrochemical mechanisms remains limited, especially in particularly regarding how ultrasound regulates mass transfer by disrupting diffusion boundary layers, and how the synergistic effects between physical detachment and chemical dissolution inhibit passivation layer formation. It should be specifically noted that the electrochemical mechanisms underlying ultrasound-enhanced oxidative dissolution of tin have not been systematically reported to date. These critical knowledge gaps directly hinder further optimization and practical application of ultrasound-enhanced oxidative tin dissolution technology.
Given that tin oxidative dissolution in the NaOH-H2O2 system is fundamentally an electrochemical process, passivation constitutes the core electrochemical bottleneck limiting efficiency, and existing research lacks a comprehensive understanding of how ultrasound influences this process at the electrochemical level (particularly in mitigating passivation and enhancing kinetics), this study addresses these voids. We investigate the impact of ultrasound on the oxidative dissolution efficiency and passivation behavior of Sn in NaOH-H2O2. The interface process is elucidated through the integration of electrochemical technology and microscopic characterization methods. The study examines the electrochemical effects of ultrasound on metal corrosion processes, the fragmentation of passivation layers by ultrasound, the enhancement of mass transfer resistance by ultrasound, and the influence of mass transfer diffusion. The objective of these methodologies is to elucidate the augmented impact of ultrasound on the tin oxidative dissolution process from the electrochemical domain. This endeavor facilitates the advancement of comprehension regarding the mechanism of ultrasound and offers novel insights for the eco-friendly preparation of sodium stannate and the promotion of non-ferrous metal oxidative dissolution and recovery processes.

2. Materials and Methods

2.1. Materials

All reagents used were analytical grade reagents (AR). Sodium hydroxide (NaOH) and hydrogen peroxide (H2O2, 30%) were purchased from Tianjin Zhiyuan Co., Ltd. (Tianjin, China). High-purity tin sheets were produced by Tengfeng Metal Materials Co., Ltd. (Xingtai, China), with a thickness of 1 mm and purity of 99.99%. For spin-trapping electron paramagnetic resonance (EPR) analysis, employing 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) was obtained from Shanghai McLean Biochemical Technology Co., Ltd., Shanghai, China. The purity of tin sheets was determined in accordance with Chinese National Standards GB/T 3260.11-2023 and GB/T 3260.9-2013 [22,23] through quantification of 12 trace elements (Cu, Fe, Bi, Pb, Sb, As, Al, Zn, Cd, Ag, Ni, Co) by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and sulfur content by high-frequency induction furnace combustion-infrared absorption method, with final purity calculated by subtracting total impurities from 100%.

2.2. Experimental Procedure

Electrochemical measurements were performed with a CHI760E electrochemistry workstation (CH Instruments, Inc., Shanghai, China) using a three-electrode electrochemical cell with a high-purity platinum sheet and mercuric oxide electrode used as the counter electrode and the reference electrode, respectively. The AC impedance test was performed with a PMC multi-channel multifunctional electrochemical workstation (Ametek Princeton, Oak Ridge, TN, USA). The working electrode was the tin sheet with an effective area of 1 cm2, ultrasonic power ranged from 0–150 W, and the temperature was 20 °C. The corresponding potential range of cyclic voltammetry (CV) was −1.5 to 0 V. The Tafel curve was tested at a scanning speed of 5 mV/s. The frequency range measured by impedance spectroscopy (EIS) was 105 Hz to 1 Hz, and the AC amplitude was 5 mV. The ultrasonic equipment and the integrated experimental setup for measuring electrochemical characteristics under ultrasonic action were both independently developed and constructed by the Key Laboratory of Unconventional Metallurgy, Ministry of Education at Kunming University of Science and Technology, Kunming, China. The experimental setup featured 40 kHz ultrasound generated from the bottom, with precisely controlled energy input through percentage-based power regulation (full-scale output: 300 W).
Sodium hydroxide was weighed and dissolved to achieve the predetermined concentration. After cooling to room temperature, 40 mL of the solution was transferred to the electrochemical cell. Then, 30% hydrogen peroxide solution was added at volume ratios of “0%, 5%, 10%” relative to the sodium hydroxide solution. The mixture was stirred uniformly and allowed to stand for 5 min before electrodes were inserted for measurement. During the electrochemical tests, a polished high-purity tin sheet with an area of 1.0 ± 0.1 cm2 was used as the working electrode. A cleaned high-purity platinum sheet of the same area (1.0 ± 0.1 cm2) served as the counter electrode. The reference electrode was an Hg/HgO electrode. The three electrodes were arranged in a triangular layout, with the tin and platinum electrodes positioned opposite each other at a distance of 1 cm. To avoid interference from accumulated tin ions and decomposition of hydrogen peroxide, the electrolyte was replaced before each set of experiments. During ultrasonic-assisted experiments, both the electrolyte and the water bath solution were refreshed to maintain a constant temperature.
The acoustic power delivered to the electrochemical cell was quantified using calorimetry. Under the conditions employed in this study (40 mL solution volume, 40 kHz ultrasonic bath, preset power of 30 W), the measured acoustic power was 29.6 ± 0.2 W. The corresponding acoustic intensity (I) at the electrode surface (effective area A = 1.0 ± 0.1 cm2) was estimated accordingly, resulting in a calculated intensity of 29.6 ± 0.2 W/cm2. Ultrasound was applied in continuous mode, with the transducer positioned 3 cm from the working electrode.
To maintain a constant temperature and minimize thermal effects from ultrasound, the water in the ultrasonic bath was replaced concurrently with the electrolyte solution throughout the experiments. The temperature of the water bath was monitored in real-time during all ultrasonic measurements and maintained at 20 ± 1 °C.

2.3. Characterization Equipment

The surface morphology of the tin sheet and passivation layer was examined using scanning electron microscopy (SEM, ZEISS Sigma 300, Carl Zeiss AG, Oberkochen, Germany). The phase composition of the samples was studied via X-ray diffraction (XRD, D2 Advance, Bruker, Karlsruhe, Germany). X-ray photoelectron spectra (XPS) were acquired to investigate the chemical composition and elemental state using a Thermofisher (XPS, Al Kα X-ray source, Thermofisher, Waltham, MA, USA). An electron paramagnetic resonance spectrometer (EPR JES-FA200, JEOL, Tokyo, Japan) was used to analyze free radicals in the solution.

3. Results and Discussion

3.1. Dissolution Behavior of Tin in NaOH/H2O2 Solutions Under Ultrasonic Treatment

3.1.1. Effect of NaOH Concentration

The concentration of sodium hydroxide (NaOH) is a pivotal parameter in the alkaline oxidative dissolution of tin. Its role extends beyond providing an alkaline medium; it critically determines the stability of the passive layers and the dissolution pathway. High alkalinity promotes the chemical dissolution of both Sn(II) and Sn(IV) oxide layers into soluble stannate ions (e.g., Sn(OH)62−), thereby suppressing passivation and sustaining the reaction kinetics. To systematically investigate the passivation modulation and dissolution enhancement effects of sodium hydroxide on the tin leaching process, tests were conducted using NaOH solutions at varying concentrations.
Figure 1 demonstrated the electrochemical behavior of tin during the oxidative dissolution process in an alkali solution. At a scan rate of 0.05 V/s, the cyclic voltammogram of tin electrode in 0.1 mol/L NaOH solution exhibits two anodic current peaks, including the O1 peak at −0.76 V and the O2 peak at −0.69 V, corresponding to the two-step oxidation process of tin. The first stage involves the oxidation of Sn (0) to Sn(II) (literature reports that the primary oxidation products are SnO and Sn(OH)2), followed by the second stage where Sn(II) is further oxidized to Sn(IV). During the forward potential scan (initiated from −1.6 V to 0.5 V vs. Hg/HgO), oxidation commenced at point A (≈−1.1 V), with the current density increasing as the potential rises; continuous oxidation of Sn(0) occurred in segment A → B, reached the first anodic peak O1 at point B (−0.88 V) with a current density of ≈3.8 mA/cm2, followed by the current density decreasing (3.8 mA/cm2 → 2.15 mA/cm2) in segment B → C, indicating the onset of pre-passivation where a Sn(II) compound (SnO/Sn(OH)2) film covered the electrode surface. Subsequently, secondary oxidation occurred in segment C → D, where Sn(II) is further oxidized to Sn(IV), and the second anodic peak O2 was formed at point D (≈−0.69 V), with the current density recovering to 3.9 mA/cm2 at this point; as the scanning potential continued to increase, the current density decayed (3.9 mA/cm2 → 0.2 mA/cm2) in segment D → E, due to the formation of a dense Sn(IV) oxide/hydroxide layer (secondary passivation), which completely inhibits ion transport; finally, the current remains near zero in segment E → F, confirming that the electrode enters a fully passivated state [24]. The detailed justification for the determination of points A through F has been provided in the Supporting Information (Part 1).
(1) Effect of NaOH concentration on the cyclic voltammetry
The effect of NaOH concentration on the cyclic voltammetry of a Sn electrode with and without ultrasound assistance was shown in Figure 2a,b. Increasing NaOH concentration (0.1 → 3 mol/L) significantly enhanced anodic current density in cyclic voltammetry, indicating accelerated tin oxidative dissolution. The initial oxidation potential (point A) remained unchanged, confirming unaltered thermodynamic driving force for oxidation initiation. Both oxidation peaks exhibited positive potential shifts: O1 from −0.884 ± 0.001 V to −0.756 ± 0.001 V and O2 from −0.691 ± 0.001 V to −0.576 ± 0.001 V, reflecting an increase in passivation potential and decreased stability of the passive layer at higher alkalinity. Notably, the current enhancement was attributed primarily to OH− disrupting nascent SnO films through the formation of soluble stannite species (Sn(OH)3−), which increases the number of active sites in the O1 step. Although OH− also promotes dissolution of SnO2 to Sn(OH)62−, the persistent passivation caused by SnO2 imposes stronger kinetic limitations on the O2 step, resulting in significantly smaller current enhancement for O2 compared to O1. Under ultrasound, the current density of the oxidation process was significantly increased, indicating enhanced electron transfer kinetics and disruption of passivation. Notably, ultrasound caused the merging of the two distinct oxidation peaks (O1/O2) into single broad peaks, providing direct evidence of cavitation-induced exfoliation of passive films. Current oscillations manifested real-time competition between passivation formation and ultrasonic detachment. High NaOH concentrations (≥2 mol/L) suppressed passivation chemically through oxide dissolution, while ultrasound mechanically disrupted nascent passive layers via cavitation. This dual mechanism synergistically facilitated sustained tin dissolution.
(2) Effect of NaOH concentration on the Tafel polarization
Tafel polarization measurements were conducted to quantitatively assess corrosion kinetics and passivation stability during tin oxidation. The Tafel polarization curve were obtained both without and with ultrasound at various sodium hydroxide concentrations, as shown in Figure 3a,b, respectively [25]. The corrosion potential (Ecorr) and corrosion current density (icorr) were determined by automated fitting and analysis of the Tafel polarization curves using an electrochemical workstation, as shown in Table 1. The results demonstrate that the Ecorr of tin shifts negatively with increasing NaOH concentration regardless of ultrasonic application, indicating an enhanced thermodynamic tendency for dissolution corrosion. This is attributed to the increased concentration of hydroxide ions, which reduces concentration polarization and leads to a rise in icorr. However, as the NaOH concentration further increases, the elevated viscosity of the solution partially hinders ion diffusion, resulting in minor fluctuations in icorr. Under ultrasound, a positive shift in the Ecorr is observed (as evidenced by Ecorr data in Table 1), which theoretically would reduce dissolution tendency and promote passivation layer formation. However, the experimental results reveal a significant increase in current density (icorr). This phenomenon suggests that ultrasound enhances mass transfer and diffusion effects, thereby simultaneously weakening the deposition of passivation layers and significantly accelerating stannate dissolution [26].

3.1.2. Effect of H2O2 Additive Amount

Hydrogen peroxide (H2O2) serves as the primary oxidant in the industrial alkali leaching process for the production of sodium stannate. Compared to traditional nitrate-based oxidizers, it eliminates the emission of harmful gases such as nitric oxide and ammonia. Additionally, its decomposition products are primarily water and oxygen, thereby avoiding the introduction of extraneous impurity ions. H2O2 acts as the oxidant driving the cathodic reaction, and its concentration directly influences the dissolution rate and passivation behavior of tin. While it facilitates the oxidation of Sn(0), an excess can lead to the rapid formation of a passive Sn(IV) oxide film that hinders further dissolution if not concurrently dissolved by OH−. To investigate the impact of H2O2 concentration (0–10%) and elucidate the balance between enhanced oxidation kinetics and passivation, tests were conducted using H2O2 solutions at varying concentrations.
(1) Effect of H2O2 Amount on the cyclic voltammetry
Figure 4a presents the investigation on the effect of H2O2 concentration on the oxidation dissolution process of tin sheets at 2 mol/L NaOH concentration. To highlight the effect of hydrogen peroxide, comparisons were made among addition volume ratios of 0% (no-H2O2), 5%, and 10%, respectively. The selection of this specific alkali concentration was based on three critical considerations to ensure optimal experimental conditions and accurate analysis of the H2O2 effect. Experimental results demonstrated that insufficient NaOH concentration led to a decline in the oxidation peak potential (Epa), consequently expediting the passivation of tin sheets, while excessive alkali concentration weakened the passivation effect and excessively enhanced the dissolution of intermediate products, making the characteristic peak changes indistinct and severely compromising the evaluation of H2O2 concentration effects. Under these optimized conditions, increasing H2O2 concentration resulted in a continuous positive shift of the oxidation peak potential in cyclic voltammetry curves, accompanied by the gradual merging of two oxidation characteristic peaks into a single peak. From this perspective, the dissolution reaction of tin is deemed to be conducive. However, when the H2O2 addition increased to 10%, the peak potential of the oxidation peak (O3) also shifted positively, which not only delayed the onset potential of passivation but more importantly increased the energy barrier of the oxidation process. Besides, the peak current ipa reduced from 111 mA/cm2 to 88 mA/cm2, confirming that the increase in hydrogen peroxide concentration leads to a more pronounced passivation phenomenon, resulting in an increase in mass transfer resistance. The cyclic voltammetry curves in Figure 3b under ultrasound all exhibited a single oxidation peak. However, as the hydrogen peroxide concentration increases from 0% to 10%, the anodic current density decreases from 400 mA/cm2 to 310 mA/cm2, accompanied by a positive shift in the oxidation peak potential (from −0.378 ± 0.001 V to −0.369 ± 0.010 V). Concurrently, significant current oscillations occur within the potential range of −0.52 V~−0.34 V, which directly confirms the dynamic competition of oxidative passivation and ultrasonic exfoliation in triggering dynamic surface reactions. Although ultrasound enhances mass transfer, the continuous current density decay at high oxidant concentrations indicates that the enhancing effect of ultrasound decreases under high-concentration oxidant conditions [27,28,29].
(2) Effect of H2O2 Amount on the Tafel polarization
The Tafel polarization curves in Figure 5a,b reveal that the cathodic reduction enhances with increasing H2O2 concentration from 0% to 10% in a 2 mol/L NaOH solution, as evidenced by the upward shift of the cathodic branch both with and without ultrasonic conditions. However, the anodic branch exhibits a significantly increased Tafel slope at high H2O2 concentrations (e.g., 10%), indicating a decrease in anodic current density, which aligns with the conclusion that H2O2 exacerbates passivation and impedes mass transfer. The corrosion potential (Ecorr) continuously shifts positively with increasing H2O2 (Figure 5a,b), whereas the corrosion current density (icorr) initially increases and then decreases, peaking at 5% H2O2 (Table 2). This phenomenon can be explained as follows: as the H2O2 concentration increases from 0% to 5%, the initial rise in anodic current density is primarily driven by the accelerated cathodic reduction of H2O2. Simultaneously, at this NaOH concentration, the passive film remains effectively soluble. Consequently, the corrosion current density increases. However, a further increase in H2O2 concentration to 10% leads to excessive passivation. Although the cathodic reaction is enhanced by more H2O2, the anodic reaction becomes severely limited by the thickened passive film, resulting in an overall decrease in corrosion current density. The competition between cathodic enhancement and anodic passivation thermodynamically drives the positive shift in Ecorr, thermodynamically hindering spontaneous reaction progression [30].
Notably, while increasing H2O2 promotes tin oxidation, excessive amounts (e.g., 10%) induce severe passivation, inhibiting dissolution. A comparison between conditions with and without ultrasound conditions demonstrates that ultrasound disrupts the passive layer via cavitation effects, manifesting as a significant increase in anodic current under ultrasonic treatment. From a practical standpoint, excessive H2O2 at low NaOH concentrations readily induces complete passivation, halting dissolution, whereas high NaOH concentrations (e.g., 2 mol/L) mitigate passivation through alkaline dissolution, sustaining tin dissolution in the form of sodium stannate. By continuously disrupting passivating films through cavitation, ultrasound overcomes mass transfer limitations and maintains efficient tin dissolution even under challenging electrochemical conditions.

3.2. Mechanism of Ultrasonic Enhancement on Tin Dissolution in NaOH/H2O2

3.2.1. Mass Transfer Intensification

To reveal the intrinsic effects of ultrasound, and to avoid the complex effects caused by H2O2, cyclic voltammetry tests were conducted with (30 W) and without ultrasonic treatment in 2 mol/L NaOH solution without H2O2, and the results are shown in Figure 6. The cavitation and mechanical effects of ultrasound generate significant microjets, which enhance solution agitation, alleviate diffusion limitations, and accelerate mass transfer. These effects directly influence the electrochemical process by increasing the current density of the oxidation reaction and enhancing charge transfer kinetics. As illustrated in the results, under without ultrasound conditions, the oxidation peak current density ipa (Conv.) was 165.9 mA/cm2, whereas ultrasonic treatment (30 W) increased it to 234 mA/cm2. Furthermore, ultrasound shifted the oxidation peak potential of tin from −0.76 V to −0.70 V, which indicates the disruption of the diffusion boundary layer. This positive shift in the oxidation peak potential extends the active dissolution window, which can be attributed to the delayed formation of the passivation layer and its accelerated removal by ultrasound. As a result, the dissolution rate exceeds the passivation rate, thereby enhancing tin dissolution. This phenomenon is consistent with the conclusions in Figure 3a,b, where ultrasound increases the anodic current and disrupts the passivation layer, collectively demonstrating that ultrasound optimizes the electrochemical process by improving mass transfer and suppressing passivation [31,32].
To quantify the improvement of the apparent diffusion coefficient of the oxidation process by ultrasonication, a series of cyclic voltammetry tests were performed at varying scan rates. The change in peak current was then compared between without and with ultrasonic (30 W) conditions. The results are shown in Figure 7a,b, respectively.
As illustrated in Figure 7, both in without ultrasound conditions and with ultrasound at 30 W, the anodic oxidation peak potential shifts significantly towards more positive values as the scan rate increases. Conversely, the cathodic reduction peak potential shifts towards more negative values. The application of ultrasound increases the current density of the electrode reaction; this effect can be attributable to ultrasound reducing the thickness of the diffusion layer and diminishing diffusion limitations.
The oxidation of tin in a sodium hydroxide solution (without H2O2) was confirmed to be irreversible. Through electrochemical impedance spectroscopy (EIS) tests in this system, we observed typical Warburg impedance under both with and without ultrasonic conditions, indicating that the process is diffusion-controlled. Therefore, we used the Randles–Ševčík model for irreversible system for the analysis.
ip = (2.99 × 103) n(αnα)1/2AD1/2Cv1/2
where ipc represents the peak current density, n represents the total number of electrons in the reaction, α represents the transfer coefficient, nα represents the number of electrons that determine the rate step (usually 1), A represents the effective electrode area, D represents the diffusion coefficient, C represents the concentration of the species in solution, and v represents the scan rate. Considering the impact of changes in parameters such as nα and α on data accuracy, and to isolate their influence, the ratio of the diffusion coefficients with ultrasound to that under without ultrasound conditions was directly calculated to evaluate the improvement effect of ultrasound on mass transfer. Based on the calculation, the diffusion coefficient increased by approximately 1.65 times under the ultrasound. (Dultra/Dconv. = 1.65).

3.2.2. Reaction Path Optimization and Kinetic Enhancement

To investigate the effect of ultrasonic power on kinetic acceleration and mass transfer enhancement under the action of oxidants, this study evaluated the oxidative dissolution of tin sheets in a 2 mol/L NaOH + 5% H2O2 system using Tafel polarization measurements under varying ultrasonic power (0-150 W), and the results are shown in Figure 8. The parameters of Ecorr and icorr effect of ultrasound power was shown in Table 3.
As shown in Figure 8, systematic shifts in the Tafel curves were observed with ultrasonic power increases from 0 to 150 W. The self-corrosion potential (Ecorr) exhibited a positive shift from −1.071 ± 0.001 V (0 W) to −1.027 ± 0.001 V (150 W), representing the positive shift of Ecorr by 44 mV. Concurrently, the corrosion current density (icorr) demonstrated a notable increase from 0.29 ± 0.01 mA/cm2 to 15.82 ± 0.01 mA/cm2, representing a 55-fold rise. The significant increase in icorr despite a minor positive shift in Ecorr strongly confirms the dominant role of ultrasound in enhancing reaction kinetics [33,34].
The observed concurrent positive Ecorr shift and icorr surge align with a dual mechanistic effect of ultrasound: cathodic depolarization and anodic depassivation. In cathodic depolarization, ultrasonic cavitation generates ·OH radicals and accelerates the cathodic H2O2 reduction (·OH + e− → OH−), effectively depolarizing the cathode. This is evidenced by the upward shift of the cathodic Tafel branches in Figure 8a, indicating enhanced cathodic kinetics and increased availability of electron acceptors. This cathodic enhancement is the primary driver for the positive shift in Ecorr. Additionally, ultrasound enhances mass transfer of depolarizers (like dissolved oxygen and ·OH) to the cathode surface, further contributing to the depolarization effect. In anodic depassivation, ultrasound generates cavitation bubble collapse and associated microjetting forces, which disrupt and remove the passive oxide film on the tin anode surface. This depassivation process exposes fresh, active metal sites, thereby facilitating the anodic dissolution reaction. Although the slight positive shift in Ecorr suggests a minor reduction in the thermodynamic driving force for tin ionization, the removal of the passivation barrier leads to the significant increase in icorr and a substantial kinetic enhancement of the anodic reaction. This synergism (·OH-enhanced cathodic depolarization coupled with cavitation-driven anodic depassivation) explains the overall acceleration of corrosion kinetics under ultrasound [35]. The dominant cathodic kinetics govern the potential (Ecorr shift), while the removal of the anodic passivation barrier enables the substantial increase in corrosion current density (icorr).
Following the implementation of ultrasound, a substantial increase in the cathodic current density was observed, as shown in Figure 8a. This increase suggests a notable acceleration in mass transfer to the cathode surface. The destruction of the mass transfer boundary layer on the cathode surface due to ultrasonic action facilitates several key phenomena. These include the acceleration of the mass transfer of H2O2 and hydroxyl radical (·OH) to the cathode surface, the promotion of the cathodic reduction reactions, involving both the direct reduction of H2O2 and the reduction of the highly reactive ·OH radicals (Equations (2)–(4)), and the general increase in current density with the continuous increase in of ultrasonic power.
H2O2 + 2e− → 2OH−
H2O2 + US → 2⋅OH
OH + e− → OH−
A key advancement revealed by this study is that ultrasound enhances the cathodic reaction kinetics. The enhancement in cathodic current density is ascribed, in part, to the generation of hydroxyl radicals (·OH) through ultrasonic cavitation, which serve as highly reactive cathodic oxidants (depolarizers). To explicitly confirm the presence of ·OH in the alkaline solution under ultrasound, spin-trapping EPR spectroscopy was employed. The results, presented in Figure 9, demonstrate a direct correlation between ·OH radical production and ultrasonic power, consistent with the observed increase in cathodic current.
The thermodynamic favorability of ·OH reduction is evident from its high standard oxidation potential. The oxidation potential for the ·OH/OH− couple (Equation (4)) is 1.454 V vs. Hg/HgO, significantly higher than that for the H2O2/OH− couple (Equation (2)) at −0.056 V vs. Hg/HgO. This substantial difference in potential indicates that ·OH is a much stronger oxidant than H2O2 and is thermodynamically more readily reduced at the cathode. The presence of this highly oxidizing species, generated in situ by ultrasound and concentrated at the electrode surface due to enhanced mass transfer, significantly promotes the rate of electron transfer (cathodic reduction), resulting in the increased cathodic current density.
The cathode surface is enhanced in a synergistic manner by the following processes: (1) Mass transfer-enhanced cavitation acoustic flow disrupts the diffusion boundary layer and accelerates the transport of H2O2/·OH to the cathode surface. (2) Ultrasonic cleavage of H2O2 produces highly active ·OH radicals, and their high reduction potential (·OH/OH− = +1.454 V vs. Hg/HgO) significantly reduces the cathode activation energy barrier. The anodic delayed passivation can be described as follows:(1) Physical stripping: The microjets generated by ultrasonic cavitation directly remove the passive film, exposing fresh active surfaces; (2) Chemical depassivation and dissolution promotion: ·OH readily chemically oxidizes exposed tin metal, and the synergistic effect of ultrasound converts the passive layer (SnO2) into soluble Sn(OH)62− (Equation (5)), inhibiting passive film regeneration. Although the positive shift in the self-corrosion potential (ΔE = +44 mV in Figure 7) suggests a weakening of the thermodynamic driving force, the kinetic gain fully compensates for this effect, thereby dominating the reaction efficiency.
SnO2 + 2OH− + 2H2O → Sn(OH)62−

3.2.3. Passivation Layer

According to previous studies, ultrasound can reduce the stability of anode passivation [36]. To investigate the effects of ultrasound on the passivation layer of the tin oxidation process, an electrochemical impedance spectroscopy (EIS) test was employed [37,38,39]. These tests generated Nyquist plots, which were subsequently analyzed. The results are displayed in Figure 10a. Charge transfer resistance (Rct) and solution resistance (Rs) as shown in Table 4 and Table 5, the AC impedance data has been presented in a fitted format. The frequency range for the impedance measurements was 105 Hz to 1 Hz, and the AC amplitude was 5 mV.
As shown in Figure 10a, the Nyquist plot provides a visual representation of the charge transfer inhibition effect of the passivation layer. The semicircular arc observed in the high-frequency region is characteristic of charge transfer resistance (Rct) at the electrode/electrolyte interface. Crucially, the diameter of this semicircle is directly proportional to the magnitude of Rct, meaning a larger diameter signifies greater resistance to charge transfer. The Nyquist plot of the fresh tin sheet exhibited a small semicircle, corresponding to a low Rct value of 1.07 ± 0.01 Ω. The test results of the passivated tin sheet after without ultrasound (0 W) reaction demonstrated a significantly enlarged semicircle with a Rct of 8.09 ± 0.01 Ω, thereby confirming that the accumulated passivation layer (Figure 10b) blocked the active sites on the tin surface and hindered the charge transfer. In contrast, the tin plate under ultrasonication exhibited a significant reduction in its semicircular diameter and a decrease in its charge transfer resistance Rct to 1.15 ± 0.01 Ω, which was comparable to that of the polished fresh tin sheet. This confirms that ultrasound effectively removes the passivation layer and restores the tin surface condition to a state close to the original [40].
EIS tests were performed on tin sheets in H2O2-NaOH solution under different ultrasonic power level, the results are shown in Figure 10b. In 0 W conditions, the Rct registered at 1.15 ± 0.01 Ω; however, upon the application of 30 W of ultrasound, it decreased to 1.07 ± 0.01 Ω. Subsequently, when the ultrasound power was increased to 120 W, the Rct further decreased to 0.93 ± 0.02 Ω. These results suggest that ultrasound can promote the charge transfer process on the surface of the tin electrodes. However, the Rct exhibited only 12.9% decrease with the increase in ultrasound power from 30 to 120 W, indicating a relatively limited impact on the overall charge transfer process. This phenomenon suggests that the rate-limiting step of the overall electrode reaction is no longer the charge transfer step under the current experimental conditions [41].
The Bode plots (Figure 11) clearly demonstrate the critical role of the passivation layer in governing tin’s corrosion behavior. The passivated electrode exhibits a high, stable impedance (∣Z∣ ≈ 0–12.8 Ω) over the measured frequency range and a broad phase angle peak near approximately −40°, indicative of the presence of a protective, capacitive barrier that severely limits charge transfer. In stark contrast, once this layer is removed, the impedance plummets (∣Z∣ ≈ 0–2.5 Ω) and the phase angle peak diminishes, consistent with a shift to resistive behavior and drastically increased charge transfer kinetics at the newly exposed active surface. This unpassivated state is mirrored by the new tin plate (∣Z∣ ≈ 0–2.0 Ω), which, lacking a developed passive film, demonstrates similarly high corrosion susceptibility, confirming that the elevated impedance of the passivated sample is a direct result of its surface layer and not an intrinsic property of the bulk material.
As shown in Figure 12. The Bode plots illustrate the influence of ultrasonic power (30 W, 60 W, 90 W and 120 W) on the electrochemical impedance behavior of tin electrodes in alkaline media. Consistent across all spectra is a decrease in impedance magnitude (∣Z∣) with increasing frequency, characteristic of capacitive-like behavior associated with electrode—electrolyte interfaces. The phase angle generally becomes more negative at intermediate frequencies, suggesting a dominant capacitive response due to the double layer. With increasing ultrasonic power, the observed decrease in total impedance magnitude (|Z|) and the corresponding negative shift in the phase angle are consistent with enhanced charge transfer and reduced interfacial resistance. This behavior is consistent with the ability of ultrasonic cavitation to disrupt the diffusion layer, mitigate passivation, and promote tin dissolution. The most significant enhancement occurs at 90 W, where the lowest impedance and the most negative phase angle indicate the highest interfacial activity.
To clarify why ultrasonic treatment reduces Rct, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to characterize the surface morphology and composition of tin-coated sheets under different conditions. As shown in Figure 13, the surface state without ultrasound (passivated state) was as follows: After reacting in an H2O2-NaOH solution without ultrasonic assistance, the tin surface was covered by a black passivation layer (Figure 13a). EDS analysis confirmed a high surface oxygen content, which was attributed to the accumulation of intermediate products formed during the reaction. This passivation layer tightly wrapped the tin surface, physically blocking direct contact between the metal and the electrolyte. Consequently, the transport of charge carriers (electrons and ions) across the interface was hindered, resulting in the high Rct observed in EIS tests. Under ultrasonic irradiation (120 W), the tin surface morphology changed significantly (Figure 13b, right). SEM images showed that the dense passivation layer was partially stripped, exposing the tin substrate. The EDS results confirmed that the oxygen content on the surface of the sample with passivation reached 46.1%, whereas under ultrasound, the oxide layer was peeled off, and the oxygen content decreased to 39.7%, indicating a significant decrease in surface oxygen content.
The EIS and SEM-EDS results collectively reveal an ultrasonic depassivation mechanism involving the coordinated action of mechanical stripping and chemical dissolution. The micro-jets generated by ultrasonic mechanical and cavitation effects continuously scour the passivation film on the surface of the tin sheet, thereby reducing the thickness and weakening the passivation effect. Furthermore, the flow field generated by cavitation accelerates the diffusion of OH− to the surface of the passivation layer of the tin sheet, thereby promoting the generation of soluble stannate. As shown in the reaction Equations (5) and (6).
SnO + OH− + H2O → Sn(OH)3−
The XPS detailing the chemical composition of the surface layers formed on the tin electrode under with and without ultrasound conditions are presented in Figure 14. In the absence of ultrasound, a black passivation layer was observed on the sample surface. Without ultrasound, a black passivation layer composed of mixed Sn(II) (peaks at 486.7 eV and 495.1 eV) and Sn(IV) (486.9 eV and 495.3 eV) oxides was observed. The stable Sn(II) intermediate contributes to passivation and inhibits further dissolution. In contrast, under ultrasound irradiation, the Sn(IV) peak (487.0 eV) dominates, showing significantly higher intensity relative to Sn(II), indicating enhanced surface oxidation and a shift toward Sn(IV) species. This suggests that ultrasound disrupts and removes the passivation layer, promoting continuous oxidation.

3.2.4. The Impact of Tin Dissolution Rate

Electrochemical analysis revealed a significant increase in the corrosion rate of tin, indicating a higher spontaneous reaction current. Cyclic voltammetry further confirmed that, at the same oxidation potential, the current density under ultrasound was greater than that under without ultrasound conditions. This suggests that ultrasound enhances the electron transfer rate, leading to more tin being oxidized and dissolved into the solution per unit time, which is consistent with the actual dissolution efficiency measurements. To further verify this effect, under the conditions of 20 °C, 3 mol/L NaOH, and hydrogen peroxide dosage at 1.5 times the theoretical requirement, with an ultrasonic power of 240 W, we compared the tin dissolution efficiency with and without ultrasound. The results (as shown in Table 6) demonstrate a remarkable increase in the dissolution rate under ultrasonic treatment within the same time frame.
Quantifying radical concentration is highly challenging. To further evaluate the contribution of radicals to the tin dissolution process, tert-butanol was added to the ultrasonic experimental group as a hydroxyl radical scavenger. The results showed that, within 50 min, the dissolution rate decreased to 71.35% when hydroxyl radicals were scavenged, representing a 23.87% reduction compared to the condition with radicals present. This clearly demonstrates that ultrasound-generated radicals play a significant role in enhancing the oxidation dissolution of tin.
The ultrasonic cavitation effect has been shown to significantly enhance the electrochemical dissolution process of tin through a series of synergistic effects, as shown in Figure 15. First, the micro-jet and mechanical stripping action generated by ultrasound break the passivation package, continuously expose the highly active tin surface, effectively reduce the charge transfer resistance (Rct), and promote the electron transfer between tin and oxidant (Sn → Sn2+ + 2e−). Second, the cavitation effect induces shear micro-etching on the tin surface, forming tiny grooves and defects (visible in SEM). This increases the real reaction surface area and provides more electron transfer sites, further reducing the Rct and enhancing the reaction current. Third, ultrasound disrupts the mass transfer boundary layer, intensifying the diffusion of oxidant and OH− to the electrode surface and the removal of dissolution products (SnO32−), and significantly suppressing the concentration polarization to maintain the highly efficient reaction kinetics.
The combined effect of the aforementioned mechanisms is ultimately reflected in the significant acceleration of the tin dissolution rate. The increase in the corrosion current (icorr) in the Tafel curve and the increase in the current in the cyclic voltammetry curve directly confirm that ultrasonic waves facilitate the transfer of electrons per unit of time, thereby strongly promoting the kinetics of oxidative dissolution of tin, which significantly enhances the actual dissolution output efficiency.

4. Conclusions

The electrochemical analysis of tin oxidation under ultrasonic irradiation reveals a multi-scale enhancement mechanism.
  • Mass transfer intensification: The cavitation microjet generated by ultrasound has been shown to enhance the diffusion process. This acceleration of the electron transfer has been demonstrated to increase the peak current from 165.9 mA/cm2, to 234 mA/cm2. Furthermore, the microjet has been observed to destroy the mass-transfer boundary layer and to promote the dissolution of passivation products, with the oxidation peak potential increasing from −0.76 V to −0.70 V, which resulted in a weakening of the passivation.
  • Passivation suppression: Ultrasound effectively removes the passivation layer on the surface of the tin sheet through the action of micro-jets generated by cavitation. Consequently, the charge transfer resistance (Rct) decreases from 8.09 ± 0.01 Ω to 1.15 ± 0.01 Ω. The removal of the passivation layer by ultrasound reduces the activation barrier.
  • Reaction path optimization and kinetic enhancement: The generation of hydroxyl radicals under ultrasound optimizes the reaction path, accelerates the diffusion of oxidant to the cathode surface, increases the self-corrosion current from 0.286 mA/cm2 to 15.8 mA/cm2, and improves the cathodic reaction kinetics.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/met15091016/s1, Figure S1. Correlation analysis of ipa and Epa with v and v1/2 (a,b) without ultrasound; (c,d) ultrasound with 30 W. Figure S2. Residuals of the real and imaginary parts from the equivalent circuit modeling of the impedance spectra at different conditions. Figure S3. The raw spectra without 120 W ultrasonic power. Figure S4. The raw spectra with 120 W ultrasonic power. Figure S5. Surface photographs of the electrode before and after ultrasonic testing: (a) before ultrasonic scanning, (b) after ultrasonic scanning. Figure S6. Electrochemical impedance spectroscopy (EIS) of the tin electrode.

Author Contributions

Conceptualization, T.L.; methodology, D.W.; validation, M.F. and T.W.; formal analysis, D.W., M.F., T.W., W.M. and L.X.; investigation, M.F., W.M. and L.X.; resources, T.L. and L.Z.; writing—original draft preparation, D.W.; writing—review and editing, M.F., T.W., W.M., L.X., T.L. and L.Z.; supervision, L.Z.; project administration, T.L. and L.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Yunnan Province Key R&D Plan, grant number 202403AK140009 and Yunnan Revitalization Talents Support Plan—High-end Foreign Talents Program.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Metals 15 01016 g001
Figure 1. Cyclic voltammetry curve at 0.1 mol/L NaOH solution of a newly polished Sn electrode.
Figure 1. Cyclic voltammetry curve at 0.1 mol/L NaOH solution of a newly polished Sn electrode.
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Figure 2. Effect of NaOH concentration on the cyclic voltammetry of a newly polished Sn electrode (a) without ultrasound and (b) with ultrasound-assisted.
Figure 2. Effect of NaOH concentration on the cyclic voltammetry of a newly polished Sn electrode (a) without ultrasound and (b) with ultrasound-assisted.
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Metals 15 01016 g003
Figure 3. Tafel curves density under different NaOH concentrations (a) without ultrasound and (b) with ultrasound-assisted.
Figure 3. Tafel curves density under different NaOH concentrations (a) without ultrasound and (b) with ultrasound-assisted.
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Figure 4. Cyclic voltammetry curves under different hydrogen peroxide addition (a) without ultrasound-assisted and (b) with ultrasound-assisted.
Figure 4. Cyclic voltammetry curves under different hydrogen peroxide addition (a) without ultrasound-assisted and (b) with ultrasound-assisted.
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Figure 5. Tafel curves under different hydrogen peroxide addition (a) without ultrasound-assisted and (b) with ultrasound-assisted.
Figure 5. Tafel curves under different hydrogen peroxide addition (a) without ultrasound-assisted and (b) with ultrasound-assisted.
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Metals 15 01016 g006
Figure 6. Effect of ultrasound on the cyclic voltammetry of a newly polished Sn electrode (NaOH2 mol/L, without H2O2).
Figure 6. Effect of ultrasound on the cyclic voltammetry of a newly polished Sn electrode (NaOH2 mol/L, without H2O2).
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Metals 15 01016 g007
Figure 7. Cyclic voltammetry testing at different scanning speeds (a) Without Ultrasound; (b) ultrasound with 30 W.
Figure 7. Cyclic voltammetry testing at different scanning speeds (a) Without Ultrasound; (b) ultrasound with 30 W.
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Metals 15 01016 g008
Figure 8. (a) The effect of ultrasonic power on tin plates in Tafel curve testing. (b) Changes in self-corrosion potential of tin sheets.
Figure 8. (a) The effect of ultrasonic power on tin plates in Tafel curve testing. (b) Changes in self-corrosion potential of tin sheets.
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Metals 15 01016 g009
Figure 9. EPR testing of the effect of ultrasound on hydroxyl radicals.
Figure 9. EPR testing of the effect of ultrasound on hydroxyl radicals.
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Figure 10. AC impedance plots of (a) raw, passivated and removed passivated; (b) at different ultrasound power.
Figure 10. AC impedance plots of (a) raw, passivated and removed passivated; (b) at different ultrasound power.
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Metals 15 01016 g011
Figure 11. Bode plots of tin sheet (a) passivated; (b) passivation-removed tin sheets and (c) raw.
Figure 11. Bode plots of tin sheet (a) passivated; (b) passivation-removed tin sheets and (c) raw.
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Metals 15 01016 g012
Figure 12. Bode plots of the tin sheets at different ultrasonic power (a) 30 W; (b) 60 W; (c) 90 W; (d) 120 W.
Figure 12. Bode plots of the tin sheets at different ultrasonic power (a) 30 W; (b) 60 W; (c) 90 W; (d) 120 W.
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Metals 15 01016 g013
Figure 13. Morphology and elemental distribution of tin sheet cross−section (a) without and (b) with 120 W ultrasonic power.
Figure 13. Morphology and elemental distribution of tin sheet cross−section (a) without and (b) with 120 W ultrasonic power.
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Figure 14. Analysis of XPS for Tin Electrodes (a) without and (b) with ultrasonic treatment.
Figure 14. Analysis of XPS for Tin Electrodes (a) without and (b) with ultrasonic treatment.
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Figure 15. Schematic of ultrasound-enhanced tin dissolution electrochemical mechanism.
Figure 15. Schematic of ultrasound-enhanced tin dissolution electrochemical mechanism.
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Table 1. Effect of NaOH concentration on the parameters of Ecorr and icorr of tin.
Table 1. Effect of NaOH concentration on the parameters of Ecorr and icorr of tin.
Without UltrasoundWith Ultrasound
CNaOH (mol/L)0.1 mol/L0.5 mol/L1 mol/L0.1 mol/L0.5 mol/L1 mol/L
Ecorr (V)−1.022 ± 0.001−1.062 ± 0.001−1.089 ± 0.001−0.088 ± 0.001−1.025 ± 0.001−1.063 ± 0.001
Log icorr (mA/cm2)0.06 ± 0.010.15 ± 0.010.14 ± 0.010.06 ± 0.010.76 ± 0.011.11 ± 0.01
Table 2. Effect of H2O2 addition on the parameters of Ecorr and icorr of tin.
Table 2. Effect of H2O2 addition on the parameters of Ecorr and icorr of tin.
Without UltrasoundUltrasound-Assisted
H2O2 addition0%5%10%0%5%10%
Ecorr (V)−1.081 ± 0.001−1.076 ± 0.001−1.067 ± 0.001−1.081 ± 0.001−1.036 ± 0.001−1.048 ± 0.001
Log icorr (mA/cm2)1.02 ± 0.018.08 ± 0.016.20 ± 0.012.93 ± 0.0132.84 ± 0.0124.32 ± 0.01
Table 3. Effect of ultrasound power on the parameters of Ecorr and icorr of tin.
Table 3. Effect of ultrasound power on the parameters of Ecorr and icorr of tin.
0 W30 W60 W90 W120 W150 W
Ecorr (V)−1.071 ± 0.001−1.069 ± 0.001−1.063 ± 0.001−1.045 ± 0.001−1.030 ± 0.001−1.027 ± 0.001
icorr (mA/cm2)0.29 ± 0.010.48 ± 0.010.90 ± 0.015.79 ± 0.0113.67 ± 0.0115.82 ± 0.01
Table 4. The variation of charge transfer resistance at different condition.
Table 4. The variation of charge transfer resistance at different condition.
Tin Remove Passivation LayerTin RawTin with Passivation Layer
Rs (Ω)1.355 ± 0.021.34 ± 0.012.10 ± 0.01
Rct (Ω)1.145 ± 0.011.07 ± 0.018.09 ± 0.02
CPE1-T0.014 ± 0.010.018 ± 0.010.015 ± 0.01
CPE1-P0.737 ± 0.010.7115 ± 0.010.706 ± 0.01
χ20.001480.00150.0015
Table 5. The variation of charge transfer resistance at different ultrasound powers.
Table 5. The variation of charge transfer resistance at different ultrasound powers.
0 W30 W60 W90 W120 W
Rs (Ω)1.36 ± 0.021.35 ± 0.011.35 ± 0.021.37 ± 0.011.35 ± 0.01
Rct (Ω)1.15 ± 0.011.07 ± 0.011.04 ± 0.020.94 ± 0.010.93 ± 0.02
CPE1-T0.014 ± 0.010.020 ± 0.010.019 ± 0.010.017 ± 0.010.014 ± 0.01
CPE1-P0.737 ± 0.010.700 ± 0.010.702 ± 0.010.728 ± 0.010.756 ± 0.01
χ20.001480.001200.001620.0018360.00159
Table 6. Tin dissolution rate at different times under with and without ultrasound conditions.
Table 6. Tin dissolution rate at different times under with and without ultrasound conditions.
Time Tin Dissolution Rate
(Ultrasonic)		Tin Dissolution Rate
(Without Ultrasound)
10 min27.15%13.49%
20 min56.74%30.95%
30 min78.61%45.66%
40 min91.38%54.43%
50 min95.22%61.48%
60 min98.16%68.27%
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Wang, D.; Fu, M.; Wang, T.; Miao, W.; Xiang, L.; Le, T.; Zhang, L. Ultrasonic Enhancement of Tin Dissolution in NaOH/H2O2 System: Electrochemical and Passivation Modulation. Metals 2025, 15, 1016. https://doi.org/10.3390/met15091016

AMA Style

Wang D, Fu M, Wang T, Miao W, Xiang L, Le T, Zhang L. Ultrasonic Enhancement of Tin Dissolution in NaOH/H2O2 System: Electrochemical and Passivation Modulation. Metals. 2025; 15(9):1016. https://doi.org/10.3390/met15091016

Chicago/Turabian Style

Wang, Dongbin, Mingge Fu, Tian Wang, Wenlong Miao, Liuxin Xiang, Thiquynhxuan Le, and Libo Zhang. 2025. "Ultrasonic Enhancement of Tin Dissolution in NaOH/H2O2 System: Electrochemical and Passivation Modulation" Metals 15, no. 9: 1016. https://doi.org/10.3390/met15091016

APA Style

Wang, D., Fu, M., Wang, T., Miao, W., Xiang, L., Le, T., & Zhang, L. (2025). Ultrasonic Enhancement of Tin Dissolution in NaOH/H2O2 System: Electrochemical and Passivation Modulation. Metals, 15(9), 1016. https://doi.org/10.3390/met15091016

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