2024 Volume 92 Issue 8 Pages 087006
To investigate the feasibility of the electrorefining process for aluminum (Al) upgrade recycling, Al electrodeposition employing an ionic liquid consisting of anhydrous aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium chloride (EMIC) was conducted. The effects of the operating temperature on the current efficiency, specific energy consumption, deposit properties, and deposition rate were investigated using the AlCl3-EMIC bath containing 1,10-phenanthroline anhydride (OP) as an additive at the current density of 100 mA cm−2. A constant-current electrodeposition showed that the specific energy consumption decreased to 5605 kWh t−1 at 80 °C with increasing the operating temperature in the OP-added bath and the current efficiency was over 90 % at the operating temperatures of 60–80 °C, but decreased to below 90 % at 90–100 °C. The cross-sectional ultra-low accelerating voltage scanning electron microscope (ULV-SEM) images showed the smoothness of the deposit obtained from the OP-added bath at 70 °C, but not at 90 °C. The XRD patterns of the Al deposits obtained from the OP-added bath showed a preferential orientation to the {100} plane at 60–80 °C, but almost no preferential orientation at 90–100 °C. It has been revealed that the improvement in the specific energy consumption requires an increase in the operating temperature, and that the surface roughness of the Al deposit must be improved by preferentially orienting the {100} plane in the texture to prevent any Al deposit from dropping out in order to improve the current efficiency at the cathode, which implies Al recovery.
Aluminum (Al) is used in a wide range of fields due to its light weight, high corrosion resistance, and excellent electrical conductivity. The Hall-Héroult process consumes a large amount of electricity as the specific energy consumption required to produce Al is 13000–15000 kWh t−1. In contrast, the amount of energy required for producing the recycled Al is only 3–5 % of the amount of energy input when smelting the primary Al.1
From the perspective of resource circulation (recycling), the recycling of Al alloys is important. However, most Al is recycled with a decrease in purity (cascade-recycle) due to the contamination by impurities in the process of recovering Al scrap. In other words, with the exception of beverage cans, it is difficult to recycle the used products into the original products (horizontal recycling) using existing processes, and impurities, mainly iron (Fe) and silicon (Si), accumulate in cascade-recycled aluminum, which is ultimately disposed as Al scrap that is difficult to reclaim.2
By using the electrorefining method, there is the possibility to recycle the low-grade Al scrap, which is difficult to recycle using the conventional methods, into high-grade Al (high-upgrade recycling). However, the standard electrode potential of Al (−1.676 V vs. SHE) is much lower than that of hydrogen, which makes it difficult to electrodeposit Al from aqueous solutions. Therefore, nonaqueous solutions, such as molten salts, ionic liquids, organic solvents, and deep eutectic solvents, have been used as the electrolytes for the Al electrodeposition. Attempts have been proposed to recycle the Al scrap by molten salt electrolysis.3 In the 1990s, it was carried out by Ishikawa and co-worker in Japan,1 and Schwarz and co-worker overseas,3 and it was reported that Al with a purity of 99.8 % or higher could be recovered. However, the electrolysis temperature was extremely high at around 1000 K. Therefore, it is difficult to implement this technology in society, as is a time when processes under mild conditions are important. In the 2000s, Reddy et al. revealed that the use of room-temperature molten salts, so-called ionic liquids, consisting of aluminum chloride (AlCl3) and an organic chloride, in the electrolysis bath enables the electrorefining of Al at a simpler and relatively lower temperature (363–376 K) than the process employing the molten salts described above.4,5 Specifically, they reported the recovery of Al from Al scrap with about 25 wt% Si by using the 62.3–37.7 mol% AlCl3-EMIC (1-ethyl-3-methylimidazolium chloride, Fig. S1a) ionic liquid as the electrolyte at about 363 K, and the specific energy consumption required for the process was 4790–5050 kWh t−1.5 This significant reduction in the specific energy consumption suggests that the Al electrorefining process using the AlCl3-based ionic liquids is worth considering as an energy-saving recycling process. However, the maximum electrolytic current density is only 1/50–1/100 of the process described for the Hall-Héroult method, which poses a problem in productivity.
Although the Al deposition using the AlCl3-based ionic liquids as the electrolyte is generally known to produce dense and very-adhesive Al deposits, the production process requires a high deposition rate and smooth surface morphology. If dendrite growth is suppressed by smoothing, the distance between the electrodes can be shortened and then the operating voltage can be reduced. The relation between the deposition conditions and the grain size of the deposit has been reported.6 It is postulated that the finer the grain size, the smoother the surface morphology. Control factors include the concentration of the reactive ionic species, additives, current density, deposition temperature (operating temperature), stirring, and overvoltage. The described deposit can be obtained by appropriately combining these factors. As an example, for the constant-current pulsed electrolysis using the AlCl3-EMIC melt, it has been reported that increasing the operating temperature of the electrolysis bath changes not only the grain size of the deposit but also the crystal morphology.7
As one of the production processes of electrolytic Al foil, our research group investigated the use of a Lewis acidic AlCl3-EMIC melt as the electrolyte to improve both the surface smoothness and the deposition rate of electrolytic Al foil.8 By adding 1,10-phenanthroline (1,10-phenanthroline anhydrate: OP, Fig. S1b) to the bath and increasing the operating temperature to 50 °C, the current efficiency of 96.5 % was achieved at the current density of 52.6 mA cm−2. The foil thickness of 8.29 µm, the arithmetic mean roughness (Sa) of 45.8 nm, and the deposition rate of approximately 0.9 µm min−1 were obtained. The single phase of Al (fcc) was obtained in the OP-free bath, and moreover, the addition of OP resulted in the preferential orientation of the texture toward the {100} plane, finer crystal grains, and a smooth surface morphology. In addition, it was revealed that the operating temperature needs to be increased to improve the deposition rate of the electrolytic Al foil, and the OP addition to the electrolyte is necessary to improve the surface roughness (smoothness) of the electrolytic Al foil.
Our research group focused on the high-upgrade recycling of Al using the electrorefining method. In this paper, the effects of the operating temperature and additives (OP) on the current efficiencies and the surface morphology of Al deposit were investigated using pure Al as an anode to obtain the Al deposit of about 50 µm thickness at a high current density, aiming to recover a large amount of Al based on the above-mentioned results.8
EMIC (Tokyo Chemical Co., Inc., $ \geqslant 98$ %) was dried under reduced pressure at 60 °C for 24 h to remove any residual water. The AlCl3-EMIC melt was prepared by mixing anhydrous AlCl3 (Sigma Aldrich, $ \geqslant 99.99$ %) and EMIC in a 2 : 1 molar ratio. An Al wire treated with a phosphoric acid solution was immersed in the bath for 2 weeks at room temperature, and the above melt was purified by the Al substitution method.9 The above melt was purified to obtain the OP-free bath. As an additive, 20 mmol dm−3 OP anhydride (Sigma-Adrich, $ \geqslant 99$ %) was added to the above bath to obtain the OP-added bath. These preparations were performed in an Ar gas-filled glove box (UNICO, UL-1000AC).
2.2 Electrochemical measurementsA three-electrodes cell was used for the electrochemical measurements. A Cu plate (Nilaco, 99.96 %, thickness: 0.26 mm) was used as the working electrode, which was mirror polished with waterproof paper (#600, #1500, #2000), sonicated with 15.8 wt% hydrochloric acid, distilled water, ethanol, and acetone in that order for 5 min, and dried in cold air. The circulator exposed area was masked with Nitoflon tape (Nitto, No. 903UL, thickness: 0.23 mm) so that the area was 0.95 cm2 (φ = 1.1 mm). The counter electrode was an Al plate (Nilaco, 99.99 %, thickness: 1.2 mm) sonicated in acetone for 5 min and masked with Nitoflon tape (Nitto, No. 903UL, thickness: 0.08 mm) so that the exposed area was 5.4 cm2. The distance between the working and the counter electrodes was defined as 2 cm. The reference electrode was constructed by placing an Al wire (Aluminium Wire Rod Company, Ltd., 99.99 %, diameter: 0.99 mm) and the OP-free bath in a Pyrex tube terminated with a porous G4 fritted glass with 6 mm diameter and 80 mm length (Asahi Glassplant, Inc.). The electrolyte was a prepared OP-free bath and the OP-added bath.
For the electrochemical measurements, a computer-controlled electrochemical measurement system (Hokuto Denko, HZ-7000) was used to perform the constant-current (CC) electrodeposition method to observe the potential of the working electrode (EWE), that of the counter electrode (ECE), and the operating voltage (EWE-ECE). The conditions of the CC method were as follows: the current density of 100 mA cm−2, the deposition time of 2896 s, and the total charge of 289.6 C cm−2. A magnetic stirrer hotplate (AS ONE, HSH-1D) was used to control the operating temperature at 60–100 °C with the stirring speed of 1500 rpm. After deposition, the working electrode was washed with distilled water and acetone to obtain the deposits.
2.3 Analysis of the depositsAn ultra-low acceleration voltage scanning electron microscope (ULV-SEM, JEOL Ltd., JSM-7800PRIME) was used to observe the surface and the cross-section of the deposits. To measure the film thickness, the cross-section of the deposits was fixed with a resin mixture of bisphenol A liquid epoxy resin (Mitsubishi Chemical Group, 100 %) and 3-aminomethyl-3,5,5-trimethylcyclohexylamine (Mitsubishi Chemical Group, about 26 %) in a 9 : 1 mass ratio. The deposition rates were calculated from the deposition time and the film thickness. An atomic force microscope (AFM, Park Systems, NX-10) was used to observe the Sa values on the deposit’s surface. The measurement mode was set to the non-contact mode. An X-ray diffractometer (Rigaku, MiniFlex600) was used to analyze the crystal structure of the deposits. Cu Kα rays (λ = 0.15418 nm) were used as the line source and the measurements were made in the range 30–80° at the scan speed of 2.0° min−1.
Figure 1 shows the CC polarization curves for the Al deposition at the operating temperature of 60–100 °C and the current density of 100 mA cm−2. Figures 1a and 1b show the potential at the working electrode and the operating voltage, respectively. It is considered that the cathodic reaction shown by Eq. 1 occurs at the working electrode.
| \begin{equation} \text{4Al$_{2}$Cl$_{7}{}^{-}$} + \text{3e$^{-}$} \to \text{Al} + \text{7AlCl$_{4}{}^{-}$} \end{equation} | (1) |
(a) Potential-time transition and (b) operating voltage-time transition for depositing Al on the Cu plate substrate in the AlCl3-EMIC melt at (green line) 60 °C, (orange line) 70 °C, (red line) 80 °C, (blue line) 90 °C, and (black line) 100 °C with 20 mmol dm−3 of OP additive; current density: 100 mA cm−2; total charge for all deposits: 289.6 C cm−2.
Although the potential was lower than −2.2 V vs. Al/Al (III) during the initial stage of the deposition at 50 °C, the potential was higher than −2.2 V vs. Al/Al (III) at 60–100 °C. Since the reductive decomposition of the EMI+ cation occurred at −2.2 V vs. Al/Al (III),10 the deposition was carried out at 60 °C or higher. It was considered that no side reactions occurred at 60–100 °C, and only the Al deposition reaction shown by Eq. 1 occurred. As the operating temperature increased, the potential of the working electrode became higher (Fig. 1a) and the operating voltage decreased (Fig. 1b). In addition, the potential of the counter electrode was about 0.87 V vs. Al/Al (III) at 60 °C, which was lower than that of oxidative decomposition (about 2.2 V vs. Al/Al (III)),10,11 and the potential shifted lower as the operating temperature increased (not shown). These shifts in the potential and the operating voltage were attributed to the increase in the electrical conductivity of the electrolyte and decrease in the solution resistance as the operating temperature increased. This indicated that the deposition can be carried out at a lower operating voltage by increasing the operating temperature.
Figure 2 shows close-up images of the deposits obtained on the Cu plate substrate under various deposition conditions. No metallic luster was observed on the surface of the deposit obtained from the OP-free bath at 70 °C and the roughness was especially high around the circumference (Fig. 2a). No specular luster was observed on the deposit obtained from the OP-free bath (Fig. 2a′). In contrast, a metallic luster was observed on the deposit obtained from the OP-added bath at 70 °C (Fig. 2b′). This is probably because the smoothness of the deposited surface is dramatically improved by chemical action rather than by the thermodynamic action rate (polarization effects).8 A mirror-like luster was observed on the deposit obtained from the OP-added bath (Fig. 2b′). However, even in the OP-added bath, when the operating temperature was increased to 90 °C, the deposited surface became significantly roughened (Fig. 2c) and the metallic luster disappeared (Fig. 2c′). To evaluate the roughness of the deposited surface, the reflection of the green logo was observed. The reflection of the green logo was observed in Fig. 2b′, while it was not observed in Figs. 2a′ and 2c′. This indicates that the roughness of the deposit surface shown in Fig. 2b′ is small. This suggests that the smoothing of the deposited surface by the OP addition would be temperature dependent.
Photographs of deposits obtained on the Cu plate substrate from a) the OP-free bath at 70 °C and the OP-added bath at b) 70 °C and c) 90 °C. (a′), (b′), and (c′) correspond to the mirror surface reflection tests in (a), (b), and (c), respectively; current density: 100 mA cm−2, total charge for all deposits: 289.6 C cm−2.
Table 1 shows the relation between the current efficiency of the working electrode of the deposit and the counter electrode, and the operating temperature. We defined the current efficiency as the ratio between the actual amount of the deposits to that theoretically calculated from Faraday’s laws.12 In the case of the counter electrode, it was defined as the ratio to the dissolved amount of the counter electrode. The current efficiency of the working electrode at 70 °C in the OP-free bath was 76.4 %. This is because a part of the deposit would peel off from the end surface of the Cu plate substrate. In contrast, the current efficiencies of the working electrode at 60–80 °C in the OP-added bath were 90 % or more. This is considered to be because the addition of OP to the bath smoothed the deposit’s surface and would suppress the delamination of the deposit. On the other hand, the current efficiency of the working electrode decreased to below 90 % when the operating temperature was increased to 90–100 °C. This is considered to be due to the loss of the smoothness of the deposit’s surface, which would make the deposit easier to peel off. This suggests that the effect of the OP addition on the current efficiency would be temperature dependent.
| Additives | Operating temperature °C |
Current efficiencies % | |
|---|---|---|---|
| Working electrode |
Counter electrode |
||
| OP | 60 | 95.9 | 110.3 |
| 70 | 96.2 | 104.9 | |
| 80 | 91.3 | 99.4 | |
| 90 | 85.4 | 103.7 | |
| 100 | 79.2 | 109.2 | |
| None | 70 | 76.4 | 100.2 |
Figure 3 shows the operating voltage and specific energy consumption for the deposition in the OP-added bath at the operating temperature of 60–100 °C. The specific energy consumption was calculated from the product of the absolute value of the operating voltage with respect to the deposition amount, the applied current, and the deposition time. As the operating temperature increased, the operating voltage decreased, and the specific energy consumption decreased to 3790 kWh t−1 at 100 °C. The specific energy consumption at 70 °C, at which the current efficiency was 90 % or more, was 6299 kWh t−1, suggesting that Al could be sufficiently recovered at a temperature below 100 °C.
Temperature dependence of operating voltage (black open circle) and specific energy consumption (red open circle) of the AlCl3-EMIC melt with 20 mmol dm−3 of OP additive at 60–100 °C; current density: 100 mA cm−2, total charge for all deposits: 289.6 C cm−2.
Figure 4 shows the ULV-SEM images of the surface of the deposits obtained on the Cu plate substrate at the operating temperature of 70 °C. While grain-like crystallites were observed in the deposit obtained from the OP-free bath at the operating temperature of 70 °C (Fig. 4a), a uniform and smooth surface was observed in the deposits obtained from the OP-added bath (Fig. 4b). The addition of OP significantly reduced the grain size. As reported in previous studies,8,13 this is considered to be due to the suppression of the Al crystal growth by the adsorption of OP on the substrate, the same action as nicotinic acid and methyl nicotinic acid.14 However, when the operating temperature was increased to 90 °C, the surface became non-uniform and irregularities were observed, correlating with the results shown in Fig. 2 and Table 1 (Fig. 4c). This suggested that the effect of the OP addition on the suppression of the crystal growth would be temperature dependent.
ULV-SEM images of deposits obtained on the Cu plate substrate from (a) the OP-free bath at 70 °C, (b) the OP-added bath at 70 °C, and (c) at 90 °C; current density: 100 mA cm−2, total charge for both deposits: 289.6 C cm−2.
Figure 5 shows the cross-sectional ULV-SEM images of deposits obtained on the Cu plate substrate under the various deposition conditions. The film thickness was calculated from the maximum and minimum values of the film thickness at the center of the deposit’s surface. The film thicknesses of the deposits obtained from the OP-free bath (Fig. 5a) and the OP-added bath (Fig. 5b) at 70 °C were 11.1–40.7 µm and 55.6–58.8 µm, respectively. The thickness of the deposit obtained from the OP-added bath was thicker than that obtained from the OP-free bath, so that the smoothness of the deposit was improved. On the other hand, the film thickness of the deposit obtained from the OP-added bath at 90 °C ranged from 36.7–57.5 µm, indicating an increase in the surface roughness compared to that at 70 °C. This is consistent with the surface roughness of the deposit shown in Fig. 2c. In addition, the decrease in the film thickness and the smoothness with increasing the operating temperature would correlate with the decrease in the current efficiency shown in Table 1.
Cross-sectional ULV-SEM images of deposits obtained on the Cu plate substrate from (a) the OP-free bath at 70 °C, (b) the OP-added bath at 70 °C, and (c) at 90 °C; current density: 100 mA cm−2, total charge for all deposits: 289.6 C cm−2.
Table 2 shows the relation between the OP addition, the operating temperature, and the deposition rate calculated from the film thickness obtained from the cross-sectional ULV-SEM images. At the operating temperature of 70 °C, the deposition rates in the OP-free bath and the OP-added bath were 0.23–0.84 µm min−1 and 1.15–1.22 µm min−1, respectively. In contrast, the deposition rate decreased to 0.76–1.19 µm min−1 when the operating temperature was increased to 90 °C. This would be because the presence of OP does not affect the diffusion of Al2Cl7− ions during the current control.8 As shown in Table 1, in the OP-free bath and the OP-added bath at the operating temperature of 90 °C, the deposition is considered to have decreased due to the thinning of the film thickness caused by the detachment and dropout of the deposit.
| Additives | Operating temperature °C |
Thickness of deposit µm |
Deposition rate µm min−1 |
|---|---|---|---|
| OP | 70 | 51.3–57.9 | 1.06–1.20 |
| 90 | 36.7–57.5 | 0.76–1.19 | |
| None | 70 | 11.1–40.7 | 0.23–0.84 |
Figure 6 shows the AFM image and the Sa value of the deposit obtained on the Cu plate substrate from the OP-added bath at the operating temperature of 70 °C. The Sa value was 18 nm, which was smoother than that of a commercial Al foil (Sa = 105.8 nm)8 for the battery current collector. The authors reported that the Sa value of the deposit obtained on the Ti plate substrate from the OP-added bath was 45.8 nm at the operating temperature of 50 °C and the current density of 52.6 mA cm−2.8 This indicated that the effect of the OP addition was obtained even as the operating temperature increased and the current density increased. In general, whereas the grain size increased with increasing as the operating temperature,6 it was thus revealed that the OP addition provided the smoothness.
AFM image of deposit obtained on the Cu plate substrate from the OP-added bath at 70 °C; current density: 100 mA cm−2, total charge for deposit: 289.6 C cm−2.
Figure 7 shows the XRD patterns of the deposits obtained on the Cu plate substrate under various operating conditions. The XRD peaks were identified and indexed by comparison with the standards obtained from JCPDS cards (#04-0787) and (#04-0836). All the peaks were attributed to Al (fcc) and Cu (fcc), thus the single phase of Al was obtained. The 38.47° and 44.72° peaks were attributed to the (111) and (200) reflections, respectively. The peak intensity of the (200) reflection was stronger in the OP-added bath than in the OP-free bath. In the OP-added bath, the peak intensities of the (111) reflection at 38.47° and the (311) reflection at 78.23° were stronger at the operating temperature of 90–100 °C than at the bath temperatures of 60–80 °C. It is thus revealed that the addition of OP and the operating temperature would affect the texture of the resulting Al deposits.
XRD patterns of deposits obtained on the Cu plate substrate from the OP-added bath at (a) 60 °C, (b) 70 °C, (c) 80 °C, (d) 90 °C, (e) 100 °C, and (f) the OP-free bath at 70 °C; current density; 100 mA cm−2, total charge for all deposits: 289.6 C cm−2.
In order to now discuss the crystal orientation of the resulting Al deposit, the orientation coefficient was calculated using Wilson’s equation depicted by Eq. 2:
| \begin{equation} \textit{Orientation coefficient} = \frac{I\biggm/\displaystyle\sum I}{I_{\textit{JCPDS}}\biggm/\displaystyle\sum I_{\textit{JCPDS}}} \end{equation} | (2) |
where I is the peak intensity attributed to each reflection of the measured data and IJCPDS is the respective peak intensity listed on the JCPDS card. Figure 8 and Table S1 show the orientation coefficients of the Al deposits obtained on the Cu plate substrate under the various deposition conditions. An orientation coefficient of 1 or more means preferential orientation. The orientation coefficients of the Al deposits obtained from the OP-added bath at the operating temperatures of 60–80 °C were approximately 3.0 for the (200) plane, and where those for the (111), (220), and (311) planes were below,1 indicating the preferential orientation to the {100} plane. Although it cannot be assured that the preferential orientation to the {100} plane and the metallic luster surface were involved based on these calculations alone, the surface conditions exhibiting a metallic luster reported by Takahashi et al.13 and Wang et al.14 are similar to the present results. The mechanism of crystal growth is considered to be that OP would preferentially adsorb on the {111} plane, which has a high atomic concentration of atoms in the fcc structure, and suppresses the growth of the ⟨111⟩ direction, resulting in the preferential growth of the ⟨100⟩ direction, which has the next highest atomic concentration.13 Therefore, it is considered that there is a relation between the preferential orientation to the {100} plane and the formation of the metallic luster. In contrast, the orientation coefficients of the Al deposits obtained from the OP-free bath at the operating temperature of 70 °C were 1.479 for the (200) plane, 0.998 for the (111) plane, and 1 or less for the (110) and the (311) planes. Although the preferential orientation to the {100} plane was shown, the preferential orientation was weaker than that of the OP-added bath described above. Furthermore, the orientation coefficient of the Al deposit obtained from the OP-added bath at the operating temperature of 90 °C was almost the same as that of the Al deposit obtained from the OP-free bath at the operating temperature of 70 °C. These relations suggest that increasing the operating temperature to 90–100 °C would decrease the adsorption capacity of OP. Li et al. suggested that higher temperatures would cause a decrease in the adsorption of OP from the Al surface.15 Therefore, when the operating temperature was increased to 90 °C, the growth of the {100} plane of the Al deposit due to the adsorption of OP observed up to 70 °C would not preferentially progress.
Orientation coefficient of resulting Al films obtained on the Cu plate substrate from the OP-added bath at 60 °C (green closed circle), 70 °C (orange closed circle), 80 °C (red closed circle), 90 °C (blue closed circle), 100 °C (black closed circle), and the OP-free bath at 70 °C (black open triangle) calculated from Wilson’s equation; current density; 100 mA cm−2, total charge for all deposits: 289.6 C cm−2.
The Al electrodeposition was verified in the ionic liquid consisting of anhydrous aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium chloride (EMIC) with the addition 1,10-phenanthroline anhydride (OP) at the current density of 100 mA cm−2 and various operating temperatures with the following findings.
As already stated, the current efficiency, the specific energy consumption, the smoothness, and the preferential orientation of the resulting Al deposit obtained from the OP-added bath are temperature dependent and the operating temperature needs to be appropriately controlled in order to recover Al.
This article is based on results obtained from a project, JPNP14014, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).
The data that support the findings of this study are openly available under the terms of the designated Creative Commons License in J-STAGE Data at https://doi.org/10.50892/data.electrochemistry.26352880.
Koichi Ui: Conceptualization (Equal), Data curation (Lead), Funding acquisition (Lead), Investigation (Supporting), Methodology (Lead), Project administration (Lead), Resources (Lead), Supervision (Lead), Writing – original draft (Equal), Writing – review & editing (Lead)
Ryohei Hibino: Data curation (Supporting), Formal analysis (Lead), Investigation (Lead), Validation (Lead), Visualization (Lead), Writing – original draft (Equal), Writing – review & editing (Lead)
Kuniaki Sasaki: Investigation (Supporting), Resources (Supporting), Validation (Supporting)
Tatsuya Takeguchi: Funding acquisition (Supporting), Supervision (Supporting)
Tetsuya Tsuda: Conceptualization (Equal), Methodology (Supporting), Project administration (Supporting), Writing – review & editing (Supporting)
Mikito Ueda: Conceptualization (Equal), Methodology (Supporting), Project administration (Supporting), Writing – review & editing (Supporting)
Junji Nunomura: Conceptualization (Equal), Methodology (Supporting), Project administration (Supporting), Writing – original draft (Supporting), Writing – review & editing (Supporting)
Yoshihiko Kyo: Supervision (Supporting)
Yoichi Kojima: Supervision (Supporting)
The authors declare no conflict of interest in the manuscript.
New Energy and Industrial Technology Development Organization: JPNP14014
A part of this MS has been presented at the 2023 Joint Symposium on Molten Salts (MS12) (Poster Presentation P54) and the 91st ECSJ Annual Meeting (Oral Presentation S6_2_07).
K. Ui, T. Takeguchi, T. Tsuda, M. Ueda, J. Nunomura, Y. Kyo, and Y. Kojima: ECSJ Active Members
R. Hibino: ECSJ Student Member
