Origin of the Adsorption-Controlled Redox Behavior of Quinone-Based Molecules: Importance of the Micropore Width

Abstract

Redox-active organic materials have emerged as promising alternatives to inorganic electrode materials in electrochemical devices owing to advantages such as low cost and flexible design. However, the kinetics of their electrochemical reactions are typically slow due to the slow diffusion of organic materials dissolved in the electrolyte. Generally, peak separation of the redox reaction is observed (mass-transfer-controlled system), while no peak separation is obtained when the active molecules, such as high surface carbon material, are adsorbed onto the electrode material (adsorption-controlled system). Aromatic compounds confined in activated carbon (AC) micropores exhibit an adsorption-controlled reaction, improving the reaction kinetics. To elucidate this behavior, a well-defined and accurate understanding of the pore geometry is required. Although various synthetic techniques have been used to tune the micropore size, these afford different surface properties. This study reports an approach to achieve an adsorption-controlled redox reaction of quinone-based molecules and a tool to analyze their reaction environment. AC micropores sized <1 nm were filled with n-nonane without any change occurring in the AC surface properties. It was thus concluded that AC micropores in the sub-nanometer scale are necessary for an adsorption-controlled redox reaction to occur. This study reveals new insights on the micropore confinement effect in electrochemistry.

1. Introduction

Quinone and its derivatives are important redox-active organic materials that have been investigated as potential electrode materials for various energy storage applications, such as redox flow batteries^1,2 and electrochemical capacitors.^3,4 The electrochemical reactions of quinone-based molecules dissolved in the electrolyte are mass-transfer-controlled processes, resulting in the slow kinetics of electrochemical reactions because the rate-determining step is diffusion limited. If the reaction process is changed to an adsorption-controlled process (peak-potential separation (ΔE_p) = 0 mV), the charge transfer step becomes the rate-determining step of the redox reaction of quinone-based molecules, which is faster than the diffusion kinetics of the molecules; consequently, the overall reaction kinetics can be enhanced. Accordingly, various approaches have been proposed to adsorb quinone-based molecules on an electrode surface.^5–8

For example, the π–π stacking interaction between quinone-based aromatic compounds and carbon surfaces results in strong adsorption.^9,10 Strong electrostatic interactions between oxygen functional groups on a carbon surface and quinone-based aromatic compounds also enable strong adsorption.¹⁰ The covalent bonding between absorbates and the carbon surface can be monitored via chemical or electrochemical methods.^5–8 In most of these studies, a ΔE_p greater than 0 mV has been reported, indicating that the reaction was a mass-transfer-controlled process.

A novel approach of an adsorption-controlled process has recently been proposed by employing quinone-based aromatic compounds confined in the slit-shaped graphitic micropores of activated carbon (AC).¹¹ This effect was not only obtained from quinone-based aromatic compounds and other anthraquinone-based aromatic compounds. In addition, this depended on the concentration of quinone-based molecules; when the BQDS content is high (>1 mM), the reaction mechanism is dominated by a charge-transfer-controlled to a mass-transfer-controlled process.¹² The results revealed that the micropores played an essential role in achieving an adsorption-controlled process since this behavior has not been previously observed with carbon black (CB). This variation can be attributed to the physical properties of both the carbonaceous material and confined compound; the surface and intermolecular interactions can be remarkably enhanced by the spatial overlap of interactions based on the overlapping potentials of the opposite pore walls in micropores that are less than 1 nm in diameter.¹³ Consequently, the effect of the micropore width on the adsorption-controlled redox reactions of micropore-confined quinone-based molecules should be clarified to elucidate the physicochemical mechanism.

Many carbonaceous materials with fine-tuned micropores have been synthesized to date.¹⁴ For example, carbide-derived carbons have a narrow pore width distribution, which can be tuned with an accuracy of 0.05 nm,¹⁵ and ordered microporous carbon can be prepared using a zeolite template.¹⁶ The micropore width in these studies was tuned by varying the synthetic conditions such as the precursor, reaction temperature, time, and atmosphere. However, varying these conditions inevitably led to a simultaneous change in the degree of graphitization, surface local structure, and surface functional groups, which affected conductivity and wettability. As these properties directly affect the redox behavior of quinone-based molecules,^1,4,9,10,17 carbonaceous materials with the same physical properties but with different micropore widths are required to elucidate the effect of the width on the adsorption-controlled reaction of micropore-confined quinone-based molecules.

In this study, the effect of the micropore geometry of AC on the adsorption-controlled redox reaction using micropore-confined 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate (BQDS) in an aqueous electrolyte (the electrochemical reaction is shown in Fig. 1) was investigated. A straightforward micropore-filling approach was employed to prepare carbonaceous materials with and without micropores while retaining the surface properties. Researchers have reported the confinement of n-nonane (C₉H₂₀) in the micropores of AC.^18–20 The n-nonane molecule is hydrophobic and poorly soluble in water (0.2 µg mL⁻¹), and consequently, it is expected to suppress the desorption of the filled molecule into an aqueous electrolyte during electrochemical measurements. This phenomenon was employed to compare the redox behavior of BQDS using pristine AC and AC with n-nonane impregnated into its slit-shaped graphitic micropores.

Figure 1.

Electrochemical reaction of BQDS in H₂SO₄.

2. Experimental

2.1 Reagents

BQDS was purchased from Sigma-Aldrich and used as an electroactive material. Slit-shaped graphitic-micropore-rich AC (MSP-20; Kansai Coke and Chemicals Co.) and micropore-poor CB (Vulcan XC-72, Cabot Corp.) were used as the electrode materials for the flowable electrode. Because CB has been employed as the carbon material for flow-assisted energy storage devices,^21,22 it was selected as the control sample in this study. H₂SO₄ and n-nonane were purchased from FUJIFILM Wako Pure Chemicals. Milli-Q deionized water (>18.2 MΩ cm; Millipore) was used in all experiments. All materials were used as-received without further purification.

2.2 Preparation of n-nonane-adsorbed AC

n-nonane was confined in the slit-shaped graphitic micropores using a previously reported method.^18,19,23 First, AC was vacuum-dried at 473 K for 48 h to remove adsorbed water from the micropores. Then, 15 g of the AC was dispersed in 40 mL n-nonane. The suspension was subsequently evaporated at 303 K for 24 h to obtain n-nonane/AC powder with n-nonane confined in the slit-shaped graphitic micropores of the AC.

2.3 Structural and compositional analysis

The morphology of AC and n-nonane/AC was characterized by transmission electron microscopy (TEM, JEM-1011KMII, 80 kV accelerating voltage, JEOL). Adsorption and desorption isotherms were obtained using a volumetric apparatus (Autosorb-1, Quantachrome) with liquid N₂ gas as the adsorbate at 77 K. Prior to the measurements, adsorbed water was carefully removed by vacuum drying at 423 K for 2 h. In case of n-nonane/AC, to suppress the desorption of n-nonane from AC surface, adsorbed water was removed by vacuum drying at 373 K for 2 h. The Brunauer–Emmett–Teller (BET) equation was used to calculate the surface area (S_BET) in the p/p₀ range of 0.01–0.05 to prevent overestimation.^24,25 Non-local density functional theory (NLDFT) calculations were used to determine the specific surface area (S_DFT) and pore width distributions. Thermogravimetric analysis (TGA, Thermo plus EVO2, Shimadzu) was conducted under N₂ flow (5 K min⁻¹). The microstructure of AC and n-nonane/AC was characterized by Raman spectroscopy (Hololab 5000, Kaiser Optical Systems, Inc.) using a YAG laser (Raman excitation wavelength = 532 nm) as the excitation source. X-ray photoelectron spectrometry (XPS, 15 kV and 10 mA, MgKα standard; AXIS-ULTRA DLD, Kratos Analytical Ltd.) was conducted to analyze the chemical states and surface functional groups of AC and n-nonane/AC. All binding energies were calibrated by referencing to Au (4f_7/2). The amount of adsorbed BQDS on AC and n-nonane/AC was established by ultraviolet-visible spectroscopy (UV-vis, V-530, 190–600 nm, 400 nm min⁻¹, JASCO Corporation). AC or n-nonane/AC powder (50 mg) was dispersed in 1 mM BQDS + 0.5 M H₂SO₄ (25 mL), stirred for 15 min at 500 rpm, and ultrasonicated for 30 min. The suspension was then centrifuged at 20,000 rpm for 30 min, and the supernatant was analyzed by UV-vis spectroscopy (quartz cell, 1 cm × 1 cm).

2.4 Electrochemical measurement of flowable electrodes

A flowable electrode was prepared by simply dispersing AC or n-nonane/AC in 1 mM BQDS + 0.5 M H₂SO₄ (1.6 mg mL⁻¹, Fig. 2). Electrochemical measurements of the flowable electrodes were conducted using a rotating disk electrode (SC-5, Nikko Keisoku) connected to an automatic polarization system (HZ-7000, Hokuto Denko). A mirror-polished glassy carbon rod (diameter, 6 mm) was used as the working electrode (current collector), a Pt mesh as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. Before the electrochemical measurements, break-in potential cycling between 0 and 1200 mV vs. RHE was conducted using a de-aerated flowable electrode (298 K) at a scan rate of 200 mV s⁻¹ for 100 cycles while rotating the working electrode (1600 rpm). The redox behavior of the flowable electrode was investigated by potential cycling at scan rates of 500–2 mV s⁻¹. Before cyclic voltammetry, the working electrode dispersion was stirred at 2500 rpm for 2 min, and the measurement was commenced after 1 min to obtain reproducible data.

Figure 2.

Rotating disk electrode setup and preparation of the flowable electrode.

3. Results and Discussion

3.1 Characterization of n-nonane/AC

As shown in Figs. 3a and 3b, the morphology of AC did not change after adsorption of n-nonane. The adsorption of n-nonane was characterized using N₂ adsorption–desorption isotherms. The values were calculated using the weight of AC or n-nonane/AC. The amount of adsorbed N₂ decreased after confining n-nonane in AC (Fig. 3c); the specific surface area of n-nonane/AC was 39 m² g⁻¹ (Table 1), which was considerably lower than that of AC (1812 m² g⁻¹). Furthermore, the cumulative pore volume of n-nonane/AC was significantly lower than that of AC (Table 1 and Fig. 3d). Notably, the cumulative pore volume of pores with widths of less than 1 nm in n-nonane/AC was negligible. The amount of n-nonane on AC was characterized by TGA (Fig. 3e), and the n-nonane loading in n-nonane/AC was found to be 21.1 mass%. Considering the density of n-nonane (1.39 cm³ g⁻¹), the volume occupied by n-nonane can be calculated to be 0.371 cm³ g_AC⁻¹. Given that the volume of a micropore less than 1 nm is approximately 0.3 cm³ g⁻¹,²⁶ the micropore is fully occupied by n-nonane, indicating dense packing in the micropores (<1 nm) of AC. The average micropore width increased from 0.86 nm for AC to 1.77 nm for n-nonane/AC due to the loss of micropores (with widths of less than 1 nm) in n-nonane/AC. These results clearly indicate successful micropore-filling with n-nonane.

Figure 3.

Typical TEM images of (a) AC and (b) n-nonane/AC. (c) N₂ adsorption–desorption isotherms at 77 K of AC (red) and n-nonane/AC (blue). Closed circles and open squares represent adsorption and desorption, respectively. The scales of the left and right axes were changed to render the graphs easier to read. (d) Pore width distribution profiles of AC (red) and n-nonane/AC (blue) derived using NLDFT. The scales of the left and right axes were changed to render the graphs easier to read. (e) Thermogravimetry profiles of AC (red) and n-nonane/AC (blue) under N₂ flow.

Table 1. Specific surface area (S_BET and S_DFT), total pore volume (V_total), mesopore volume (V_meso), micropore volume (V_micro), and average micropore width of AC and n-nonane/AC.

Sample	S/m2 g−1		V/cm3 g−1			w/nm
	BETa	DFTb	Totalc	Mesod	Microe	Avg.f	Avg.g
AC	2223	1812	0.97	0.11	0.86	0.79	0.86
n-nonane/AC	78	39	0.05	0.01	0.04	—	1.77

^aSpecific surface area calculated using the Brunauer–Emmett–Teller (BET) equation.

^bSpecific surface area calculated using NLDFT.

^cTotal pore volume estimated from amount adsorbed at p/p₀ = 0.96.

^dMesopore volume calculated as V_total − V_micro.

^eMicropore volume calculated using the NLDFT method.

^fAverage micropore width obtained from the α_s-plots.

^gAverage micropore width obtained using the NLDFT method.

The microstructures of AC and n-nonane/AC were characterized by Raman spectroscopy (Fig. 4a). For both samples, two peaks assigned to the D- and G-bands were observed at approximately 1330 and 1590 cm⁻¹, respectively. The existence of the D- and G-bands in the spectra indicated the presence of defects in the sp² carbon network and graphitic structure, respectively.^27,28 No differences in the peak positions, D- and G-band intensity ratio (I_D/I_G), and area ratio (S_D/S_G) were observed after the adsorption of n-nonane molecules (Table 2). The C 1s XPS spectra were deconvoluted into C–C (284.2 eV), C–O (286.1 eV), and C=O (287.1 eV),²⁹ as shown in Figs. 4b and 4c. The area ratios of these peaks were similar for AC and n-nonane/AC. These results confirmed that the crystallinity and graphene domain of AC, as well as the chemical states and surface functional groups of carbon, did not change with the adsorption of n-nonane.

Figure 4.

(a) Raman spectra of AC (red) and n-nonane/AC (blue). The C 1s XPS spectra of (b) AC and (c) n-nonane/AC.

Table 2. Microstructural properties of AC and n-nonane/AC characterized by Raman spectroscopy.

Samples	Raman shift of peak G (cm−1)	Raman shift of peak D (cm−1)	ID/IGa	SD/SGb
AC	1589	1334	1.3	2.5
n-nonane/AC	1594	1336	1.1	2.4

^aThe peak intensity ratio of the D- and G-bands (I_D/I_G).

^bThe area ratio of the D- and G-bands (S_D/S_G).

To investigate the effect of the pore width of AC on the redox reaction of BQDS, the confined n-nonane must be stable with respect to electrochemical reactions such as dissolution and oxidation. Therefore, the stability of confined n-nonane was investigated using Nafion-coated electrodes (Fig. S1). The specific capacitance of AC was 168 F g⁻¹ while that of n-nonane/AC was 96 F g⁻¹, which corresponds to a loss of 43 %. The N₂ adsorption–desorption isotherms revealed that this loss can be attributed to the confinement of n-nonane which prevented the formation of an electrical double layer on the slit-shaped graphitic micropores with a width less than 1 nm. The specific surface area and specific capacitance of n-nonane/AC decreased by 98 % and 43 %, respectively. This large difference suggests that n-nonane desorbed during the preparation of the Nafion-coated electrode. In this study, n-nonane/AC was fixed onto glassy carbon using a Nafion ionomer diluted by methanol (80 wt% methanol, Table S1). Owing to its solubility in methanol (129 g/L at 25 °C³⁰), n-nonane can desorb from the AC surface, resulting in the difference between the observed specific capacitance and specific surface area losses. After 500 potential cycles, both samples retained their original specific capacitances. This clearly indicates that the confined n-nonane did not dissolve in the electrolyte during electrochemical measurements, which might be attributable to the low solubility of n-nonane in water (0.2 µg mL⁻¹).

3.2 Redox behavior of BQDS on AC and n-nonane/AC

The redox reactions of carbon dispersed in 1 mM BQDS + 0.5 M H₂SO₄ were characterized using a flowable electrode cell configuration (Fig. 2). To investigate the effect of micropores, CB was selected as the control. Redox peaks assigned to the oxidation and reduction reactions of BQDS were observed in the cyclic voltammogram (Fig. 5a, no iR correction); a non-zero peak separation (ΔE_p ≈ 30 mV) of CB dispersed in 1 mM BQDS + 0.5 M H₂SO₄ was observed. The anodic peak current density (j_pa) was proportional to the square root of the scan rate (v^0.5) (Fig. 5b) and not the scan rate (v) (Fig. 5c), indicating that the reaction was a mass-transfer-controlled process. The behavior of CB differed from that observed for the AC flowable electrode (Figs. 5d–5f). The ΔE_p of AC dispersed in 1 mM BQDS + 0.5 M H₂SO₄ was 0 mV (Fig. 5d). As j_pa is proportional to v and not v^0.5, the reaction system can be categorized as an adsorption-controlled process (Figs. 5e and 5f). In contrast, a ΔE_p of 30 mV was observed for n-nonane/AC dispersed in 1 mM BQDS + 0.5 M H₂SO₄ (Fig. 5g), and its j_pa was proportional to v^0.5, indicating a mass-transfer-controlled process (Figs. 5h and 5i).

Figure 5.

Electrochemical responses of (a–c) CB, (d–f) AC, and (g–i) n-nonane/AC flowable electrodes. (a, d, g) Cyclic voltammograms in 1 mM BQDS + 0.5 M H₂SO₄ (298 K) at a scan rate of 5 mV s⁻¹. (b, e, h) Changes in the anodic and cathodic peak current densities as a function of the scan rate. (c, f, i) Changes in the anodic and cathodic peak current densities as a function of the square root of the scan rate.

The electrical double-layer capacitance of the n-nonane/AC flowable electrode (Fig. 5g) was much smaller than that of the AC flowable electrode (Fig. 5d). The retention rate in the electrical double-layer capacitance of the flowable AC electrode was approximately 5 %, which is similar to the loss in the specific surface area (8 %). An alcohol solution was not used in the preparation of the flowable electrode, clearly indicating that the difference between the specific surface area and specific capacitance of n-nonane/AC can be attributed to the use of an alcohol solution in the preparation of the Nafion-coated electrode.

The mass-transfer-controlled process of CB and n-nonane/AC dispersed in 1 mM BQDS + 0.5 M H₂SO₄ were analyzed using log(i_p) vs. log(v) plots (Fig. 6). The currents associated with the mass-transfer- and adsorption-controlled processes were separated based on the b-value analysis.³¹   

\begin{equation} j_{p} = av^{b} \end{equation} (1)

Here, j_p is the measured current and v is the scan rate. Both a and b are adjustable parameters. The b value can be determined from the slope of the log(i_p) vs. log(v) plots; b values of 0.5 and 1.0 indicate mass transfer- and adsorption-controlled processes, respectively. Both CB and n-nonane/AC had a b value of 0.57, indicating a mass-transfer-controlled process. This result was in good agreement with the results from the j_pa vs. v^0.5 plots (Figs. 5b and 5h). As reported previously, a mass-transfer-controlled process indicates that the presence of the dissolved BQDS in the electrolyte.¹² The b value of AC was 0.98, indicating that the electrochemical reaction was an adsorption-controlled process. The amount of BQDS adsorbed on n-nonane/AC (<0.1 mg/g) was much lower than that on AC (166 mg/g), which was attributed to the filling of micropores by n-nonane (Figs. 3c–3e). The redox current of BQDS was observed for the CB and n-nonane/AC flowable electrodes despite the small amount of adsorbed BQDS (Figs. 5a and 5g). This was attributed to the dissolved BQDS in the flowable electrodes. It has been demonstrated that the adsorption site of BQDS on pristine AC was a slit-shaped graphitic-micropore with a width less than 1 nm.¹¹ This result indicated that slit-shaped graphitic micropores with widths less than 1 nm are required to confine BQDS and facilitate an adsorption-controlled process. The adsorption mechanism has not yet been elucidated and is a goal for future work.

Figure 6.

b values (slopes) obtained from the current peaks (j_p = av^b) of the cyclic voltammograms of CB (black circles), AC (red squares), and n-nonane/AC (blue triangles) flowable electrodes.

3.3 Origin of the adsorption-controlled process of confined molecules

Figure 7 shows a schematic of the adsorption- and mass-transfer-controlled reactions. Labels (i) and (ii) indicate the regions with micropores with widths less than 1 nm and greater than 1 nm, respectively. Because the micropores in n-nonane/AC were filled with n-nonane (region (i) in Fig. 7a), BQDS was not adsorbed in micropores of less than 1 nm. In contrast, in the absence of n-nonane (pristine AC, region (i) in Fig. 7b), BQDS was confined in the micropores of the AC. In the case of n-nonane/AC dispersed in 1 mM BQD + 0.5 M H₂SO₄, a mass-transfer-controlled process was observed (Figs. 5g–5i) because BQDS could not penetrate the pores with widths less than 1 nm (Fig. 7a). In contrast, AC dispersed in 1 mM BQDS + 0.5 M H₂SO₄ exhibited an adsorption-controlled process (Figs. 5d–5f) because BQDS was confined in the slit-shaped graphitic wall (Fig. 7b).

Figure 7.

Schematics of the (a) n-nonane/AC and (b) AC flowable electrodes. The adsorption-controlled process of redox reaction for BQDS was attributed to the presence of micropores with widths less than 1 nm.

The confined BQDS was densely packed in the micropores, resulting in the strong adsorption of oxidized and reduced molecules on the carbon surface.¹¹ It has been established that the surface and intermolecular interactions can be remarkably enhanced by the spatial overlap of interactions based on the overlapping potentials of the opposite pore walls in micropores that are less than 1 nm in diameter.¹³ For example, when CCl₄, C₂H₅OH, and carbonate molecules are confined in slit-shaped graphitic wall, the assembly structure of molecules depend on the size of the micropores.^32–34 Based on the electronic radial distribution function and reverse Monte Carlo analysis,^32–34 Kaneko et al. found that the anomalous assembly structure of molecules confined in micropores could be attributed to a unique interaction potential profile of slit-shaped graphitic walls less than 1 nm. Therefore, because ΔE_p was zero when the concentrations of the oxidized and reduced molecules were equal, we demonstrated that micropores with widths less than 1 nm are effective for the adsorption-controlled redox reaction of quinone-based molecules by confinement effects. Because micropore-confined BQDS molecules are densely packed between the pore walls, they become strongly adsorbed despite the absence of a covalent bond. Thus, micropore-confined aromatic compounds behave as adsorbed species in an adsorption-based system.

Our analysis only describes the effect of micropores less than 1 nm in diameter of AC; however, typical carbonaceous materials have wide pore distributions. Furthermore, if carbon with different pore diameters is fabricated, surface properties and chemical states often change as well. In the future, the development of carbonaceous materials with uniform pore sizes without changing their surface properties will allow for a detailed investigation of the pore size that causes the confinement effect.

4. Conclusions

This study revealed that quinone-based molecules can undergo adsorption-controlled redox reactions by utilizing AC with slit-shaped graphitic micropores with widths less than 1 nm. The N₂ adsorption–desorption isotherms and Raman and XPS spectra revealed that the confinement of n-nonane in the micropores did not cause any changes in the surface properties of AC. For BQDS, ΔE_p was 0 mV with the AC flowable electrode (adsorption-controlled process) and 30 mV with the n-nonane/AC flowable electrode (mass-transfer-controlled process). These results indicated that the adsorption-controlled process of the redox reaction for BQDS could be achieved using slit-shaped graphitic micropores with widths less than 1 nm in AC. This study provides new insights for obtaining an adsorption-controlled process of redox reactions of quinone-based molecules.

Acknowledgments

This work was partially supported by the Electrotechnology of Chubu (R–02124), the Kondo Memorial Foundation (2020-01), and the Tokyo Ohka Foundation for The Promotion of Science and Technology.

Data Availability Statement

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.23355236.

• 1) Redox-active organic materials have emerged as promising alternatives to inorganic electrode materials in electrochemical devices owing to advantages such as low cost and flexible design. However, the kinetics of their electrochemical reactions are typically slow due to the slow diffusion of organic materials dissolved in the electrolyte. Generally, peak separation of the redox reaction is observed (mass-transfer-controlled system), while no peak separation is obtained when the active molecules, such as high surface carbon material, are adsorbed onto the electrode material (adsorption-controlled system). Aromatic compounds confined in activated carbon (AC) micropores exhibit an adsorption-controlled reaction, improving the reaction kinetics. To elucidate this behavior, a well-defined and accurate understanding of the pore geometry is required. Although various synthetic techniques have been used to tune the micropore size, these afford different surface properties. This study reports an approach to achieve an adsorption-controlled redox reaction of quinone-based molecules and a tool to analyze their reaction environment. AC micropores sized <1 nm were filled with n-nonane without any change occurring in the AC surface properties. It was thus concluded that AC micropores in the sub-nanometer scale are necessary for an adsorption-controlled redox reaction to occur. This study reveals new insights on the micropore confinement effect in electrochemistry.

CRediT Authorship Contribution Statement

Daisuke Takimoto: Conceptualization (Lead), Funding acquisition (Lead), Investigation (Lead), Writing – original draft (Lead), Writing – review & editing (Lead)

Keisuke Suzuki: Conceptualization (Lead), Data curation (Lead), Investigation (Lead), Writing – original draft (Lead), Writing – review & editing (Lead)

Sho Hideshima: Investigation (Supporting), Validation (Supporting), Writing – review & editing (Equal)

Wataru Sugimoto: Investigation (Supporting), Validation (Supporting), Writing – review & editing (Equal)

Conflict of Interest

The authors declare no conflict of interest in the manuscript.

Funding

Research Foundation for the Electrotechnology of Chubu

Kondo Memorial Foundation

Tokyo Ohka Foundation for The Promotion of Science and Technology

Footnotes

A part of this paper has been presented in the 2021 ECSJ fall Meeting (Presentation #1J03).

D. Takimoto: Present address: Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, 1-Senbaru, Nishihara, Nakagami, Okinawa 903-0213, Japan

S. Hideshima: Present address: Department of Applied Chemistry, Faculty of Science and Engineering, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya, Tokyo 158-8557, Japan

D. Takimoto and S. Hideshima: ECSJ Active Members

W. Sugimoto: ECSJ Fellow

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