Synthesis of MnS/MnO Decorated N, S‐Doped Carbon Derived from a Mn(II)‐Coordinated Polymer for the Catalytic Oxidation of H2O2 and Bisphenol A

A way to synthesize a Mn2+‐ coordinated polymer precursor ligated by sulfur atoms with acetate counter ions (Mn‐DTOGA) is proposed, which is achieved by an imine formation reaction between dithiooxamide and glutaraldehyde in the presence of manganese (II) acetate. MnS/MnO decorated N, S‐doped carbon nanoparticles (MnS/O‐SNC) are then prepared by calcination of the Mn ion‐coordinated polymer for the practical applications of catalytic reactions. The Mn‐DTOGA and MnS/O‐SNC structures prepared at different temperatures (700, 800, and 900 °C) are characterized using various physical and electrochemical and chemical analyses. The nanoparticles prepared at 900 °C reveal the best performance for the catalytic oxidation of Hydrogen peroxide (H2O2) and bisphenol A. The decomposition potentials of H2O2 (1.0 mm) and bisphenol A (100.0 µm) on the catalyst modified electrode are observed to be +0.40 and +0.15 V (versus Ag/AgCl), respectively. It is observed that the catalytic performances to the oxidation reactions are mainly related to MnO decorated outside the SNC particles compared to MnS formed inside the particles. The electrode reveals a wide dynamic range with the low detection limits for H2O2 (0.08 (±0.02) µm) and bisphenol A (0.17 (±0.04) µm). This study will provide essential clues for the future catalyst design.

In particular, the catalytic oxidative decomposition reactions of hydrogen peroxide (H 2 O 2 ) and phenolic compounds are crucial in biological systems and industrial applications. [11,12] Of these, hydrogen peroxide is well known as a reactive oxygen species produced by various enzyme reactions, and it plays important roles in oxidative biosynthetic reactions and functions as a signaling agent. However, it is a fatal species in body systems and high concentrations of H 2 O 2 in living systems are harmful to cells, and excessive intake can lead to cell death. [13,14] Additionally, there are many industrial applications, such as a bleaching agent, antiseptic, etc. Therefore, it is significant to develop a new oxidative catalyst to decompose H 2 O 2 for living systems such as enzyme catalase and/or for industrial applications, not only as an oxidant but also for practical O 2 production. In addition to H 2 O 2 , phenolic compounds are also important chemicals in biological and industrial systems. Among them, bisphenol A (BPA) is a well-known endocrine disrupter, because it is structurally similar to natural hormones. [15] A low amount of BPA, even at sub-ng levels, can affect human health. Hence, it is important to study selective and active catalysts for the BPA oxidation reaction applicable to degradation and detection reactions. BPA is electrochemically active; however, continuous electrochemical oxidation of BPA shows low performance due to electrode surface poisoning. To improve the catalytic performance, new catalysts with exceptional catalytic activity are still demanded. Recently, various nanoparticles have been reported as catalysts for the oxidative decomposition of H 2 O 2 and bisphenol A, which are mostly metal, [16] metal sulfide, [17] metal oxide, [18,19] and metal complex. [9] Even though these catalysts show good performance for some catalytic reactions, they should still be further enhanced.

Introduction
Catalysis is one of the important processes in science and industry, extending across various fields. Since a catalytic phenomenon was first reported by J. J. Bercellus in 1835, it has been used to achieve faster chemical reactions in the pres-In this regard, many attempts have been made to achieve the enhanced catalytic properties by changing the shape, size, and composition of materials decorated on catalytic solid supports. The solid support method has been widely employed due to their attractive features including availability, enhanced metal nanoparticles stabilization properties and resistance to particle sintering/agglomeration. Among the wide range of solid supports employed for the deposition of nanoparticles, carbonaceous materials, metal oxides, and polymers are main of various solid supports. [20] Of these, carbonaceous materials support decorated with metal or metal oxide represents one of the most interesting catalyst preparation processes. [21,22] To synthesize the carbon-support catalysts, the preparation of 3D porous coordination polymers as a carbon precursor lends many advantages, such as rich active sites, high porosity, etc., and this has led to a new class of catalytic electrode materials for various applications involving carbon [23] and hybrid materials. [24,25] Thus, we tried to design a new synthesis way of a coordination polymer precursor containing N, S, and O atoms, which can be used as an artificial enzyme or a mild catalyst to generate oxygen without explosive liberation of H 2 O 2 . In addition, we also tried to preliminarily demonstrate the catalytic oxidation of phenolic compounds with the proposed catalytic nanoparticles.
In the present work, we synthesized for the first time a new kind of coordination polymer precursor of Mn ligated by S atoms of dithiooxamide (DTO) with acetate count ions, and the polymeric structure was formed through the imine bond formation by glutaraldehyde (GA). The polymer was calcinated to prepare the S, N doped-carbon nanoparticles decorated with MnO and MnS nanoparticles (MnS/O-SNC). The physical and chemical properties of the Mn-DTOGA precursor and MnS/O-SNC were obtained using SEM, XPS, FT-IR, and elemental analyses. MnS/O-SNC nanoparticles were characterized using surface analyses including TEM, XPS, XRD, and electrochemical analyses. The oxidation of H 2 O 2 and bisphenol A were respectively demonstrated by several electrochemical methods including CV, CA, and EIS. In addition, the prepared materials were applied as sensing probe materials for the detection of trace H 2 O 2 and bisphenol A through the catalytic oxidation reaction.

Results and Discussion
MnO/MnS decorated S, N doped-carbon nanoparticles (MnS/O-SNC) were prepared through the pyrolysis of a Mn-coordinated polymer precursor (Mn-DTOGA), as shown in Scheme 1. The precursor polymer of Mn-DTOGA was synthesized by a condensation reaction between two ligands of dithiooxamide (DTO) and glutaraldehyde (GA) through imine bond formation in the presence of manganese(II) acetate (Mn(OAc) 2 ) under weak acid conditions, resulting in polymerization of the Mn-DTOGA complex having acetate counter ions of Mn 2+ ions. The final product of coordinated polymer was orange-colored nanoparticles after reflux of the reaction mixture for ≈12 h, which were washed with water and ethanol and then recovered by centrifugation. Prior to the heat treatment of the coordination polymer to prepare the final catalytic particles, it was characterized by various analytical methods to obtain information on the morphology, structure, and chemical composition.

Characterization of Mn-Coordinated Polymer Precursor
First, to confirm the morphology of the synthesized coordination polymer (Mn-DTOGA) particles, the FE-SEM images of particles were obtained in different magnifications (Figure 1a). The images reveal that the particles have a homogeneous sphere shape having a diameter in the range between 351 and 650 nm, and the average size is estimated to be ≈500 nm (Figure 1b). To confirm the elemental composition of Mn-DTOGA, an Energy-dispersive X-ray spectrosocopy (EDAX) of SEM analysis was performed, and the synthesized polymer particles were placed on a Cu disk to determine the precise carbon content. The EDAX spectrum revealed that the contents of C, N, O, S, and Mn were 67.73%, 9.29%, 9.41%, 9.98%, and 3.59%, respectively, as shown in Figure 1c. Eventually, the chemical structure of Mn-DTOGA is established based on a chemical analysis using Fourier-transform infrared spectroscopy (FT-IR), EDAX, and X-ray photoelectron spectroscopy (XPS), and the energy simulation program of ChemDraw, which displays the determined chemical structure, as presented in the inset of Figure 1a. The Matrix-assist laser desorption/ionization-time of flight (MALDI-TOF) mass analysis confirmed that the molecular weight of a unit for coordination polymer structure was calculated 569.64 and found 569.01. In this case, Mn 2+ ions were coordinated by sulfur atoms and the counter ions of acetic acid, and a condensation reaction through the formation of an imine bond between NC in DTO and CO in GA contributed to the construction of the polymer structured nanoparticles in a smooth, round shape.
The bond formation of Mn-DTOGA was confirmed by FT-IR spectroscopy, as shown in Figure S1 (Supporting Information). The ligand, DTO, displays a bending band of δ(-NH 2 ) (1568 cm −1 ), deformation vibration bands of NH 2 (1196, 1031, and 716 cm −1 ), and a stretching band of CS (837 cm −1 ). When DTO and glutaraldehyde (GA) in the absence of Mn ions react to form a DTOGA polymer structure, the amine bands of DTO disappear to create a new imine band (1639 cm −1 ) and a strong NCS band (2055 cm −1 ) with a weak CS band (864 cm −1 ). In this structure, there is no remaining aldehyde band from the glutaraldehyde at 1720 cm −1 for (CO), and 2725 and 2825 cm −1 for Fermi resonance of the aldehyde group. [26] Otherwise, the spectrum of Mn-DTOGA shows an imine peak at 1639 cm −1 , a weak NCS band (2055 cm −1 ), and a strong CS at 803 cm −1 due to the coordination bond formation between S and Mn atoms. Additionally, we confirmed the presence of acetate groups by the observation of a new band formed at CC (1445 cm −1 ) and CH 3 (1378 cm −1 ), even though a COOH band (≈1760 cm −1 ) overlapped a broad imine band. In addition, the XRD and Thermogravimetric analysis (TGA) were also performed for MnDTOGA polymer; however, the XRD pattern does not show any peaks due to its amorphous structure ( Figure S2, Supporting Information). In the TGA curve, the complex reveals three steps of weight loss, where the first stage shows the weight loss of 8.5% in the temperature range of 30-200 °C and the second step of weight loss is rapidly decreased to ≈40.0% between 200 and 440 °C. After 440 °C, the weight is slowly decreased until 900 °C.
The XPS analysis was performed to further confirm the bond formation in both the DTOGA and Mn-DTOGA polymer structures ( Figure S3, Supporting Information), where the peak positions in the spectra were calibrated with the binding energy of the internal standard (C1s = 284.6 eV). The survey spectra for i) DTOGA and ii) Mn-DTOGA revealed C, N, and S peaks originating from DTO and GA ( Figure S3a  Meanwhile, Mn-DTOGA shows slightly shifted CSC S2p 1/2 (163.47 eV) and CSC S2p 3/2 (164.31 eV) peaks as well as MnS S2p 1/2 (161.23 eV) and MnS S2p 3/2 (162.72 eV) peaks. The MnS and shifted CSC peaks indicate that the Mn +2 ions are coordinated via the S atom in the coordination polymer. In addition, the deconvoluted spectra of Mn2p reveal that Mn 2+ predominated in the Mn-DTOGA. The FT-IR and XPS results clearly suggest the complex formation of Mn-DTOGA.

Preparation and Characterization of MnS/O-N, S-Doped Carbon
By heat treatment of the Mn-DTOGA precursor, MnS and MnO decorated N, S-doped carbon (MnS/O-SNC) particles were prepared at different temperatures (700, 800, and 900 °C), which were obtained in a spherical shape with particle size of  shows that the lattice spacing is 0.264 nm, corresponding to the (002) crystal planes of the MnS phase. [27] This result is consistent with the SAED patterns. In addition, the XRD pattern does not show the presence of MnO, due to MnO forming an amorphous structure on the carbon. Thus, we performed a soft X-ray analysis using PAL-XREL soft X-ray beamline to demonstrate the presence of MnO nanoparticles decorated on SNC ( Figure S7, Supporting Information). The MnO/S-SNC particles obtained at 700, 800, and 900 °C were further analyzed using X-ray absorption spectroscopy at an energy range from 636 to 658 eV of Mn L 2,3 -edges, as shown in Figure S6   in a previous report, [28] which is also consistent with the afore-  Figure 4a shows a pair of quasi-reversible peaks at the bare SPCE in the K 3 [Fe(CN) 6 ] solution, while DTOGA and Mn-DTOGA show rather irreversible peaks relative to that of bare SPCE with similar response currents. This indicates that the electron transfer at the electrode interface is disturbed by the movement of negatively charged ([Fe(CN) 6 ] 3− ) ions at the negatively charged Mn-DTOGA surface and at the low conductivity of neutral DTOGA. The negatively charged surface of Mn-DTOGA resulted in acetate groups (CH 3 COO − ) composing as counter ions in the Mn-DTOGA complex structure. Otherwise, SNC reveals better reversible redox peaks than the complex precursors, because high pyrolysis temperature elevates the degree of graphitization of neutral carbon material, giving rise to high conductivity. [29,30] Meanwhile, MnS/O-SNC nanoparticles (700, 800, and 900 °C) show less current than SNC, but reversible redox peaks of [Fe(CN)6] 3− . This means that MnS/O decorated SNC is slightly negatively charged and/or less conductive than the SNC nanoparticles due to the presence of manganese oxide on the carbon particles.
When CVs were recorded for DTOGA in [Ru(NH 3 ) 6 ] Cl 3 solution (Figure 4b), irreversible peaks with a decreased current are also observed compared with a bare SPCE, due to the low conductivity of DTOGA. However, Mn-DTOGA shows more reversible redox peaks than DTOGA. It can be explained by electrostatic interaction between the acetate counter ions of Mn-DTOGA and the positively charged [Ru(NH 3    The preliminary experiments revealed that the prepared nano particles catalyze the oxidation reactions of H 2 O 2 and some organic compounds including phenol compounds. Hence, we demonstrated the decomposition and detection of H 2 O 2 along with bisphenol A detection as catalyst applications. To examine the electrochemical and electrical characteristics, LSV and impedance spectroscopy were performed for all the prepared materials. First, the H 2 O 2 and bisphenol A catalytic oxidation reactions were carried out, as shown in  Figure 5a demonstrates the Mn effect of prepared materials on the catalytic anodic current of H 2 O 2 . As shown in the figure, the carbon particles including MnS/O reveal the catalytic reactivity to hydrogen peroxide oxidation at ≈0.7 V, while SNC and MnDTOGA particles without MnS/O SNC do not show clear catalytic reactivity. To elucidate the active surface area of catalyst, the electrochemical surface area (ECSA = C DL /C s ) was determined with the double layer capacitance ( Figure S8, Supporting Information), [31][32][33] where C DL is double layer capacitance, C s is the specific capacitance of the sample. For our estimates of surface area, a general specific capacitance of C s = 0.029 mF cm In addition, SNC showed the second highest anodic current, and the Mn-DTOGA showed a phenol oxidation peak at 0.45 V. SNC catalysts with a high conductivity also showed a large catalytic current of phenols oxidation. Similarly, it was reported that Mn species functioned as a catalyst for phenol decomposition. [34] In the present study, MnS/O-SNC 900 also shows good catalytic performance to phenol due to the synergistic effect of carbon with excellent conductivity and Mn species. Hence, we run the experiment for phenol and biphenol A oxidation reactions using the MnS/O-SNC 900 electrode in the PBS solution. The oxidation potential of biphenol and phenol was observed at ≈0.15 and 0.45 V, respectively ( Figure S9, Supporting Information). This indicates that MnS and MnO doped carbon nanoparticles can be used as co-catalysts to enhance the efficiency for H 2 O 2 and phenol decomposition, resulting in a decrease of the required dosage for the catalytic oxidation of  2 O 2 and phenolic compounds. This work can drive advances in the oxidation processes of specific chemicals for large-scale practical applications, such as environmental remediation. [35] To provide further understanding for H 2 O 2 oxidation with the prepared catalysts, LSV was recorded and Tafel slope analysis was conducted, as presented in Figure 6.    (Figure 7d). In Figure 7e, the Mn2p spectrum is deconvoluted into Mn 2+ , Mn 3+ or Mn 4+ , and satellite peaks, which correspond to MnS (642.2 eV) and MnO (641.02 eV) bonds, respectively. After oxidation, the intensity of the MnO peak was reduced in O1s spectra. In addition, the intensity of the peaks of S2p 3/2 (MnS and CSC) decreased. Interestingly, the peak intensity of manganese oxide at 641.02 eV, as shown in Mn2s spectra (Figure 2e), decreased after the oxidation reaction compared to the spectrum obtained before oxidation. Otherwise, the amount of manganese sulfide relatively increased after the oxidation. This result indicates that manganese oxide is mainly distributed outside the SNC particles and is mainly involved in the H 2 O 2 oxidation reaction. To further confirm this, XPS depth profiling was also performed ( Figure S11, Supporting Information) before H 2 O 2 oxidation. As shown in Figure S11a (Supporting Information) inset, it was confirmed that the atomic % of O1s decreased as etching proceeded. However, the atomic % of C1s decreased by ≈60%, while the atomic % of O1s increased by ≈30% in after oxidation. It can be seen that the oxygen peak decreases, but the carbon peak increases, which is continuous until the etching time reaches 200 s, and there was no change after 200 s. This means that manganese oxide present at the surface of MnS/OSNC particles is mainly involved in the catalytic oxidation reaction. Based on the CV and XPS obtained for the MnS/OSNC electrode surface, we tentatively suggest the hydrogen peroxide oxidation mechanism as follows; When the MnS/OSNC coated electrode put into the measuring solution, the MnO is converted to the Mn(OH) 2 in the presence of water (Equation 1). [36] After that, the catalyst surface on the electrode undergoes the oxidation due to the electrochemical potential application (Equation 2). In this case, hydrogen peroxide is absorbed onto the Mn active sites, [37] which goes to the equilibrium state (Equation 3). After the adsorption step, the internal electron transfer take places on the equilibrium mixture by the formation of a reduced Mn active site and the release of the products H 2 O and O 2 (Equation 4). [38] In this case, the active site is regenerated and the current can be observed.

MnO H O hydroxylation
Mn OH In case of BPA, it might be oxidized on the surface of MnO to give hydroquinone through the formation of radical intermediates. [39] (Figure S12

Electrochemical Detection of H2O2 and Bisphenol A
The as-prepared catalyst was further applied as a sensing material to detect H 2 O 2 . Before the detection experiment, the electrode surface was stabilized by cycling the potential between 0. In the blank solution, the anodic peak current of Mn 2+ ion decreased ≈5% by 10 cycles. After that, the peak current value was maintained to 100 cycles. In the potential cycling experiment in the 0.5 mm hydrogen peroxide solution, the peak current was maintained at 95% until 12 cycles, however the peak current was reduced to 82% after 60 cycles ( Figure S14, Supporting Information). As shown in the Figure S15 , respectively. In this case, the relative standard deviations (RSDs) for sensor-tosensor were 1.00%, 1.49%, 1.58%, 1.87%, 1.76%, 1.75%, 1.38%, 1.71%, 1.87%, 1.95%, 1.80%, 2.02%, and 2.03%, respectively. These small deviations were due to the variation in the sensor preparation and measurements. However, the deviation in acceptable value of ≤2.03% clearly suggests that the developed sensor exhibits excellent reproducibility. In addition, the experiments were conducted on the validation of the sensor using Certified Reference Materials of 99.9% BPA (Sigma-Aldrich, catalog No. 1075892) and 3% (0.88 m) H 2 O 2 (Green Pharmaceutical Co. Ltd., Republic of Korea). Hydrogen peroxide was quantified using the standard addition method after precisely diluting it at concentration to be ≈1 mm. The concentration of H 2 O 2 measured using this sensor considering the dilution ratio was 0.897 (±0.008) m. In addition, the t-test was carried out at the 95% confidence level (n = 5) to verify the experimental results, which showed that the calculated t value (1.93) was less than the critical t value (2.36). Therefore, the sensor shows an excellent and reproducible for the detection of H 2 O 2 ( Figure S16, Supporting Information). Specificity was demonstrated with monitoring of the interference species in higher concentration than the biologicals uric acid (500 µm), ascorbic acid (100 µm), dopamine (2 µm), and serotonin (2 µm)). After the monitoring interference species, hydrogen peroxide was added by 50.0 µm. The results show that the interference effect of each species was 0.32%, 0.31%, 4.50%, and 2.25% for uric acid, ascorbic acid, dopamine, and serotonin, respectively ( Figure S17, Supporting Information). Further comparison of our performance of H 2 O 2 detection with previous literature is shown in Table S2 (Supporting Information).
To validate the reliability of the MnS/O-SNC sensor, the moni toring of H 2 O 2 from cancer (A549) and normal (Vero) cells was explored. For the experiment, phorbol 12-myristate 13-acetate (PMA) was used as a cell activator to stimulate the release of H 2 O 2 from living cells. Figure 8b depicts the amperometric response of the optimized sensing electrode upon injection of PMA to normal and cancer cells. As a control experiment, PBS buffer without any cells was initially examined, which did not show any significant changes in the signal. Otherwise, there was a significant change in the response current (0.094 µA) for the cancer cells, which was higher than that of normal cells (0.056 µA). It is well known that cancer cells produce more H 2 O 2 than normal cells. [40] To ensure that the current response was solely due to the release of H 2 O 2 , catalase, a scavenger of H 2 O 2 , was injected into the same cell solution. As shown in the figure, the response went back to the baseline owing to the H 2 O 2 scavenging effect of catalase, indicating that the current response was entirely attributed to the H 2 O 2 release from the cells.
As a result of measurement for the prepared certified reference material containing 50.0 µm BPA, the determined concentration using the BPA sensor was 50.5 (±0.4) µm ( Figure S21, Supporting Information). The t-test was carried out at the 95% confidence level (n = 5) to verify the experimental results, which showed that the calculated t value (1.14) was less than the critical t value (2.36). Thus, BPA can be reproducibly detected by this sensor system. Further comparison of our performance of BPA detection with previous literature is shown in Table S3 (Supporting Information). Usually, it demands to monitor the BPA concentration extracted from plastic goods, since most persons are exposed to BPA by contacting with food and beverage packs produced with polycarbonate plastics or epoxy resins. Hence, this catalytic electrode was used to detect the amount of BPA released by polycarbonate bottles. Three bottles from the same manufacture were filled with distilled water (100 mL), and boiled in a water bath for 24 h. For comparison, a sample was prepared a non-PC bottle at the same condition. As shown in Figure 8d, the released BPA and other unknown species from PC-bottle shows a response peak in SWVs, while a non-PC bottle shows any anodic peak of phenolic compound. The result implies easy release of BPA from a polycarbonate bottle by hot water.

Conclusion
In conclusion, we successfully designed a new synthesis procedure for a coordination polymer as a precursor for carbon catalysts, and prepared MnS/MnO decorated S, N-doped carbon (SNC) nanoparticles using a calcination method. The prepared SNC nanoparticles decorated with MnS/O revealed excellent catalytic properties for the oxidation reaction of hydrogen peroxide and some phenolic species. The strategically designed catalyst was characterized to clearly understand its catalytic properties for these oxidation reactions. The XPS analysis revealed that the intensity of Mn 2+ (MnO) decreased after oxidation, indicating that the MnO decorated outward N, S-doped carbon nanoparticles mainly functioned for H 2 O 2 oxidation in contrast with MnS. Based on the catalytic activity, the as-prepared catalyst was applied for the electrochemical oxidation reactions, and detection of H 2 O 2 and bisphenol A. The results show that the approach described in this study has remarkable potential for biological and industrial applications involving enzymatic reactions producing H 2 O 2 , O 2 generation from H 2 O 2 , and decomposition and detection of phenolic compounds.
polymer was put into a quartz boat and placed in a tube furnace. It was then heated at different temperatures with a rate of 5 °C min −1 and maintained at 100 °C for 1 h, and then 700, 800, and 900 °C for 3 h under flowing N 2 gas.
Instruments: The Fourier transform infrared (FT-IR) spectra of the carbon precursors were obtained with a KBr medium in the region of 2500-500 cm −1 employing a NICOLET 380 FTIR spectrometer (USA). MALDI-TOF analysis was performed to analysis of unit structure in the Mn-coordination polymer by Ultraflex III, at the UNIST (Ulsan, South Korea). Field emission transmission electron microscopy (FE-TEM, TALOS F200X), field emission scanning electron microscopy (FE-SEM, SUPRA40VP), and energy-dispersive X-ray spectroscopy (EDS) were performed to characterize the morphology and composition of the catalysts. The crystal structures and compositions of the samples were characterized by X-ray diffraction (XRD, EMPYREAN) and X-ray photoelectron spectroscopy (XPS) (obtained by X'Pert PRO MRD and K-alpha X-ray Photoelectron Spectrometer, Thermo Scientific (UK), respectively, at the Conversing Material Core Facility of Dong-Eui University c, and X-ray absorption spectrum (XAS, PAL-XREL soft X-ray beam line). The samples were measured by tuning the energy of the incoming X-ray to the Mn L 2,3 -edges. All the XAS measurements were conducted in PEY mode. Electrochemical measurements were carried out using a potentiostat (Kosentech, Model PT-2 (South Korea)) with a three-electrode configuration and an EG&G PARC Model 636 instrument was used to obtain RDE measurements. The electrochemical impedance spectra were obtained using a PARSTAT 2263 (EG&G PAR, USA) from 100 kHz to 100 mHz.
Electrochemical Measurements: A three-electrode system was used for the voltametric and impedance experiments. The electrochemical measurements were conducted with a 0.070 cm 2 glassy carbon electrode with an Ag/AgCl reference electrode and a Pt wire as a counter electrode. First, 2 mg of each catalyst was dispersed in a mixture of 490 µL of water, 490 µL of ethanol, and 10 µL of Nafion to prepare the catalyst mixture. Then, 10 µL of the mixture was drop casted onto the glassy carbon electrode and dried under a vacuum condition for further experiments. For the electrochemical detection of H 2 O 2 and phenolic compounds, PBS (pH 7.4) was purged with N 2 for 20 min before the measurements. The LSVs were recorded with various sample concentrations at a scan rate of 50 mV s −1 from 0.0 to 1.0 V versus Ag/AgCl. Similarly, electrochemical impedance spectroscopy was performed in a PBS solution. Meanwhile, the decomposition reaction of H 2 O 2 was demonstrated by hydrodynamic voltammetry with a conventional RDE setup using a carbon ring-disk electrode (electrode area: 0.196 cm 2 ) at a scan rate of 30 mV s −1 from 0.0 to 1.0 V versus Ag/AgCl. Cell Culturing Procedure for Real Sample Measurements: The A549 (human adenocarcinomic alveolar basal epithelial) cell lines and Vero normal cell lines were separately maintained in T75 cell culture flasks containing Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% heat-inactivated FBS and 1% penicillin-streptomycin in a humidified CO 2 incubator (5% CO 2 /95% O 2 , 37 °C). The medium was replaced every 3 days throughout the lifetime of the cultures. Prior to electrochemical measurements, the cells were collected from the bottom of flasks by trypsinization followed by centrifugation at 200 rcf for 5 min. Phorbol 12-myristate 13-acetate (PMA) was then prepared by dissolving 1 mg of the solid compound in 10 µL of dimethylsulfoxide (DMSO), and then the resulting solution was diluted to a final volume of 1 mL with 0.1 m PBS, to give a final concentration of 1 mg mL −1

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.