CATALYST FOR PRODUCING HYDROGEN PEROXIDE, AND PREPARATION METHOD THEREFOR

Abstract

A catalyst for producing hydrogen peroxide and a preparation method therefor are provided. The catalyst for producing hydrogen peroxide according to the embodiments of the present invention comprises a carbon-based support and a catalyst moiety that is bonded to the carbon-based support and comprises an M.sub.1-N bonding structure (M.sub.1 represents a transition metal atom). The method for preparing a catalyst for producing hydrogen peroxide according to the embodiments of the present invention comprises comprises preparing a carbon-based support, providing a transition metal atom (M.sub.1) to the carbon-based support, and doping nitrogen into the carbon-based support.

Claims

1. A catalyst for producing hydrogen peroxide comprising: a carbon-based support; and a catalyst moiety that is bonded to the carbon-based support and comprises an M.sub.1-N bonding structure (M.sub.1 represents a transition metal atom).

2. The catalyst for producing hydrogen peroxide of claim 1, wherein the catalyst moiety comprises an M.sub.1-N.sub.4 bonding structure.

3. The catalyst for producing hydrogen peroxide of claim 1, wherein the M.sub.1 functions as a metal single atom catalyst.

4. The catalyst for producing hydrogen peroxide of claim 1, wherein the M.sub.1 comprises cobalt (Co).

5. The catalyst for producing hydrogen peroxide of claim 1, further comprising an electron-rich species bonded to the carbon-based support near the catalyst moiety, and wherein the electron-rich species changes the charge state of the M.sub.1.

6. The catalyst for producing hydrogen peroxide of claim 5, wherein the electron-rich species increases ΔG.sub.OOH* for H.sub.2O.sub.2 production.

7. The catalyst for producing hydrogen peroxide of claim 5, wherein the electron-rich species comprises oxygen.

8. The catalyst for producing hydrogen peroxide of claim 1, wherein the carbon-based support comprises a C—O—C bonding structure.

9. The catalyst for producing hydrogen peroxide of claim 1, wherein the carbon-based support comprises graphene oxide.

10. The catalyst for producing hydrogen peroxide of claim 1, wherein the carbon-based support is doped with nitrogen.

11. A method for preparing a catalyst for producing hydrogen peroxide comprising: preparing a carbon-based support; providing a transition metal atom (M.sub.1) to the carbon-based support; and doping nitrogen into the carbon-based support.

12. The method of claim 11, wherein the doping of nitrogen comprises forming a catalyst moiety that is bonded to the carbon-based support and comprises an M.sub.1-N bonding structure.

13. The method of claim 12, wherein the catalyst moiety comprises an M.sub.1-N.sub.4 bonding structure.

14. The method of claim 11, wherein the doping of nitrogen comprises reducing the carbon-based support by treating the carbon-based support with NH.sub.3 at 400˜600° C.

15. The method of claim 11, wherein the transition metal atom comprises cobalt (Co).

16. The method of claim 11, wherein the carbon-based support comprises an electron-rich species.

17. The method of claim 16, wherein the electron-rich species comprises oxygen.

18. The method of claim 11, wherein the carbon-based support comprises a C—O—C bonding structure.

19. The method of claim 11, wherein the carbon-based support comprises graphene oxide.

Description

DESCRIPTION OF DRAWINGS

[0009] FIG. 1 shows the catalytic activity for the production of H.sub.2O and H.sub.2O.sub.2 through the oxygen reduction reaction.

[0010] FIG. 2 shows the relative charge state and OOH* adsorption energy of cobalt metal centers in Co—N.sub.4/graphene with 4H*/2H*/O*/2O* adsorbed near the cobalt atoms.

[0011] FIG. 3 shows the charge density of Co—N.sub.4/graphene with 4H*/2H*/O*/2O* adsorbed near the cobalt atoms.

[0012] FIG. 4 schematically shows a method for preparing Co.sub.1-NG(O).

[0013] FIG. 5 shows the oxygen content of GO, Co.sub.1-NG(O) and Co.sub.1-NG(R) prepared at different NH.sub.3 reduction temperatures, respectively.

[0014] FIG. 6 shows deconvoluted oxygen is spectra of Co.sub.1-NG(O) and Co.sub.1-NG(R).

[0015] FIG. 7 shows a TEM image of Co.sub.1-NG(O).

[0016] FIG. 8 shows an atomic resolution ADF-STEM image of Co.sub.1-NG(O).

[0017] FIG. 9 shows Co K-edge K.sup.3-weighted FT-EXAFS spectra in R space for Co.sub.1-NG(O), Co.sub.1-NG(R), Co foil, CoO.sub.4, and CoO.

[0018] FIG. 10 shows the FTIR spectra of GO, Co.sub.1-NG(O) and Co.sub.1-NG(R).

[0019] FIG. 11 shows an oxygen reduction reaction pathway to produce H.sub.2O.sub.2 or H.sub.2O.

[0020] FIG. 12 shows ORR performance (solid line) at 1600 rpm and H.sub.2O.sub.2 detection current density (dashed line) at the ring electrode for NG(O), Co.sub.1-NG(O) and Co.sub.1-NG(R) in 0.1M KOH.

[0021] FIG. 13 shows the H.sub.2O: selectivity calculated as a function of applied potential.

[0022] FIG. 14 shows H.sub.2O: currents at 0.7V for NG(O), Co.sub.1-NG(O) and Co.sub.1-NG(R).

[0023] FIG. 15 shows the oxygen reduction reaction polarization curves of NG(O) and Co.sub.1-NG(O) in 0.1M PBS (phosphate buffered saline).

[0024] FIG. 16 shows the oxygen reduction reaction polarization curves of NG(O) and Co.sub.1-NG(O) in 0.1M HClO.sub.4.

[0025] FIG. 17 shows the kinetic current density of Co.sub.1-NG(O) compared to other catalysts.

[0026] FIGS. 18 and 19 show the mass activity of Co.sub.1-NG(O) compared to other catalysts.

[0027] FIG. 20 shows the stability of Co.sub.1-NG(O).

BEST MODE

[0028] Hereinafter, a detailed description will be given of the present invention with reference to the following embodiments. The purposes, features, and advantages of the present invention will be easily understood through the following embodiments. The present invention is not limited to such embodiments, but may be modified in other forms. The embodiments to be described below are nothing but the ones provided to bring the disclosure of the present invention to perfection and assist those skilled in the art to completely understand the present invention. Therefore, the following embodiments are not to be construed as limiting the present invention.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. It will be further understood that the terms “comprises” or “has,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0030] A catalyst for producing hydrogen peroxide according to the embodiments of the present invention comprises a carbon-based support and a catalyst moiety that is bonded to the carbon-based support and comprises an M.sub.1-N bonding structure (M.sub.1 represents a transition metal atom).

[0031] The catalyst moiety may comprise an M.sub.1-N.sub.4 bonding structure. The M.sub.1 may function as a metal single atom catalyst. The M.sub.1 may comprise cobalt (Co).

[0032] The catalyst for producing hydrogen peroxide may further comprise an electron-rich species bonded to the carbon-based support near the catalyst moiety, and the electron-rich species may change the charge state of the M.sub.1. The electron-rich species can increase ΔG.sub.OOH* for H.sub.2O.sub.2 production. The electron-rich species may comprise oxygen.

[0033] The carbon-based support may comprise a C—O—C bonding structure. The carbon-based support may comprise graphene oxide. The carbon-based support may be doped with nitrogen.

[0034] A method for preparing a catalyst for producing hydrogen peroxide according to the embodiments of the present invention comprises comprises preparing a carbon-based support, providing a transition metal atom (M.sub.1) to the carbon-based support, and doping nitrogen into the carbon-based support.

[0035] The doping of nitrogen may comprise forming a catalyst moiety that is bonded to the carbon-based support and comprises an M.sub.1-N bonding structure. The catalyst moiety may comprise an M.sub.1-N.sub.4 bonding structure. The doping of nitrogen may comprise reducing the carbon-based support by treating the carbon-based support with NH.sub.3 at 400˜600° C.

[0036] The transition metal atom may comprise cobalt (Co).

[0037] The carbon-based support may comprise an electron-rich species. The electron-rich species may comprise oxygen. The carbon-based support may comprise a C—O—C bonding structure. The carbon-based support may comprise graphene oxide.

[0038] FIGS. 1 to 3 are views for explaining the structure and activity of a catalyst for producing hydrogen peroxide according to an embodiment of the present invention.

[0039] FIG. 1 shows the catalytic activity the production of H.sub.2O and H.sub.2O.sub.2 through the oxygen reduction reaction. In FIG. 1, point A represents M-N.sub.4/graphene used to draw the catalytic activity graph, and point B represents Co—N.sub.4/graphene with electron-rich species (O*/2O*) adsorbed near the cobalt atom, and point C represents Co—N.sub.4/graphene with electron-poor species (4H*/2H*) adsorbed near the cobalt atom.

[0040] Referring to FIG. 1, the oxygen reduction reaction activity can be expressed as a function of OOH* adsorption energy (ΔG.sub.OOH*). H.sub.2O.sub.2 production is energetically preferred to H.sub.2O production for Ni, Ag and Pt, whereas it is the other way for Ru, Fe and Co. Since the former metal centers are not as oxophilic as the latter metal centers, the latter metal centers prefer the breaking of the OOH* intermediates to O*, leading to H.sub.2O formation, whereas the former metal centers are prone to OOH* protonation to H.sub.2O.sub.2.

[0041] According to the calculation results, none of the M-N.sub.4/graphene catalysts exists near the peak of the graph for H.sub.2O.sub.2 production (ΔG.sub.OOH*=4.2 eV). Even the catalysts (Ni, Ag and Pt) preferring H.sub.2O.sub.2 production require relatively high overpotentials (>0.5V) for H.sub.2O.sub.2 production compared to, for example, the most active Co—N.sub.4/graphene that produces H.sub.2O. In the above M-N.sub.4/graphene, M represents a transition metal atom, M-N.sub.4 represents a catalyst moiety bonded to the graphene, and the graphene represents a carbon-based support supporting the catalyst moiety.

[0042] It is desirable to modify Co—N.sub.4/graphene to maintain most of the catalytic activity of Co—N.sub.4/graphene toward H.sub.2O.sub.2 production rather than H.sub.2O. Therefore, fine-tuning of the interaction between the metal center and the surrounding atomic configuration is required in addition to changing the metal center of the Co—N.sub.4 moiety to reach the optimal ΔG.sub.OOH* value for H.sub.2O.sub.2 producing.

[0043] FIG. 2 shows the relative charge state and OOH* adsorption energy of cobalt metal centers in Co—N.sub.4/graphene with 4H*/2H*/O*/2O* adsorbed near the cobalt atoms, and FIG. 3 shows the charge density of Co—N.sub.4/graphene with 4H*/2H*/O*/2O* adsorbed near the cobalt atoms.

[0044] Referring to FIGS. 2 and 3, ΔG.sub.OOH* can be adjusted by attaching functional groups near the Co—N.sub.4 moiety. For example, when an electron-rich species such as O* is adsorbed near the Co—N.sub.4 moiety (Co—N.sub.4(O)), ΔG.sub.OOH* increases from 3.9 to 4.1 eV getting very close to the optimal value for the H.sub.2O.sub.2 production. ΔG.sub.OOH* can be further increased to 4.5 eV when two O* are adsorbed near the Co—N.sub.4 moiety (Co—N.sub.4 (2O)). Co—N.sub.4 (O) represents that one O* is adsorbed near the Co—N.sub.4 moiety, and Co—N.sub.4 (2O) represents that two O* are adsorbed near the Co—N.sub.4 moiety.

[0045] Similar results can be drawn for the case where another electron-rich species OH* is adsorbed near the Co—N.sub.4 moiety. On the other hand, when an electron-poor species such as H.sup.+ is adsorbed near the Co—N.sub.4 moiety, ΔG.sub.OOH* decreases from 3.9 to 3.8 eV in Co—N.sub.4(2H) and to 3.1 eV in Co—N.sub.4(4H). Similar trends are observed when another electron-poor element, carbon, is introduced.

[0046] These effects of the functional groups on ΔG.sub.OOH* can be explained by the differences in the charge state of the cobalt atom. In the cases of Co—N.sub.4(O) and Co—N.sub.4(2O), the charge state of the cobalt atom becomes more positive by 0.05e.sup.− and 0.10e.sup.−, whereas in the cases of Co—N.sub.4(2H) and Co—N.sub.4(4H), it becomes more negative by 0.21e.sup.− and 0.35e.sup.−, respectively. A strategy for designing a single atom catalyst for H.sub.2O.sub.2 production is to slightly increase ΔG.sub.OOH* of Co—N.sub.4/graphene by creating electron-rich oxygen species near the Co—N.sub.4 moiety such that they can slightly increase the charge state of the cobalt atom. Therefore, it is preferable to use graphene oxide (GO) as the carbon-based support. In addition, epoxides in graphene oxide are thermally more stable than other functional groups such as hydroxyl groups that desorb at low temperature.

[0047] FIGS. 4 to 10 are views for explaining the structural characteristics of the catalyst for producing hydrogen peroxide according to an embodiment of the present invention.

[0048] FIG. 4 schematically shows a method for preparing Co.sub.1-NG(O). Referring to FIG. 4, cobalt atoms are adsorbed on the surface of graphene oxide by the impregnation method. Graphene oxide to which cobalt is adsorbed is mildly reduced at 500° C. in NH.sub.3/Ar. As such, the Co.sub.1-NG(O) represents that the Co—N.sub.4(O) moiety is bonded to the nitrogen-doped graphene oxide and heat-treated at 500° C.

[0049] FIG. 5 shows the oxygen content of GO, Co.sub.1-NG(O) and Co.sub.1-NG(R) prepared at different NH.sub.3 reduction temperatures, respectively. The Co.sub.1-NG(R) is prepared in the same manner as Co.sub.1-NG(O) except that the reaction temperature is 900° C. Referring to FIG. 5, a high oxygen ratio (about 6.6%) can be maintained at a reducing temperature of about 500° C. In addition, a relatively high percentage (5.87%) of nitrogen can be incorporated despite the low annealing temperature.

[0050] FIG. 6 shows deconvoluted oxygen 1s spectra of Co.sub.1-NG(O) and Co.sub.1-NG(R). Referring to FIG. 6, the C—O—C content of Co.sub.1-NG(O) is 3.22%, which is higher than the C—O—C content (0.72%) of Co.sub.1-NG(R).

[0051] FIG. 7 shows a TEM image of Co.sub.1-NG(O), and FIG. 8 shows an atomic resolution ADF-STEM image of Co.sub.1-NG(O).

[0052] During the thermal reduction step, many vacancies are formed, providing anchoring sites for nitrogen atoms and preferential binding sites for metal atoms. The atomic structure of Co.sub.1-NG(O) can be imaged by ADF-STEM (annular dark-field scanning transmission electron microscope).

[0053] Referring to FIG. 8, individual cobalt atoms are uniformly dispersed throughout the entire graphene matrix. Optimized Co.sub.1-NG(O) single atom catalysts have a high concentration of single metal atoms (1.4 wt %) Other M.sub.1-NG(O) (M=Fe, Ni) can be prepared in the same manner and the active surface areas determined by electrochemical measurement are similar.

[0054] FIG. 9 shows Co K-edge K.sup.3-weighted FT-EXAFS (Fourier transform extended X-ray absorption fine structure) spectra in R space for Co.sub.1-NG(O), Co.sub.1-NG(R), Co foil, Co.sub.3O.sub.4, and CoO, and FIG. 10 shows the FTIR (Fourier-transform infrared spectroscopy) spectra of GO, Co.sub.1-NG(O) and Co.sub.1-NG(R). The atomic structure of Co.sub.1-NG(O) can be analyzed by X-ray absorption spectroscopy.

[0055] Referring to FIG. 9, the FT-EXAFS curves for Co.sub.1-NG(O) only showed a main peak (1.4 Å), which can be attributed to Co—N coordination, while the Co—Co peak (2.2 Å) was not detected. The structural parameters of cobalt atoms can be analyzed by performing EXAFS fitting. The coordination number of the fitted parameters is approximately 4. Similarly, the FT-EXAFS curves of other M.sub.1-NG(O) single atom catalysts were also fitted and their coordination numbers are also close to 4, demonstrating the presence of metal atoms coordinated by four surrounding N atoms.

[0056] XPS (X-ray photoelectron spectroscopy) analysis confirmed that nitrogen was readily incorporated into the graphene matrix at 500° C. and pyridinic N was dominant for Co.sub.1-NG(O). Co.sub.1-NG(R) was also prepared by ammonia treatment at 900° C., which is a typical carbonization temperature and is much higher than the preparation temperature (500° C.) of Co.sub.1-NG(O).

[0057] In comparison to Co.sub.1-NG(R), the Co 2p spectra of Co.sub.1-NG(O) shows a upshift to higher binding energy and the spin-orbit splitting (15.875 eV) of Co.sub.1-NG(O) is larger than that (15.504 eV) of Co.sub.1-NG(R), indicating the lower charge density state of cobalt atoms. Thus, the Co.sub.1-NG(O) has highly oxidized cobalt atom centers, but the Co.sub.1-NG(R) is composed of relatively electron-rich cobalt single atoms.

[0058] Although not shown in the figure, according to the O K-edge NEXAFS (near edge X-ray absorption fine structure) spectra, the Co.sub.1-NG(O) single atom catalyst has more intense and sharp peaks at 535 and 540.4 eV, which can be assigned as the transitions of O is core level to π* states and σ* states from C—O bond (e.g. C—O—C epoxides), than Co.sub.1-NG(R). This can be confirmed by FTIR spectra of FIG. 10.

[0059] Comprehensive analyses by XPS, NEXAFS, and FTIR indicate that cobalt centers become relatively electron-poor by nearby C—O—C atomic structures. These C—O—C groups are thermodynamically stable at the mild reduction temperature of 500° C. which is further supported by the DFT analysis. Therefore, the presence of oxygen species (C—O—C epoxides) near the Co—N.sub.4 moiety is desirable for highly active H.sub.2O.sub.2 production. After reduction at 900° C., most oxygen species, including C—O—C groups, are desorbed.

[0060] FIGS. 11 to 16 are views for explaining the electrochemical oxygen reduction reaction performance of the catalyst for producing hydrogen peroxide according to an embodiment of the present invention.

[0061] FIG. 11 shows an oxygen reduction reaction pathway to produce H.sub.2O.sub.2 or H.sub.2O. Referring to FIG. 11, the oxygen reduction reaction kinetics can proceed via either 2e.sup.− or 4e.sup.− pathway and the selectivity is determined by the propensity to break the O—O bond during the oxygen reduction reaction process.

[0062] FIG. 12 shows ORR (oxygen reduction reaction) performance (solid line) at 1600 rpm and H.sub.2O.sub.2 detection current density (dashed line) at the ring electrode for NG(O), Co.sub.1-NG(O) and Co.sub.1-NG(R) in 0.1M KOH. Referring to FIG. 12, The amount of H.sub.2O.sub.2 formed can be quantified using a rotating ring-disk electrode at 1,600 rpm in oxygen-saturated 0.1M KOH electrolyte. The ring electrode was held at 1.2V to oxidize only H.sub.2O.sub.2 formed from the disk electrode, avoiding other oxygen reduction reaction currents at the ring electrode. The Co.sub.1-NG(O) catalyst, which has electron-poor cobalt center induced by surrounding oxygen species (e.g. C—O—C epoxides), is able to catalyze the 2e.sup.− oxygen reduction reaction showing superior activity for H.sub.2O.sub.2 production.

[0063] FIG. 13 shows the H.sub.2O.sub.2 selectivity calculated as a function of applied potential. Referring to FIG. 13, the electronic structure of Co—N.sub.4 site is modified by nearby C—O—C epoxides such that it is difficult to break the O—O bond, ensuring a high selectivity to H.sub.2O.sub.2 (about 82%). On the other hand, Co.sub.1-NG(R) that is mainly composed of Co—N.sub.4 sites predominantly produce water, which matches well with the DFT results (FIG. 1).

[0064] FIG. 14 shows H.sub.2O.sub.2 currents at 0.7V for NG(O), Co.sub.1-NG(O) and Co.sub.1-NG(R). Referring to FIG. 14, the Co.sub.1-NG(O) catalyst delivered much higher H.sub.2O.sub.2 production current than the Co.sub.1-NG(R) or NG(O), showing its superior activity and selectivity towards H.sub.2O.sub.2 production.

[0065] Although not shown in the figure, Co.sub.1-G(O) which is composed of Co metal centers without nitrogen atom bonding shows hardly any change in the onset-potential and oxygen reduction reaction kinetics with increasing Co amount. This represents that the oxygen reduction reaction performance is associated with the Co—N.sub.4 moieties.

[0066] FIG. 15 shows the oxygen reduction reaction polarization curves of NG(O) and Co.sub.1-NG(O) in 0.1M PBS (phosphate buffered saline), and FIG. 16 shows the oxygen reduction reaction polarization curves of NG(O) and Co.sub.1-NG(O) in 0.1M HClO.sub.4. Referring to FIGS. 15 and 16, the Co.sub.1-NG(O) shows a significant amount of H.sub.2O.sub.2 production in acidic (0.1M HClO.sub.4), neutral (0.1M phosphate), and basic (0.1M KOH) electrolytes.

[0067] Without Co atoms, the NG(O) showed poor activity. However, the electron-poor cobalt metal centers serve as O.sub.2 adsorption sites on the graphitic carbon matrix facilitating the adsorption of O.sub.2 molecules while preventing further 4e.sup.− reduction of oxygen effectively. In addition, the Co.sub.1-NG(O) exhibited a significantly higher activity for H.sub.2O.sub.2 production than NG(O), Fe.sub.1-NG(O) or Ni.sub.1-NG(O), with an onset potential of about 0.8V. These indicate that Co.sub.1-NG(O) is highly active for H.sub.2O.sub.2 production in a wide range of pH levels while effectively preventing the electrochemical dissociation of H.sub.2O.sub.2 to H.sub.2O.

[0068] FIGS. 17 to 20 are views for explaining the H.sub.2O.sub.2 production activity and stability of the catalyst for producing hydrogen peroxide according to an embodiment of the present invention.

[0069] FIG. 17 shows the kinetic current density of Co.sub.1-NG(O) compared to other catalysts. For the comparison, the kinetic current density for H.sub.2O: production has been derived by correcting for mass transport limitations using Koutecky-Levich equation. Referring to FIG. 17, the calculated kinetic current density of Co.sub.1-NG(O) for H.sub.2O.sub.2 production was 2.84 mA/cm.sup.2 at 0.65V, demonstrating its superior H.sub.2O.sub.2 production activity that surpasses that of the state-of-the-art electrocatalysts.

[0070] FIGS. 18 and 19 show the mass activity of Co.sub.1-NG(O) compared to other catalysts. FIG. 18 shows the mass activity at 0.65V and FIG. 19 shows the mass activity at 0.75V.

[0071] Referring to FIG. 18, Co.sub.1-NG(O) produces H.sub.2O.sub.2 with a high mass activity of 277.3 A/g (at 0.65V, with 2,500 rpm). Referring to FIG. 19, a few layered, mildly reduced graphene oxide (F-mrGO) has been known to exhibit the highest mass activity, but Co.sub.1-NG(O) exhibits 4 times higher H.sub.2O.sub.2 production activity than that of F-mrGO.

[0072] To evaluate the amount of H.sub.2O.sub.2 generated in real devices, the Co.sub.1-NG(O) catalyst was prepared onto carbon paper with a loading of 1 mg/cm.sup.2 and tested in a custom-made electrochemical H-type cell. In alkaline electrolyte, the electrochemical H.sub.2O.sub.2 production of Co.sub.1-NG(O) catalyst was performed. Co.sub.1-NG(O) showed a very high H.sub.2O.sub.2 productivity of 418(±19) mmol/g.sub.cath (at 50 mA), which is more than twice the amount of H.sub.2O.sub.2 produced by Au—Pd catalyst.

[0073] FIG. 20 shows the stability of Co.sub.1-NG(O). Referring to FIG. 20, 98.7% of the initial current density was maintained after 110 hours. Co.sub.1-NG(O) is stable throughout the entire pH level for a long-term production of H.sub.2O.sub.2 notably, with the negligible activity loss over 110 hours in alkaline condition. This high stability of Co.sub.1-NG(O) represents that the highly active Co—N.sub.4(O) moieties are very stable in either alkaline or acidic environment. The stability in a wide pH range and the enhanced H.sub.2O.sub.2 production activity can be achieved by electron-poor cobalt metal centers modulated by the surrounding atomic configuration. The high kinetic current density (2.84 mA/cm.sup.2 at 0.65V) and mass activity (277.3 Å/g at 0.65V) can be achieved by the fine-tuning of heterogeneous catalytic activity for H.sub.2O.sub.2 production over a wide pH range.

[0074] [Preparation Example of Co.sub.1-NG(O)]

[0075] Graphene oxide was washed with HCl solution and acetone to remove metal impurities (e.g., manganese) that are left as impurity during producing graphene oxide. The washed graphene oxide was then dried in an electric oven at 40° C. overnight. 30 mg of the dried graphene oxide was dispersed in 30 ml of water. CoCl.sub.2.6H.sub.2O was dispersed in water at 3 mg/ml of the concentration and 202 μl of the solution was added into the graphene oxide solution. The mixed solution was sonicated for 1 hour and then freeze-dried for 2 days. The prepared metal-adsorbed graphene oxide foam was collected into an alumina crucible and then placed at the center of a tube furnace. With the continuous feeding of ammonia (50 sccm) and argon (150 sccm) gas, the furnace was heated up to 500° C. (ramping rate=5° C./min) and held at 500° C. for 1 hour, followed by natural cooling under the continuous flow of Ar (150 sccm). Thereby, a dark brown Co.sub.1-NG(O) catalyst was prepared.

[0076] Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that the present invention may be embodied in other specific ways without changing the technical spirit or essential features thereof. Therefore, the embodiments disclosed in the present invention are not restrictive but are illustrative. The scope of the present invention is given by the claims, rather than the specification, and also contains all modifications within the meaning and range equivalent to the claims.

INDUSTRIAL APPLICABILITY

[0077] A catalyst for producing hydrogen peroxide according to the embodiments of the present invention may have good performance. For example, the catalyst for producing hydrogen peroxide may have high kinetic current density and mass activity with good stability for a long time. In addition, the catalyst for producing hydrogen peroxide can be prepared by a simple method and the manufacturing cost is low.