WO2013162470A1

WO2013162470A1 - A three-dimensional graphene network composite for hydrogen peroxide detection

Info

Publication number: WO2013162470A1
Application number: PCT/SG2013/000161
Authority: WO
Inventors: Hua Zhang; Xiehong CAO; Qiyuan HE
Original assignee: Nanyang Technological University
Priority date: 2012-04-23
Filing date: 2013-04-22
Publication date: 2013-10-31

Abstract

A three-dimensional graphene network composite for hydrogen peroxide detection, the composite comprising: an electrically conductive graphene network electrode having a three-dimensional porous structure comprising a macroscopic entirety of continuous graphene films having a plurality of pores therein; and at least one electroactive material deposited on the three-dimensional graphene network electrode, the at least one electroactive material configured to function as an electrochemical sensor for detecting hydrogen peroxide.

Description

A THREE-DIMENSIONAL GRAPHENE NETWORK COMPOSITE FOR

HYDROGEN PEROXIDE DETECTION

FIELD OF THE INVENTION

This invention relates to composites synthesized from three-dimensional graphene networks (3DGN) for sensors used in detection of H₂0_2.

BACKGROUND OF THE INVENTION

Recently, graphene has attracted increasing interest due to its unique properties and broad applications^1"4 in electronics,^5"8 sensors,^9"19 energy storage,^20"26 solar cells,^27"29 surface enhanced Raman scattering,³⁰' ³¹ etc. Particularly, in the area of electrochemical analysis, graphene has shown good performance in detection of dopamine, hydrogen peroxide (H₂0₂), ascorbic acid, uric acid, etc. 32 ^" 37 Recent work has revealed that composites of graphene with other nanomaterials, such as noble metal nanoparticles (NPs) and metal oxide, could be used as good electrochemical sensing platforms,^38"40 due to synergistic effects between graphene and the nanomaterials.⁴¹ As known, graphene sheets not only provide a large surface area for anchoring nanomaterials, but also serve as the electrical conduction channel for electron transfer in such graphene-based composites.

To date, most of the recent graphene-related electrochemical research are based on the reduced graphene oxide (rGO) sheets, while only few work used graphene prepared by other methods such as chemical vapor deposition (CVD) and epitaxial growth.^{42, 43} Although graphene (actually rGO here) prepared from the reduction of graphene oxide (GO) is one of the most favourable and widely used ways, graphene grown by CVD possesses higher quality and better electrical conductivity than does rGO,⁴⁴' ⁴⁵ leading to faster electron transfer that is essential in electrochemical detection⁴¹ applications. Various groups²²'⁴⁶ have reported the synthesis of novel three-dimensional graphene networks (3DGNs) by CVD. The 3DGNs are composed of high-quality, few-layer graphene films.²² However, CVD-produced graphene is confronted with the problems of low yield and difficulty in its functionlization.

On the other hand, H 0₂ is one of the most important and widely used analytes in electrochemical analysis, since it is an intermediate of biological reactions and an oxidant in industry and municipal waste water treatment. The precise and rapid detection of H₂0₂ is therefore of significant importance. There is thus a need to develop effective sensors for detecting H₂0₂.

SUMMARY OF INVENTION

Compared with other carbon electrode materials, 3DGNs have the following advantages: (1) The 3D porous structure facilitates easy access of electrolyte and analyte to the 3DGN electrode surface; (2) the interconnected and electrical conductive 3DGNs provide multiple electron paths that lead to a rapid and sensitive detection of analyte; (3) the surface of 3DGNs has numerous wrinkles and ripples, which could provide high surface area and plenty of active sites for the subsequent decoration of other electroactive materials with high massloading level as shown in FIG. 9; (4) 3DGNs can be used as an electrode directly. Thus, for the first time, CVD-grown 3DGN have been developed for use as a template for anchoring electroactive materials used as an electrochemical sensor to detect Η₂0₂. Different types of electroactive materials, i.e., Pt nanoparticles (PtNPs), multi- walled carbon nanotubes (MWCNTs) and Mn0₂ nanowalls, were successfully deposited on 3DGN templates. These 3DGN-based composite electrodes exhibit a low detection limit, quick response time, and wide linear range toward the detection of H₂0₂.

The three-dimensional graphene network (3DGN) prepared by CVD is thus successfully used as a template to synthesize various composites to be used as electrodes for electrochemical sensors, which exhibit the low detection limit, quick response time and wide linear range toward the detection of H₂0₂.

According to a first aspect, there is provided a three-dimensional graphene network composite for hydrogen peroxide detection, the composite comprising: an electrically conductive graphene network electrode having a three-dimensional porous structure comprising a macroscopic entirety of continuous graphene films having a plurality of pores therein; and at least one electroactive material deposited on the three-dimensional graphene network electrode, the at least one electroactive material configured to function as an electrochemical sensor for detecting hydrogen peroxide.

The at least one electroactive material may be selected from the group consisting of: platinum nanoparticles, multi-walled carbon nanotubes and Mn0₂ nanowalls.

A first of the at least one electroactive material may comprise multi-walled carbon nanotubes and a second of the at least one electroactive material comprises platinum nanoparticles.

The three-dimensional graphene network composite may have a response time of less than or equal to 1.5 seconds.

The three-dimensional graphene network composite may have a detection limit of less than 0.009 μΜ when calculated in terms of a signal-to-noise ratio of 3.

The three-dimensional graphene network composite may have a linear detection range from about 0.025μιη to about 6.3μιη.

According to a second aspect, there is provided a method of synthesizing a three-dimensional graphene network composite for hydrogen peroxide detection, the method comprising: synthesizing via chemical vapour deposition an electrically conductive graphene network electrode having a three-dimensional porous structure comprising a macroscopic entirety of continuous graphene films having a plurality of pores therein; and depositing at least one electroactive material on the three-dimensional graphene network electrode, the at least one electroactive material configured to function as an electrochemical sensor for detecting hydrogen peroxide.

A first of the at least one electroactive material may comprise multi-walled carbon nanotubes and a first of the depositing may comprise using eletrophoretic deposition to deposit the multi-walled carbon nanotubes on the three-dimensional graphene network electrode to form a three-dimensional graphene network / multi-walled carbon nanotubes composite electrode.

A second of the at least one electroactive material may comprise platinum nanoparticles and a second of the depositing may comprise using electrochemical deposition to deposit the platinum nanoparticles on the three-dimensional graphene network / multi-walled carbon nanotubes composite electrode.

The at least one electroactive material may comprise Mn0₂ nanowalls and the depositing may comprise using cathodic deposition to deposit the Mn0₂ nanowalls on the three- dimensional graphene network electrode.

BRIEF DESCRIPTION OF FIGURES

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments of the present invention, the description being with reference to the accompanying illustrative drawings, in which:

FIG. 1 is SEM images of (A) 3DGNs and after deposition of (B) PtNPs, (C) MWCNTs, and (D) Mn0₂ nanowalls on 3DGNs; inset in (A): HRTEM image of a graphene sheet of 3DGNs;

FIG. 2 is images of morphology and structure of 3DGN-based composites: (A) SEM and (B) TEM images of 3DGN/PtNP; inset in (A): Magnified SEM image of PtNPs on 3DGN; insets in (B): (Top) SAED pattern and (Bottom) HRTEM image of PtNPs. SEM images of (C) 3DGN/MWCNT and (D) 3DGN/MWCNT/PtNP; inset in (D): magnified SEM image of PtNPs on 3DGN/CNT; (E) SEM and (F) TEM images of 3DGN/Mn0₂; inset in (E): magnified SEM image of Mn0₂ nanowalls; inset in (F): HRTEM image of Mn0₂;

FIG. 3 is graphs of amperometric responses of the 3DGN-based composite electrodes to H₂0₂:

(A) 3DGN/PtNP, (B) 3DGN/MWCNT, (C) 3 DGN/M WCNT/PtNP , and (D) 3DGN/Mn0₂; inset: the lowest H₂0₂ concentration detected by the corresponding 3DGN-based composite electrodes;

FIG. 4 is TEM images of PtNPs grown on 3DGNs; the arrow in (A) indicates edge of the graphene sheet;

FIG. 5 is SEM images of the edges of (A) 3DGN/MWCNT and (B) 3DGN/MWCNT/PtNP indicate lots of protruded MWCNT tips, which are highly active to the electrochemical reaction and capable of serving as conduction channels for the electron transfer;

FIG. 6 is Raman spectrum of 3DGNs after deposition of Mn0₂ nanowalls (3DGN/Mn0₂); the typical Raman spectra of 3DGN/Mn0₂ shows the distinct G and 2D peaks of 3DGNs and also one additional peak at -640 cm^"1, which is corresponding to the symmetric stretching vibration (Mn-O) of the Mn0₆ group;

FIG. 7 is graphs of cyclic voltammograms (CVs) of electrodes of (A) 3DGN/PtNP, (B) 3DGN/MWCNT, (C) 3 DGN/M WCNT/PtNP, (D) 3DGN/Mn0₂ and (E) 3DGN in the absence (black curves) and presence (gray curves) of 2 mM H₂0₂ in PBS (pH=7.4);

(F) the amperometric response of 3DGN electrode to H₂0₂; Inset: (Top) the detection limit of 1 10 μΜ and (Bottom) the linear range from 0.1 1 to 1 .234 mM (R2 = 0.99207,

I = 0.00233 + 0.09037 C);

FIG. 8 is corresponding plots of oxidation current vs. H₂0₂ concentration obtained by using

3DGN-based composite electrodes: (A) 3DGN/PtNP, (B) 3DGN/MWCNT, (C)

3 DGN/M WCNT/PtNP , and (D) 3DGN/Mn0₂;

FIG. 9 is SEM images of wrinkles and ripples on the surface of 3DGNs; the arrows indicate wrinkles and ripples. (B) Nitrogen adsorption and desorption isotherm gives a BET surface area of 3DGNs is 174.9 m² g^"1 ; and

FIG. 10 is XRD patterns of Mn0₂ nanowalls exhibit the characteristic peaks of orthorhombic- phase Mn02 (JCPDS 44-0142) at 20 = 21.84 (101), 36.73 (210), 42.06 (21 1), 55.46

(212) and 65.0 (020); due to the low crystallinity of cathodic deposited Mn0₂ nanowalls, and to prevent from the influence of high-intensity XRD peaks of graphene, only Mn0₂ nanowalls on the top surface of 3DGN/Mn0₂ electrode were carefully collected for XRD characterization.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will be described with reference to FIGS. 1 to 10 below.

Materials

Multi-walled carbon nanotubes (MWCNTs) were purchased from NanoLab, Inc. (USA). Hydrogen peroxide (H₂0₂) (35%), potassium hexachloroplatinate (Κ₂Ρΐ0₆), perchloric acid (HC10₄) (70%), phosphate buffer saline (PBS) tablets, iron (III) chloride (FeCl₃)_, poly(methyl methacrylate) (PMMA), hydrogen chloride (HC1), magnesium nitrate hexahydrate (Mg(N0₃)₂-6H₂0), manganese (II) acetate tetrahydrate (Mn(CH₃COO)₂-4H₂0) and sodium sulfate (Na₂S0₄) were purchased from Sigma-Aldrich Co. LLC (USA). Nickel foams were purchased from Changsha lyrun new material Co. Ltd (China). All used solutions were prepared in Milli-Q water (18.2 ΜΩ cm, Milli-Q System, Millipore, USA).

Growth of 3D graphene networks by C VD The 3D graphene networks (3DGNs) were prepared according to a previously reported method²² with slight modifications. Typically, nickel foams were placed in a quartz tube furnace and heated to 1000 °C at a heating rate of -37 °C min^"1 with the mixed gas of Ar (200 seem) and H₂ (40 seem). The temperature was kept at 1000 °C for 10 min and then naturally cooled down to 950 °C. After the temperature of furnace was stable at 950 °C, ethanol was bubbled into the tube with the Ar flow (50 seem) for 15 min. Then the furnace was fast cooled down to room temperature under the protection of Ar (200 seem) and H₂ (40 seem) at a cooling rate of -100 °C min^{" 1}. To remove the Ni foam template, the obtained 3DGNs were immersed into the PMMA solution (4.5 wt% PMMA with molecular weight -996,000 in anisole) for several seconds in order to coat the 3DGNs with PMMA. After the solvent was evaporated, the PMMA-coated 3DGNs were immersed into an etchant solution containing 1 mol L^"1 FeCl₃ and 2 mol L^"1 HCl at 60 °C to remove the Ni foam. Then, the PMMA coated on the 3DGNs was removed by hot acetone vapor followed by annealing at 450 °C under Ar (200 seem) and H (40 seem).

Preparation of a composite of 3DGNs and PtNPs

A composite of 3DGNs with PtNPs (3DGN/PtNP) was prepared according to a reported electrochemical deposition method.⁴⁷ Typically, the 3DGN electrode was immersed in a solution of 2 mmol L^{" 1} K₂PtCl₆ and 0.5 mol L^"1 HC10₄ under a deposition potential of -0.4 V (vs. Ag/AgCl) for 50 s. Then the electrode was rinsed with Milli-Q water and dried at room temperature.

Preparation of a composite of 3DGNs with MWCNTs

A composite of 3DGNs with MWCNTs (3DGN/MWCNT) was prepared by an electrophoretic deposition method (EPD).⁴⁸ Typically, a stable dispersion of MWCNTs (0.05 mg mL^"1) and Mg(N0₃)₂-6H₂0 (0.025 mg mL^"1) in isopropyl alcohol (IP A) was prepared by sonication of the mixture for 3 h. A piece of nickel foam and the 3DGN electrode were used as anode and cathode, respectively. The distance between these two electrodes was fixed at 1 cm. Direct current (DC) voltage (150 V) provided by a DC power supply (SPS 1.2 kW series programmable DC switching power supplies K-Panel version, AMREL, USA) was then applied to deposit MWCNTs on the 3DGN electrode for 1 min. The deposition process was repeated for 7 times.

Preparation of composite of 3DGNs with MWCNTs and PtNPs The composite of 3DGNs with MWCNTs and PtNPs (3DGN/ MWCNT/PtNP) was prepared by the electrochemical deposition method, which is similar to that used for deposition of PtNPs on 3DGNs as mentioned above. A deposition potential of -0.2 V (vs. Ag/AgCl) for 20 s was applied to the 3DGN/MWCNT composite electrode in the solution containing 2 mmol L^"1 K₂PtCl6 and 0.5 mol L^"1 HC10₄. Then the electrode was rinsed with Milli-Q water and dried at room temperature.

Preparation of composite of 3DGNs with Mn0₂ nanowalls

The composite of 3DGNs with Mn0₂ nanowalls (3DGN/Mn0₂) was prepared by the cathodic deposition.⁴⁹ It was performed on an electrochemical workstation with a conventional three- electrode cell (CHI 660C, CH Instrument Inc., USA), where the 3DGN, a Pt net, and a Ag/AgCl electrode (sat. KC1) were used as working, counter, and reference electrodes, i. e. WE, CE and RE, respectively. The electrode gap between WE and CE was fixed at 1 cm. First, the cyclic voltammetry (CV) was carried out in the electrolyte of 1 mol L^"1 H₂S0₄ at scan rate of 50 mV/s from 0 to 1 V for 10 cycles to make the surface of 3DGN more hydrophilic. Then, the 3DGN electrode was washed with Milli-Q water and it was immersed into a mixture, i.e., 0.1 mol L^"1 Mn(CH₃COO)₂-4H₂0 and 0.1 mol L^"1 Na₂S0₄ in Milli-Q water. A constant voltage of -1.6 V was applied for 5 min and the deposition process was repeated for 2 times. Then the samples were dried at 60 °C.

Electrochemical measurements

Electrochemical measurements were performed in a conventional three-electrode system (CHI 660C, CH Instrument Inc., USA), where the 3DGN, a Pt wire, and a Ag/AgCl electrode (sat. KC1) were used as working, counter, and reference electrodes, i.e. WE, CE and RE, respectively. In order to prepare the 3DGN electrode, 3DGN was first fixed on a 1 cm x 1.5 cm glass wafer by silicon rubber, the exposure area was fixed at 0.5 x 1 cm². Then, the silver paint was coated on the one end of 3DGN as electrode pad. The amperometric experiments were performed in the stirring electrolyte solution (10 mmol L^"1 PBS, pH=7.4) at 25 °C with successive additions of H₂0₂ at a potential of +0.45 V (vs. Ag/AgCl).

Characterization

SEM images were obtained using a field emission scanning electron microscopy (FESEM, Model JSM-7600F, JEOL Ltd., Tokyo). TEM images were obtained with a transmission electron microscopy (JSM-2100F and JSM-2010, JEOL Ltd., Tokyo). Raman spectra were collected with a WITEC CRM200 Raman System (488 nm laser, 2.54 eV, WITec, Germany). XPvD patterns were obtained by X-ray diffractometer (XRD-600, Shimadzu, Japan). To prepare TEM samples of 3DGN-based composites, the composites were first sonicated in ethanol for 1 min. Then a drop of the suspension was placed on TEM grid. To prepare samples for XRD, the Mn0₂ nanowalls were collected by carefully scratching the top surface of 3DGN/Mn0₂ electrode and sonicated in ethanol, then dropped on a glass slice for subsequent XRD characterization.

Results and discussion

FIG. 1 shows the scanning electron microscopy (SEM) images of 3D graphene networks (3DGNs) before and after deposition of PtNPs, MWCNTs and Mn0₂ nanowalls. The 3DGN has a 3D porous structure, in which the graphene sheets connect together and form a macroscopic entirety of continuous graphene films with plenty of pores inside (FIG. 1A). HRTEM image indicates a 4-layer graphene film of 3DGNs (inset in FIG. 1A). After deposition of PtNPs, MWCNTs and Mn0₂ nanowalls, as compared to the original 3DGNs (FIG. 1A), the graphene films exhibit more textured morphology (FIG. 1B-D), which were further examined by SEM, transmission electron microscopy (TEM) and Raman spectroscopy. FIG. 2A shows the SEM image of PtNP-decorated 3DGN (3DGN/PtNP). High-magnification SEM image (inset in FIG. 2A) and TEM image reveal that these PtNPs were formed by the aggregated small PtNPs (FIG. 2B and 4). The HRTEM image shows a lattice spacing of 0.19 nm (bottom inset in FIG. 2B), which can be assigned to the interplanar distance of the (200) planes of Pt with the face-centered cubic (fee) structure. The selected area electron diffraction pattern (SAED, top inset in FIG. 2B) exhibits three distinct diffraction rings corresponding to (1 1 1), (200) and (220) planes of fee Pt (Joint Committee for Powder Diffraction Standards (JCPDS) 87-0647).⁴⁷

FIG. 2C shows the SEM image of MWCNT-decorated 3DGN (3DGN/MWCNT), which presents a hierarchical structure composed of 3D porous graphene networks and entangled

MWCNT networks. Lots of protruded MWCNT tips are also observed at the edge of 3DGNs

(FIG. 5), which are highly active to the electrochemical reaction, and capable of serving as conduction channels for the electron transfer.⁵⁰ This novel structure of 3DGN/MWCNT was further functionalized with PtNPs, referred to as 3DGN/MWCNT/PtNP, to enhance the electrochemical performance. As shown in FIG. 2D, PtNPs were simultaneously deposited on both graphene and MWCNTs.

FIG. 2E is the SEM image of the composite of 3DGNs and Mn0₂ nanowalls (3DGN/ n0₂), which clearly shows that the Mn0₂ film coated on 3DGNs, consisted of the interconnected, petal-like and vertically standing nanowalls. XRD characterization in FIG. 10 indicates the Mn0₂ nanowalls correspond to the orthorhombic-phase Mn0₂ (JCPDS 44-0142). FIG. 2F shows a typical TEM image of Mn0₂ on 3DGN. From the HRTEM image, a lattice distance of 0.48 nm corresponding to the (200) planes of tetragonal-phase Mn0₂ (JCPDS 44-0141) is observed (inset in FIG. 2F).⁵¹ The typical Raman spectra of 3DGN/Mn0₂ shows the distinct G and 2D peaks of 3DGNs²² and also an additional peak at -640 cm^"1 (FIG.6), which is corresponding to the symmetric stretching vibration (Mn-O) of the Mn0₆ group.⁵² By using the 3DGN-based composite electrodes, their amperometric responses to H₂0₂ are shown in FIG. 3.

FIG. 7 shows the typical cyclic voltammograms (CVs) of the 3DGN and its composite electrodes. All electrodes exhibited great increase of oxidation and reduction current in the presence of 2 mM H₂0₂. The overpotentials of the 3DGN-based composite electrodes were lower than that of 3DGN, indicating the enhanced electrocatalytic activity toward H₂0₂. Their amperometric response to H₂0₂ is shown in FIG. 3 and FIG. 7F. The relationship between the oxidation current and H₂0₂ concentration are shown in FIG. 8 and Table 1 below.

Έχρ.: The detection limit measured according to the lowest H₂C>2 concentration detected experiments.

bCal.: The detection limit calculated in terms of a signal-to-noise ratio (S/N) of 3. Table 1. Analytical parameters for the amperometric determination of Η₂0₂ by using the graphene-based composite electrodes

As shown in FIG. 3 A and 8, the linear range for detection of H₂0₂ by the 3DGN/PtNP composite electrode is from 0.167 to 7.486 μΜ (R² = 0.9991). The detection limit of H₂0₂ was found to be 0.125 μΜ. FIG. 3B shows a typical amperometric response of the 3DGN/MWCNT composite electrode to H₂0₂. The detection limit of 6.54 μΜ was obtained with a linear relationship between the oxidation current and H₂0₂ concentration from 20 to 280 μΜ (R² = 0.9871). Although the 3DGN/MWCNT composite electrode showed a higher detection limit toward H₂0₂, the sensor performance was found to be improved after deposition of PtNPs on 3DGN/MWCNT. As indicated in FIG. 3C, the 3DGN/MWCNT/PtNP composite electrode exhibits a significantly enhanced detection limit (8.6 nM) to H₂0₂, and a linear detection range from 0.025 to 6.3 μΜ (R² = 0.9980). In addition, the typical amperometric response of 3DGN/Mn0₂ composite electrode to H₂0₂ is indicated in FIG. 3D. The 3DGN/Mn0₂ composite electrode showed a linear relationship between oxidation currents and H₂0₂ concentrations ranging from 0.38 to 13.46 μΜ (R² = 0.9937), and the detection limit was found to be0.27 μΜ.

To emphasize the advantages of using 3DGN-based composite electrodes for the amperometric detection of H₂0₂, our present results are compared with those previously reported by using other electrodes as shown in Table 2 below.

References :

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Table 2. Summary of the previously reported results for the amperometric determination of

Η₂0₂ by using different electrodes

The comparison as shown in Table 2 clearly indicates that the 3DGN-based composite electrodes exhibit a wide linear range, low detection limit and fast response for sensing ¾0₂.

The excellent performance of 3DGN-based composite electrodes can be ascribed to the combination of 3DGN and the functionalized electroactive materials, where the CVD- synthesized graphene film plays an essential role as not only the high-surface-area matrix to anchor active materials, but also the excellent conductive channel to facilitate the fast electron transfer. The porous structure of 3DGN also enables the efficient contact between the electrolyte and electrode surface, resulting in a rapid response to analyte. The aforementioned results indicate that the 3DGN-based composite could be a promising material used for electrochemical sensing applications

It is thus demonstrated that the three-dimensional graphene networks (3DGNs) can be used as templates for construction of graphene-based composites, which are further used as electrochemical sensors. All of the prepared 3DGN-based composite electrodes have exhibited good electrochemical response to H2O2 detection. In particular, the detection limit is found as low as 8.6 nM by using the composite consisting of 3DGNs, MWCNTs and PtNPs. The present invention thus provides a novel platform for electrochemical sensing.

Whilst there has been described in the foregoing description exemplary embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations in details of design, construction and/or operation may be made without departing from the present invention.

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Claims

1. A three-dimensional graphene network composite for hydrogen peroxide detection, the composite comprising:

an electrically conductive graphene network electrode having a three-dimensional porous structure comprising a macroscopic entirety of continuous graphene films having a plurality of pores therein; and

at least one electroactive material deposited on the three-dimensional graphene network electrode, the at least one electroactive material configured to function as an electrochemical sensor for detecting hydrogen peroxide.

2. The three-dimensional graphene network composite of claim 1, wherein the at least one electroactive material is selected from the group consisting of: platinum nanoparticles, multi- walled carbon nanotubes and Mn0₂ nano walls.

3. The three-dimensional graphene network composite of claim 2, wherein a first of the at least one electroactive material comprises multi- walled carbon nanotubes and a second of the at least one electroactive material comprises platinum nanoparticles.

4. The three-dimensional graphene network composite of claim 3, having a response time of less than or equal to 1.5 seconds.

5. The three-dimensional graphene network composite of claim 3 or claim 4, having a detection limit of less than 0.009 μΜ when calculated in terms of a signal-to-noise ratio of 3.

6. The three-dimensional graphene network composite of any one of claims 3 to 5, having a linear detection range from about 0.025 μπι to about 6.3 μπι.

7. A method of synthesizing a three-dimensional graphene network composite for hydrogen peroxide detection, the method comprising:

synthesizing via chemical vapour deposition an electrically conductive graphene network electrode having a three-dimensional porous structure comprising a macroscopic entirety of continuous graphene films having a plurality of pores therein; and depositing at least one electroactive material on the three-dimensional graphene network electrode, the at least one electroactive material configured to function as an electrochemical sensor for detecting hydrogen peroxide.

8. The method of claim 7, wherein a first of the at least one electroactive material comprises multi-walled carbon nanotubes and a first of the depositing comprises using eletrophoretic deposition to deposit the multi- walled carbon nanotubes on the three- dimensional graphene network electrode to form a three-dimensional graphene network / multi-walled carbon nanotubes composite electrode.

9. The method of claim 8, wherein a second of the at least one electroactive material comprises platinum nanoparticles and a second of the depositing comprises using electrochemical deposition to deposit the platinum nanoparticles on the three-dimensional graphene network / multi-walled carbon nanotubes composite electrode.

10. The method of claim 7, wherein the at least one electroactive material comprises Mn0₂ nanowalls and the depositing comprises using cathodic deposition to deposit the Mn0₂ nanowalls on the three-dimensional graphene network electrode.