Description:CEMENT SUPPORTED CONDUCTIVE SALTS COMPOSITED PROTON EXCHANGE MEMBRANE FOR A MICROBIAL FUEL CELL

CROSS-REFERENCES TO RELATED APPLICATION

[0001] None.

FIELD OF THE INVENTION

[0002] The disclosure generally relates to renewable electricity production in microbial fuel cell technology using a Novel Cement Supported Conductive Salts (NCSCS) composited Proton Exchange Membrane (PEM) and in particular to a method of preparing the NCSCS PEM through a unique indigenous method.

DESCRIPTION OF THE RELATED ART

[0003] Many efforts have been made worldwide to produce alternative energy through low-cost methods. The utilization of waste sources having biodegradable organics plays significant responsibility bioelectricity production. With the world's increasing industrialization, the urgent need of the hour is to address the considerable waste disposal problem.

[0004] Nowadays, bioelectricity production is significantly increasing at the industrial level and it is the next generation power source for household and industrial applications, etc, because of alarming climate change. For efficient bioelectricity production, new and novel materials are needed to transform the carbon economy into a bio economy and control the emission of polluted gases. India intends to achieve carbon neutrality by 2070. However, there is a need for practical solutions and direct resources in the right direction to make this a reality and to have a green environment.

[0005] Dual chamber Microbial fuel cell systems are disclosed in the US patents US10700375B2, US11105002B2, US9149845B2, US8283076B2, US20090017512A1 and the Chinese patent CN104558654B using various membrane-based technologies and different modules.

[0006] Proton Exchange Membrane (PEM) transfers protons in a Microbial Fuel Cell (MFC) system. Membrane-based microbial fuel cells are costly, however comparatively power production is higher when compared to membrane-less MFC methods. Nevertheless, it hasn’t been used in large scale applications due to the scarcity of the elements and high cost of the material. Numerous efforts have been taken to replace the high-cost materials to low-cost using earth-abundant materials.

[0007] The main function of the PEM is to distinguish the anodic and cathodic products and to permit only proton transportation to overcome the recombination of the generated ions. So, the PEM must have high proton conductivity, high mechanical and thermal stability. The membrane properties are intimately related to the ionic, mechanical, thermal stability, cross-linking density, nature, and concentration of the ionic charges (ionic conductivity, charge density, ion exchange capacity, and transport number).

[0008] The most commonly used PEM is a perfluorosulfonic acid polymer membrane. Nafion membranes are chemically stable due to their unique perfluorinated structure and are essential for long fuel cell battery life. Recently, PEMFCs are considered as a potential candidate and it is a key component for future energy source applications such as portable equipment, industries and powertrain for transport. However, the Korean patent KR100978117B1 describes that the Nafion membrane can deform as it expands during moisture absorption and shrinks during moisture loss under operating conditions of microbial fuel cell. In addition, once Nafion membrane absorbs water, the strength of the wet membrane is significantly reduced. Since fuel cells are usually operated at high humidity, such adverse effects can seriously impact the Nafion membrane's lifetime. The leading disadvantage in Nafion membrane are luxurious manufacturing process and robust diminution in proton conductivity at the temperature of above 90°C.

[0009] To overcome this problem, US Patent US6045230 introduced microporous ePTFE membranes as support for the catalyst layer during the fabrication of the catalyst layer. Catalyst / Nafion dispersion solution is painted or coated on the ePTFE membrane. However, the Korean patent KR100978117B1 stated that Nafion manufacturing needs high-cost raw materials.

[0010] Further, different types of membranes are disclosed in the US patents US8436057B1, US8492049B2, and US7888397B1. Although it has made great attraction in application in MFC and has had early success, there are still several limitations in addition to its higher cost.

[0011] Systems and methods are developed that may overcome the problem of the PEM discussed above.

SUMMARY OF THE INVENTION

[0012] In various embodiments a Proton Exchange Membrane (PEM) comprising a composite having one or more Cement supported conductive salts is disclosed. The PEM is stable up to a temperature of 500oC. In various embodiments, the membrane when used in a Microbial Fuel Cell (MFC) assembly produces power of at least 204 mW/m2 in a 500ml capacity MFC assembly.

[0013] In various embodiments, a method of preparing a PEM is disclosed. The method includes mixing a cement component and a conductive salt material and water in a ratio 1: 1: 0.25 to obtain a mixture, curing the obtained mixture by mixing the obtained mixture with a mixture of salts in the ratio 1: 1 to obtain a cured mixture and pouring the cured mixture into a pipe for casting and drying to form a membrane.

[0014] In various embodiments, the cement component is Portland cement and the mixture of salts comprises potassium chloride and sodium chloride. In various embodiments, the pipe is a Poly Vinyl Chloride (PVC) pipe. In various embodiments, drying comprises heating the cured mixture in a 60ºC hot air oven for 24 hrs in intervals of 1 hr.

[0015] In various embodiments, a microbial fuel cell assembly is disclosed. The microbial fuel cell assembly includes an anode chamber comprising a graphite electrode, a cathode chamber comprising a graphite electrode, and a PEM comprising a composite having one or more conductive salts and Cement, wherein the PEM is placed between the anode chamber and the cathode chamber.

[0016] In various embodiments, the MFC assembly produces power of at least 204 mW/m2 in a 500ml capacity MFC assembly.

[0017] This and other aspects are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention has other advantages and features, which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0019] FIG. 1 illustrates a flow diagram of the method of preparing a Novel Cement Supported Conductive Salts (NCSCS) Proton Exchange Membrane (PEM), in accordance with an embodiment of the present disclosure.

[0020] FIG, 2 depicts a schematic diagram of the Microbial Fuel Cell (MFC) assembly with an anode chamber, a cathode chamber and the NCSCS PEM connecting the anode chamber and the cathode chamber.

[0021] FIG. 3 depicts the Nyquist plot obtained from the NCSCS PEM in the conductive Warburg curve obtained during a MFC bioelectricity production.

[0022] FIG. 4 depicts the thermal stability of the NCSCS PEM, given by Thermogravimetric Analysis (TGA) and Differential thermal analysis (DTA) curve.

[0023] FIG. 5 depicts the X-ray diffraction method that analyzed desired NCSCS PEM.

[0024] FIG. 6 depicts the MFC OCV curve presentation attained with the invented proton exchange membrane with different MFC conditions (NCSCS PEM with raw STWW, raw STWW with our bacterial culture AATB1 and control (sterile STWW).

[0025] FIG. 7 depicts the polarization curve of a MFC comprising the NCSCS PEM with different MFC conditions (NCSCS PEM with raw STWW, raw STWW with our bacterial culture AATB1 and control (sterile STWW).

[0026] FIG. 8A-8F illustrates the surface analysis of the NCSCS PEM through SEM.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0028] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on.” Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0029] The present subject matter is further described with reference to FIG. 1- FIG.8A-8F. It should be noted that the description and figures merely illustrate principles of the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, encompass the principles of the present subject matter. Moreover, all statements herein reciting principles, aspects, examples, and embodiments of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0030] The present subject matter discloses a Novel Cement Supported Conductive Salts (NCSCS) composited Proton Exchange Membrane (PEM) for use in Microbial Fuel Cells (MFC). The NCSCS PEM is stable up to a temperature of 500°C. In various embodiments, a method of preparing the NCSCS PEM is disclosed. Further, a Microbial Fuel Cell (MFC) assembly incorporating the NCSCS PEM is disclosed. The MFC generates bioelectricity in an economically feasible manner.

[0031] In various embodiments a method 100 of preparing the NCSCS PEM is disclosed. FIG. 1 illustrates the steps involved in the preparation of the NCSCS PEM, according to an embodiment of the present disclosure. At block 101, the method includes mixing a cement component, a conductive salt material and water in a ratio 1: 1: 0.25 to obtain a mixture. In another embodiment, the method includes mixing the cement component, the conductive salt material and water in a ratio 2: 2: 0.5 to obtain the mixture. The mixture is prepared by stirring the cement component, the conductive salt material and water for a predetermined time of 4 hours. When the cement component is mixed with water, C3S and C2S are hydrated and produce Calcium Silicate Hydrate (3CaO.2SiO2.3H2O in short form C—S—H) by the following exothermic reaction:

2Ca3SiO5+6H2O 3CaO.2SiO2.3H2O+3Ca (OH) 2 …….(1)
2Ca2SiO4+4H2O 3CaO.2SiO2.3H2O+Ca (OH) 2…….(2)

[0032] Further, the mixture is porous. The prepared mixture is allowed to set for a predetermined time. In various embodiments the calcium silicate component is Portland cement.

[0033] At block 103, the method includes curing the obtained mixture by mixing the obtained mixture with a mixture of salts in the ratio 1: 1 to obtain a cured mixture. The mixing of the mixture obtained in block 101 and the mixture of salts in equal quantities binds protonic elements with solid Portland cement, salts with water.

[0034] At block 105, the method includes pouring the cured mixture into a pipe for casting and drying to form a membrane. Drying includes heating the cured mixture in a 60ºC hot air oven for 24 hrs in intervals of 1 hr. This allows formation of desired structure for proton flow. In various embodiments, the pipe is a Poly Vinyl Chloride (PVC) pipe. Further, the major composition of the NCSCS PEM is Cement supported conductive salts and the conductive salts work as ion exchangers. Hence the conductivity increases.

[0035] In various embodiments, a Microbial Fuel Cell (MFC) assembly is disclosed. FIG. 2 illustrates a MFC assembly 200 comprising an anode chamber 201, a cathode chamber 203 and a NCSCS PEM 205 placed between the anode chamber 201 and the cathode chamber 203. The anode chamber has a graphite electrode 207 and the cathode chamber has a graphite electrode 209. In various embodiments the graphite electrodes 207, 209 may be the same or may have different composition and characteristics. In various embodiments, the NCSCS PEM 205 connects the anode chamber 201 and the cathode chamber 203. The NCSCS PEM 205 is a highly conductive and stable inorganic proton exchange membrane. Further, NCSCS may conduct protons or electrons in a highly salty environment. In various embodiments, the proton transfer involves transporting protons by MX phase changing crystal structure. The assembly 200 avoids crossover of anion liquid to cation, creating a strong barrier which is useful for large-scale MFC systems. In various embodiments, the MFC assembly produces power of at least 204 mW/m2 in a 500ml capacity MFC assembly.

[0036] The advantages of the NCSCS PEM are the membrane is scalable, low-cost, stable and environmentally friendly. Further, the NCSCS PEM is suitable to operate at elevated temperatures and pressures and may be applied in large-scale MFC systems. Furthermore, with increased water content, the NCSCS PEM has excellent mechanical stability, dimensional stability and power production in MFC.

[0037] Examples

[0038] Example 1: Preparing a NCSCS PEM and constructing a MFC comprising the NCSCS PEM and analyzing the properties of the NCSCS PEM

[0039] To synthesize the NCSCS PEM Ordinary Portland Cement (OPC) and conductive salts are brought from Chettinad cement and Himedia salts.
[0040] The four significant compounds in OPC are tricalcium silicate (Ca3SiO5 in short form C3S), dicalcium silicate (Ca2SiO4 in short form C2S), tricalcium aluminate (Ca3Al2O6 in short form C3A), tetra calcium aluminoferrite (Ca4Al2Fe2O10 in short form C4AF) and the extent of its composition are given in Table 1.

Table 1: Composition of Ordinary Portland Cement
Compound Composition as %
C3S 48-52
C2S 22-26
C3A 6-10
C4AF 13-16
Free lime 1-2

Since C3S and C2S are the major compositions of OPC, they play a crucial role in determining its properties.

Table 2: Composition of the mixture

Element Weigh percent Atom percent
O 57.11 76.63
Ca 41.15 22.04
Si 1.73 1.32
Total 100.00 100.00

When OPC is mixed with water, C3S and C2S are hydrated and produce Calcium Silicate Hydrate (3CaO.2SiO2.3H2O in short form C—S—H) by the exothermic reaction in equation (1) and (2).

[0041] So, the major composition of the NCSCS PEM is Cement and conductive salts once Portland cement is blended with conductive salts followed by casting and conductivity, as illustrated in Table. 2. Hence, the conductivity increases when salinity increases. The NCSCS PEM is directly proportional to the conductivity, such as proton and electron movement is faster and higher conductivity represented in the OCV of output voltage. So, NCSCS can conduct protons/electrons in a highly salty environment of MFC assembly.

[0042] Further, the mechanism in the MFC relates to commercial Nafion membranes, hence reducing the cost of MFC and the PEM by 94% comparing currently market available membranes, i.e., Nafion, AXM 7000 and CXM. Table. 3 illustrates a comparison of the cost of available PEMs with that of NCSCS PEM.

Table. 3: comparison of the cost of available membranes with that of NCSCS PEM.

Name of the membrane Cost of Membrane Cost reduction % by NCSCS PEM Reference

Dupont Nafion 117 Variable (the lowest assumed value= $500/m2) 96 ± 2 % https://www.energy.gov/eere/fuelcells/articles/manufacturing-cost-analysis-pem-fuel-cell-systems-5-and-10-kw-backup-power

CXM-200 (CMI-7000S) Variable (the lowest assumed value= $400/m2) 92 ± 5% https://ionexchangemembranes.com/price-list/

AXM-100 (AMI-7001S) Variable (the lowest assumed value= $400/m2) 92 ± 5 % https://ionexchangemembranes.com/price-list/

[0043] The ionic conductivity and static and dynamic transport of the NCSCS PEM were analyzed using Nyquist plot (EIS Impedance spectra). FIG. 3 depicts the Nyquist plot obtained from NCSCS PEM in the proton conductive Warburg curve obtained during the MFC bioelectricity production. The NCSCS membrane electrode assembly contained EIS circle Nyquist plot obtained. The thermal and mechanical stability of the developed membrane were investigated by TGA graph, respectively. FIG. 4 depicts the thermal stability of the invented proton exchange membrane (NCSCS), given by Thermogravimetric Analysis (TGA) and Differential thermal analysis (DTA) curve. When compared with commercial PEM, the NCSCS PEM reduced weight by 2% only at 500ºC. But Commercial membranes showed 50% degraded weight loss at 500ºC.

[0044] Elemental analysis was carried out by X-ray diffraction (XRD) methods. FIG.5 depicts the X-ray diffraction method that analyzed desired NCSCS PEM. The phase of the crystalline structure was obtained at 2Ø position number 31.7300 at 100% intensity. FIG.6 depicts the Microbial fuel cell Open circuit Voltage (OCV) curve presentation attained with NCSCS PEM with different MFC conditions (with raw STWW, raw STWW with our bacterial culture AATB1 and control (sterile STWW).

[0045] FIG.7 depicts the polarization curve of a Microbial fuel cell comprising the NCSCS PEM with different MFC assembled conditions with NCSCS PEM in raw STWW and raw STWW with our bacterial culture AATB1 and control (sterile STWW). From the polarization curve, X-axis represents the current density (mA/m2), and Y-axis represents the power density (mW/m2) and OCV.

[0046] When ordinary Portland cement is mixed with conductive salt and water, the cement creates porosity to form the NCSCS structure. The conductive salts work as ion exchangers in cement paste. The micrometer level is in the form of “Nano porous proton exchange membrane”. It has a “sandwich”-like layered structure with a layer of salts clipped in two layers of silicon-oxygen tetrahedron. The distribution (ionic clouds) of Ca2+ forms bonds (bridges) only near isoelectric point surfaces (pH 11.6). FIG. 8A-8F depicts the Surface analysis of NCSCS PEM through SEM. The porosity of the crystalline structure is indicated. From evolution NCSCS, Conductive labile salts act as bridges in OPC as Na2+ ion becomes supersaturated at a high value with respect to precipitation of Sodium ions. Table. 4 illustrates the comparison of properties of PEMs available with NCSCS PEM.

Table. 4: Comparison of properties of PEMs with NCSCS PEM

Membrane/ Properties Nafion 117 Salt bridge NCSCS PEM
Mechanical stable at large volume Less stable Very less stable Highly stable
Conductivity at 30°C (mS/cm) 69 ± 0.15 54 ± 0.32 84 ± 0.38
Ion Exchange Capacity (mequiv/g) 0.9026 0.7534 1.5691
Internal
Resistance (?) 318 ± 3.78 231± 2.56 187 ± 3.12
Max OCV (mV) in 500ml MFC 571 ± 3.51 654 ± 3.60 721 ± 2.51
Power production in MFC (mW/m2) 126.6 ± 1.06 188 ± 2.10 204 ± 2.87
Current production in MFC
(mA/m2) 475.6 ± 0.67 542.5 ± 4.56 600.5 ± 2.63
Weight loss at 500ºC (%) 50 100 2

[0047] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the system and method of the present invention disclosed herein without departing from the spirit and scope of the invention as described here.

, Claims:WE CLAIM:
1. A Proton Exchange Membrane comprising a composite having conductive salts and cement components.

2. The Proton Exchange Membrane as claimed in claim 1, wherein the membrane is stable up to a temperature of 500oC.

3. The Proton Exchange Membrane as claimed in claim 1, wherein the membrane when used in a Microbial Fuel Cell (MFC) assembly produces power of at least 204 mW/m2 in a 500ml capacity MFC assembly.

4. A method (100) of preparing a Proton Exchange Membrane (PEM) comprising:
mixing (101) a cement component, a conductive salt and water in a ratio 1: 1: 0.25 to obtain a mixture;
curing (103) the obtained mixture by mixing the obtained mixture with a mixture of salts in the ratio 1: 1 to obtain a cured mixture; and
pouring (105) the cured mixture into a pipe for casting and drying to form a membrane.

5. The method (100) as claimed in claim 4, wherein the cement component is Portland cement.

6. The method (100) as claimed in claim 4, wherein the mixture of salts comprises potassium chloride and sodium chloride.

7. The method (100) as claimed in claim 4, wherein the pipe is a Poly Vinyl Chloride (PVC) pipe.

8. The method (100) as claimed in claim 4, wherein drying comprises heating the cured mixture in a 60ºC hot air oven for 24 hrs in intervals of 1 hr.

9. A microbial fuel cell assembly (200) comprising:
an anode chamber (201) comprising a graphite electrode (207);
a cathode chamber (203) comprising a graphite electrode (209); and
a Proton Exchange Membrane (PEM) (205) comprising a composite having cement supported conductive salts, wherein the PEM (205) is placed between the anode chamber (201) and the cathode chamber (203).

10. The microbial fuel cell assembly (200) as claimed in claim 9, wherein the 500ml capacity MFC assembly produces power of at least 204 mW/m2.

Dated this 27th day of November 2023

R. Malini Devi
IN/PA 4638
Of PATWISE CONSULTING SOLUTIONS
Applicant’s Agent