A composite material, a method for producing the composite material and use thereof

Abstract

The disclosure relates to a composite material, consisting of: titania mesoparticles (TiO2 MPPs) consisting of one-dimensional lepidocrocite (1DL) TiO2 sub- and / or nano- filaments, and activated carbon (AC). The disclosure further relates to a method for producing the composite material and use thereof as electrode materials, materials for water purification, or catalysts.

Description

[0001] A composite material, a method for producing the composite material and use thereof

[0002] Technical field

[0003] The present disclosure relates to a composite material, a method for producing the composite material, and use thereof.

[0004] Background art

[0005] The climate crisis, exponential population growth, and ever-depleting fossil fuels have led to the initiated adoption of a carbon-neutral green economy. Therefore, the progress of energy storage technologies from renewable sources is paramount for a sustainable environment. Electrochemical energy storage (EES) systems have garnered significant appeal from both business sectors and academics due to their easy handling, storage capacity, and efficiency. In this genre, supercapacitors (SCs) have received increasing interest owing to their low cost, simple, safe operation, prolonged lifespan, higher power density, pulsed power supply, and high dynamics of charge propagation. SCs can bridge the gap between traditional shunt capacitors and batteries, addressing the shortcomings of the latter (e.g., short lifetime and manufacturing cost). Although carbon materials, polymers, metal oxides, and hydroxides are the most explored electrode materials for SC electrodes, fatal limitations (e.g., low capacitance and energy density, poor mechanical and electrochemical stability) of those materials have limited their applications. Thus, designing electrode materials with higher specific capacitance, energy density (without compromising power density), and lower selfdischarge is necessary for the desired device performance in real applications.

[0006] WO 2022 / 174264 discloses a composition comprising titanium oxide-based nanofilaments and / or sub-nanofilaments prepared by a bottom-up, scalable synthesis. The composition can be present as a mesoporous powder in which the powder particulates comprise the oxide-based nanofilaments and / or sub-nanofilaments. The composition is suggested for therapeutic use and in energy storage devices such as batteries or supercapacitors (SCs).

[0007] While the porous TiO? mesoparticles possess excellent ionic conductivity and exhibit enhanced faradic behavior in acidic aqueous media, they lack the electronic conductivity needed for efficient interfacial reactions. SCs are essential components of many electronic devices. They are designed to store electrical energy and release it quickly when needed. However, there are challenges and limitations hindering widespread use of SCs as reliable and efficient energy sources for various applications. One of the most critical challenges for SCs is to achieve high capacitance and energy storage capacity while at the same time maintaining high power output and cycle stability. Furthermore, the cost of manufacturing SCs can be relatively high compared to traditional batteries.

[0008] Furthermore, designing and tailoring high-end electrode materials is not cost-effective and straightforward.

[0009] There is thus a need for improved electrode materials for energy storage and energy conversion.

[0010] The present inventors have surprisingly been able to provide a unique composite material in a cost-effective way possessing exceptional mechanical and electrochemical characteristics.

[0011] On this basis, the present invention has been provided.

[0012] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above-mentioned problem.

[0013] It is thus a main object of the present invention to provide a stable high-quality material useful for energy conversion and energy storage.

[0014] Another object of the present invention is to provide a method for producing such a material in a facile and cost-effective way.

[0015] These and other objects are obtained by the subject-matter as defined in the accompanying claims. Definitions

[0016] The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

[0017] Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the material described or steps of the methods described since such material and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting.

[0018] It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several means, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[0019] The term TiO? as used in the present application (in the form of ID or 2D filaments, 2D flakes, and 3D mesoporous particles) covers both pure TiOz, titanates, where the O:Ti ratio is > 2, and TiOz that contains defects in the form of both Ti- and / or O-vacancies.

[0020] The terms "TiOz MPPs" and "MPPs" as used herein have the same meaning, i.e. mesoporous particles with TiOz as defined above, and are used interchangeably in the present disclosure.

[0021] The composite according to the invention is indicated interchangeably as "TiOz MPPs@AC" and "MPPs@AC" in the present disclosure. Activated Carbon (AC) possesses a large surface area and a porous structure, which is easy to synthesize at low cost. The activated carbon used herein covers all possible carbon sources such as commercial, doped, waste-derived, bio-derived, etc.

[0022] Brief descriptions of the drawings

[0023] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

[0024] Figure 1 shows a synthesis scheme of a TiO? MPPs@AC composite according to an embodiment of the present disclosure.

[0025] Figure 2 shows SEM micrographs of 25 wt.% MPPs@AC composites at varying magnification (d=3 pm, e=l pm and f=500 nm).

[0026] Figure 3 shows an electron image (g), and SEM-EDS maps of 25 wt.% MPPs@AC composites (h=Ti atom distribution, i=O atom distribution and j=C atom distribution across the AC surface).

[0027] Figure 4 shows typical X-ray diffraction (XRD) patterns of AC, MPPs, and their composites.

[0028] Figure 5 shows BET isotherms of AC and TiO? MPPs@AC composites with varying concentration of TiO? MPPs.

[0029] Figure 6 shows pore distribution of AC and TiO? MPPs@AC composites with varying concentration of TiO? MPPs.

[0030] Figure 7 shows a Ragone plot of pristine AC and TiO? MPPs@AC composites with varying concentration of TiO? MPPs. Figure 8 shows electrochemical characterization of 25 wt.% MPPs@AC symmetric cell in IM H2SO4, cycle stability and coulombic efficiency. Inset shows first and last five cycles of galvanostatic charge-discharge (GCD) response.

[0031] Detailed description

[0032] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0033] In a first aspect, the present invention provides a composite material, consisting of: titania mesoparticles (TiO? MPPs) consisting of one-dimensional lepidocrocite (1DL) TiO? sub- and / or nano-filaments (NFs), and activated carbon (AC).

[0034] In a preferred embodiment of the composite material, the TiO? MPPs are on the surface of the AC.

[0035] In another embodiment of the composite material, the TiO? MPPs are on the surface and / or in the pores of the AC.

[0036] The activated carbon may be of any carbon source, such as commercial carbon, doped carbon, waste-derived carbon, bio-derived carbon or any mixture thereof.

[0037] The composite material (TiO? MPPs@AC) of the invention has a unique morphology, which is totally different from the laminar lepidocrocite titanate structures according to prior art. That is, lepidocrocite titania mesoparticles are immobilized on an activated carbon surface to create a unique composite structure with exceptional electrochemical properties.

[0038] The TiO? MPPs@AC composite of the invention exhibit superior ionic conductivity at the expense of electronic conductivity. Adsorption of TiO? MPPs into the pores of AC enables the composite to participate in faster and more efficient ion dispersion at the electrode / electrolyte interface.

[0039] AC's higher surface area and abundance of mesopores provide active sites for TiO?

[0040] MPPs adsorption, as puzzle pieces fall into places. The TiO? MPPs exhibit enhanced ionic conductivity, generating many ions in an acidic medium, but suffer from poor electronic conductivity. Adding AC, which has high electrical conductivity, enhances charge storage. The invented composite (TiO? MPPs@AC) exhibits a unique architecture that facilitates enhanced electrochemical performances (specific capacitance of 1082 Fg1with a specific energy of 571 Whkg1at 2mVs-1scan rate with 97% cyclic stability over 10,000 cycles in IM H2SO4).

[0041] The inclusion of double-layer (AC) and faradic (TiOz MPPs) components complements each other's shortcomings and results in an improved composite structure for the SC electrode. The galvanostatic charge-discharge (GCD) reveals the highest specific capacitance of 478 Fg1with specific energy and power of 252.6 Whkg1and 487.5 Wkg-1, respectively, at 0.5 Ag ~1. The highest specific power of 4875 Wkg1was recorded at 5 Ag1current density while maintaining a specific energy of 150.5 Whkg-1.

[0042] In addition to the superior properties of energy storage and conversion, the composite material of the invention is also suitable for use in membranes, electrodes, powders, filters, etc. for water purification and as catalysts.

[0043] In an embodiment, the concentration of TiO? MPPs in the composite material is in the range from 5-80 wt%.

[0044] The concentration of TiO? MPPs will vary dependent on the application. For instance, in energy storage, the concentration of TiO? MPPs is preferably in the range from 5 to 25 wt% for aqueous electrolytes, and for organic electrolytes, the concentration of TiO? MPPs is preferably in the range from 50 to 75 wt%.

[0045] In another embodiment, the composite material is stable in ambient conditions. That is, the material does not oxidize and degenerate at ambient conditions over time. In a second aspect, the invention provides a method for producing the composite material defined above, comprising the following steps:

[0046] -preparing three-dimensional titania mesoparticles (TiOz MPPs (3D)) by contacting a mono-, binary, ternary, or higher carbide, nitride, boride, phosphide, phosphate, chloride, perchlorate, aluminide, silicide, sulphate or oxysulphate of titanium with a quaternary ammonium salt and / or base under heating to a temperature of from 25 to 95 °C and stirring for from about 1 hour to about one week, followed by washing with a C1-C3 alcohol until pH is about 6-8, and drying;

[0047] -washing the TiOz MPPs (3D) with a metal salt and / or water-soluble metal compounds to obtain TiOz MPPs consisting of IDL TiOz sub- and / or nano-filaments (NFs);

[0048] -mixing the TiOz MPPs with AC in a C1-C3 alcohol under stirring for from about 1 hour to about 48 hours at room temperature; and

[0049] - drying the resulting solution to obtain the composite material as a powder.

[0050] The TiOz MPPs consisting of IDL TiOz NFs are synthesized via a bottom-up process and dispersed through the surface and / or pores of the AC. That is, the formation of larger nanostructures from smaller atoms and molecules by means of chemical reactions among the atoms / ions / molecules. This is in contrast to a top-down processes, where the layered structure is present initially and treated in such a way as to delaminate the structure.

[0051] The method of the invention enables mixing titania mesoparticles (TiOz MPPs) consisting of IDL TiOz sub- and / or nano-filaments on the surface and / or in the pores of activated carbon.

[0052] According to the present invention, a simple and efficient method is developed that combines TiOz MPPs with AC, resulting in a TiOz MPPs@AC composite exhibiting exceptional supercapacitive performance.

[0053] Thereby, a facile, scalable, cost-effective, and high-quality synthesis of electrode material is obtained. In an embodiment of the method, the quaternary ammonium salt and / or base comprises an ammonium hydroxide, such as tetramethylammonium hydroxide (TMAOH or TMAH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH), ammonium hydroxide NH4OH, their amine derivatives, or any combination thereof.

[0054] In another embodiment of the method, the metal in the metal salt is selected from the group consisting of: H, Li, Na, Mg, Mn, Fe, Co, Ni, and Zn.

[0055] Preferable metal salts are selected from LiCI, NaCI, FeSC , NiCb, C0CI2, MgCb, ZnCb, HNO3, etc.

[0056] In another embodiment of the method, the C1-C3 alcohol is methanol, ethanol, 1- propanol, or 2-propanol or any mixture thereof. Preferably, the C1-C3 alcohol is methanol or ethanol.

[0057] In a preferred embodiment of the method, the mixing step of the TiC MPPs with AC takes place for about from 8 hours to about 48 hours.

[0058] In a further embodiment of the method, the drying is air drying, vacuum drying, freeze- drying or any combination thereof.

[0059] In a third aspect, the present invention provides use of the composite material as defined above in the first aspect, as an electrode material, a material for water purification, or catalysts.

[0060] In one embodiment of the invention, the composite material is used as an electrode material in an energy storage device, such as a supercapacitor or a battery.

[0061] In another embodiment of the invention, the composite material is used in a material for water purification such as membranes, electrodes, powders, filters, etc.

[0062] The invention is explained in more detail in the examples below. The examples are only meant to be illustrative and shall not be considered as limiting. Example 1

[0063] Synthesis of TiOz MPPs

[0064] TiBz precursor was mixed with 25 wt.% TMAH aqueous solution in a molar ratio of Ti:TMA of 0.51 in a polyethylene bottle. The mixture was heated at 80 °C for 48 hours (h). The resultant solution was washed with ethanol several times to remove excess TMA (until the pH was 7) and air dried. To remove the TMA cations and improve the stability in water, the powders were further washed (at least 3-4 times) with a 5 M LiCI solution and then dried at 50 °C in a vacuum oven. This procedure resulted in the formation of free-flowing MPPs.

[0065] Preparation of TiOz MPPs@AC composites

[0066] TiOz MPPs were mixed with AC, in various ratios, viz. 25, 50, and 75 wt.%. The blend was dispersed in 20 ml methanol. The solution was then stirred at 500 rpm at room temperature (RT) overnight. Lastly, the resultant suspension was freeze-dried and characterized.

[0067] The composite morphologies were imaged in a field emission scanning electron microscopy, FESEM (Zeiss; Model: Sigma 300, Germany) at varying magnifications. The qualitative analysis of the composites was carried out using energy dispersive X-ray spectroscopy (EDS) analysis with an Oxford Instruments X-Max 80 mm2silicon drift detector (SDD). The structure and crystallinity were analyzed by powder X-ray diffraction, XRD (Pa na lytica I; model: X'pert, Netherlands). The scan was conducted at 2q values ranging from 5 to 80°, with a step size of 0.02° and a scan rate of 0.5 s / step. The radiation used was CuKa (40 kV, 40 mA). The Nz adsorption-desorption (surface area and porosimetry measurements) was evaluated via Micromeritics (Model: ASAP2020, USA).

[0068] In Fig. 1, a synthesis scheme of the TiOz MPPs@AC composite is shown.

[0069] Typical SEM micrographs of 25 wt.% TiOz MPPs@AC composites are shown in Fig. 2 at varying magnifications (3 pm, 1 pm and 500 nm). The micrographs depict that MPPs are well dispersed through the mesopores of the AC. This arrangement allows for optimal utilization of the high surface area of AC to enhance the electrochemical performance by channelling ions through the MPPs.

[0070] Fig. 3 map the Ti and O atom distributions across the AC surface. Notably, the carbon support also contributes to the C map, overshadowing the C from the composite.

[0071] Typical XRD patterns of AC, TiO2MPPs, and their composites are shown from bottom to top, respectively, in Fig. 4. The (010) diffraction peak at the lower 20° angle (9.4°) and its higher 0B0 reflections (indicated by asterisks) represent the spacing between NFs along the b- direction. The distance between the 1DL NFs is calculated to be 9.39A at 20=9.4°. This is unlike stacking along the c-direction in 2D materials like MXene, 2D oxides, and others. However, like their 2D counterparts, the peak positions are a strong function of the intercalated cations. The fundamental peaks for lepidocrocite structure are at 20 values of 48.6° and 62.5°, indexed as 200 and 002, respectively. Regardless of the cation's nature, these characteristic peaks confirm the crystallographic arrangement of the NFs. The diffraction pattern of AC indicates an amorphous nature with broad peaks centered at 22.8° and 43.5°, attributed to reflections from the (002) and (100) planes. Based on the constant number of peaks observed after forming the TiO2MPPs@AC composite, we can confidently conclude that both components exhibit excellent crystallographic stability.

[0072] The textual parameters (e.g., porosity, surface area, etc.) were investigated through N2 adsorption-desorption at 77 K. The BET (Brunauer-Emmett-Teller) model was employed to calculate the surface areas and pore size distributions. The AC and the varying concentration of TiO2MPPs in AC show a combination of type I and type IV isotherm Fig. 5 according to the IUPAC classification. The rapid uptake at the lower relative pressure suggested the presence of micropores. The hysteresis loop at a higher relative pressure region (P / Po) represents the capillary condensations in mesopores. The presence of an abundance of mesopores is further confirmed via pore size distribution in Fig. 6. The surface areas of the AC and 25 wt.% MPPs@AC composite are calculated to be 1,473 and 1,146 m2g1with pore volumes of 0.75 and 0.62 cm3g-1, respectively. The specific surface area (SSA) decreases with increasing MPP concentrations (748 and 450 m2g1for 50 and 75 wt.%, respectively) in AC. This is supported by the pore volume distribution (Fig. 6) of the composite at higher MPPs concentrations. and electrochemical measurements

[0073] The active material, MPPs@AC, was mixed with polyvinylidene (PVDF) and acetylene black in an 8:1:1 ratio, and a slurry was prepared with the help of N-methyl-2-pyrrolidone (NMP) solutions. The slurry was then drop-cast on a 7 mm in diameter carbon cloth. The loading of the active material on the carbon cloth was ~ 0.585 mg / cm2. All configurations used a glassy carbon electrode (CHI instruments, China) as a current collector and glass microfiber membrane as the separator (Whatman, General Electrics, USA). An AC disc (with 10 wt.% polytetrafluoroethylene (PTFE) binder) was used as the counter electrode. Ag / AgCI and Hg / HgO were used as the reference electrodes for acidic / neutral and basic electrolyte medium, respectively.

[0074] The fabricated electrode material was subject to electrochemical characterization, e.g., cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). These experiments were carried out in three-electrode systems immersed in different electrolyte solutions viz. 1, 3, 6 M H2SO4, 1 M I 2SO4, 1 M Na2SO4 and 1 M KOH). Subsequently, the supercapacitor (SC) device behavior was evaluated in a two- electrode arrangement. The execution of all electrochemical assessments was recorded with a potentiostat (VSP, Biologic, France).

[0075] Fig. 7 plots the Ragone plot of the pristine AC and the various composites tested herein. While the three composites have comparable specific power, the 25 wt.% sample exhibits the highest specific energy. The increased capacitance and energy in the 25 wt.% composite can be explained by the homogeneous distribution of MPPs into the mesopores of AC, developing a uniform and substantial redox reaction on the underlying surface of the electroactive material. All three composites were further tested in 3 and 6 M of H2SO4 to understand the effects of proton concentrations in the system. The faradaic counterpart becomes predominant in the charge storage at higher electrolyte concentrations. However, the ionic conductivity of the electrolyte decreased with increases in concentration, resulting in reduced capacitance and energy.

[0076] The electrochemical cycle stability of the assembled cell is tested for 100,000 cycles at 10 Ag1current density. Fig. 8 shows the capacitance retention and the variation of the coulombic efficiency over the sweeping cycles. The cell retains around 90% of the initial capacitance after 10,000 cycles with almost 100% coulombic efficiency. Further, increasing the cycle number to 100,000 eventually decreases capacitance and coulombic efficiency over time. The cell retains 46% of its initial capacitance after 100,000 cycles with 92% of coulombic efficiency. The inset pictures of Fig. 8 show the first and last five cycles of the charge discharge, indicating no significant change in response.

[0077] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Claims

CLAIMS1. A composite material, consisting of: titania mesoparticles (TiOz MPPs) consisting of one-dimensional lepidocrocite (1DL) TiOz sub- and / or nano-filaments, and activated carbon (AC).

2. The composite material according to claim 1, wherein the TiOz MPPs are on the surface of the AC.

3. The composite material according to claim 1 or 2, wherein the activated carbon originates from any carbon sources, such as commercial carbon, doped carbon, waste-derived carbon, bio-derived carbon and mixtures thereof.

4. The composite material according to any one of the preceding claims, wherein the concentration of TiOz MPPs is in the range from 5-80 wt.%.

5. The composite material according to any one of the preceding claims, wherein the material is stable in ambient conditions.

6. A method for producing the composite material defined in any one of claims 1 to 5, comprising the following steps:-preparing three-dimensional titania mesoparticles (TiOz MPPs (3D)) by contacting a mono-, binary, ternary, or higher carbide, nitride, boride, phosphide, phosphate, chloride, perchlorate, aluminide, silicide, sulphate or oxysulphate of titanium with a quaternary ammonium salt and / or base under heating to a temperature of from 25 to 95 °C and stirring for from about 1 hour to about one week, followed by washing with a C1-C3 alcohol until pH is about 6-8, and drying;-washing the TiOz MPPs (3D) with a metal salt and / or water-soluble metal compounds to obtain TiOz MPPs consisting of IDL TiOz sub- and / or nano-filaments;-mixing the TiOz MPPs with AC in a C1-C3 alcohol under stirring for from about 1 hour to about 48 hours at room temperature; and- drying the resulting solution to obtain the composite material as a powder.

7. The method according to claim 6, wherein the quaternary ammonium salt and / or base comprises an ammonium hydroxide, such as tetramethylammonium hydroxide (TMAOH or TMAH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH), ammonium hydroxide (NH4OH), their amine derivatives, or any combination thereof.

8. The method according to claim 6 or 7, wherein the metal in the metal salt is selected from the group consisting of: H, Li, Na, K, Mg, Mn, Fe, Co, Ni, and Zn.

9. The method according to any one of claims 6 to 8, wherein the C1-C3 alcohol is methanol, ethanol or any mixture thereof.

10. The method according to any one of claims 6 to 9, wherein the drying is airdrying, vacuum drying, freeze-drying or any combination thereof.

11. The method according to any one of the claims 6 to 10, wherein the TiO? MPPs to be mixed with AC is obtained in a bottom-up manner.

12. Use of the composite material as defined in any one of claims 1 to 5, as an electrode material, a material for water purification, or catalysts.

13. The use according to claim 12, wherein the electrode material is useful in an energy storage device, such as a supercapacitor or a battery.

14. The use according to claim 12, wherein the material for water purification is selected form the group consisting of membranes, electrodes, powders and filters.

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