The invention relates to the technical field of catalysts. In particular, it relates to an alternation of a degree of curvature of a molecular catalyst for higher catalytic activity.
The electrochemical conversion of CO2 is a promising method for producing chemicals and plays a crucial role in carbon recycling and storing renewable electricity in a convenient and high energy-density form. Although many studies have achieved industrial-scale conversion of CO2-to-CO with high CO selectivity (over 90 %) and current density (larger than 200 mA cm−2), most reactions are limited to a two-electron reduction process that produces carbon monoxide or formate (HCOO−). However, reducing CO2 beyond two electrons on an industrial scale remains a significant challenge.
Methanol (MeOH) is a versatile one-carbon (C1) product and widely used green fuel with an energy density of 15.6 MJ/L. It is also an extremely important intermediate for the production of useful chemicals and fuels such as dimethyl ether (CH3OCH3, DME) and methyl tert-butyl ether (CH3-OC(CH3)3, MTBE). Methanol has advantages over hydrogen as it can be stored at atmospheric pressure and directly used in internal combustion engines due to its high-octane rating. Methanol can also be added into fuel cells. However, the carbon dioxide reduction reaction (CO2RR) to methanol through a six-electron reduction pathway is still in an early stage of development. Although copper has been shown to catalyze the CO2RR by a multi-electron pathway, the copper induced reaction usually results in a mixture of products that require an extensive separation process.
In 1984, a study of molecular catalyst using cobalt phthalocyanine (CoPc) showed a methanol Faradaic efficiency (FE) of less than 5%, but this low FE number was not given much attention until more recently. Research groups, led by Wang and Robert, respectively reported improved methanol FE when CoPc is deposited on multiwalled carbon nanotubes (MWCNT). This improvement is attributed to the dispersion of CoPc on the conductive substrate. MWCNTs have since been widely used with different catalysts, but the methanol production rate remains marginal (Wang et al., Nature 575, 639-642, 2019) (Robert et al., Angew. Chemie Int. Ed. 58, 16172-16176, 2019). Questions have arisen about the underlying mechanism of the CoPc/MWCNT activity. Conventional methods for tuning the activities of molecular catalysts require the design of new structures or change to functional groups, which can be time-consuming and costly.
There is a need to create a more efficient reaction pathway for catalytic activity without complex chemical modification. In particular, the industry is searching for a solution for a solution that can yield a high amount of methanol from the CO2RR in the six-electron reduction pathway.
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some further embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the above-mentioned problems of the need of a more efficient reaction pathway for catalytic activity without complex chemical modification. The structure of the catalyst is finely tuned to alter the morphology of its active site. A catalyst having a substantially flat structure undergoes distortion to an extent that its active site is bent, or a curvature is created by the distortion. This distortion will have an effect on the bonding strength between the active site and the target molecule. The curvature of the target molecule can be manipulated by single wall carbon nanotube (SWCNT). The distorted target molecule exhibits a higher Faraday efficiency value in the catalytic process.
In accordance with a first aspect of the present invention, the present invention provides a method of altering degree of curvature of a molecular catalyst for CO2 reduction reaction (CO2RR) for higher catalytic activity. The method includes providing a single-walled carbon nanotube (SWCNT). Next, a molecular catalyst having active sites for CO2 reduction reaction is provided. The molecular catalyst is dispersed on the SWCNT. A curvature of the active sites of the molecular catalyst is then induced.
In a further embodiment of the present invention, dispersing the molecular catalyst on the SWCNT includes providing a solution having N,N-dimethylformamide. The molecular catalyst and the SWCNT are then added into the solution. A sonication is performed to the solution. A magnetic stirring is performed to the solution.
In a further embodiment of the present invention, the inducing the curvature of the active sites of the molecular catalyst by the SWCNT includes initiating a non-parallel π-π interaction between the molecular catalyst and the SWCNT.
In a further embodiment of the present invention, the inducing the curvature of the active sites of the molecular catalyst by the SWCNT includes bending the active sites of the molecular catalyst from a flat configuration to a curved configuration.
In a further embodiment of the present invention, after the inducing the curvature of the active sites of the molecular catalyst by the SWCNT further includes receiving CO2 at the active site, releasing CO from the active site, and releasing methanol from the active sites.
In a further embodiment of the present invention, the SWCNT is smaller in size than the molecular catalyst. In another embodiment of the present invention, the SWCNT is bigger in size than the molecular catalyst.
In a further embodiment of the present invention, the SWCNT has a diameter of at least 1 nm.
In a further embodiment of the present invention, the SWCNT has a diameter between 1 and 6 nm.
In a further embodiment of the present invention, the molecular catalyst is cobalt phthalocyanine.
In a further embodiment of the present invention, the molecular catalyst is nickel phthalocyanine.
In accordance with a second aspect of the present invention, the present invention provides a method of altering degree of curvature of a molecular catalyst including providing a single-walled carbon nanotube (SWCNT) and providing a molecular catalyst. The molecular catalyst is dispersed on the SWCNT. A curvature of the active sites of the molecular catalyst is induced by the SWCNT.
In a further embodiment of the present invention, the molecular catalyst is iron phthalocyanine.
In a further embodiment of the present invention, after inducing the curvature of the active sites of the molecular catalyst by the SWCNT further includes effecting an oxygen reduction reaction by the molecular catalyst.
In a further embodiment of the present invention, the oxygen reduction reaction is a four-electron process.
In a further embodiment of the present invention, the inducing the curvature of the active sites of the molecular catalyst includes bending the active sites of the molecular catalyst from a flat configuration to a curved configuration.
In a further embodiment of the present invention, the SWCNT is smaller in size than the molecular catalyst. In another embodiment of the present invention, the SWCNT is bigger in size than the molecular catalyst.
In accordance with a third aspect of the present invention, the present invention provides a molecular catalyst having an altered degree of curvature, more particularly, the molecular catalyst is dispersed on a single-walled carbon nanotube (SWCNT) for altering degree of curvature.
In a further embodiment of the present invention, the molecular catalyst having active sites for CO2 reduction reaction (CO2RR).
In a further embodiment of the present invention, the SWCNT has a diameter of 1-6 nm.
In a further embodiment of the present invention, the altered degree of curvature ranges from 1 to 96 degree.
In accordance with a fourth aspect of the present invention, the present invention provides a fuel cell with a molecular catalyst having active sites for oxygen reduction reaction.
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise, in which:
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.
In accordance with a first aspect of the present invention, a method of
altering degree of curvature of a molecular catalyst for CO2 reduction reaction (CO2RR) for higher catalytic activity is provided. Briefly, a single-walled carbon nanotube (SWCNT) is first provided. Next, a molecular catalyst having active sites for CO2RR is also provided. The molecular catalyst is dispersed on the SWCNT. A curvature of the active sites of the molecular catalyst is then induced.
In one embodiment, the dispersing the molecular catalyst on the SWCNT includes providing a solution having N,N-dimethylformamide; adding the molecular catalyst and the SWCNT into the solution; performing a sonication to the solution; and performing a magnetic stirring to the solution.
In one embodiment, the inducing the curvature of the active sites of the molecular catalyst includes initiating a non-parallel π-π it interactions between the molecular catalyst and the SWCNT.
In one embodiment, the inducing the curvature of the active sites of the molecular catalyst includes bending the active sites of the molecular catalyst from a flat configuration to a curved configuration.
In one embodiment, after the inducing the curvature of the active sites of the molecular catalyst, it further includes receiving CO2 at the active site, releasing CO from the active site, and releasing methanol from the active sites.
In one embodiment, the SWCNT is smaller in size than the molecular catalyst. In particular, the diameter of SWCNT is less than the size of the molecular catalyst.
In another embodiment of the present invention, the SWCNT is bigger in size than the molecular catalyst.
In one embodiment, the SWCNT has a diameter of at least 1 nm.
In another embodiment, the SWCNT has a diameter of 1-6 nm.
In one embodiment, the molecular catalyst is cobalt phthalocyanine. In another embodiment, the molecular catalyst is nickel phthalocyanine.
In accordance with a second aspect of the present invention, a method of altering degree of curvature of a molecular catalyst is provided. The method includes the following steps: providing a single-walled carbon nanotube (SWCNT); providing a molecular catalyst; dispersing the molecular catalyst on the SWCNT; and inducing a curvature of the active sites of the molecular catalyst.
In one embodiment, the molecular catalyst is iron phthalocyanine.
In one embodiment, after inducing the curvature of the active sites of the molecular catalyst, it further includes effecting an oxygen reduction reaction by the molecular catalyst.
In one embodiment, the oxygen reduction reaction is a four-electron process.
In one embodiment, the inducing the curvature of the active sites of the molecular catalyst includes bending the active sites of the molecular catalyst from a flat configuration to a curved configuration.
In one embodiment, the SWCNT is smaller in size than the molecular catalyst. In another embodiment of the present invention, the SWCNT is bigger in size than the molecular catalyst.
In accordance with a third aspect of the present invention, the present invention provides a molecular catalyst having an altered degree of curvature, more particularly, the molecular catalyst is dispersed on a single-walled carbon nanotube (SWCNT) for altering degree of curvature.
In one embodiment, the molecular catalyst having active sites for CO2 reduction reaction (CO2RR).
In one embodiment, the altered degree of curvature ranges from 1 to 96 degree.
In one embodiment, the SWCNT has a diameter of 1-6 nm.
In accordance with a fourth aspect of the present invention, the present invention provides a fuel cell with a molecular catalyst having active sites for oxygen reduction reaction.
The molecular catalyst for CO2 reduction reaction (CO2RR) is prepared by adding the molecular catalyst and the single-walled carbon nanotube (SWCNT) into the N,N-dimethyl formamide (DMF) solution, followed by sonication and magnetic stirring. In one embodiment, the molecular catalyst used is cobalt phthalocyanine (CoPc). A comparison sample is prepared using the same method, but by adding the molecular catalyst and multi-walled carbon nanotube (MWCNT) to the DMF solution. The transmission electron microscopy (TEM) images, as shown in
The SWCNT has a diameter that is smaller than the size of the molecular catalyst. For example, a CoPc molecule has a side length of ca. 1.24 nm, while the SWCNT has a diameter of approximately 2 nm. The curvature of the molecular catalyst is initiated by the interactions between the SWCNT and the molecular catalyst through the nonparallel π-π interactions. Referring to
Referring to
Referring to
The electrochemical CO2 reduction reaction (CO2RR) is carried out in a customized glass H-cell with continuous CO2 saturated in 0.5M KHCO3 at 3 sccm flow rate. Turning to
Referring to
Referring to
CoPc/SWCNT is further analyzed by density functional theory (DFT) calculations on the basis of the model of EXAFS fitting results. The stabilization of CO2⋅−on the surfaces of the molecular catalysts plays an important role in CO2RR. The overpotential of SO42−adsorption over the samples can be used to measure the binding strength of the intermediate CO2⋅−on the molecular catalyst surface during CO2RR. SO42−adsorption of SWCNT, MWCNT, CoPc/SWCNT and CoPc/MWCNT is studied by measuring the CV scans from 0.6 to 2.1 V (vs RHE) at 50 mV/s in 0.1 M H2SO4 electrolyte solution, as shown in
The OH binding strength at the surface of the electrode is measured over SWCNT, MWCNT, CoPc/SWCNT and CoPc/MWCNT with the CV scans from 0.9 to 1.6 V (vs RHE) at 50 mV/s in the 0.1 M NaOH electrolyte solution, as shown in
Referring to
Referring to
A higher current density is achieved by minimizing the CO2 mass transport issue in the H-cell. An electrochemical microflow with gas diffusion electrode (GDE) configuration has been employed. In the flow cell configuration, 1M KOH medium instead of KHCO3 is used as an electrolyte to improve ionic mobility and obtain better current density. The total current density in the flow cell increases to approximately 200-350 mA/cm2. It is about 7 times more than that in the H-cell condition. Referring to
The curvature induced by SWCNT in molecular catalyst is tested in other systems. The oxygen reduction reaction (ORR) activity of FePc/SWCNT is investigated in O2-saturated 0.1 M KOH with rotating disk electrode (RDE) measurement. Turning to
The alternation of molecular catalyst curvature can upregulate the activity at the active sites. The highly curved molecular catalyst undergoes severe distortion to release strain. This distortion has effects on the binding affinity between the molecular catalyst and its target upon receiving and releasing, for example, in the multi-electron transfer in CO2RR. A distorted CoPc/SWCNT exhibits a 3.2-fold improvement in Faraday efficiency (FE) of Me0H compared to flat CoPc/MWCNT.
By monodispersing CoPc on SWCNT tailors the activity of molecular catalysts with significantly higher methanol selectivity. In contrast, a higher loading of CoPc or a larger-diameter SWCNT degrades the CO 2 -to-methanol conversion. X-ray spectroscopies combined with theoretical calculations suggest that the strong catalyst/support interaction induces molecular curvature and modulates the electronic structure of CoPc, leading to a balanced transition in receiving and releasing CO2 rather than a CO desorption. A flow electrolyzer using CoPc/SWCNT as the catalyst achieves high FE for MeOH. Other supports such as using C60 also improves the CO2-to-methanol conversion with high selectivity.
CNT (XFNANO, Co., Ltd.) was pretreated in 6 mol L−1 HCl solution for 12 h to remove any impurities. After that, the CNT sample was filtrated, washed with ultra-pure water and freeze-dried.
20 mg of the purified CNTs was subsequently dispersed in 20 ml of DMF using sonication. Then, an appropriate amount of CoPc dissolved in 5 ml DMF was added to the CNT suspension. The mixture was sonicated for 30 min to obtain a well-mixed suspension, which was further stirred at room temperature for 24 h. Subsequently, the mixture was centrifuged, and the precipitate was washed with DMF, ethanol and DI water. Finally, the precipitate was lyophilized to yield the final product. The samples with CNT substrates of different diameters SWCNT, MWCNT, 4-6 nm, 5-15 nm, 20-30 nm and >50 nm were denoted as CoPc/SWCNT, CoPc/MWCNT, 4-6, 5-15, 20-30, 50 respectively.
ICP-atomic emission spectroscopy (ICP-OED) measurements were conducted on Optima 8000 spectrometer. Samples were digested in hot concentrated HNO3 for 1 h and diluted to desired concentrations. UV-vis spectrum was performed on a Shimadzu 1700 spectrophotometer in ethanol solution with a concentration of 1×10-5 mol/mL. The X-ray photoelectron spectroscopy data were collected on a Thermo ESCALAB 250Xi spectrometer equipped with a monochromatic AlK radiation source (1486.6 eV, pass energy 20.0 eV). The data were calibrated with C 1s 284.8 eV.
In H-cell, catalyst ink was prepared by dispersing 2 mg of catalyst in 1 mL of ethanol with 20 μL 5 wt. % Nafion solution (Sigma Aldrich, Nafion 117, 5 wt. %) and sonicated for 1 h. Then 200 μL of the ink was drop-casted on the glassy carbon working elctrode and subsequently dried naturally overnight. The loading on of the electrode was 0.4 mg/cm2.
The electrochemical performance was carried out in a customized glass H-cell as previously reported. A platinum foil and Ag/AgCl were used as the counter and reference electrode, respectively. The working electrode was separate from the counter electrode by the Nafion-117 membrane (Fuel Cell Store). Before using, the Ag/AgCl reference was calibrated as reported. All potentials in this study were converted to the reversible hydrogen electrode (RHE) according to the Nernst equation (Evs.RHE=Evs.Ag/AgCl+0.231+0.0592×pH). The 10 mL of 0.5 M KHCO3 solution electrolyte was added into the working and counter compartment, respectively. The cell was purged with high-purity CO2 gas (Linde, 99.999%, 20 sccm) for 30 min prior to and throughout the duration of all electrochemical measurements. The electrochemical measurements were controlled and recorded with a CHI 650E potentiostat. The automatic iR (85%) compensation was used. The pH values of CO2 and N2 saturated 0.5 M KHCO3 electrolyte were 7.25 and 8.36, which was detected by a pH meter (HI 2211, Hanna instruments). Gas-phase products were quantified by an on-line gas chromatograph (Ruimin GC 2060, Shanghai) equipped with a methanizer, a Hayesep-D capillary column, flame ionization detector (FID) for CO and thermal conductivity detector (TCD) for H2. The CO2 flow rate was controlled at 3 sccm using a standard series mass flow controller (Alicat Scientific mc-50 sccm). Each run was 8 min long. GC was calibrated using standard mixture gas (Linde) and diluted with nitrogen (Linde 99.999%). The liquid products were quantified after electrocatalysis using 1H NMR spectroscopy with solvent (H2O) suppression. 450 μl of electrolyte was mixed with 500 μl of a solution of 10 mM dimethyl sulfoxide (DMSO) and in D2O as internal standards for the 1H NMR analysis. The concentration of MeOH was calculated using the ratio of the area of the MeOH peak (at a chemical shift of 3.31 ppm) to that of the DMSO internal standard.
As used herein, terms “approximately”, “basically”, “substantially”, and “about” are used for describing and explaining a small variation. When being used in combination with an event or circumstance, the term may refer to a case in which the event or circumstance occurs precisely, and a case in which the event or circumstance occurs approximately. As used herein with respect to a given value or range, the term “about” generally means in the range of ±10%, ±5%, ±1%, or ±0.5% of the given value or range. The range may be indicated herein as from one endpoint to another endpoint or between two endpoints. Unless otherwise specified, all the ranges disclosed in the present disclosure include endpoints. The term “substantially coplanar” may refer to two surfaces within a few micrometers (μm) positioned along the same plane, for example, within 10 μm, within 5 μ, within 1 μm, or within 0.5 μm located along the same plane. When reference is made to “substantially” the same numerical value or characteristic, the term may refer to a value within ±10%, ±5%, ±1%, or ±0.5% of the average of the values.
The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated.
The present application claims priority from U.S. provisional patent application Ser. No. 63/355,662 filed Jun. 27, 2022, and the disclosure of which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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63355662 | Jun 2022 | US |