A formate fuel cell electrode and its preparation method and application

Abstract

The present invention discloses a formate fuel cell electrode, a preparation method thereof and an application thereof. The formate fuel cell electrode is synthesized by a hydrothermal method and an electrodeposition method. The fuel cell electrode prepared by the present invention can directly oxidize formate to CO2 under alkaline conditions, thereby converting the chemical energy of formate into electrical energy. Moreover, the electrode has a stable nanowire-like and interstitial structure, and is attached with Pd nanoparticles and / or embedded Pd nanocluster particles, thus providing rich reactive sites for the formate oxidation reaction; the present invention provides a "synergistic detoxification" strategy to solve the problem of Pt and Pd hydrogen poisoning (Pd / Pt-H ad ), and improve the service life of the anodic formate oxidation electrode. That is, TiO2 and CuFe2O4 on the surface of titanium foam are used to generate highly oxidative *OH to synergistically oxidize Pd / Pt-H ad to release Pt and Pd active sites. Therefore, the formate fuel cell electrode prepared by the present invention has excellent formic acid oxidation stability and formic acid oxidation efficiency during the methanol oxidation reaction.

Description

Technical Field

[0001] The invention relates to the technical field of fuel cell electrode material preparation, and in particular to a formate fuel cell anode electrode and a preparation method and application thereof. Background Art

[0002] Fuel cells are increasingly gaining attention as a green, clean, and low-emission energy conversion device. Among the many fuel cells, direct formate fuel cells (DFFCs) are an ideal product for household vehicles, portable devices, and emergency power supplies. Its anode fuel is a widely available formate such as potassium formate, and its cathode fuel is oxygen in the air, so it has high safety and application value. At present, the development of cathode oxygen reduction electrodes for direct formate fuel cells has made breakthrough progress, and there are many commercial products. However, since its key catalytic components Pd or Pt are easily deactivated by hydrogen poisoning, and the reaction mechanism of the poisoning process is complex and unavoidable, its development has been slow, and its service life is generally low. Therefore, a key point in the development of formate fuel cells is to produce formate fuel cell anode electrodes with high durability and activity. Summary of the invention

[0003] In order to solve the problem that the electrodes of the existing direct formate fuel cells are easily poisoned by hydrogen and have a short service life, one of the purposes of the present invention is to provide an anode formate oxidation battery electrode to solve the problems existing in the prior art.

[0004] Based on this, the present invention designs a "synergistic detoxification" strategy from the perspective of external "synergy" to solve the hydrogen poisoning of Pt and Pd (Pd / Pt-H ad ) problem, and prolong the service life of the anode formate oxidation electrode. That is, TiO2 and CuFe2O4 on the surface of titanium foam produce highly oxidizing *OH to synergistically oxidize Pd / Pt-H ad The active sites of Pt and Pd are released, so that Pt and Pd can resume their activity and continue to work. Therefore, this application is different from previous cases in terms of design concept, material structure and application effect.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: an anode formate oxidation battery electrode, the fuel cell electrode comprising: a porous foam titanium with rutile TiO2 on the surface, a porous foam titanium with conductive titanium function inside, and TiO2 with rutile structure on the external surface; CuFe2O4 nanowires, which are in-situ grown on the TiO2 surface; Pd nanoparticles, the Pd nanoparticles are attached to the surface or gaps of the CuFe2O4 nanowires.

[0006] The beneficial effects of the present invention are as follows: the Ti / TiO2 / CuFe2O4 / Pd composite structure system in the present invention enables the composite material to produce the function of synergistic detoxification and enhanced durability that cannot be achieved by Ti, TiO2, CuFe2O4, and Pd alone, and the porous titanium foam inside is also conducive to increasing the loading amount of CuFe2O4 and Pd, thereby reducing the resistance of electron transmission. Therefore, the anode formate oxidation battery electrode in the present invention has good formate oxidation activity and durability.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows:

[0008] Furthermore, the thickness of TiO2 on the surface of the titanium foam is adjusted to 10-100 nm, and the coverage of the CuFe2O4 nanowire layer is 100-200 nm. The diameter of the CuFe2O4 nanowire is 10-20 nm, and the length is 10-500 um.

[0009] The beneficial effects of adopting the above-mentioned further technical scheme are as follows: TiO2 and CuFe2O4 nanowire layers of this thickness can reduce the transmission distance of the reaction charge on the Pd surface to the internal metal titanium during the catalytic reaction while ensuring the synergistic effect, thereby improving the overall performance of the electrode; TiO2 and CuFe2O4 nanowire layers of this thickness can also effectively reduce the risk of surface catalyst falling off during the reaction.

[0010] Furthermore, the dispersion of precious metal Pd nanoparticles was increased to 0.05-0.01 mg / cm 2 , reduce the amount of Pd and reduce the cost of Ti / TiO2 / CuFe2O4 / Pd

[0011] Furthermore, the existing block-shaped porous titanium substrate is replaced with a nanowire-shaped porous Ti sheet to reduce the substrate material.

[0012] The second object of the present invention is to provide a method for preparing a fuel cell electrode, wherein the fuel cell electrode is produced in situ by electrodeposition and hydrothermal method, and three interfaces are formed in sequence between Ti, TiO2, CuFe2O4 and Pd from the inside to the outside, including Ti / TiO2, TiO2 / CuFe2O4 and CuFe2O4 / Pd two-phase interfaces. The method comprises the following steps:

[0013] Step 1, pretreatment of the porous titanium foam surface;

[0014] The pretreated porous titanium foam was placed in an oxygen-saturated 6M KOH solution for electrochemical oxidation. The oxidation time was 3 hours, the load potential was 2V, and the electrode system was a three-electrode system including a Pt counter electrode, a Hg / HgO reference electrode and a porous titanium foam working electrode.

[0015] Step 2, CuFe2O4 covers the porous foam Ti / TiO2 prepared in step 1;

[0016] The porous foamed Ti / TiO2 prepared in step 1 is placed in a precursor solution and subjected to a hydrothermal reaction. After the reaction is completed, the precursor is successively cleaned and dried to obtain a precursor; wherein the precursor solution includes copper nitrate, iron nitrate and urea; after the hydrothermal reaction, the porous foamed Ti / TiO2 / CuFe2O4 electrode substrate is obtained after cleaning and drying.

[0017] Step 3: Preparation of fuel cell electrodes;

[0018] The Ti / TiO2 / CuFe2O4 electrode substrate obtained in step 2 is placed in a PdCl2 solution for electrochemical deposition, and a Ti / TiO2 / CuFe2O4 / Pd composite electrode is obtained after reaction and cleaning.

[0019] The beneficial effects of the present invention are as follows: the porous titanium foam, copper ferrite and Pd are sequentially formed into functional layers using the above methods (electrochemical oxidation, hydrothermal and electrodeposition), namely the innermost layer of metal titanium, the second innermost layer of TiO2, the second outermost layer of CuFe2O4 and the outermost layer of Pd. This combination of step-by-step treatment methods can functionalize each layer, and each functionalized surface is independent of each other during the preparation process without mutual interference. The CuFe2O4 fiber and porous titanium foam composite matrix formed by this step-by-step functionalization method has a large gap, which can ensure the entry of the electrolyte, increase the specific surface area of ​​the electrode, and ensure the formation of the three-phase interface of the catalyst, reactant and electrolyte; at the same time, the surface active sites of the formate oxidation catalyst are increased, the functionalized structure of the electrode is optimized, the utilization rate of Pd is improved, and the cost of using precious metals is reduced.

[0020] Furthermore, in step 1, the concentration of the potassium hydroxide solution is 2-10 mol, the load voltage is 3-5 V, and the time is 4-10 h.

[0021] Furthermore, the conditions for the hydrothermal reaction in step 2 are: reaction temperature of 120-150° C., and reaction time of 8-20 h.

[0022] Furthermore, in step 1, the molar ratio of copper nitrate to iron nitrate is (1:9) to (9:1); and 0.5 to 1.2 g of urea is added to every 100 mL of water in the precursor solution.

[0023] Furthermore, the concentration of PdCl2 in the precursor solution in step 3 is 10-200mmol.

[0024] The third object of the present invention is to use the fuel cell electrode in the first object as the anode electrode of a formate fuel cell. Its unique function is that the titanium metal inside the porous titanium foam provides electrical conductivity to ensure the electron conduction during the reaction; the composite layer formed by the TiO2 and CuFe2O4 on the surface has a strong system effect and can form OH ad , promoting Pd-H ad Oxidation eliminates hydrogen poisoning reaction and prolongs service life; the surface Pd is a catalytic entity, promoting the formate oxidation reaction. The realization of this composite function is inseparable from the unique functional structure and system effect of Ti / TiO2 / CuFe2O4 / Pd.

[0025] The present invention has the following beneficial effects:

[0026] 1. The formate fuel cell anode prepared by the present invention has four special functional layers. The titanium metal inside the porous titanium foam improves the conductivity to ensure the electron conduction during the reaction. The composite layer formed by TiO2 and CuFe2O4 can form OH ad , promoting Pd-H ad Oxidation eliminates hydrogen poisoning reaction, and at the same time, the surface Pd provides sufficient active sites to promote the formate oxidation reaction. At the same time, while the porous titanium foam and the fiber CuFe2O4 form gaps, the attachment sites of Pd are increased to improve the utilization rate of Pd. Compared with pure Pd, the Pd usage of the present invention is less and the dispersion is higher, which can improve the electrode's ability to promote formate oxidation reaction. In addition, the formate oxidation electrode prepared in the present invention is directly formed on the surface of the porous titanium foam. The preparation process is carbon-free and adhesive-free, which avoids the problem of catalytic layer shedding caused by adhesive aging and carbon corrosion, and can reduce the preparation process to a certain extent, and improve the stability and life of the fuel cell.

[0027] 2. The present invention adopts a combination of step-by-step treatment methods to sequentially form functional layers of porous titanium foam, copper ferrite and Pd, namely the innermost layer of metal titanium, the next innermost layer of TiO2, the next outermost layer of CuFe2O4 and the outermost layer of Pd. This combination of step-by-step treatment methods can functionalize each layer, and each functionalized surface is independent of each other during the preparation process without mutual interference. The CuFe2O4 fiber and porous titanium foam composite matrix formed by this step-by-step functionalization method has large gaps, which can ensure the entry of electrolyte, increase the specific surface area of ​​the electrode, and ensure the formation of a three-phase interface of the catalyst, reactant and electrolyte; at the same time, it increases the surface active sites of the formate oxidation catalyst, optimizes the surface structure of the electrode, improves the utilization rate of Pd and reduces the cost of using precious metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1XRD characterization diagram of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in Example;

[0029] FIG. 2( a ) is a porous titanium foam with surface oxidation in an embodiment;

[0030] FIG2( b ) shows the surface morphology of the embodiment after covering with CuFe2O4 and Pd;

[0031] Figure 3 Cyclic voltammetry (CV) diagram of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in Example;

[0032] Figure 4 is a CV decay curve diagram of an embodiment fuel cell electrode;

[0033] Figure 5 This is a diagram of the long-term operation durability of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in the example. DETAILED DESCRIPTION

[0034] A formate fuel cell electrode, a preparation method and an application thereof in the present application will be described below in conjunction with embodiments. However, the present application can be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein. Rather, the purpose of providing these embodiments is to make the present application thorough and complete and to fully convey the scope of the present application to those skilled in the art.

[0035] The present invention investigates battery anode electrode materials for formate oxidation reaction (FOR) and finds that Pd-based materials have excellent formate oxidation catalytic performance. Currently, a variety of structures have been designed to improve the formate oxidation catalytic performance of Pd materials. Although their activity has been greatly improved, their durability is still insufficient. Therefore, synthesizing efficient and stable fuel cell electrodes for formate oxidation reaction is the key to the development of formate fuel cell technology.

[0036] Among the many fuel cells, direct formate fuel cells (DFFCs) are an ideal product for household vehicles, portable devices and emergency power supplies. Its anode fuel is formate such as potassium formate, which is widely available, and its cathode fuel is oxygen in the air, so it has high safety and application value. At present, the development of cathode oxygen reduction electrodes for direct formate fuel cells has made breakthrough progress, and there are many commercial products. However, because its key catalytic components Pd or Pt are easily deactivated by hydrogen poisoning, and the reaction mechanism of the poisoning process is complex and unavoidable, its development has been slow, and its service life is generally low. Therefore, a key point in the development of formate fuel cells is to produce anode formate oxidation electrodes with high durability and activity.

[0037] Based on this, the present invention designs a "synergistic detoxification" strategy from the perspective of external "synergy" to solve the hydrogen poisoning of Pt and Pd (Pd / Pt-H ad ) problem, and prolong the service life of the anode formate oxidation electrode. That is, TiO2 and CuFe2O4 on the surface of titanium foam produce highly oxidizing *OH to synergistically oxidize Pd / Pt-H ad The active sites of Pt and Pd are released, so that Pt and Pd can resume their activity and continue to work. Therefore, this application is different from previous cases in terms of design concept, material structure and application effect.

[0038] An embodiment of the present invention provides a formate fuel cell electrode, which includes: porous titanium foam, with gaps formed between Ti / TiO2 and TiO2 / CuFe2O4; Pd nanoparticles, the Pd nanoparticles are attached to CuFe2O4 nanowires, and / or embedded in the gaps between TiO2 / CuFe2O4 nanowires as Pd nanocluster particles, wherein the Pd nanocluster particles are formed by Pd nanoparticle clusters.

[0039] In addition, the formate fuel cell electrode in this embodiment also includes a substrate, wherein the CuFe2O4 nanowire array is located on the substrate; the substrate in this embodiment includes any one of porous titanium foam, nickel foam (porous titanium foam), copper foam, aluminum foam, carbon paper and carbon cloth of rutile TiO2; of course, in the actual process, the substrate can also be other materials, which will not be illustrated in this embodiment.

[0040] The specific structure of the fuel cell electrode in this embodiment is: the porous titanium foam substrate of rutile TiO2 is formed by stacking a large amount of porous titanium foam of rutile TiO2 on the TiO2 substrate, and when the porous titanium foam of TiO2 and CuFe2O4 are stacked to form Ti / TiO2 / CuFe2O4, a certain gap is formed between Ti / TiO2 / CuFe2O4, so the formate fuel cell electrode prepared in this embodiment has the characteristics of nanowire and rich gap structure; in addition, the Ti / TiO2 / CuFe2O4 in this embodiment is a nanowire structure with a large surface area. Therefore, this structure is conducive to the loading, dispersion and mass transfer of Pd nanoparticles, increases the loading amount of Pd nanoparticles, reduces the electron transmission distance between CuFe2O4 nanowires in the formate fuel cell electrode, increases the electrochemical active surface area of ​​the formic acid oxidation reaction for the formate fuel cell electrode in this embodiment, optimizes the electronic structure of the fuel cell electrode, and thus improves the performance of the fuel cell electrode in the FOR catalytic reaction (i.e., stability and formic acid oxidation activity).

[0041] In addition, the fuel cell electrode prepared in this embodiment also includes Pd nanoparticles and / or Pd nanocluster particles, wherein the Pd nanoparticles are mainly attached to the CuFe2O4 nanowires, and the Pd nanocluster particles are mainly embedded in the gaps formed between the CuFe2O4 nanowires; the Pd nanocluster particles in this embodiment are formed by clusters of Pd nanoparticles. The Pd nanocluster particles in this embodiment can be obtained by clustering the Pd nanoparticles attached to the CuFe2O4 nanowires, or can be obtained by clustering the Pd nanoparticles during the preparation process and then embedding them in the gaps between the CuFe2O4 nanowires. In this embodiment, the Pd nanoparticles attached to the CuFe2O4 nanowires and the Pd nanocluster particles embedded in the gaps between the CuFe2O4 nanowires both reduce the electron transmission distance between the CuFe2O4 nanowires, promote the increase in the formic acid oxidation rate, and reduce the charge transfer impedance, thereby reducing the consumption of Pd in ​​the FOR process and improving the stability of the formate fuel cell electrode.

[0042] In addition, in some embodiments, the thickness of TiO2 on the surface of titanium foam is 10-100nm, and the coverage of the CuFe2O4 nanowire layer is 100-200nm. In this embodiment, the TiO2 nanowires in this thickness range are conducive to increasing the number of CuFe2O4 nanowires per unit area of ​​the substrate, that is, increasing the number of CuFe2O4 nanowires in the CuFe2O4 nanowire array, providing a larger surface for Pd nanoparticle loading, and increasing the Pd nanoparticle loading in the formate fuel cell electrode, thereby increasing the electrochemically active surface area of ​​the fuel cell electrode for formic acid oxidation reaction and improving FOR activity; at the same time, it also avoids the situation that when the thickness of the CuFe2O4 nanowire is greater than 100nm, the number of CuFe2O4 nanowires in the CuFe2O4 nanowire array is reduced, thereby causing the electrochemically active surface area of ​​the fuel cell electrode for formic acid oxidation reaction to decrease.

[0043] In addition, the CuFe2O4 nanowires in this range of diameters in this embodiment further increase the electrochemically active surface area of ​​the fuel cell electrode for formic acid oxidation reaction. The CuFe2O4 nanowires in this range of diameters can also avoid the problem that when the thickness of the CuFe2O4 nanowires is greater than 200 nm, the CuFe2O4 nanowires are easily detached from the substrate during the FOR process, resulting in a decrease in the activity of the formate fuel cell electrode.

[0044] In addition, in some embodiments, the particle size of the Pd nanocluster particles is 10-20 nm. The Pd nanocluster particles in this particle size range can further shorten the electron transmission distance between CuFe2O4 nanowires, reduce the charge transfer impedance, and promote the improvement of the formic acid oxidation rate in the formic acid fuel cell.

[0045] In addition, in some embodiments, the Pd nanoparticles in the fuel cell electrode are formed in the gaps between the CuFe2O4 nanowire textile structures or on their surfaces, and their mass distribution is: 0.5 mg / cm 2

[0046] In addition, the CuFe2O4 nanowires in the fuel cell electrode of the present invention produce highly oxidative active *OH on the surface of titanium foam during the FOR process, which synergistically oxidizes Pd / Pt-H ad The active sites of Pt and Pd are released, so that Pt and Pd can resume their activity and continue to work. Therefore, the fuel cell electrode prepared in the present invention effectively solves the problem of hydrogen poisoning of Pt and Pd (Pd / Pt-H ad ) question.

[0047] The second aspect of the present invention provides a method for preparing a formate fuel cell electrode according to the first aspect of the present invention, comprising the following steps:

[0048] Step 1: Oxidation of the surface of porous titanium foam.

[0049] The pretreated porous titanium foam was placed in an oxygen-saturated 6M KOH solution for electrochemical oxidation. The oxidation time was 3 hours, the load potential was 2V, and the electrode system was a three-electrode system including a Pt counter electrode, a Hg / HgO reference electrode and a porous titanium foam working electrode.

[0050] Step 2: The oxidized porous titanium foam is composited with CuFe2O4.

[0051] The surface oxidized porous titanium foam obtained in step 1 is placed in a 100 ml aqueous solution containing Cu(NO3)2·3H2O, Fe(NO3)3·9H2O and urea and subjected to a hydrothermal reaction. After the reaction is completed, the porous titanium foam is cleaned and dried to obtain a porous Ti / TiO2 / CuFe2O4 electrode substrate.

[0052] Step 3: Composite the porous foam Ti / TiO2 / CuFe2O4 electrode substrate with Pd.

[0053] The porous foam Ti / TiO2 / CuFe2O4 electrode substrate obtained in step 2 is placed in 100 ml 10 mmol PdCl2 solution for electrochemical deposition to obtain a porous foam Ti / TiO2 / CuFe2O4 / Pd composite electrode.

[0054] In this embodiment, formate fuel cell electrodes are prepared by electrodeposition and hydrothermal methods. This method is less affected by the size and shape limitations of nanocrystals during the preparation process. Therefore, the TiO2 thickness on the surface of the titanium foam can be prepared to 10-100nm, and the coverage of the CuFe2O4 nanowire layer is 100-200nm, providing a larger surface area for the attachment of Pd nanoparticles; it is also beneficial to the production of Pd nanocluster particles.

[0055] In addition, the formate fuel cell electrode prepared by the hydrothermal method and the electrodeposition method has a stable three-dimensional structure and a rich gap structure, which is conducive to the attachment of Pd nanoparticles and the embedding of Pd nanocluster particles, which not only increases the Pd content and effectively increases the electrochemically active surface area of ​​the formic acid oxidation reaction, but also reduces the electron transmission distance between the CuFe2O4 nanowires; therefore, the formate fuel cell electrode prepared by the hydrothermal method and the electrodeposition method not only increases the electrochemically active surface area of ​​the formic acid oxidation reaction and optimizes the electronic structure of the formate fuel cell electrode, but also improves its FOR performance.

[0056] In addition, in this embodiment, in step 1, an electrode substrate composed of a large amount of porous foam Ti / TiO2 / CuFe2O4 is grown on the substrate by a hydrothermal method; wherein nickel in copper nitrate and iron in ferric nitrate are used as metal ions on the layer plates constituting the CuFe2O4 nanowires; urea is used to adjust the pH value of the precursor solution in the hydrothermal reaction process and simultaneously provide anions NO3 inserted into the interlayer of the CuFe2O4 nanowires. - and OH - .

[0057] In addition, in this embodiment, the substrate pretreatment in step 1 is performed in the following manner:

[0058] The pretreated porous titanium foam was placed in an oxygen-saturated 6M KOH solution for electrochemical oxidation. The oxidation time was 3 h, the load potential was 2 V, and the electrode system was a three-electrode system including a Pt counter electrode, a Hg / HgO reference electrode and a porous titanium foam working electrode.

[0059] In this embodiment, the substrate may be any one of TiO2, foamed nickel (porous foamed titanium), foamed copper, foamed aluminum, carbon paper and carbon cloth.

[0060] In step 2 of this embodiment, a hydrothermal reaction is first used to form a porous foam Ti / TiO2 / CuFe2O4 electrode substrate, and then a precipitant is used to embed CuFe2O4 nanowires into the gaps formed by Ti / TiO2.

[0061] In addition, in some embodiments, the conditions of the hydrothermal reaction in step 1 are: the reaction temperature is 100-150°C and the reaction time is 6-15h. The reaction temperature and reaction time first ensure the size of the Ti / TiO2 and CuFe2O4 nanowires formed, and ensure that the formed CuFe2O4 nanowires have a large surface area to provide more attachment sites for Pd nanoparticles; at the same time, they also ensure the formation of Pd nanoparticles and the ability of Pd nanoparticles to attach to the CuFe2O4 nanowires, thereby avoiding the problem of low attachment amount of Pd nanoparticles on the CuFe2O4 nanowires due to the small diameter of the CuFe2O4 nanowires, and also avoid the problem of the inability to form Pd nanoparticles.

[0062] In addition, in some embodiments, the molar ratio of copper nitrate to iron nitrate in step 1 is (1:9) to (9:1); 0.5-0.6g of urea is added to every 20-50mL of water in the precursor solution. First, the copper nitrate and iron nitrate in this molar ratio range ensure that CuFe2O4 nanowires can be formed, and the amount of urea in this range can ensure that the pH value of the precursor solution is stable in a range (9-10) during the hydrothermal reaction, avoiding excessive or insufficient urea so that CuFe2O4 nanowires cannot be obtained. In addition, in order to improve the conductivity of the formate fuel cell electrode, in some embodiments, the precursor solution also includes graphene. In this embodiment, the composition of the precursor solution is generally 0.291g of copper nitrate, 0.403g of iron nitrate and 0.6g of urea, and the content of graphene powder in the prepared precursor is 0.005g.

[0063] In addition, in this embodiment, in order to facilitate the stacking of CuFe2O4 nanowires on the substrate, the precursor solution also includes ammonium fluoride. In the embodiment, when the precursor is prepared from 0.291g copper nitrate, 0.403g iron nitrate and 0.6g urea, the amount of ammonium fluoride used is 0.1-0.15g.

[0064] In addition, the precipitating agent in step 2 of this embodiment includes urea and ammonium fluoride. The amount of urea and ammonium fluoride used in this embodiment is generally 0.6g of urea and 0.12g of ammonium fluoride are required to be added to 0.015g of palladium chloride.

[0065] In addition, in order to promote the various substances in the precursor solution and the PdCl2 precursor solution to be fully dissolved and dispersed, ultrasound is selected to treat the precursor solution and the PdCl2 precursor solution during the preparation of the precursor solution and the PdCl2 precursor solution. In addition, the precursor drying conditions in step 1 of this embodiment and the formate fuel cell electrode drying conditions in step 2 are preferably: the drying temperature is 60° C. and the drying time is 5 h.

[0066] The embodiment of the third aspect of the present invention is to use the formate fuel cell electrode in the embodiment of the first aspect as an anode electrode of a formic acid fuel cell. When the formate fuel cell electrode in the present invention is used as an anode electrode of a formic acid fuel cell, it has excellent formic acid oxidation stability and formic acid oxidation efficiency during the formic acid oxidation reaction.

[0067] Example

[0068] Example 1

[0069] A method for preparing a Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode comprises the following steps:

[0070] Step S1, preparation of Ti / TiO2 / CuFe2O4 precursor, comprising:

[0071] Step 1: Surface pretreatment of porous titanium foam

[0072] The pretreated porous titanium foam was placed in an oxygen-saturated 1M KOH solution for electrochemical oxidation. The oxidation time was 3 hours, the load potential was 2V, and the electrode system was a three-electrode system including a Pt counter electrode, a Hg / HgO reference electrode and a porous titanium foam working electrode.

[0073] Step S2: CuFe2O4 covers the porous foam Ti / TiO2 prepared in step 1

[0074] The porous foamed Ti / TiO2 prepared in step 1 is placed in a precursor solution and subjected to a hydrothermal reaction. After the reaction is completed, the precursor is successively cleaned and dried to obtain a precursor; wherein the precursor solution includes copper nitrate, iron nitrate and urea; after the hydrothermal reaction, the porous foamed Ti / TiO2 / CuFe2O4 electrode substrate is obtained after cleaning and drying.

[0075] Step S3: Preparation of fuel cell electrodes

[0076] The Ti / TiO2 / CuFe2O4 electrode substrate obtained in step 2 is placed in a PdCl2 solution for electrochemical deposition, and a Ti / TiO2 / CuFe2O4 / Pd composite electrode is obtained after reaction and cleaning.

[0077] The beneficial effects of the present invention are as follows: the porous titanium foam, copper ferrite and Pd are sequentially formed into functional layers using the above methods (electrochemical oxidation, hydrothermal and electrodeposition), namely the innermost layer of titanium, the second innermost layer of TiO2, the second outermost layer of CuFe2O4 and the outermost layer of Pd. This step-by-step treatment method combination can functionalize each layer, and each functionalized surface is independent of each other during the preparation process without mutual interference. The CuFe2O4 fiber and porous titanium foam composite matrix formed by this step-by-step functionalization method has a large gap, which can ensure the entry of the electrolyte, increase the electrode specific surface, and ensure the formation of the three-phase interface of the catalyst, reactant and electrolyte; at the same time, the surface active sites of the formate oxidation catalyst are increased, the functionalized structure of the electrode is optimized, the utilization rate of Pd is improved, and the cost of using precious metals is reduced.

[0078] Test analysis:

[0079] 1. XRD test analysis

[0080] The Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in Example 1 was subjected to XRD test analysis, and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen that in the XRD pattern of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode, the diffraction peaks at 36.2°, 39.1°, 46.6°, 62.3°, 67.5°, 74.8° and 83.1° correspond to the (004), (111), (200), (213), (220), (215), and (311) crystal planes of Ti / TiO2 / CuFe2O4 / Pd, indicating the successful synthesis of Ti / TiO2 / CuFe2O4 / Pd.

[0081] 2. SEM (Scanning Electron Microscope) Test Analysis

[0082] The surface oxidized porous titanium foam and Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in Example 1 were subjected to SEM test analysis, and the test results are shown in Figure 2(a) and Figure 2(b), respectively.

[0083] As can be seen from Figure 2(a), Ti / TiO2 grows on porous foam titanium (foam nickel) and gaps are formed between CuFe2O4 nanowires. This type of spatial structure provides more attachment sites for Pd nanoparticles. Therefore, the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared using this precursor provides abundant reaction active sites for FOR.

[0084] Pd nanoparticles are attached to CuFe2O4 nanowires, and the Pd nanoparticles are in clusters (i.e., after the CuFe2O4 nanowires are clustered to form Pd nanocluster particles or Pd nanoparticle clusters are embedded in the gaps between the CuFe2O4 nanowires), and the Pd nanocluster particles are located in the gaps formed between the CuFe2O4 nanowires in the Ti / TiO2 / CuFe2O4 precursor. Therefore, this type of composite structure optimizes the surface electronic structure of the formate fuel cell electrode, reduces the electron transfer resistance, and promotes electron transport during formic acid oxidation, thereby effectively improving the formic acid oxidation activity of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode.

[0085] 4. Test and analyze formate fuel cell electrodes using voltammetry

[0086] (1) The Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared in Example 1 and the pure Pd formate fuel cell electrode were tested by cyclic voltammetry. During the test, the two formate fuel cell electrodes were placed in a solution containing KOH and formic acid. The size of the formate fuel cell electrode tested was 1 cm×1 cm, and the molar concentration of KOH in the solution was 1.0 mol / L, and the molar concentration of formic acid was 1.0 mol / L.

[0087] The cyclic voltammograms of Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode and pure Pd formate fuel cell electrode are shown in Figure 2. Figure 3 As shown, from Figure 3 As can be seen from the figure, as the potential increases, the current density corresponding to the oxidation peak of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode at a potential of -0.1 V vs. Hg / HgO reaches a peak value (550 A g -1), and its peak value is significantly higher than that of pure Pd formate fuel cell electrode (320A g-1). The data show that Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode has better formic acid oxidation performance than pure Pd formate fuel cell electrode. This is because the composite of CuFe2O4 nanowires and Pd nanoparticles increases the surface active sites of Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode, thereby promoting the improvement of formic acid oxidation performance of Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode. In addition, after the CuFe2O4 nanowires and Pd nanoparticles are fully mixed, the Pd nanocluster particles enter the gaps between the CuFe2O4 nanowires, reducing the electron transmission distance between the CuFe2O4 nanowires, promoting the improvement of formic acid oxidation rate, and reducing the charge transfer impedance. At the same time, the unique spatial structure formed between the CuFe2O4 nanowires is conducive to the loading, dispersion and mass transfer of Pd nanoparticles, while forming a unique spatial layered structure, increasing the electrochemically active surface area of ​​the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode.

[0088] (2) The CV decay test was performed on the pure Pd formate fuel cell electrode and the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode using the voltammetric test method. The decay test results are shown in the figure. Figure 4 As shown in the figure, after 10000 CV cycles, the peak current density of the formic acid oxidation peak decreases from 500A g -1 Down to 350A g -1 ; The data changes indicate that as formic acid oxidation proceeds, Pd is continuously poisoned, eventually leading to a decrease in the formic acid oxidation peak current of the pure Pd formate fuel cell electrode.

[0089] (3) The IT decay test of Ti / TiO2 / CuFe2O4 / Pd was carried out by using the instantaneous current method. Figure 5 As shown. Figure 5 It can be seen that after a durability test of up to 6000 s, the mass specific activity of the Ti / TiO2 / CuFe2O4 / Pd formate fuel cell electrode prepared by the hydrothermal method and electrodeposition method of the present invention is 350A g -1 Down to 40A g -1 , which indicates that Ti / TiO2 / CuFe2O4 / Pd has excellent formate oxidation durability.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A formate fuel cell electrode, characterized in that: The fuel cell electrode comprises: The surface of the porous titanium foam is rutile TiO2, the interior is porous titanium foam with conductive function, and the external surface is rutile TiO2; CuFe2O4 nanowires are stacked and staggered to form a textile structure, and there are gaps between the CuFe2O4 nanowire textile structures; the CuFe2O4 nanowire textile structure is in-situ grown on the surface of porous titanium foam; Pd nanoparticles, the Pd nanoparticles are attached to the surface of CuFe2O4 nanowires, and / or Pd nanocluster particles are embedded in the gaps between CuFe2O4 nanowire textile structures or on their surface, wherein the diameter of the Pd nanoparticles is less than 1um.

2. A formate fuel cell electrode according to claim 1, characterized in that: The porous titanium foam has Ti metal inside and a layer of TiO2 on the surface.

3. A formate fuel cell electrode according to claim 1, characterized in that: The CuFe2O4 nanowire has a diameter of 10-20 nm and a length of 10-500 um.

4. A formate fuel cell electrode according to claim 1, characterized in that: The Pd nanoparticles are formed in the gaps between the CuFe2O4 nanowire textile structures or on their surfaces, and their mass distribution is: 0.5 mg / cm 2 .

5. The method for preparing a formate fuel cell electrode according to any one of claims 1 to 4, characterized in that: The fuel cell electrode is in-situ grown by electrodeposition and hydrothermal method, and three interfaces are formed in sequence between Ti, TiO2, CuFe2O4 and Pd from the inside to the outside, including Ti / TiO2, TiO2 / CuFe2O4 and CuFe2O4 / Pd two-phase interfaces.

6. The method for preparing a formate fuel cell electrode according to claim 5, characterized in that: The following steps are involved: Step 1, surface oxidation of porous titanium foam; The pretreated porous titanium foam was placed in an oxygen-saturated 6M KOH solution for electrochemical oxidation for 3 hours at a load potential of 2V. The electrode system was a three-electrode system including a Pt counter electrode, a Hg / HgO reference electrode and a porous titanium foam working electrode. Step 2, the oxidized porous titanium foam is compounded with CuFe2O4; The surface oxidized porous titanium foam obtained in step 1 is placed in a 100 ml aqueous solution containing Cu(NO3)2⋅3H2O, Fe(NO3)3⋅9H2O and urea and subjected to a hydrothermal reaction. After the reaction is completed, the porous titanium foam is cleaned and dried to obtain a porous Ti / TiO2 / CuFe2O4 electrode substrate; Step 3, the porous foam Ti / TiO2 / CuFe2O4 electrode substrate is composited with Pd; The porous foamed Ti / TiO2 / CuFe2O4 electrode substrate obtained in step 2 was placed in 100 ml of 10 mmol PdCl2 solution for electrochemical deposition to obtain a porous foamed Ti / TiO2 / CuFe2O4 / Pd composite electrode.

7. The method for preparing a formate fuel cell electrode according to claim 6, characterized in that: The conditions of the hydrothermal reaction in step 2 are: reaction temperature of 120-150° C., reaction time of 8-20 h.

8. The method for preparing a formate fuel cell electrode according to claim 6, characterized in that: In step 1, the molar ratio of Cu(NO3)2⋅3H2O to Fe(NO3)3⋅9H2O is 1:9~9:1; 0.5~1.2g of urea is added to every 100mL of water in the precursor solution.

9. Use of a formate fuel cell electrode according to any one of claims 1 to 4 for preparing an anode electrode material for a formate fuel cell.

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