CN114540876B - Sulfonated polybenzimidazole-based electrocatalyst for oxygen evolution reaction and preparation method thereof - Google Patents

Abstract

The invention relates to the field of preparation and research of oxygen evolution reaction electrocatalysts, and provides a sulfonated polybenzimidazole electrocatalyst for oxygen evolution reaction and a preparation method thereof. The electrocatalyst for oxygen evolution reaction is prepared by a dipping-annealing combination method by taking sulfonated polybenzimidazole as a carrier. The beneficial effects of the invention are as follows: the raw materials are low in cost, nontoxic and harmless; the reaction temperature is stable and easy to control. An OER electrocatalyst in the form of nanoparticles is prepared, the graphite structure present in such nanoparticles optimising OER conductivity. And after annealing treatment, pyrrole-N metal coordination sites are generated, and Co-N coordination bonds are formed through strong interaction of Co and sPBI, so that the structural stability of the nano particles is improved. Simultaneously generate pyridine-N species, can accelerate O ₂ And reduces OER overpotential. Finally, crystal defects are generated after annealing treatment, more active sites are exposed, and the adsorption capacity of the intermediate is improved, so that the electrocatalyst has quite large OER activity.

Description

Sulfonated polybenzimidazole-based electrocatalyst for oxygen evolution reaction and preparation method thereof

technical field

The invention relates to an electrocatalyst for oxygen evolution reaction and a preparation method thereof, in particular to a sulfonated polybenzimidazole-based electrocatalyst and a preparation method thereof.

Background technique

Clean, high-energy-density hydrogen energy is an important direction for the development of green energy today, and an environmentally friendly electrolysis water system is an important hydrogen production technology. Oxygen evolution reaction (OER) is one of the half-reactions and the rate-controlling step in water electrolysis. During the OER process, the transfer of electrons with the formation of OO bonds slows down the entire kinetic process of hydrolysis. Therefore, the study of more efficient and advanced electrocatalysts has a profound impact on promoting the development of water electrolysis. Currently, noble metal electrocatalysts such as _RuO2 and _IrO2 have been widely reported for their excellent OER performance, but their high cost limits their extensive commercialization. Therefore, low-cost transition metals have become the focus of research in recent years, and complexes containing various transition metals also provide a direction for the preparation of OER electrocatalysts.

Sulfonated polybenzimidazole (sPBI) is a class of high-performance polymers with high thermal stability, oxidation resistance and good mechanical properties, which are usually used to make proton exchange membranes. In addition, -SO ₃ H in the polymer can make sPBI have good conductivity; meanwhile, the N species in sPBI can generate lone electron pairs. This allows sPBI to be used as an electrocatalyst matrix material, but it needs to anchor suitable metal ligands to exert excellent electrocatalytic properties.

Aiming at the above problems, a low-cost and high-performance OER electrocatalyst and its preparation method are proposed.

Contents of the invention

The object of the present invention is to provide a sulfonated polybenzimidazole-based OER electrocatalyst and a preparation method thereof. The first is to synthesize sPBI by direct polycondensation method, and its repeating unit structure is as follows:

Among them, _X1 can be hydrogen, lithium, sodium _{, potassium or magnesium} by soaking sPBI in HCl solution, _Li2CO3 solution, _Na2CO3 solution, _K2CO3 solution and _Mg2CO3 solution, respectively Plasma.

The X ₂ structure is produced by the corresponding aromatic dicarboxylic acid. According to the selected aromatic dicarboxylic acid monomer, the sPBI structure contains one or more X ₂ structures. The following figure lists different X ₂ structures And its corresponding aromatic dicarboxylic acid monomer, the present invention uses the sulfonated polybenzimidazole as the structural unit containing flexible ether bonds as an illustration, that is, the selected aromatic dicarboxylic acid monomer is 4, 4-dicarboxydi phenyl ether.

Secondly, the sPBI and cobalt acetate powders were treated by water impregnation and thermal annealing to obtain the OER electrocatalyst with nanoparticle morphology.

The preparation method of the OER electrocatalyst provided by the invention comprises the following preparation steps:

(1) Preparation of sPBI: 3, 3'-diaminobenzidine (DAB), 4, 4-dicarboxydiphenyl ether (PE) and 3, 3'-sodium disulfonate-4 , 4'-dicarboxybiphenyl (SCBP) is polymerized, filtered with suction, soaked in salt, washed with water, and finally vacuum-dried to obtain sPBI.

(2) Preparation of the precursor (Co/sPBI Pre): Grind the sPBI obtained in (1) into powder and add it to the ultrasonically treated Co(OAc) ₂ solution, evaporate it with water heat, and dry it in vacuum to obtain the Co/sPBI Pre. sPBI Pre.

(3) Preparation of nanoparticle catalyst (Co/sPBI NPs): The Co/sPBI Pre obtained in (2) was annealed in a tube furnace under N ₂ atmosphere to obtain Co/sPBI NPs.

Preferably, in step (1), the concentration of SCBP is 60%; the solution used for salt immersion is 5 wt % Na ₂ CO ₃ solution, and the soaking time is 24 h; the vacuum drying temperature is 100 °C, and the drying time is 36 h.

Preferably, in step (2), the mass percentages of Co element in sPBI are 0.2, 0.4, and 0.6 respectively.

Preferably, in step (2), the power value of the ultrasonic treatment is 1500 W, and the ultrasonic treatment is performed at 90% energy output value for 15 min; the hydrothermal evaporation temperature is 60 °C; the vacuum drying temperature is 80 °C, and the drying time is 24 h.

Preferably, in step (3), the annealing temperatures are 800 °C, 850 °C and 900 °C respectively, the annealing time is 3 h, and the heating rate is 6 °C/min.

Compared with the prior art, the preparation method of the OER electrocatalyst provided by the invention has the following progress:

(1) The preparation process of the OER electrocatalyst provided by the present invention has low raw material cost, is non-toxic and harmless, and is easy to obtain; the reaction temperature is stable, the reaction is mild, and it is easy to control.

(2) The method provided by the present invention produces an OER electrocatalyst in the form of nanoparticles, and the microcrystalline graphite structure present in the nanoparticles optimizes the OER conductivity.

The preparation method of the OER electrocatalyst proposed in the present invention will generate pyrrole-N metal coordination sites after annealing treatment, and through the strong interaction between Co and sPBI, a Co-N coordination bond can be formed, which can improve the Structural stability; in addition, the annealing process also produces pyridine-N species, which can accelerate the release of _O2 and reduce the OER overpotential; finally, crystal defects will be generated after annealing treatment, and the existence of crystal defects can expose more active sites, Accelerate electron transfer and enhance the adsorption capacity of intermediates, thus enabling electrocatalysts with considerable OER activity.

Description of drawings

The chemical structure of sPBI synthesized in the present invention was confirmed by ¹ H NMR; the crystal structures of sPBI and Co/sPBI Pre were analyzed by XRD; the morphology of Co/sPBI NPs was characterized by SEM.

Fig. 1 is the ¹ H NMR spectrogram of the sPBI that makes in the embodiment one;

Fig. 2 is the XRD spectrogram of sPBI and Co/sPBI Pre prepared in embodiment one and two;

FIG. 3 is a SEM image of Co/sPBI NPs prepared in Example 3.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Embodiment one:

1) Preparation of sPBI: sPBI was prepared by polycondensation reaction, adding 10 g of phosphorus pentoxide (P ₂ O ₅ ) and 30 g of polyphosphoric acid (PPA) into _a 100 mL three- Neck round bottom bottle. The mixture was then stirred at 175 °C until _{the P2O5} was completely dissolved and then cooled to about 25 °C. Then, 4 mmol DAB was put into the bottle and stirred at 80 °C and 120 °C for 1 h, respectively. After cooling, 2.4 mmol SCBP and 1.6 mmol PE were put into the mixture. The mixture was then stirred at 120 °C, 150 °C, 170 °C, and 190 °C for 12 h, respectively. After cooling slightly, the mixture was poured into deionized water to obtain a brown filamentary product. The _product was washed with deionized water to remove the remaining acid, and then soaked in 5 wt % _Na2CO3 solution for 24 h. The soaked product is then suction filtered and washed to neutral pH. Finally, the neutral pH product was vacuum-dried at 100 °C for 36 h. Sulfonated polybenzimidazole was obtained and named sPBI.

Sulfonated polybenzimidazole (sPBI) was synthesized by polycondensation of SCBP, DAB and PE in PPA by direct polycondensation method. As shown in Figure 1, the H atoms in sPBI matched well with all signal peaks. Meanwhile, the signal peaks (H7, H7') of H of the benzimidazole ring exhibit different chemical shifts at 13.50 and 13.60 ppm under different chemical environments of sulfonation and non-sulfonation. H1, H8, and H9 all have sharp peaks with the highest intensity, which are mainly related to the high content of H atoms. The chemical shifts of H4, H4′, H5, H5′, H6, and H6′ ranged from 7.87 to 7.63 ppm, similar to the H atom shifts in other reported sPBIs. ¹ H NMR spectrum confirmed the chemical structure of sPBI, and sPBI was successfully prepared.

also,

Embodiment two:

1) Preparation of the precursor (0.2 Co/sPBI Pre): Add 150 mL of deionized water and 180.2 mg of Co(OAc) ₂ into a 300 mL beaker, and sonicate at 1500 W and 90% energy output for 15 min until a homogeneous solution is formed. Subsequently, 300 mg of sPBI was added to the solution, followed by magnetic stirring at 60 °C until the water evaporated completely. Finally, the product was vacuum-dried at 80 °C for 24 h. The precursor was prepared and named as 0.2 Co/sPBI Pre.

2) Preparation of the precursor (0.4 Co/sPBI Pre): Add 150 mL of deionized water and 360.5 mg of Co(OAc) ₂ into a 300 mL beaker, and sonicate at 1500 W and 90% energy output for 15 min until a homogeneous solution is formed. Subsequently, 300 mg of sPBI was added to the solution, followed by magnetic stirring at 60 °C until the water evaporated completely. Finally, the product was vacuum-dried at 80 °C for 24 h. The precursor was prepared and named as 0.4 Co/sPBI Pre.

3) Preparation of the precursor (0.6 Co/sPBI Pre): Add 150 mL of deionized water and 540.7 mg of Co(OAc) ₂ into a 300 mL beaker, and sonicate at 1500 W and 90% energy output for 15 min until a homogeneous solution is formed. Subsequently, 300 mg of sPBI was added to the solution, followed by magnetic stirring at 60 °C until the water evaporated completely. Finally, the product was vacuum-dried at 80 °C for 24 h. The precursor was prepared and named as 0.6 Co/sPBI Pre.

The difference of all prepared precursors is that the mass percentage of Co element in sPBI is different. The mass percentage of Co element in sPBI in 0.2 Co/sPBIPre, 0.4 Co/sPBI Pre and 0.6 Co/sPBI Pre is 20%, 40% and 60%. It can be seen from Figure 2 that the results show that sPBI has a broad peak with low crystallinity at 24.5°, which is due to the periodic parallelism of the sPBI polymer backbone, indicating that sPBI has an amorphous structure. Similarly, Co/sPBI Pre also had a broad diffraction peak at 24.5°, indicating that the impregnation method preserved the polymer chains of sPBI well and provided good conditions for the adsorption of Co ²⁺ . At the same time, due to the addition of Co ²⁺ to the main chain of sPBI, the characteristic diffraction peak intensity of Co/sPBI Pre is weaker than that of sPBI. Notably, no other crystalline phases were detected in the Co/sPBI precursor, which indicated that Co ²⁺ was fully incorporated into the sPBI backbone and Co/sPBI Pre was successfully prepared.

Embodiment three:

1) Preparation of nanoparticle catalyst (0.2 Co/sPBI NPs-850 ℃): In the N ₂ atmosphere, put 150 mg0.2 Co/sPBI Pre into the tube furnace, check the airtightness, and heat at 6 ℃/ The temperature was programmed to 850 °C at a heating rate of 3 h and then calcined for 3 h. The nanoparticle catalyst was prepared and named as 0.2 Co/sPBI NPs-850 °C.

2) Preparation of nanoparticle catalyst (0.4 Co/sPBI NPs-850 ℃): In N ₂ atmosphere, put 150 mg0.4 Co/sPBI Pre into the tube furnace, check the airtightness, and heat at 6 ℃/ The temperature was programmed to 850 °C at a heating rate of 3 h and then calcined for 3 h. The nanoparticle catalyst was prepared and named as 0.4 Co/sPBI NPs-850 °C.

3) Preparation of nanoparticle catalyst (0.6 Co/sPBI NPs-850 ℃): In N ₂ atmosphere, put 150 mg0.6 Co/sPBI Pre into the tube furnace, check the airtightness, and heat at 6 ℃/ The heating rate of min was programmed to heat up to 850 °C and then baked for 3 h. The nanoparticle catalyst was prepared and named as 0.6 Co/sPBI NPs-850 °C.

The present invention also prepared 0.2 Co/sPBI NPs-900 °C, 0.4 Co/sPBINPs-900 °C, and 0.6 Co/sPBI NPs-900 °C at an annealing temperature of 900 °C. The point is the difference in annealing temperature. As shown in Figure 3 (a and d represent 0.2 Co/sPBI NPs-850 ℃ and 0.2 Co/sPBI NPs-900 ℃; b and c represent 0.4 Co/sPBI NPs-850 ℃ and 0.4 Co/sPBI NPs-900 ℃; c and f represent 0.6Co/sPBI NPs-850 °C and 0.6 Co/sPBI NPs-900 °C), the SEM images of all Co/sPBI NPs show similar morphology and structure, that is, the nanosheet structure of sPBI is completely covered by Co/sPBI The NPs are covered by nanoparticles, indicating that Co ²⁺ has been well anchored on the surface of sPBI to form the desired nanoparticle structure, and Co/sPBI NPs were successfully prepared.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (5)

1. A sulfonated polybenzimidazole-based electrocatalyst for oxygen evolution reaction, characterized in that: the sulfonated polybenzimidazole containing a repeated structural unit is used as a matrix, transition metal is used as a ligand, and transition metal ions are anchored on the surface of a polymer matrix through effective pi-pi accumulation of benzene rings and strong hydrogen bonding;

；

X ₁ hydrogen, lithium, sodium, potassium or magnesium ions;

X ₂ the structure of (2) is as follows:

；

the repeating structural unit of the sulfonated polybenzimidazole contains one or more X ₂ Structure is as follows.

2. The preparation method of the sulfonated polybenzimidazole-based electrocatalyst for oxygen evolution reaction is characterized by adopting a direct polycondensation method and an immersion-annealing treatment, and comprises the following specific steps:

(1) Preparing sulfonated polybenzimidazole, polymerizing 3, 3 '-diaminobenzidine, 4' -dicarboxyl diphenyl ether and 3, 3 '-sodium disulfonate-4, 4' -dicarboxyl biphenyl, filtering, salting, washing with water, and finally vacuum drying to obtain sulfonated polybenzimidazole sPBI;

(2) Preparation of the precursor sPBI was ground to a powder and then added to sonicated Co (OAc) ₂ In the solution, carrying out hydrothermal evaporation and vacuum drying to obtain a precursor Co/sPBI Pre;

(3) The preparation method of the nanoparticle catalyst comprises the steps of putting Co/sPBI Pre in N ₂ And annealing treatment is carried out by a tube furnace under atmosphere, so that the nano-particle catalyst Co/sPBI NPs is obtained.

3. The method for preparing the sulfonated polybenzimidazole based electrocatalyst for oxygen evolution reaction according to claim 2, wherein: the concentration of 3, 3' -disulfonic acid sodium salt-4, 4' -dicarboxybiphenyl material is 60% of the concentration of 3, 3' -diaminobenzidine material; the solution used for the salt leaching is Na with the concentration of 5 wt percent ₂ CO ₃ The soaking time of the solution is 24 h; the vacuum drying temperature was 100℃and the drying time was 36 h.

4. The method for preparing the sulfonated polybenzimidazole based electrocatalyst for oxygen evolution reaction according to claim 2, wherein: the mass percentages of Co element to sPBI are respectively 0.2, 0.4 and 0.6; the power value of the ultrasonic treatment is 1500W, and the ultrasonic treatment is carried out for 15 min under the energy output value of 90%; the hydrothermal evaporation temperature is 60 ℃; the vacuum drying temperature was 80℃and the drying time was 24 h.

5. The method for preparing the sulfonated polybenzimidazole based electrocatalyst for oxygen evolution reaction according to claim 2, wherein: the annealing temperature is 800 ℃, 850 ℃ and 900 ℃, the annealing time is 3 h, and the heating rate is 6 ℃/min.