阅读说明：本技术 一种电催化硝酸根或亚硝酸根合成氨的方法 (Method for synthesizing ammonia by electrocatalysis of nitrate or nitrite ) 是由 刘承斌 唐艳红 袁继理 于 2021-08-10 设计创作，主要内容包括：本发明公开了一种电催化硝酸根或亚硝酸根合成氨的方法,该方法采用的电催化剂为金属-金属氧化物,所述金属-金属氧化物本身作为阴极或者负载于导电材料表面作为阴极,所述金属-金属氧化物选自钌-氧化钌、铜-氧化铜、铜-氧化亚铜、镍-氧化镍、铁-三氧化二铁、铁-氧化亚铁、铁-四氧化三铁、钴-氧化钴、钴-四氧化三钴、锌-氧化锌中的一种或多种组合。本发明所提供的催化电极材料结构稳定,制备工艺简单,可以有效放大制备,实现其在将含硝酸根或亚硝酸根废水变为有价值的氨的应用。本发明所提供的催化电极材料,可以实现高效地电催化硝酸根或亚硝酸根还原为氨,选择性高。(The invention discloses a method for synthesizing ammonia by electrocatalysis of nitrate or nitrite, wherein an adopted electrocatalyst is a metal-metal oxide, the metal-metal oxide is used as a cathode or is loaded on the surface of a conductive material to be used as the cathode, and the metal-metal oxide is selected from one or more of ruthenium-ruthenium oxide, copper-copper oxide, copper-cuprous oxide, nickel-nickel oxide, iron-ferric oxide, iron-ferrous oxide, iron-ferroferric oxide, cobalt-cobalt oxide, cobalt-cobaltosic oxide and zinc-zinc oxide. The catalytic electrode material provided by the invention has a stable structure and a simple preparation process, can be effectively amplified and prepared, and realizes the application of the catalytic electrode material in converting waste water containing nitrate or nitrite into valuable ammonia. The catalytic electrode material provided by the invention can realize the efficient electrocatalysis of nitrate or nitrite to ammonia, and has high selectivity.)

1. The method for synthesizing ammonia by electrocatalysis of nitrate or nitrite is characterized in that an electrocatalyst adopted in the method is a metal-metal oxide, the metal-metal oxide is used as a cathode or is loaded on the surface of a conductive material to be used as a cathode, and the metal-metal oxide is selected from one or more of ruthenium-ruthenium oxide, copper-copper oxide, copper-cuprous oxide, nickel-nickel oxide, iron-ferric oxide, iron-ferrous oxide, iron-ferroferric oxide, cobalt-cobalt oxide, cobalt-cobaltosic oxide and zinc-zinc oxide.

2. The method for synthesizing ammonia from nitrate or nitrite according to claim 1, wherein the metal-metal oxide contains 5 to 95% by mass of metal and 95 to 5% by mass of metal oxide.

3. The method for synthesizing ammonia from nitrate or nitrite according to claim 1 or 2, wherein the metal-metal oxide is copper-copper oxide.

4. The method for synthesizing ammonia from nitrate or nitrite according to claim 3, wherein the copper-copper oxide contains 90% by mass of copper and 10% by mass of copper oxide.

5. The method for synthesizing ammonia from nitrate or nitrite according to claim 1, wherein the metal-metal oxide itself serves as a cathode, and the metal-metal oxide is in the form of foam, sheet, block or rod.

6. The method for synthesizing ammonia from nitrate or nitrite according to claim 5, wherein the metal-metal oxide is foamed.

7. The method for synthesizing ammonia from nitrate or nitrite according to claim 1, wherein the metal-metal oxide is supported on the surface of a conductive material as a cathode, and the conductive material is a carbon material.

8. The method for synthesizing ammonia from nitrate or nitrite according to claim 7, wherein the carbon material is any one of carbon cloth, carbon rod and carbon block.

Technical Field

The invention belongs to the technical field of electrocatalysis, and particularly relates to a method for synthesizing ammonia by electrocatalysis of nitrate or nitrite.

Background

The use of nitrogen fertilizers such as ammonium nitrate and urea contributes significantly to agricultural production over the past century. However, the utilization of nitrogenThe efficiency is usually less than 40% and therefore most of the nitrogen in the fertilisation is not absorbed into the plants but is easily leached from the soil into the ground water. Thus, the nitrate or nitrite concentration (NO) is increasing due to over-fertilization and industrial wastewater and human waste^3-/NO^2-). In groundwater, rivers, lakes and coastal areas, serious environmental problems such as eutrophication are caused.

Many efforts have been made to remove nitrate or nitrite from wastewater for denitrification and remediation of aqueous environments, such as: biological methods, ion exchange methods, membrane separation methods, and the like, but these methods often have the disadvantages of harsh reaction conditions, slow reaction rate, high equipment cost, and the like. Among the many efforts, electrochemical reduction of nitrate or nitrite has received considerable attention, since the electricity it requires can be provided by renewable energy sources (such as solar or wind energy). The reduction of nitrate and nitrite in water at the electrode-electrolyte interface can be very efficient, producing various products, such as: nitrogen, dissolved ammonia (NH)₃) Or NH⁴⁺And nitrite NO^2-. Many studies have aimed at converting nitrate NO^3-Or nitrite NO^2-Selective electrocatalytic conversion to N₂Can be discharged directly into the ambient air, however, from the nitrate NO^3-Or and nitrite NO^2-To N₂Compared to the conversion of nitrate NO from waste water^3-Or nitrite NO^2-Production of NH₃Can be used as another way to more effectively utilize electric energy, and NH dissolved in water₃Can be used for>99% was recovered. With industrial production, synthesis of NH by Haber-Bosch process₃Such highly energy-dense and fossil fuel-dependent processes compare NO from water^3-Or NO^2-Electrochemical synthesis of NH₃Is a device capable of realizing the production of NH by using renewable electric energy₃Can balance the nitrogen cycling problems caused by over-fertilization, and also provides a promising strategy for alleviating global energy and environmental problems caused by fossil fuel-driven nitrogen conversion.

Related art has also reported that chinese patent CN 111359615 a prepares a nickel-doped carbon material by electrostatic spinning and calcining, and the material can electrochemically reduce nitrite in water to ammonia. Chinese patent CN 112981451 a uses borohydride to treat metal to prepare metal electrode for electrocatalysis of nitrate or nitrite to reduce ammonia. Chinese patent CN 111360279A discloses that monoatomic copper is embedded in a molecular lattice structure of 3,4,9, 10-pyrenetetracarboxylic dianhydride and can catalyze nitrate radical or nitrite radical to be reduced into ammonia. However, in the prior art, the overpotential required to be applied in the electrocatalysis process of these metals or metal-doped materials is still high, the structural stability of the materials is poor, and the selectivity (faradic efficiency) needs to be improved.

Disclosure of Invention

The invention aims to provide a method for synthesizing ammonia by electrocatalysis of nitrate or nitrite, the electrocatalysis adopted by the method has the advantages of stable structure, simple preparation process, low cost and easy amplification, and nitrate or nitrite can be efficiently reduced to ammonia.

In order to achieve the purpose, the invention provides the following technical scheme:

the invention provides a method for synthesizing ammonia by electrocatalysis of nitrate or nitrite, the electrocatalysis adopted in the method is metal-metal oxide, the metal-metal oxide is used as a cathode or is loaded on the surface of a conductive material to be used as the cathode, and the metal-metal oxide is selected from one or more of ruthenium-ruthenium oxide, copper-copper oxide, copper-cuprous oxide, nickel-nickel oxide, iron-ferric oxide, iron-ferrous oxide, iron-ferroferric oxide, cobalt-cobalt oxide, cobalt-cobaltosic oxide and zinc-zinc oxide.

Preferably, the metal-metal oxide contains 5 to 95% by mass of the metal and 95 to 5% by mass of the metal oxide.

Further, the metal-metal oxide is copper-copper oxide, and the electrocatalytic effect is best.

Further, in the copper-copper oxide, the mass content of copper is 90%, and the mass content of copper oxide is 10%.

Preferably, the metal-metal oxide itself serves as a cathode, and the metal-metal oxide is in the form of a foam, a sheet, a block, or a rod.

Further, the metal-metal oxide is in a foam form.

Preferably, the metal-metal oxide is supported on the surface of a conductive material as a cathode, and the conductive material is a carbon material.

Further, the carbon material is any one of carbon cloth, carbon rod and carbon block.

The principle of the invention is as follows:

the electro-catalyst metal-metal oxide adopted by the invention can absorb protons (H) through oxygen-containing groups by introducing a proper proportion of metal oxide besides the metal catalytic active center⁺) And the reduction of nitrate radical or nitrite radical into ammonia is promoted:

NO^3-+8e^-+9H⁺→NH₃+3H₂O (1)

the technical scheme of the invention has the following beneficial effects:

(1) the catalytic electrode material provided by the invention has a stable structure and a simple preparation process, can be effectively amplified and prepared, and realizes the application of the catalytic electrode material in converting waste water containing nitrate or nitrite into valuable ammonia.

(2) The catalytic electrode material provided by the invention does not need to be treated by any chemical reagent, and can be directly stored and transported in the air and used in an ammonia preparation system by reducing electrochemical nitrate or nitrite at normal temperature and normal pressure.

(3) The catalytic electrode material provided by the invention can realize the efficient electrocatalysis of nitrate or nitrite to ammonia, and the selectivity reaches the highest level (more than 99 percent) reported at present.

Drawings

FIG. 1 is a scanning electron micrograph of copper foam-copper oxide of the cathode material of example 1;

FIG. 2 is an XPS ray energy spectrum of Cu before and after heating of the electrode of example 1, wherein only a Cu simple substance peak appears before heating, and a characteristic peak of copper oxide appears after heating in addition to the Cu simple substance peak;

FIG. 3 is a graph of current versus time (i-t) for the potentiostatic test of example 1;

FIG. 4 is a graph of the concentration of reduced nitrate at constant potential versus time (c-t) to form ammonia in example 1;

FIG. 5 is a graph of current versus time (i-t) for the potentiostatic test of example 2;

FIG. 6 is a graph of current versus time (i-t) for the potentiostatic test of example 3;

FIG. 7 is a graph of the concentration of reduced nitrate at constant potential versus time (c-t) to form ammonia in example 3;

FIG. 8 is a graph of current versus time (i-t) for the potentiostatic test of example 4;

FIG. 9 is a graph of concentration versus time (c-t) for nitrate reduction at constant potential to form ammonia in example 4;

FIG. 10 is a graph of current versus time (i-t) for the potentiostatic test of example 5;

FIG. 11 is a graph of the concentration of reduced nitrate at constant potential versus time (c-t) to form ammonia in example 5;

FIG. 12 is a graph of current versus time (i-t) for the potentiostatic test of example 6;

FIG. 13 is a graph of concentration versus time (c-t) for nitrate reduction at constant potential to form ammonia in example 6;

FIG. 14 is a graph of current versus time (i-t) for the potentiostatic test of example 7;

FIG. 15 is a graph of the concentration of reduced nitrate at constant potential versus time (c-t) to form ammonia in example 7;

FIG. 16 is a graph of current versus time (i-t) for the potentiostatic test of example 8;

FIG. 17 is a graph of the concentration of reduced nitrate at constant potential versus time (c-t) to form ammonia in example 8;

FIG. 18 is a graph of current versus time (i-t) for the potentiostatic test of example 9;

FIG. 19 is a graph of concentration versus time (c-t) for nitrate reduction at constant potential to form ammonia in example 9.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by those skilled in the art without any creative work based on the embodiments of the present invention belong to the protection scope of the present invention.

The invention is further illustrated below with reference to specific embodiments and the accompanying drawings.

Example 1

Commercially available copper foam with the thickness of 0.5cm, the width of 10cm and the length of 10cm is subjected to ultrasonic cleaning in water, acetone and ethanol for 30min respectively in sequence and then dried. Then heating for a certain time in the air atmosphere of 80 ℃ to obtain the foamy copper-copper oxide catalytic electrode, wherein the content of the copper oxide is controlled by the heating time. In this example, the heating was carried out for 40min, and the copper oxide accounted for 10%.

FIG. 1 is a scanning electron micrograph of copper foam-copper oxide in the form of foam. The XPS ray energy spectrum of figure 2 confirmed the production of copper oxide upon heating.

The obtained catalytic electrode is cut according to the size of 2cm in length and width and is used as a working electrode (cathode), and in a three-electrode (counter electrode: foamed nickel; reference electrode: Ag/AgCl electrode) system, the electrolyte is as follows: 0.5mmol/L potassium nitrate. The test was carried out at-0.15V (vs RHE) for 1800s in an atmospheric environment.

Fig. 3 is the resulting i-t plot and fig. 4 is the corresponding plot of the concentration of synthetic ammonia versus time (c-t), showing that the current decreased as the nitrate concentration decreased during the test, and nitrate was almost completely reduced to ammonia after 15 min. Measuring the ammonia concentration in the electrolyte by adopting a spectrophotometry method, and analyzing to obtain the ammonia production rate of 1.19mmol h^-1cm^-2The selectivity (Faraday efficiency) of ammonia production reaches 99.8%.

Example 2

The same procedure as in example 1 was repeated except that the 0.5mmol/L aqueous solution of potassium nitrate was replaced with the higher concentration aqueous solutions of 0.1mol/L potassium nitrate and 0.1mol/L sodium nitrite. The test was carried out at-0.15V (vs RHE) for 1800s in an atmospheric environment.

Fig. 5 is the resulting i-t plot showing that a more stable and high ammonia production current was obtained with the catalytic electrode during the test. Measuring the ammonia concentration in the electrolyte by adopting a spectrophotometry method, and analyzing to obtain the ammonia production rate of 1.24mmol h^-1cm^-2The selectivity of electrochemical ammonia production is 98.9%.

Example 3

The remainder of example 1 was the same as in example 1, except that a copper sheet was used instead of the copper foam. The ammonia and nitrite concentrations in atmospheric air were measured at-0.15V (vs RHE) for 1800s, FIG. 6 is a plot of current versus time (i-t) versus time (c-t) for the ammonia and nitrite concentrations of FIG. 7, showing that the current decreases with decreasing nitrate concentration during the test, and the ammonia production rate was analyzed to be 1.12mmol h^-1cm^-2The selectivity for electrochemical ammonia production was 93.9%.

Example 4

A nickel-nickel oxide catalytic electrode in the form of foam was prepared in the same manner as in example 1, except that the copper foam was replaced with nickel foam, and the nickel oxide accounted for 14%.

The nickel-nickel oxide was used as a working electrode, and the test was carried out in the same manner as in example 1 under-0.15V (vs RHE) for 1800s in an atmospheric environment. FIG. 8 is the obtained i-t diagram and FIG. 9 is the corresponding diagram (c-t) of the concentration of synthetic ammonia versus time, showing that the current slowly decreases with decreasing nitrate concentration during the test, and the analysis shows that the ammonia production rate is 1.08mmol h^-1cm^-2The selectivity of electrochemical ammonia production is 88.6%.

Example 5

A zinc-zinc oxide catalytic electrode in the form of foam was prepared in the same manner as in example 1 except that the copper foam was replaced with zinc foam, and zinc oxide accounted for 12%.

Using zinc-zinc oxide as the working electrode, the test was carried out in the same manner as in example 1 under-0.15V (vs RHE) for 1800s in an atmospheric environment. FIG. 10 is the obtained i-t graph and FIG. 11 is the corresponding graph (c-t) of the concentration of synthetic ammonia versus time, showing that the current slowly decreases with decreasing nitrate concentration during the test, which is calculated to give an ammonia production rate of 1.08mmol h^-1cm^-2The selectivity of electrochemical ammonia production is 85.6%.

Example 6

And fully and uniformly mixing 90mg of copper powder and 10mg of copper oxide powder, dispersing the mixture in 50mL of isopropanol and 2mL of a liquid, uniformly coating the mixture on two surfaces of a carbon cloth with the length and width of 2cm, and naturally drying to obtain the supported copper-copper oxide carbon cloth electrode.

The loading type copper-copper oxide carbon cloth is used as a working electrode, the other conditions are the same as the example 1, and the test is carried out for 1800s under the condition of-0.15V (vs RHE) in the atmospheric environment. FIG. 12 is the resulting i-t plot and FIG. 13 is the corresponding plot of ammonia synthesis concentration versus time (c-t), showing that the current decreases with decreasing nitrate concentration during the test, calculated to give an ammonia production rate of 1.01mmol h^-1cm^-2The selectivity for electrochemical ammonia production was 84.7%.

Example 7

A foamed iron-ferric oxide catalytic electrode was prepared in the same manner as in example 1 except that foamed iron was used instead of foamed copper, and the ferric oxide content was 8%.

The test was carried out in the same manner as in example 1 under the conditions of iron-ferric oxide as the working electrode and at-0.15V (vs RHE) for 1800s in an atmospheric environment. FIG. 14 is the resulting i-t plot and FIG. 15 is the corresponding plot of ammonia synthesis concentration versus time (c-t), showing that the current decreases with decreasing nitrate concentration during the test, calculated to give an ammonia production rate of 1.002mmol h^-1cm^-2The selectivity for electrochemical ammonia production was 82.6%.

Example 8

And fully and uniformly mixing 90mg of cobalt powder and 10mg of cobalt oxide powder, dispersing the mixture in 50mL of isopropanol and 2mL of a liquid, uniformly coating the mixture on two surfaces of a carbon cloth with the length and width of 2cm, and naturally drying to obtain the supported cobalt-cobalt oxide carbon cloth electrode.

The test was carried out in the same manner as in example 1 under the conditions except that a cobalt-cobalt oxide carbon cloth electrode was used as a working electrode, and the test was carried out for 1800 seconds under an atmosphere of-0.15V (vs RHE). FIG. 16 is the obtained i-t graph and FIG. 17 is the corresponding graph (c-t) of the concentration of synthetic ammonia versus time, showing that the current slowly decreases with decreasing nitrate concentration during the test, which is calculated to give an ammonia production rate of 1.13mmol h^-1cm^-2Electrochemical systemThe ammonia selectivity was 88.6%.

Example 9

Fully and uniformly mixing 10mg of ruthenium and 90mg of ruthenium oxide powder, dispersing the mixture in 50mL of isopropanol and 2mL of Nafion solution, uniformly coating the mixture on two surfaces of a carbon cloth with the length and width of 2cm, and naturally drying to obtain the supported ruthenium and ruthenium oxide carbon cloth electrode.

The same procedure as in example 1 was repeated except that the electrodes were made of ruthenium and ruthenium oxide carbon cloth and the test was carried out in an atmosphere at-0.15V (vs RHE) for 1800 s. FIG. 18 is a graph of the obtained i-t and FIG. 19 is a graph (c-t) of the concentration of synthetic ammonia versus time, which shows that the current decreases slowly with decreasing nitrate concentration during the test, and the ammonia production rate calculated is 1.188mmol h^-1cm^-2The selectivity for electrochemical ammonia production was 93.6%.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.