Background
The development of hydrogen energy and fuel cell technology is an important direction of the current energy strategy in China, and has important significance for realizing low-carbon environmental protection development. However, hydrogen is extremely difficult to liquefy, and large-scale storage and transportation technology is difficult and high in cost, so that the wide application of the hydrogen fuel cell is severely restricted. The ammonia gas can be liquefied only by 8.5 atmospheric pressures at room temperature, the volume energy density of the liquid ammonia greatly exceeds that of high-pressure hydrogen, and carbon emission can be avoided during synthesis and power generation. In addition, ammonia synthesis, liquefaction, storage and transportation technologies are well established. Therefore, ammonia is expected to be a zero-carbon emission fuel to replace hydrogen for large-scale application.
Typical Fuel Cells operate under acidic conditions, whereas ammonia can be electro-catalytically oxidized under alkaline conditions, and Anion Exchange Membrane Fuel Cells (AEMFC) operate under alkaline conditions, so that ammonia can serve as a Fuel energy source for the AEMFC.
The performance of an ammonia-fueled AEMFC depends primarily on the catalyst. Single metal catalysts such as Pt, Ru, etc. can cause the open circuit voltage to be too low when used as anode materials, mainly because of the high overpotential required for ammonia oxidation on these catalysts. In addition, the metal electrode is selectively oxidized to generate N2The catalytic activity of (a) is related to the kind of intermediate products formed by the reaction at the surface of the electrode: when the intermediate product generated on the surface of the electrode is NHads or NH2When ads is used, the catalytic activity of electrode nitrogen precipitation is strong; when the intermediate product is Nads, the catalytic activity of the electrode for nitrogen evolution is remarkably reduced. The strength of the Nads which is an intermediate product adsorbed on the surface of different metal electrodes in the electrochemical oxidation process is Ru in sequence>Rh>Pd>Ir>Pt。
Pt has relatively weak Nads adsorption energy and high catalytic dehydrogenation capacity, and is the most ideal ammonia electrocatalytic material at present. However, Pt metal is expensive, which limits its large-scale application.
Disclosure of Invention
In view of the above technical situation, the present invention aims to provide an electrocatalytic material for ammonia catalytic oxidation, which has the advantages of low cost and high catalytic performance.
To achieve the above technical object, the present inventors have found that tantalum nitride (Ta)3N5) Tantalum nitride or tantalum oxide (Ta)2O5) When Pt is attached to the carrier as a carrier, the dispersibility of Pt can be improved and the catalytic activity of Pt for catalytic oxidation of ammonia can be improved.
Namely, the technical scheme of the invention is as follows: an electrocatalytic material for catalytic oxidation of ammonia, characterized in that said electrocatalytic material is tantalum nitride (Ta)3N5) Or tantalum oxide (Ta)2O5) As a support, Pt is attached to the support.
Preferably, in the electrocatalytic material, the mass ratio of Pt to the carrier is 1:5 to 1: 1.
The invention also provides a method for preparing the electrocatalytic material for ammonia catalytic oxidation, which comprises the following steps:
reacting the vector with H2PtCl6Dissolving in a mixed solution of ethanol and water, and reacting under the protection of inert gas at a certain temperature; and then, washing and vacuum-filtering the product after reaction, and drying to obtain the Pt-based electro-catalytic material.
Preferably, the volume ratio of ethanol to water in the mixed solution of ethanol and water is 5:1 to 1:5, and more preferably 3:1 to 1: 3.
Preferably, the temperature is 120-180 ℃, and more preferably 140-170 ℃.
The reaction time is preferably 1 to 10 hours, more preferably 2 to 8 hours.
Preferably, the product after the reaction is washed with a mixed solution of ethanol and water. Compared with the prior art, the invention has the following beneficial effects:
(1) according to the invention, tantalum nitride or tantalum oxide is used as a carrier, Pt is dispersed on the carrier to form the electro-catalytic material, and compared with pure Pt as the electro-catalytic material, the electro-catalytic material has the advantages that the dispersion degree of Pt is improved, the cost is reduced, the catalytic performance of ammonia catalytic oxidation can be improved, and toxic intermediate products Nads generated in the electro-catalytic oxidation of ammonia can be reduced, so that the durability of the catalytic material is improved.
(2) The preparation method provided by the invention is simple and easy to implement, and the Pt is subjected to in-situ reduction at a certain temperature, so that the Pt is effectively fixed on the carrier to form the Pt-based electro-catalytic material on the carrier.
(3) Under the same other conditions, the Pt-based electrocatalytic materials using tantalum nitride, tantalum oxide and Keqin carbon as carriers are compared, and the Pt-based electrocatalytic material using tantalum nitride as the carrier, the Pt-based electrocatalytic material using Keqin carbon as the carrier, and the Pt-based electrocatalytic material using tantalum oxide as the carrier, which have the highest catalytic performance and durability of ammonia catalytic oxidation, are used. Therefore, when tantalum nitride is used as a carrier, the catalytic performance of the catalyst for ammonia catalytic oxidation is greatly improved.
Detailed Description
The present invention will be described in further detail with reference to the following examples and drawings, which are intended to facilitate the understanding of the present invention and are not intended to limit the present invention in any way.
Example 1:
in this example, the electrocatalytic material for the catalytic oxidation of ammonia was Ta3N5As a support, Pt was attached to the support, and the mass ratio of Pt to the support was 1: 2.
The preparation method of the electrocatalytic material comprises the following steps:
(1) 20mg of Ta3N5Dissolving the powder in 60mL of mixed solution of ethanol and water at a volume ratio of 3:2, ultrasonically dispersing for 30min, and adding 2.04mL of 50mM H2PtCl6Uniformly mixing the solution to obtain a mixed solution;
(2) transferring the mixed solution obtained in the step (1) into a three-neck flask, putting the three-neck flask into an oil bath at the temperature of 140 ℃, continuously stirring for 6 hours, introducing nitrogen, and naturally cooling;
(3) and (3) filtering and washing the product obtained in the step (2) by using a mixed solution of ethanol and water, and drying the product in a 50 ℃ oven for 5 hours to obtain the Pt-based electro-catalytic material.
A TEM image of a sample of the Pt-based electrocatalytic material prepared as described above is shown in FIG. 1, in which Pt particles are dispersed in Ta3N5On a carrier to form Pt/Ta3N5Electrocatalytic material with Pt supported in Ta3N550% of the mass of the support.
The Pt/Ta prepared above is added3N5Electrocatalytic materials were used for the catalytic oxidation of ammonia, whose catalytic performance was evaluated as follows:
(1) Pt/Ta prepared as described above using a three-electrode system3N5The catalytic electrode is a working electrode, the saturated calomel electrode is a reference electrode, the graphite electrode is a counter electrode, and the 1M KOH aqueous solution and the 1M KOH and 0.1M NH3 aqueous solution are electrolyte solutions respectively. Electrochemical workstation using CHI760E workstation from Shanghai Chenghua instruments Inc., a current density curve (CV curve) was recorded at a scanning speed of 20mv/s with a change in voltage. As a result, as shown in FIG. 3, in the curve in which the electrolyte contains ammonia, a distinct redox current peak appears at-0.38V, which is the oxidation current peak of ammonia compared to the curve in which the electrolyte is KOH. Meanwhile, compared with the curve of KOH as the electrolyte, the absorption and desorption peaks of hydrogen are changed, and researches prove that in the catalytic oxidation of ammonia, the toxic substance Nads is related to the absorption and desorption peaks of hydrogen and has an inverse relation. In addition, in the curve in which the electrolyte contains ammonia, the peak current density of ammonia oxidation gradually decreases as the number of cycles increases, and the literature reports that the performance of the electrocatalytic material is weakened and the durability is reduced due to the generation of a toxic intermediate product Nads in the catalytic dehydrogenation process of ammonia. Thus, the production of Nads is reduced and the performance of the electrocatalytic material is improved.
(2) For comparison, in the three-electrode system described above, pure platinum sheet electrodes were used instead of Pt/Ta3N5The catalytic electrode is tested, and the electrolyte is an aqueous solution consisting of 1M KOH and 0.1M NH3The CV curve in the case of the solution is shown in FIG. 4, and the curve of the current density with time (i-t curve) is shown in FIG. 5. As can be seen from FIGS. 4 and 5, the use of Pt/Ta compared to the use of pure platinum sheet catalytic electrodes3N5The oxidation reduction peak value and the hydrogen absorption and desorption peak value are obviously increased during catalyzing the electrode, and the durability is also improved, which shows that Ta3N5The carrier not only has a dispersing effect on Pt, but also reduces the generation of a toxic substance Nads.
Example 2:
in this example, the electrocatalytic material for the catalytic oxidation of ammonia was Ta2O5As a support, Pt was attached to the support, and the mass ratio of Pt to the support was 1: 2.
The preparation method of the electrocatalytic material comprises the following steps:
(1) 20mg of Ta2O5Dissolving the powder in 60mL of mixed solution of ethanol and water, wherein the volume ratio of the ethanol to the water is 3:2, ultrasonically dispersing for 30min, and then adding 2.04mL of H2PtCl6 solution with the concentration of 50mM to be uniformly mixed to obtain mixed solution;
(2) transferring the mixed solution obtained in the step (1) into a three-neck flask, putting the three-neck flask into an oil bath at the temperature of 140 ℃, continuously stirring for 6 hours, introducing nitrogen gas, and naturally cooling;
(3) and (3) filtering and washing the product obtained in the step (2) by using a mixed solution of ethanol and water, and drying the product in a 50 ℃ oven for 5 hours to obtain the Pt-based electro-catalytic material.
A TEM image of a sample of the Pt-based electrocatalytic material prepared as described above is shown in FIG. 2, in which Pt particles are dispersed in Ta2O5On a carrier to form Pt/Ta2O5Electrocatalytic material with Pt supported in Ta2O550% of the mass of the support.
The Pt/Ta prepared above is added2O5Electrocatalytic material for the catalytic oxidation of ammonia, the catalytic performance of which was evaluated in essentially the same manner as in example 1, except that Pt/Ta was used2O5Catalytic electrode replacing Pt/Ta3N5The catalytic electrode was tested, and the results are shown in FIGS. 4 and 5, which show the oxidation of ammonia corresponding to the catalytic electrodeThe reduction current peak value and the durability are higher than those of a pure platinum electrode and lower than those of Pt/Ta3N5A catalytic electrode.
Example 3:
in this example, the electrocatalytic material for catalytic oxidation of ammonia was KB as a carrier, Pt was attached to the carrier, and the mass ratio of Pt to the carrier was 1: 2.
The preparation method of the electrocatalytic material comprises the following steps:
(1) dissolving 20mg KB powder in 60mL of mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 3:2, ultrasonically dispersing for 30min, and adding 2.04mL of H with the concentration of 50mM2PtCl6Uniformly mixing the solution to obtain a mixed solution;
(2) transferring the mixed solution obtained in the step (1) into a three-neck flask, putting the three-neck flask into an oil bath at the temperature of 140 ℃, continuously stirring for 6 hours, introducing nitrogen gas, and naturally cooling;
(3) and (3) filtering and washing the product obtained in the step (2) by using a mixed solution of ethanol and water, and drying the product in a 50 ℃ oven for 5 hours to obtain the Pt-based electro-catalytic material.
The TEM image of the Pt-based electrocatalytic material sample prepared above is shown in FIG. 2, Pt particles are dispersed on a KB support to form a Pt/KB electrocatalytic material, and the loading amount of Pt accounts for 50% of the KB support.
The Pt/KB electrocatalytic material prepared as described above was used for the catalytic oxidation of ammonia, and the method for evaluating the catalytic performance was substantially the same as that in example 1, except that a Pt/KB catalytic electrode was used instead of Pt/Ta3N5The catalytic electrode is tested, and the test results are shown in fig. 4 and fig. 5, which show that the catalytic electrode corresponds to ammonia with the peak value of the oxidation-reduction current and the durability higher than that of a pure platinum electrode and lower than that of Pt/Ta3N5Catalytic electrode, and the ammonia oxidation current starting potential is higher than Pt/Ta3N5。
The embodiments described above are intended to illustrate the technical solutions of the present invention in detail, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modification, supplement or similar substitution made within the scope of the principles of the present invention should be included in the protection scope of the present invention.