Method of nitrogen-phosphorus doped porous carbon for oxygen reduction electrocatalysis within a wide PH range
A preparation method of nitrogen-phosphorus doped porous carbon for oxygen reduction electrocatalysis within a wide pH range, which uses natural mineral-based carbon sources as raw material and uses a sequential nitrogen and phosphorus doping process for synthesizing in two paths. The method provided may be highly cost-effective, sustainable, and suitable for large-scale utilization.
1. A preparation method of nitrogen-phosphorus doped porous carbon material for oxygen reduction electrocatalysis within a wide pH range, comprising:
(1) cleaning and drying natural mineral-based carbon sources, and mixing the natural mineral-based carbon sources for ball milling; pre-carbonizing the obtained mixture in a shielding gas; washing the pre-carbonized mixture with 2-3 mol ·L −1 potassium hydroxide solution at 80-90° C. for 1-3 hours, filtering, and re-washing with water till the filtrate is neutral; pickling the washed pre-carbonized mixture with 4-6 mol·L −1 hydrochloric acid solution at 50-60° C. for 1-3 hours, filtering, washing with water till the filtrate is neutral, and drying the pickled product;
(2) weighing the product to be doped from step (1) or (3), a nitrogen dopant and an activator respectively at a mass ratio of 1: (2-6): (1-3), milling and mixing, and transferring the mixture into a tube furnace, carbonizing at 850-1,050° C. for 1-4 hours in a nitrogen atmosphere at a heating rate of 2-20° C. ·min −1 , taking out the resultant product after the carbonization is finished, and then pickling, filtering, washing with water, and drying, so that a nitrogen-doped carbon is obtained;
(3) weighing the product to be doped from step (1) or (2) and a phosphorus dopant respectively at a mass ratio of 1: (3-5), adding water for dilution and mixing, drying and transferring the mixture into a tube furnace, carbonizing at 850-1,050° C. for 1-4 hours in a nitrogen atmosphere at a heating rate of 2-20° C.·min −1 , and pickling, filtering, washing with water, and drying, so that a phosphorus-doped carbon is obtained; and
(4) pickling the secondarily carbonized product obtained through the above steps in a sequence of (1), (2) and (3) or (1), (3) and (2) with 1 mol·L −1 dilute hydrochloric acid solution at 40-60° C. for 1-3 hours, filtering, washing with water till the filtrate is neutral, and drying;
(5) producing a nitrogen-phosphorus doped porous carbon material having a specific surface area in a range of 800 to 1300 m 2 ·g −1 , wherein a specific surface area of micropores is in a range of 500 to 700 m 2 ·g −1 and a specific surface area of mesopores in a range of 100 to 800 m 2 ·g −1 , and wherein the nitrogen-phosphorus doped porous carbon material comprises a nitrogen content and phosphorus content of 2.64% and 2.42% respectively, a ratio of graphite nitrogen to pyridine nitrogen in the range of 1.5 to 3, and a ratio of P-C bonds to P-O bonds in the range of 1 to 2.5.
2. The preparation method of claim 1 , wherein a nitrogen-phosphorus doped porous carbon N 4 P 4 C-900 prepared through the steps of (1), (2) and (3) has specific surface area of 845.5 m 2 ·g −1 , wherein a specific surface area of micropores is 661.8 m 2 ·g −1 and a specific surface area of mesopores is 183.7 m 2 ·g −1 , and wherein a nitrogen content and phosphorus content are 2.64% and 2.42% respectively, and a ratio of graphite nitrogen to pyridine nitrogen is 2.72, and a ratio of P-C bonds to P-O bonds is 2.35.
3. The preparation method of claim 1 , wherein a nitrogen-phosphorus doped porous carbon P 4 N 4 C-900 prepared through the steps of (1), (3) and (2) has specific surface area of 1,220.7 m 2 ·g −1 , wherein a specific surface area of micropores is 503.2 m 2 ·g −1 and a specific surface area of mesopores is 717.5 m 2 ·g −1 , and wherein a nitrogen content and phosphorus content are 2.0% and 0.5% respectively, a ratio of graphite nitrogen to pyridine nitrogen is 1.71, and a ratio of P-C bonds to P-O bonds is 1.25.
4. The preparation method of claim 1 , wherein in step (3), mixing comprises ultrasonic mixing with an ultrasonic time is 0.5-3 hours and a frequency of frequency-conversion ultrasonic is 25-60 Hz.
5. The preparation method of claim 1 , wherein the natural mineral-based carbon source in step (1) is at least one of coal, coal pitch, coal tar, coal tar pitch, petroleum pitch, or petroleum coke.
6. The preparation method of claim 1 , wherein the pre-carbonization temperature in step (1) is 600-1,000° C., carbonization is carried out in a nitrogen atmosphere for 2 hours, and a heating rate is 5° C.·min −1 .
7. The preparation method of claim 1 , wherein in step (2), the nitrogen dopant is at least one of melamine, dicyandiamide, urea, pyridine, pyrrole, aniline, amino acid, or purine, and wherein the activator is at least one of potassium hydroxide, sodium hydroxide, potassium bicarbonate, sodium bicarbonate, potassium carbonate, or sodium carbonate.
8. The preparation method of claim 1 , wherein in step (3), the phosphorus dopant is at least one of phosphoric acid, triphenylphosphine, phytic acid, red phosphorus, black phosphorus, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, magnesium phosphate, calcium phosphate, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.