KMn
O4 ⟶ K2Mn
O4 + Mn
O2 + O2 được Vn
Doc biên soạn là phương trình điều chế oxi từ KMn
O4, hi vọng giúp chúng ta viết và cân bằng đúng đắn phương trình, tương tự như biết cách vận dụng làm các dạng bài xích tập câu hỏi liên quan mang đến KMn
O4.
Bạn đang xem: Kmno4 = o2 + k2o + mno2
2KMn
O4 
O4 + Mn
O2 + O2
2. Điều kiện để phản ứng KMn
O4 ra O2
Nhiệt độ
3. Bội nghịch ứng sức nóng phân KMn
O4
Vì là chất oxi hóa mạnh mẽ nên KMn
O4 có thể phản ứng cùng với kim loại hoạt động mạnh, axit hay các hợp hóa học hữu cơ dễ dàng.
3.1. Phản bội ứng KMn
O4 phân hủy
2KMn
O4 → K2Mn
O4 + Mn
O2 + O2
Khi trộn loãng tinh thể pemanganat dưới tia nắng mặt trời trực tiếp, oxi được giải phóng
4KMn
O4 + 2H2O → 4KOH + 4Mn
O2 + 3O2
3.2. Bội nghịch ứng cùng với axit
KMn
O4 có thể phản ứng với tương đối nhiều axit to gan như H2SO4, HCl tuyệt HNO3, những phương trình phản bội ứng minh họa gồm:
2KMn
O4 + 16HCl → 2KCl + 2Mn
Cl2 + 5Cl2 + 8H2O
3K2Mn
O4 + 4HNO3 → 2KMn
O4 + Mn
O2 + 4KNO3 + 2H2O
3.3. Phản ứng cùng với bazơ
Thuốc tím tất cả thể tính năng với các dung dịch kiềm chuyển động mạnh như KOH, Na
OH, phương trình bội phản ứng minh họa:
4KMn
O4 + 4KOH → 4K2Mn
O4 + 2H2O + O2
3.4. đặc điểm oxy hóa của KMn
O4
Vì dung dịch tím là chất oxy hóa khỏe mạnh nên có thể phản ứng với tương đối nhiều loại dung dịch và tạo ra nhiều thành phầm khác nhau.
Trong môi trường thiên nhiên axit, mangan bị khử thành Mn2+2KMn
O4 + 5Na2SO3 + 3H2SO4 → 2Mn
SO4 + 5Na2SO4 + K2SO4 + 3H2O
O2 bao gồm cặn màu sắc nâu.
2KMn
O4 + 3K2SO3 + H2O → 3K2SO4 + 2Mn
O2 + 2KOH
O42-
2KMn
O4 + Na2SO3 + 2KOH → 2K2Mn
O4 + Na2SO4 + H2O
4. Câu hỏi bài tập liên quan
Câu 1: tuyên bố nào tiếp sau đây sai?
A. Khí oxi ko màu, không mùi, nặng rộng không khí.
B. Khí ozon màu xanh lá cây nhạt, bám mùi đặc trưng.
C. Ozon là 1 dạng thù hình của oxi, bao gồm tính oxi hóa bạo dạn hơn oxi.
D. Ozon với oxi hồ hết được dùng làm khử trùng nước sinh hoạt.
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Đáp án D
A đúng Khí oxi không màu, ko mùi, nặng rộng không khí.
B đúng Khí ozon greed color nhạt, có mùi đặc trưng.
C đúng Ozon là một trong dạng thù hình của oxi, có tính oxi hóa bạo gan hơn oxi.
D sai vày Chỉ bao gồm ozon dùng làm khử trùng nước sinh hoạt
Câu 2. phản bội ứng tạo nên O3 từ bỏ O2 cần điều kiện:
A. Tia lửa năng lượng điện hoặc tia cực tím
B. Xúc tác Fe
C. Áp suất cao
D. ánh sáng cao
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Đáp án A
Điều khiếu nại phản ứng: Tia rất tím (UV : Ultra Violet)
Trong tự nhiên Ôzôn được xuất hiện từ phân tử Oxy do ảnh hưởng từ tia rất tím UV, phóng năng lượng điện (Tia sét) trong khí quyển, và gồm nồng độ tốt trong bầu khí quyển trái đất.
Khi tất cả sấm sét, hiệu điện núm cao chạy qua ko trung có tác dụng phân bóc tách cấu chế tạo ra của phân oxy (O2) thành các oxy nguyên tử (O). Những nguyên tử này kết hợp với phân tử ôxy bên cạnh tạo nên O3, call là ozone.
Câu 3. Phản ứng pha chế oxi trong phòng xem sét là:
A. 2KI + O3 + H2O → I2 + 2KOH + O2
B. 5n
H2O + 6n
CO2 → (C6H10O5)n + 6n
O2
C. 2H2O
D. 2KMn
O4 → K2Mn
O4 + Mn
O2 + O2
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Đáp án D
Phản ứng pha trộn oxi vào phòng thí điểm là:
2KMn
O4 → K2Mn
O4 + Mn
O2 + O2
Câu 4. hàng gồm những chất đều tính năng được với oxi là
A. Mg, Al, C, C2H5OH
B. Al, P, Cl2, CO
C. Au, C, S, CO
D. Fe, Pt, C, C2H5OH
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Đáp án A
Phương trình làm phản ứng liên quan
Mg + O2 → Mg
O
4Al + 3O2 → 2Al2O3
2C + O2 → 2CO
C2H5OH + 2O2 → 2CO2 + 3H2O
Câu 5. Trong không khí, oxi chỉ chiếm bao nhiêu xác suất thể tích?
A. 21%
B. 25%
C. 30%
D. 78%
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Đáp án A
Thành phần của ko khí
Không khí là một hỗn thích hợp khí trong các số đó : oxi chiếm 21% về thể tích (khoảng 01/05 về thể tích không khí), khí nitơ chỉ chiếm 78% và các khí khác như hơi nước, khí cacbonic, một trong những khí hiếm như Ne, Ar, lớp bụi khói chiếm khoảng tầm 1% thể tích không khí.
Câu 6. Phát biểu nào sau đây đúng: ở nhiệt độ thường
A. O2 ko oxi hóa được Ag, O3 oxi hóa được Ag.
B. O2 oxi hóa được Ag, O3 không oxi hóa được Ag.
C. Cả O2 với O3 các không oxi hóa được Ag.
D. Cả O2 cùng O3 phần lớn oxi hóa được Ag.
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Đáp án A: O3 + 6Ag → 3Ag2O
Câu 7. Đốt cháy hoàn toàn 8,7 gam tất cả hổn hợp Mg và Al trong khí oxi (dư) thu được 15,1 gam hỗn hợp oxit. Thể tích khí oxi (đktc) vẫn tham gia phản nghịch ứng là
A. 17,92 lít.
B. 8,96 lít.
C. 11,20 lít.
D. 4,48 lít.
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Đáp án D
Bảo toàn khối lượng: n
O2 = (15,2 - 8,7)/32 = 0,2 (mol)
⇒ V = 0,2. 22,4 = 4,48 (lít)
Câu 8. Thêm 1,5 gam Mn
O2 vào 98,5 gam tất cả hổn hợp X bao gồm KCl và KCl
O3. Trộn kĩ với đun hỗn hợp đến phản bội ứng trả toàn, thu được chất rắn khối lượng 76 gam. Khối lượng KCl vào 98,5 gam X là
A. 74,50 gam.
B. 13,75 gam.
C. 122,50 gam.
D. 37,25 gam.
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Đáp án D
Bảo toàn khối lượng: m
O2 = 1,5 + 98,5 – 76 = 24 (gam)
⇒ n
O2= 24/32 = 0,75 (mol)
2KCl
O3 → 2KCl + 3O2 ↑
⇒ m
KCl = 98,5 – 0,5.122,5 = 37,25 (gam)
Câu 9. cho các chất sau: Fe
O (1), KCl
O3 (2), KMn
O4 (3), Ca
CO3 (4), bầu không khí (5), H2O (6). Phần đông chất như thế nào được dùng làm điều chế oxi trong phòng thí nghiệm?
A. 2, 3
B. 2, 3, 5, 6
C. 1, 2, 3,5
D. 2, 3, 5
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Đáp án A
Trong phòng thí nghiệm, khí oxi được điều chế bằng phương pháp đun nóng hầu hết hợp hóa học giàu oxi cùng dễ bị phân huỷ ở ánh nắng mặt trời cao như KMn
O4 và KCl
O3
=> 2 chất dùng làm điều chế oxi trong chống thí ngiệm là: KCl
O3 (2), KMn
O4 (3)
Câu 10. Muối Fe2+ làm mất màu hỗn hợp KMn
O4 trong môi trường xung quanh axit tạo thành ion Fe3+ , còn Fe3+ chức năng với I- tạo nên I2 cùng Fe2+. Sắp đến xếp những chất với ion Fe3+, I2 cùng Mn
O4- theo thiết bị tự tăng dần đều tính oxi hóa:
A. I2 4- 3+
B. Mn
O4- 3+ 2
C. Fe3+ 2 4-
D. I2 3+ 4-
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Đáp án D
Fe2+ bị KMn
O4 oxi biến thành Fe3+ => tính oxi hóa của Mn
O4- > Fe3+
Fe3+ + I → I2 + Fe2+ => tính lão hóa của Fe3+ > I2
=> Tính lão hóa : Mn
O4- > Fe3+ > I2
Câu 11. Chất nào dưới đây làm mất màu hỗn hợp KMn
O4 lúc đun nóng?
A. Benzen
B. Toluen
C. Propan
D. Metan
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Đáp án B
Chất nào tiếp sau đây làm mất màu dung dịch KMn
O4 khi làm cho nóng toluen
Phương trình phản nghịch ứng minh họa
C6H5CH3+ 2KMn
O4 → H2O + KOH + 2Mn
O2 + C6H5COOK
Câu 11. Nhỏ trường đoản cú từ mang đến dư hỗn hợp Fe
SO4 đã được axit hóa bằng H2SO4 vào hỗn hợp KMn
O4. Hiện tượng kỳ lạ quan ngay cạnh được là
A. Dung dịch màu tím hồng bị nhạt dần rồi đưa sang màu vàng
B. Dung dịch màu tím hồng bị nhạt dần mang đến không màu
C. Dung dịch màu tím hồng bị gửi dần sang nâu đỏ
D. Màu sắc tím bị mất ngay. Sau đó dần dần xuất hiện quay lại thành dung dịch bao gồm màu hồng
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Đáp án A
Phương trình bội nghịch ứng hóa học
10Fe
SO4 + 8H2SO4 + 2KMn
O4 → 5Fe2(SO4)3 + 2Mn
SO4 + 8H2O + K2SO4.
Chú ý: muối bột Fe2(SO4)3 cùng Fe
Cl3 bao gồm màu vàng
Câu 12. A tất cả công thức phân tử là C8H8, tính năng với dung dịch KMn
O4 ở nhiệt độ thường tạo nên ancol 2 chức. 1 mol A tính năng tối đa với:
A. 4 mol H2; 1 mol brom.
B. 3 mol H2; 1 mol brom.
C. 3 mol H2; 3 mol brom.
D. 4 mol H2; 4 mol brom.
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Đáp án A
Tác dụng cùng với dung dịch KMn
O4 ở nhiệt độ thường tạo thành ancol 2 chức => chứa nối đôi C=C
=> A là C6H5-CH=CH2 (stiren)
=> 1 mol A tác dụng tối đa với 4 mol H2; 1 mol brom.
Câu 13. Phát biểu nào tiếp sau đây đúng?
A. Ozon có tính oxi hóa mạnh dạn nên được dùng để làm sát khuẩn nước sinh hoạt, tẩy trắng sạch bột, dầu ăn uống và những chất khác.
B. Oxi cùng ozon đều sở hữu tính oxi hóa dạn dĩ nhưng tính lão hóa của oxi khỏe mạnh hơn ozon.
C. Fe tính năng với Cl2 và H2SO4 loãng đều tạo thành muối fe (II).
D. H2S chỉ gồm tính oxi hóa với H2SO4 chỉ tất cả tính khử.
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Đáp án C
A. Ozon bao gồm tính oxi hóa táo tợn nên được dùng để làm sát trùng nước sinh hoạt, tẩy hết sạch trơn bột, dầu ăn uống và các chất khác: Đúng.
B. Oxi và ozon đều phải sở hữu tính oxi hóa mạnh bạo nhưng tính oxi hóa của oxi to gan hơn ozon: Sai. Bởi ozon bao gồm tính oxi hóa táo bạo hơn oxi.
C. Fe chức năng với Cl2 và H2SO4 loãng đều tạo thành muối fe (II): Sai.
D. H2S chỉ gồm tính oxi hóa cùng H2SO4 chỉ gồm tính khử:Sai. Vày H2S chỉ biểu hiện tính khử, H2SO4 chỉ miêu tả tính oxi hóa.
Câu 14. Cho những phản ứng: (1) Na2S + HCl ; (2) F2 + H2O; (3) Mn
O2 + HCl đặc; (4) Cl2 + hỗn hợp H2S. Những phản ứng tạo ra đơn chất là
A. (1), (2), (4).
B. (2), (3), (4).
Xem thêm: Ngữ Pháp Tiếng Anh Lớp 3 Unit 14 Are There Any Posters In The Room?
C. (1), (2), (3).
D. (1), (3), (4).
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Đáp án B
Phương trình phản bội ứng minh họa
(1) Na2S + 2HCl → 2Na
Cl + H2S
(2) 2F2 + 2H2O → 4HF + O2
(3) Mn
O2 + 4HCl quánh → Mn
Cl2 + Cl2 + 2H2O
(4) Cl2 + H2S → 2HCl + S
=> các phản ứng tạo thành đơn hóa học là: (2), (3), (4)
Câu 15. Dãy các chất đều làm mất màu dung dịch thuốc tím là
A. Etilen, axetilen, anđehit fomic, stiren
B. Axeton, etilen, anđehit axetic, cumen
C. Benzen, but-1-en, axit fomic, toluen
D. Butan, but-1-in, stiren, axit axetic
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Đáp án A
Phương trình bội phản ứng minh họa
3C2H4 + 2KMn
O4 + 4H2O → 3C2H4(OH)2 + 2Mn
O2 + 2KOH
3C2H2 + 8KMn
O4 + 4H2O → 3(COOH)2 + 8Mn
O2 + 8KOH
2KMn
O4 + 3HCHO + H2O → 3HCOOH + 2KOH + 2Mn
O2
3C6H5-CH=CH2 + 10KMn
O4 → 3C6H5COOK + 3K2CO3 + 10Mn
O2 + KOH + 4H2O
Câu 16. Trong các phát biểu sau, gồm bao nhiêu phát biểu đúng?
(a) cho dung dịch KMn
O4 tính năng với dung dịch HF (đặc) nhận được khí F2.
(b) Dùng phương pháp sunfat pha trộn được: HF, HCl, HBr, HI,
(c) Amophot (hỗn hợp các muối NH4H2PO4 cùng (NH4)2HPO4) là phân phức hợp.
(d) Trong phòng thí nghiệm, khí CO2 được điều chế bằng phương pháp cho H2SO4 đặc vào axit fomic cùng đun nóng.
A. 1.
B. 3.
C. 2.
D. 4.
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Đáp án C
.........................................
Trên đây Vn
Doc đã giới thiệu tới chúng ta KMn
O4 ⟶ K2Mn
O4 + Mn
O2 + O2 là phương trình pha trộn oxi trong phòng thí nghiệm. Để có công dụng học tập giỏi và công dụng hơn, Vn
Doc xin reviews tới chúng ta học sinh tài liệu Giải bài tập Toán 8, Gải SBT thiết bị Lí 8, lý thuyết Sinh học 8, chuyên đề chất hóa học 8. Tài liệu tiếp thu kiến thức lớp 8 nhưng Vn
Doc tổng hợp soạn và đăng tải.
Ngoài ra, Vn
Đánh giá bài viết
trăng tròn 96.161
Chia sẻ bài xích viết
sắp xếp theo mang định tiên tiến nhất Cũ tuyệt nhất
Phương trình phản ứng
trình làng cơ chế Theo dõi chúng tôi Tải áp dụng chứng nhận
Growing Mn
O2 nanocrystals in the bulk of porous carbon nanofibers is conducted in a KMn
O4 aqueous solution aimed lớn enhance the electrochemical performance of Mn
O2. The rate of redox reaction between KMn
O4 & carbon was controlled by the concentration of KMn
O4 in a neutral solution. The Mn
O2 nanoparticles grow along with (211) crystal faces when the redox reaction happens on the surface of fibers under 1D constraint, while the nanoparticles grow along with (200) crystal faces when the redox reaction happens in the bulk of fibers under 3d constraint. The composite, where Mn
O2 nanoparticles are formed in the bulk under a constraint, yields an electrode material for supercapacitors showing good electron transport, rapid ion penetration, fast and reversible Faradaic reaction, & excellent rate performance. The capacitance of the composite electrode could be 1282 F g−1 under a current density of 0.2 A g−1 in 1 M Na2SO4 electrolyte. A symmetric supercapacitor delivers energy density of 36 Wh kg−1 with power mật độ trùng lặp từ khóa of 39 W kg−1, and can maintain 7.5 Wh kg−1 at 10.3 k
W kg−1. It exhibits an excellent electrochemical cycling stability with 101% initial capacitance & 95% columbic efficiency even after 1000 cycles of charge/discharge.
Depending on the specific charge storage mechanisms, capacitances are divided into double layer capacitance (EDLC), relying on the high surface area of electrode materials khổng lồ adsorb charges at the electrode/electrolyte interfaces, & pseudo-capacitance, relying on Faradaic reversible redox reactions near the surface of the electrode1,2. The energy density is low for EDLCs as the ions physically accumulated on the interfaces are limited3. Conversely, the potential charge storage capability as pseudocapacitance is significantly higher than that of EDLCs, while its charge-discharge rate is often limited by the reaction kinetics. Khổng lồ improve the performance of the supercapacitor, recent researches are focusing on developing nanostructured composites of a carbon having high surface area & high conductivity with a transition metal oxide for electrode materials. Transition metal oxides (e.g. Ru
O2, Mn
O2, Ti
O2, Fe2O3, VOx, etc.) and conducting polymers (e.g. Polypyrrole, polyaniline) are commonly coated or mixed with carbon materials to lớn develop the composites4, by expecting both high specific energy and high power densities of the devices. Among the various transition metal oxides, Mn
O2 is suitable for supercapacitor applications because of its high theoretical specific capacitance, long cycle life, good durability, low cost, as well as environmental friendliness5,6. To lớn make the composite of Mn
O2 with carbon scaffold is advantageous for improvement of poor electrical conductivity of Mn
O2. Therefore various carbon materials have been employed, activated carbons7,8,9, carbon nanotubes (CNTs)10,11,12, carbon nanofibers (CNFs)13,14,15,16,17,18,19, graphenes20,21,22,23 and graphene oxides24,25.
Homogeneous blending of Mn
O2 nanoparticles with carbon materials is still a challenging task. Since reversible redox reaction of Mn
O2 occurs only near the surface of the electrode because of small diffusion length of the electrolyte across the Mn
O2 as less than 10 nm, it has been greatly desirable to lớn prepare nanostructured amorphous Mn
O2 khổng lồ rise the utilization of its electrochemical activity. There are 4 representative methodologies for Mn
O2 nanocomposite preparation, including electrodeposition, electrostatic interaction assembly, in-situ redox deposition & chemical co-precipitation26. Based on these methods, several groups developed highly performance Mn
O2 nanocomposite electrode. Lang27 et al. Showed that a supercapacitors made of nanoporous gold & nanocrystalline Mn
O2 resulted in a specific capacitance of 1145 F g−1 at 50 m
V s−1. Fei group28 reported the reverse micro emulsion method to lớn prepare 3–20 nm Mn
O2/3D RGO composites. The 3 chiều RGO could provide channels for rapid ionic và electronic transport. The maximum specific capacitance of 709.8 F g−1 at 0.2 A g−1 of the Mn
O2 (66.4 wt%)/RGO composite. After 1000 cycles, 97.6% of the initial capacitance value can be maintained. Chen29 et al. Prepared nanostructured Mn
O2/CNTs-sponge composite electrodes, which could give a high specific capacitance as 1230 F g−1 at 1 m
V s−1. Based on the comparison in Table S1, the cost of the methods above is relatively high & the flexibility of the electrode is limited in most of the cases.
To develop a flexible và cost-effective method, Wang30 et al. Và Ma31 et al. Prepared Mn
O2/C composite based on an in-situ reaction between Mn
O4− and carbon as the following reaction,
However, their attention was paid mainly on the influences of the length of reaction time17,30 and p
H value of the solution31,32. The kích cỡ of Mn
O2 obtained were submicrometers to micrometers. To lớn improve the performance of Mn
O2/carbon fibers, Gao group18 and Qu group19 designed in-situ growth of Mn
O2 on the surface of activated carbon fibers. Gao18 reported that the composite displayed a capacitance of 117 F g−1. 116 F g−1 was kept after 3000 cycles. Qu19 et al. Reported that the Mn
O2/PCNFs exhibited a specific capacitance of 520 F g−1 at 0.5 A g−1 and 92.3% retention of the initial capacitance after 4000 cycles in a 6 M KOH aqueous solution. It should be indicated that although porous carbon materials were used, both of them pointed out the growth of Mn
O2 on the surface of the fiber.
To further improve the capacitance of the Mn
O2/CNFs electrode, nano-Mn
O2 in the bulk of porous carbon nanofibers are needed. Amorphous carbon materials have strong reactivity with KMn
O4. As the electrospun carbon fibers are amorphous33,34,35,36, there should be a competition of KMn
O4 diffusion into the bulk & reaction of KMn
O4 with carbon on the surface of the carbon fibers. If the diffusion time is shorter than the reaction time, the KMn
O4 can diffuse into the bulk. Otherwise, the Mn
O2 crystals cover the surface of the fibers & block the diffusion route of KMn
O4 into the bulk. Developing Mn
O2 with much smaller sizes and high dispersion in carbon scaffold is urgently needed.
Herein, we have developed a controllable method for preparing high performance supercapacitor electrode with the nanocrystalline-Mn
O2 in the bulk of porous CNFs by controlling the kinetics of an in-situ redox reaction of KMn
O4 under nanopore-constraint of CNFs (Eq. 1). The scaffold of porous CNFs, which was prepared from a mixture of polyimide (PI) and PVP via electrospinning35,36, acts as a matrix for electric double layer formation và a good electronic conductor to lớn enhance the pseudocapacitive behavior of the nanocrystalline Mn
O2. More importantly, the nanopores provide volume for nanocrystalline Mn
O2 khổng lồ grow. The pore volume limits the finial kích thước of Mn
O2. Such kind of structure provides the enhanced utilization of Mn
O2 particles by easy diffusion of the electrolyte to lớn the interfaces. In this work, reactants concentration và reaction temperature were considered to lớn control the rate of chemical reaction mentioned above. A wide range of the concentration of KMn
O4 was employed, i.e., 0.76 × 10−4, 1.52 × 10−4 và 7.60 × 10−4 M for the deposition of Mn
O2 nanoparticles onto the pristine CNFs. Since the relative concentration of KMn
O4 in the solution can be expressed by 1:2:10, the Mn
O2/CNFs composites synthesized in these solutions are denoted as MC1, MC2 and MC10, respectively. For the comparison, the pristine CNFs without Mn
O2 loading was also used by denoting as MC0. Their structures, particularly those of deposited Mn
O2 on CNFs, và capacitive performance in Na2SO4 were characterized.
Structure
Figure 1 shows the SEM images of the Mn
O2/CNFs composites. It is seen that the external surface of the pristine CNFs (MC0) is smooth và the diameters of fibers are in the range of 300–600 nm (Fig. 1a). After loading Mn
O2 by a redox reaction with KMn
O4, the appearance of CNFs is in sharp contrast khổng lồ that of MC0, particularly that of MC10. For those CNFs reacted with KMn
O4 in a low concentration, MC1 and MC2, the surfaces of CNFs became rough and nanoparticles of Mn
O2 can be recognized, as shown in Fig. 1b & c, respectively. For MC10, which is prepared in a high concentration of KMn
O4, large-sized needle-like crystals of Mn
O2 are formed on the fiber surface (Fig. 1d).
Figure 1
Detailed transmission electron microscope (TEM) observations were carried out by using thin slices of the fibers. Figure 2a shows TEM image of the cross-section of a MC2 fiber. High resolution TEM (HRTEM) images of an external part and an inner part of the cross-section are shown in Fig. 2b and c, respectively. In these HRTEM images of MC2, lattice fringes are clearly seen, spacing of fringes being ca. 0.24 nm in the external part and ca. 0.50 nm in the inner part (Fig. 2d). In the HRTEM images of MC10 (Fig. 2e,f), lattice fringes are clearly seen, spacing of fringes being ca. 0.24 nm in the external part và no clear Mn
O2 were formed in the inner part.
Figure 2
N2 adsorption/desorption measurements were performed at 77 K lớn characterize the surface areas, pore volumes & the pore-size distributions of MC1, MC2, MC10 as well as pristine CNFs. All isotherms shown in Fig. 3a are typical IUPAC type I, suggesting the microporous structure37. As can be seen in Fig. 3b, MC10 & MC0 mô tả a similar micropore distribution with peaks positioned below 0.4 nm và at around 1.2 nm in the pore form size range of 0.5–2 nm, while a broad peak appeared in the range of 0.8–1.1 nm on MC2. As shown in Fig. 3c, the mesopores are detected in the range of 2–8 nm for MC0, but MC2 composites with Mn
O2 have only negligibly small amount of mesopores. When the concentration of KMn
O4 increased to 0.12 g L−1 (MC10), pore-size distribution in micropore range becomes very similar khổng lồ the pristine fibers (MC0), but the mesopores at 2–8 nm in MC0 disappear completely. On MC2 composite prepared by using the concentration of KMn
O4 of 0.024 g L−1, very different distribution of micropore-size is observed.
Figure 3
In Table 1, surface areas and pore volumes are shown by dividing them into three regions, 2 nm, together with BET surface area SBET và total pore volume Vtotal. With increasing KMn
O4 concentration for the Mn
O2 loading onto MC0 fibers, both SBET and Vtotal increase slightly. For MC2 composite, however, surface area & pore volume contributed by the pores with the sizes less than 0.7 nm, S and V, decrease markedly and those by 0.7–2 nm increase markedly, although only slight increases in these parameters are detected for MC10.
Table 1 Surface areas and pore volumes for Mn
O2/CNFs composites.
Full kích cỡ table
X-ray diffraction patterns are shown for the composites, including MC0, in Fig. 4a. For MC0, there are two broad peaks at 2θ of around 26 and 44°, which can be ascribed khổng lồ 002 & 10 diffraction of amorphous carbon36. For the composites loaded by Mn
O2 (MC1, MC2 và MC10), the diffraction peaks of Mn
O2 at around 12, 17, 24, 37 và 66° in 2θ, of which index are 110, 200, 220, 211 và 002, respectively (JCPDS No. 44–0141).
Figure 4
Raman spectra of the composites are shown in Fig. 4b. The D- & G-bands of amorphous carbon38 are observed for the composites as well as the pristine MC0, of which intensity ratio ID/IG was calculated lớn be 2.7, indicating the turbostratic structure of the CNFs. For the composites, one additional band from Mn
O2 is observed at 646 cm−1, which can be assigned lớn the symmetric stretching vibration of Mn-O in the Mn
O6 groups25,39. It should be noted that the bands belonging khổng lồ Mn
O2 become more and more distinct with the increase of KMn
O4 concentration.
To investigate the chemical composition & chemical states of various elements in the composites, XPS analysis was performed. The spectrum in Fig. 5a reveals the existence of O, Mn & C in the MC2 composite. From the binding energy separation of 11.7 e
V between the peaks at 653.9 & 642.2 e
V attributed to lớn Mn2p1/2 & Mn2p3/2, respectively40 (Fig. 5b) and the separation energy of 4.95 e
V of the Mn 3 s spin orbit doublet (Fig. 5c), an intermediate oxidation state of manganese was estimated41 to be around 3.7 for MC2. The valence of Mn was also estimated to be 3.66 from the intensities of the Mn-O-Mn (529.9 e
V) and Mn-OH (531.4 e
V) (Fig. 5d) according to the literature42,43. The intermediate valence state at around 3.7 in the composite MC2 seems to lớn be benefiting the energy storage as a pseudocapacitance via the redox switching41.
Figure 5
Electrochemical performances of MC composites (a) Cyclic Voltammetry (CV) curves of the MC composites at the scan rate of 2 m
V s-1, (b) charge/discharge curves of the MC composites at the current density of 0.2 A g-1, dependences of (d) specific capacitance on current mật độ trùng lặp từ khóa for the MC composites và (e) specific capacitance và coulombic efficiency on cycle number for MC2 with the inset showing the charge/discharge curves in different cycles, (f) Nyquist plots of the EIS for MC1, MC2 and MC10 composites with the inset showing the equivalent circuit used, (g) Ragone plots for the present MC2 composites in comparison with published data.
Galvanostatic charge/discharge curves measured with the current mật độ trùng lặp từ khóa of 0.2 và 10 A g−1 are summarized for the composites in Fig. 6b and Supplementary Fig. S1, respectively. For the composites MC2 và MC10, the curves are not straight during both charging and discharging, revealing certain contribution of pseudocapacitance due lớn Mn
O2. The specific capacitance calculated from these curves with 0.2 A g−1 was 1282 F g−1 for MC2, while 151 và 515 F g−1 for MC0 và MC10, respectively. When increasing the charging/discharging current density to 10 A g−1, all curves present representative relatively linear voltage-time relationship with quasi-symmetric triangular shapes compare to the charging/discharging curve at 2 A g−1, revealing a remarkable reversibility, which indicate the capacity is mainly contributed by physically adsorption under larger current density.
The dependences of specific capacitance on current mật độ trùng lặp từ khóa are plotted for the composites in Fig. 6c. It is seen that the specific capacitance decreases with the increase of current density, abruptly up khổng lồ 10 A g−1 & then gradually. For MC2, the specific capacitance remains as high as 335 F g−1 at a current density of 50 A g−1, the capacity retention ratio being 26%. The capacitance retention with the current density of 1 A g−1 is shown for MC2 in Fig. 6d, the capacitance fluctuating during the first 200 cycles and then being stabilized at about 100%. The capacitance fluctuation in the beginning is probably due khổng lồ the low utilization of inner Mn
O2 as the limitation of electrolyte diffusion into the bulk of the fibers. After 200 cycles, as the electrodes gradually soaked by electrolyte, more Mn
O2 are involved in the charge storage process. The retention ratio start khổng lồ increase, then slowly exceed its initial value. Electrodes display an ideal cycling stability with full permeation of electrolyte after approximate 500 cycles, reaching a remarkable capacitance retention of 101%. 95% Coulombic efficiency remained after 1000 continuous cycles measured using the galvanostatic charge-discharge technique.
The electrochemical impedance spectroscopy (EIS) of the composite is displayed in Fig. 6e, the equivalent circuit diagram being in the inset. The equivalent circuit includes bulk solution resistance Rs, charge transfer resistance Rct, pseudo-capacitance Cp due lớn the redox reactions of Mn
O2 & Warburg impedance Zw. It is seen that all composite electrodes exhibit the nearly vertical line along the imaginary axis in the low-frequency region, revealing an ideally capacitive behavior of the electrode materials due to the fast và reversible Faradic reaction of nano-Mn
O2. It should be noted that the slope is larger with MC10 than MC2. The Rs for composite electrodes remained almost the same because this parameter is insensitive lớn the electrode surface. In the high frequency region, the charge transfer resistance (Rct) was 11.5 & 2.5 Ω for MC2 và MC10, respectively, which seems to lớn depend strongly on the concentration of KMn
O4 during loading of Mn
O2.
Ragone plot is presented to lớn characterize the Mn
O2/CNFs composites in Fig. 6f together with the data published. It is noteworthy lớn mention that energy density of MC2 is 36 Wh kg−1 with power mật độ trùng lặp từ khóa of 39 W kg−1, & can maintain 7.5 Wh kg−1 at 10.3 k
W kg−1. Comparing the present composite MC2 with those published on electrospun carbon fibers và activated carbons, the performance of MC2 surpasses most of Mn
O2/carbon composites reported12,13,14,20,44,45,46,47,48,49,50,51,52,53. With regard lớn active materials, the energy density can be calculated through the following equations:
Two strategies are commonly used to develop electrode with high energy density under high power nguồn density. (1) One is to lớn extend the potential window in aqueous electrolytes via designing an asymmetric configuration50,54,55 or using special electrolyte with high potential window14,49,56,57. By using Na2SO4 aqueous electrolyte, the potential window of the supercapacitor can be 1.6–2.2 V14,49,57. The achieved performance curve is overlapped with our results, although the Mn
O2/C composite performance is about 292 F g−1 (2.5 A g−1). (2) The other is designing electrode with high specific capacitance. Many efforts have been done to lớn design the host material micro-architecture for loading nanoscopic Mn
O2 lớn balance electron và ion transport inside the composites, as well as mass loading. Except the energy & power density shown in Fig. 6(f), more details for comparison are shown in Table S3. Several groups reported that, shorter redox reaction time of KMn
O4 & carbon in neutral solution can help khổng lồ achieve thinner Mn
O2 with higher specific capacitance và high energy density12,13,30. Larger mass loading accompanies with lower specific capacitance in most of the cases. With porous structure, more nano-sized Mn
O2 can be loaded50. High utilization of active materials can be achieved by combining the homogeneous deposition of Mn
O2 nanocrystals in the bulk because the rapid intercalation/deintercalation of Na+ on the surface layer of Mn
O2 has been widely accepted as the charge-storage mechanism in mild electrolytes. The combination of Mn
O2 & porous CNFs can achieve excellent capacitive performance. More interface between the Mn
O2/conductive material can improve the Mn
O2 utilization mass ratio. In most of the cases shown in Fig. 6d, The Mn
O2 crystal form size is tens of nanometers. Although the Mn
O2 is exposed lớn the electrolyte, the interface between the Mn
O2 and carbon is limited. The interface between 3d contrained nano-Mn
O2 and porous CNFs has been enhanced dramatically while the resistance of the matrix increases with more loading of nano-Mn
O2 in the bulk of CNFs. So it is a trade-off between the energy density and power density. Furthermore, comparing CNFs with activated carbons và porous carbon spheres, the pores in CNFs are shallow ones since the fiber diameter is only sub-micros while the pores in activated carbons or carbon spheres are deep & narrow. The electrolyte penetration resistance of CNFs should be smaller than that of activated carbons. So, the electron transport loops và the diffusion loops of cations in most of the cases are longer than the structure shown in this work, which is related lớn the nguồn performance of an electrode.
To get more insights into the advantages of the MC2 electrode, a high resolution TEM has been used. Figure 2(c–e) clearly revealed that Mn
O2 crystals with an interlayer spacing of about 0.24 nm were composed of on the external surface of the fibers, corresponding lớn α-Mn
O2 (211) crystal faces, while Mn
O2 with an interlayer spacing of about 0.5 nm were deposited on the inner surface of the pores at the central part of fibers, exhibiting the character of α-Mn
O2 (200) crystal faces. The results are in good agreement with XRD information. The results indicate that Mn
O2 nanoparticles grow along with (211) crystal face when the redox reaction between KMn
O4 & carbon happens on the surface of CNFs, in other words, under an un-limited 1D constraint; while Mn
O2 nanoparticles grow along with (200) crystal face when the redox reaction happens inside of mesopores, under a strong 3d constraint from the inner surface of pores.
To figure out the affection of porous structure in CNFs on in-situ reaction between KMn
O4 and carbon to size Mn
O2, the electrospun CNFs prepared from PI without PVP were used as scaffold for Mn
O2 by the same condition as MC2 (KMn
O4 concentration of 0.024 g L−1). Pore-size distributions for the pristine (Mn
O2-unloaded) & Mn
O2-loaded CNFs are shown in Fig. 7(a,b), displaying an increase of pores having the kích cỡ of 1.0–1.5 nm by sacrificing the mesopores having 2–8 nm sizes. The change in pore structure in the CNFs with Mn
O2-loading is very similar to lớn that happened in the composite MC2 (Fig. 3). Comparing khổng lồ the pristine CNFs, the pore volume contributed from pores smaller than 0.7 nm disappear, a big increase of pore volume from pores in the range of 0.7–2 nm appeared và a decrease of pore volume happens with the pore volume contributed from pores larger than 2 nm for MC2 (Fig. 3) and also another CNFs (Mn
O2-loaded in Fig. 7). This should be related lớn the PVP induced pores. Porous CNFs has a larger pore volume & more defects. The defects in the bulk can prove more active-edges for the reaction with KMn
O4 to lớn produce Mn
O2 in the 3 chiều constrains.
Figure 7
Based on the pore distribution & TEM images, we could conclude that KMn
O4 penetrated to the pores situated inside of the porous CNFs. The Mn
O2 nanoparticles formed inside of the pores covered the inner surface of the pores. So, the pores smaller than 0.7 are blocked by Mn
O2 either deposited at the entrances of pores or formed in the pores, resulting in the disappearance of the peaks for the pores smaller than 0.7 nm. The increase of pore volume in the range of 0.7–1.2 nm should be related to the Mn
O2 nanoparticles formed in the pores larger than 2 nm.
Based on the CV test and galvanostatic charge/discharge results, it could be seen that the performances of Mn
O2/PVP induced porous CNFs electrode are all better than Mn
O2/PVP free CNFs electrode. The PVP không tính phí samples Mn
O2
CNFs shows better capacity at smaller current density & the lower capacity at larger current mật độ trùng lặp từ khóa than MC10 (Fig. 7c). The results indicate that Mn
O2 with low crystalline was produced in low concentration KMn
O4, which bring us a higher utilization rate of Mn
O2 in the supercapacitor performances.
As shown in Fig. 6a, Supplementary Fig. S1 and Fig. 6e of the CV test and EIS results, MC2 shows larger capacitance than MC10 while the resistance of MC10 is much lower than MC2 & MC1. This should be related khổng lồ formation of Mn
O2 in the bulk of the electrode.
With a high concentration of KMn
O4, the redox reaction is reasonably supposed to lớn occur very fast with amorphous carbons, and so Mn
O2 nanoparticles are formed on the surface of the fibers, which seems khổng lồ prevent the penetration of KMn
O4 into the bulk of the fiber. The morphology of the electrode is quite different with that in a low concentration KMn
O4, even in the size of flaks, as shown in Fig. 1d for MC10. The crystallinity of Mn
O2 produced in a high concentration KMn
O4 is lower than that of Mn
O2 produced in low concentration KMn
O4, which is proved by XRD as shown in Fig. 4a. In MC10, the pore volume does not change too much. Such a pore-size distribution suggested that Mn
O2 deposition occurs only on the surface of the CNFs. The resistance of such kind of structure should be low which is also approved by EIS data.
When the time for the diffusion of KMn
O4 into pores is the same order of magnitude with the time for the redox reaction of KMn
O4 with carbon, Mn
O2 nanocrystals can be precipitated in the pores of the fibers under a strong constraint. As Mn
O2 is an insulator, the bulk resistance should increase. Such kind of Mn
O2/C interface connection is very well. Therefore, the performance under larger current is also good.
Conclusion
A 3 chiều Mn
O2/C nano-composite with remarkable electrochemical behaviors can be on-site synthesized with porous carbon nanofibers as a scaffold. For MC2, the capacitance of the composite electrode could be 1282 F g−1 under a certain current density of 0.2 A g−1 in 1 M Na2SO4 electrolyte. It is noteworthy to mention that energy density of MC2 is 36 Wh kg−1 with power density of 39 W kg−1, và can maintain 7.5 Wh kg−1 at 10.3 k
W kg−1. The key point of the work is khổng lồ make the diffusion time of KMn
O4 into the bulk of the porous carbon fibers và the redox reaction time of KMn
O4 with carbon on the same order of magnitude by adjusting the concentration of KMn
O4. The results indicate that the Mn
O2 growth along with (211) crystal face when KMn
O4 và carbon redox reaction happens with an un-limited 1D constrain; while the Mn
O2 growth along with (200) crystal face when KMn
O4 and carbon redox reaction happens with a comparable 3d constrain. The optimized KMn
O4 concentration in our case should be 0.024 g L−1. The good capacitance performance of the Mn
O2/CNFs composite electrode is clearly attributed to its unique nanostructure. The porous CNFs serves as a highly conductive matrix for fast ion và electron transport, while the ultrathin Mn
O2 nanocrystals on the inner surface of the pores enable a short diffusion path of electrolyte and provide a more electrochemically active surface area for pseudocapacitance through fast and reversible Faradic reaction.
Experimental section
Materials
Pyromelliticdianhydride (PMDA) (Mw = 218.12 g mol−1, Sinopharm Chemical Reagent Co., Ltd), 4,4′-oxydianiline (ODA) (Mw = 200.24 g mol−1, Sinopharm Chemical Reagent Co., Ltd), polyvinyl pyrrolidones (PVP) (Mw = 1300,000 g mol−1, Sinopharm Chemical Reagent Co., LTD), N,N-dimethylformamide (DMF) (Xilong Chemical Co., Ltd) và potassium permanganate (KMn
O4, 99.5%) (Sinopharm Chemical Reagent Co., Ltd) were used as received.
Fabrication of carbon nanofibers
The electrospinning solution was prepared with PMDA, ODA và PVP in DMF with molar ratio of PMDA và ODA 1:1. The PVP was dissolved in the solution with mass ratio 20% (to total masses of PMDA & ODA). The blended solution was stirred at 0 °C for 24 h. Electrospinning parameters were set as follows: applied voltage of 20 k
V, tip-to-collector distance of 20 cm and flow rate of 0.8 ml h−1. As-spun fibers were imidized & carbonized in a horizontal tubular furnace. Temperature of the furnace was first increased from room temperature lớn 300 °C at the rate of 3 °C min−1 and was maintained for 30 min in a flow of air for imidization. Then the temperature was increased to lớn 900 °C at the same heating rate và was maintained for 1 h under N2 atmosphere for carbonization.
KMn
O4 was dissolved into de-ionized water. The concentration of KMn
O4 solution were prepared at 0.012 g L−1 (0.076*10−3 M), 0.024 g L−1 (0.152*10−3 M), & 0.12 g L−1 (0.76*10−3 M). Composites derived from these solutions were labeled as MC1, MC2 & MC10, respectively.
The carbon fiber electrode was soaked into the KMn
O4 solution & the weight ratio of CNFs lớn KMn
O4 was set lớn 4:1. The CNFs was taken out until the purple màu sắc of KMn
O4 solution had fade into golden brown. The mass loading remains lớn 10–11% for all samples. The Mn
O2/CNFs composites were rinsed by deionized water for several times, và finally dried at 80 °C for 10 h under vacuum condition.
Characterization
The morphology of CNFs was investigated using a scanning electron microscope (SEM, LEO 1530). A high-resolution transmission electron microscopy (HRTEM) was employed khổng lồ characterize the distribution and crystallization of the composites. The CNFs, pristine and Mn
O2-loaded, embedded in epoxy resin was cut into 20 nm slices using a microtome (EM UC6, Leica, Germany) with a kim cương blade (Di
ATOME) and then placed onto a 300 mesh Cu grid for examination by TEM.
X-ray diffraction (XRD) pattern of the composites was examined using D/MAX-RM 2000 at the scanning rate of 2° min−1 in a range of diffraction angle 2θ from 5° to 70°. Raman spectrum was recorded by HR800 (HORIBA spectrometer) with a wavelength of 633 nm. X-ray photoelectron spectroscopy (XPS) measurement was performed with a thermo ESCALAB 250 spectrometer. XPS data analysis was performed using Thermo Avantage software. Sorption/desorption isotherms of N2 at 77 K were measured by a Belsorp Max apparatus (Japan) và analyzed khổng lồ evaluate specific surface areas of the composites by using the Brunauer-Emmett-Teller (BET) method, SBET, and pore-size distribution of the composites by density functional theory (DFT) method.
A symmetrical two-electrode supercapacitor was assembled using two pieces of the composite and a separator to lớn investigate the electrochemical performance as an electrochemical capacitor. Lớn achieve sufficient saturation of the electrodes and separator by the electrolyte, they were immersed in 1 M Na2SO4 solution under vacuum for 24 hrs before being assembled. Cyclic voltammetry (CV) và galvanostatic charge/discharge analysis were carried out to evaluate electrochemical performance of the electrodes with a potential window ranging from 0 to lớn 1 V in 1 M Na2SO4 electrolyte using an electrochemical workstation (CHI 600, Shanghai Chen Hua Instrument Company). The electrochemical impedance spectroscopy (EIS) was conducted in the frequency range of 0.01 Hz ~100 k
Hz with perturbation amplitude of 5 m
V versus the xuất hiện circuit potential. The average specific capacitance was calculated according khổng lồ the charge/discharge tests based on the following equation:
Le, T. H., Yang, Y., Yu, L., Huang, Z. H. Và Kang, F. Y. Polyimide‐based porous hollow carbon nanofibers for supercapacitor electrode. J. App. Polym. Sci. 133, doi: 10.1002/APP.43397 (2016).
Lowell, S., Shield, J. E., Thomas, M. A. & Thommes, M. Characterization of porous solids và powders: Surface Area. Pore form size and Density, Springer Publisher, Netherlands, 43–44 (2006).
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