The development of highly efficient catalysts for cathodes remains an important objective of fuel cell research. Here, we report Co3O4 nanoparticles assembled on a polypyrrole/graphene oxide electrocatalyst （C...The development of highly efficient catalysts for cathodes remains an important objective of fuel cell research. Here, we report Co3O4 nanoparticles assembled on a polypyrrole/graphene oxide electrocatalyst （Co3O4/Ppy/GO） as an efficient catalyst for the oxygen reduction reaction （ORR） in alkaline media. The catalyst was prepared via the hydrothermal reaction of Co2＋ ions with Ppy-modified GO. The GO, Ppy/GO, and Co3O4/Ppy/GO were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The incorporation of Ppy into GO nanosheets resulted in the formation of a nitrogen-modified GO po-rous structure, which acted as an efficient electron-transport network for the ORR. With further anchoring of Co3O4 on Ppy/GO, the as-prepared Co3O4/Ppy/GO exhibited excellent ORR activity and followed a four-electron route mechanism for the ORR in alkaline solution. An onset potential of -0.10 V vs. a saturated calomel electrode and a diffusion limiting current density of 2.30 mA/cm^2 were achieved for the Co3O4/Ppy/GO catalyst heated at 800 ℃; these values are comparable to those for noble-metal-based Pt/C catalysts. Our work demonstrates that Co3O4/Ppy/GO is highly active for the ORR. Notably, the Ppy coupling effects between Co3O4 and GO provide a new route for the preparation of efficient non-precious electrocatalysts with hierarchical porous structures for fuel cell applications.展开更多
The bulk specimens with preferable orientation were utilized to investigate atom exchange of martensite in Cu-13Zn-15Al alloy during non-isothermal aging by in-situ X-ray diffraction. It is found that the exchange of ...The bulk specimens with preferable orientation were utilized to investigate atom exchange of martensite in Cu-13Zn-15Al alloy during non-isothermal aging by in-situ X-ray diffraction. It is found that the exchange of Zn atoms at position Ⅲ and Cu atoms at Ⅱ and the exchange of Zn atoms at position Ⅲ and Al atoms atⅠon the basal plane of martensite occur during heating at a heating rate of 5 ℃/min. 13% (2/25 ) of Al atoms transfer from positionⅠto position Ⅲ when temperature goes up to 160 ℃.展开更多
Fe doped Beta zeolite with different Fe contents were prepared by ion exchange by changing the volume or the concentration of a Fe salt solution. For a particular mass of Fe salt precursor, the concentration of the me...Fe doped Beta zeolite with different Fe contents were prepared by ion exchange by changing the volume or the concentration of a Fe salt solution. For a particular mass of Fe salt precursor, the concentration of the metal salt solution during ion exchange influenced the ion exchange capacity of Fe, and resulted in different activities of the Fe-Beta catalyst. Fe-Beta catalysts with the Fe contents of （2.6, 6.3 and 9） wt% were synthesized using different amounts of 0.02 mol/L Fe salt solution. These catalysts were studied by various characterization techniques and their NH3-SCR activities were evaluated. The Fe-Beta catalyst with the Fe content of 6.3 wt% exhibited the highest activity, with a temperature range of 202-616℃ where the NOx conversion was 〉 80%. The Fe content in Beta zeolite did not influence the structure of Beta zeolite and valence state of Fe. Compared with the Fe-Beta catalysts with low Fe content （2.6 wt%）, Fe-Beta catalysts with 6.3 wt% Fe content possessed more isolated Fe3. active sites which led to its higher NH3-SCR activity. A high capacity for NH3 and NO adsorption, and a high activity for NO oxidation also contributed to the high NH3-SCR activity of the Fe-Beta catalyst with 6.3 wt%. However, when the Fe content was further increased to 9.0 wt%, the amount of FexOy nanoparticles increased while the amount of isolated Fe3＋ active sites was unchanged, which promoted NH3 oxidation and decreased the NH3-SCR activity at high temperature.展开更多
基金Supported by the National Natural Science Foundation of China(20171015,20171016)the Natural Science Foundation of Heilongjiang Province(E00-16)the Science Foundation for Excellent Youth of Heilongjiang University(J200106).
基金supported by the National Natural Science Foundation of China(21373042)~~
文摘The development of highly efficient catalysts for cathodes remains an important objective of fuel cell research. Here, we report Co3O4 nanoparticles assembled on a polypyrrole/graphene oxide electrocatalyst （Co3O4/Ppy/GO） as an efficient catalyst for the oxygen reduction reaction （ORR） in alkaline media. The catalyst was prepared via the hydrothermal reaction of Co2＋ ions with Ppy-modified GO. The GO, Ppy/GO, and Co3O4/Ppy/GO were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The incorporation of Ppy into GO nanosheets resulted in the formation of a nitrogen-modified GO po-rous structure, which acted as an efficient electron-transport network for the ORR. With further anchoring of Co3O4 on Ppy/GO, the as-prepared Co3O4/Ppy/GO exhibited excellent ORR activity and followed a four-electron route mechanism for the ORR in alkaline solution. An onset potential of -0.10 V vs. a saturated calomel electrode and a diffusion limiting current density of 2.30 mA/cm^2 were achieved for the Co3O4/Ppy/GO catalyst heated at 800 ℃; these values are comparable to those for noble-metal-based Pt/C catalysts. Our work demonstrates that Co3O4/Ppy/GO is highly active for the ORR. Notably, the Ppy coupling effects between Co3O4 and GO provide a new route for the preparation of efficient non-precious electrocatalysts with hierarchical porous structures for fuel cell applications.
基金Project(05JJ3005) supported by the Natural Science Foundation of Hunan Province, China Project(20040553069) supported by the PhD Programs of Ministry of Education of China
文摘The bulk specimens with preferable orientation were utilized to investigate atom exchange of martensite in Cu-13Zn-15Al alloy during non-isothermal aging by in-situ X-ray diffraction. It is found that the exchange of Zn atoms at position Ⅲ and Cu atoms at Ⅱ and the exchange of Zn atoms at position Ⅲ and Al atoms atⅠon the basal plane of martensite occur during heating at a heating rate of 5 ℃/min. 13% (2/25 ) of Al atoms transfer from positionⅠto position Ⅲ when temperature goes up to 160 ℃.
基金supported by the National Key Basic Research Program of China (973 Program, 2013CB933201)the National Natural Science Foun-dation of China (21577034, 21333003, 91545103)+1 种基金Science and Technology Commission of Shanghai Municipality (16ZR1407900)Fundamental Research Funds for the Central Universities (WJ1514020)~~
文摘Fe doped Beta zeolite with different Fe contents were prepared by ion exchange by changing the volume or the concentration of a Fe salt solution. For a particular mass of Fe salt precursor, the concentration of the metal salt solution during ion exchange influenced the ion exchange capacity of Fe, and resulted in different activities of the Fe-Beta catalyst. Fe-Beta catalysts with the Fe contents of （2.6, 6.3 and 9） wt% were synthesized using different amounts of 0.02 mol/L Fe salt solution. These catalysts were studied by various characterization techniques and their NH3-SCR activities were evaluated. The Fe-Beta catalyst with the Fe content of 6.3 wt% exhibited the highest activity, with a temperature range of 202-616℃ where the NOx conversion was 〉 80%. The Fe content in Beta zeolite did not influence the structure of Beta zeolite and valence state of Fe. Compared with the Fe-Beta catalysts with low Fe content （2.6 wt%）, Fe-Beta catalysts with 6.3 wt% Fe content possessed more isolated Fe3. active sites which led to its higher NH3-SCR activity. A high capacity for NH3 and NO adsorption, and a high activity for NO oxidation also contributed to the high NH3-SCR activity of the Fe-Beta catalyst with 6.3 wt%. However, when the Fe content was further increased to 9.0 wt%, the amount of FexOy nanoparticles increased while the amount of isolated Fe3＋ active sites was unchanged, which promoted NH3 oxidation and decreased the NH3-SCR activity at high temperature.
