Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction(ORR)due to their M-N_(4) active sites and large conjugated elec-tronic...Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction(ORR)due to their M-N_(4) active sites and large conjugated elec-tronic molecular structures.Herein,the“substituents optimization”strategy combined with“push effect”modification was innovatively employed to target a single Co-N_(4) active site in three substituted phthalo-cyaninato cobalt complexes:tetranitrophthalocyaninato cobalt(CoTNPc),tetra(4-nitrophenoxy)phthalo-cyaninato cobalt(CoTPNPc),and tetraphenoxy phthalocyaninato cobalt(CoTPPc)electrocatalyst,also with 4-phenylpyridine axial coordination on Co-N_(4) unit.Through substituents screening,the half-wave poten-tial(E_(1/2))for ORR increases in the order of CoTPNPc(0.75 V)<CoTPPc(0.80 V)<CoTNPc(0.83 V)along with decreased electron-withdrawing ability of their substituents from-OC_(6) H_(4)-NO_(2),-OC_(6) H_(5) to-NO_(2) in the three cobalt phthalocyanine derivatives.CoTNPc with the weakest electron-withdrawing substituent exhibits the best ORR performance among the three compounds.This is attributed to its higher elec-tron delocalization and lifted HOMO energy level with the lower energy barrier in the rate-determining step relative to the other two compounds,which facilitate the electron transfer and reduction of oxy-gen as evidenced by XPS,UPS,and DRS analysis combined with DFT calculations.Further coordination of 4-phenylpyridine shifts the E_(1/2) up to 0.78,0.82,and 0.85 V for CoTPNPc,CoTPPc,and CoTNPc.DFT calcu-lations demonstrate that the introduction of the electron-donating phenylpyridine ligand into the cobalt phthalocyanines breaks the symmetry of the Co-N_(4) center and also raises the electron density of Co sites,which promotes O_(2) adsorption and improves ORR performance.After comparing the two strategies,the substituents on metallophthalocyanine are more determined by the electroactivity than the axial group,which directly regulates the coordination environment and then the activation barrier of the ORR pro-cess.This work provides theoretical and experimental guidance by two coupling strategies for the design of highly active molecular CoPc-based ORR electrocatalysts in the practical application.展开更多
The applications of magnetrons are greatly limited because of the poor output spectrum of the free-running magnetron.Currently, one of the best ways to solve this problem is injection locking. However, the injection l...The applications of magnetrons are greatly limited because of the poor output spectrum of the free-running magnetron.Currently, one of the best ways to solve this problem is injection locking. However, the injection locking theory which is widely used nowadays is based on the simplified oscillator, which does not include the frequency pushing effect of the magnetron. In this paper, the theory of injection locking magnetrons with frequency pushing effect is systematically studied.Analytical analysis shows that the locking bandwidth turns larger with the consideration of the pushing parameter(α), and the increase of locking bandwidth is expanded with α increasing. Experimental results show that the locking bandwidth is expanded by 0.3 MHz, 1 MHz, and 1.6 MHz compared with the locking bandwidth from the conventional locking theory under an injection ratio(ρ) of 0.05, 0.075, and 0.1, respectively. This research provides a more accurate prediction of the properties of the injection-locked magnetron.展开更多
基金supported by the Key Program of the National Natural Science Foundation of China(No.22133006)National Nat-ural Science Foundation of China(No.21771192)+2 种基金Program for Tais-han Scholar of Shandong Province(No.ts201712019)NSF of Shan-dong Province(No.ZR2017ZB0315)Shandong Energy Group 2019 Science and Technology Program(Nos.YKKJ2019AJ11JG-R66 and YKKJ2019AJ05JG-R60).
文摘Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction(ORR)due to their M-N_(4) active sites and large conjugated elec-tronic molecular structures.Herein,the“substituents optimization”strategy combined with“push effect”modification was innovatively employed to target a single Co-N_(4) active site in three substituted phthalo-cyaninato cobalt complexes:tetranitrophthalocyaninato cobalt(CoTNPc),tetra(4-nitrophenoxy)phthalo-cyaninato cobalt(CoTPNPc),and tetraphenoxy phthalocyaninato cobalt(CoTPPc)electrocatalyst,also with 4-phenylpyridine axial coordination on Co-N_(4) unit.Through substituents screening,the half-wave poten-tial(E_(1/2))for ORR increases in the order of CoTPNPc(0.75 V)<CoTPPc(0.80 V)<CoTNPc(0.83 V)along with decreased electron-withdrawing ability of their substituents from-OC_(6) H_(4)-NO_(2),-OC_(6) H_(5) to-NO_(2) in the three cobalt phthalocyanine derivatives.CoTNPc with the weakest electron-withdrawing substituent exhibits the best ORR performance among the three compounds.This is attributed to its higher elec-tron delocalization and lifted HOMO energy level with the lower energy barrier in the rate-determining step relative to the other two compounds,which facilitate the electron transfer and reduction of oxy-gen as evidenced by XPS,UPS,and DRS analysis combined with DFT calculations.Further coordination of 4-phenylpyridine shifts the E_(1/2) up to 0.78,0.82,and 0.85 V for CoTPNPc,CoTPPc,and CoTNPc.DFT calcu-lations demonstrate that the introduction of the electron-donating phenylpyridine ligand into the cobalt phthalocyanines breaks the symmetry of the Co-N_(4) center and also raises the electron density of Co sites,which promotes O_(2) adsorption and improves ORR performance.After comparing the two strategies,the substituents on metallophthalocyanine are more determined by the electroactivity than the axial group,which directly regulates the coordination environment and then the activation barrier of the ORR pro-cess.This work provides theoretical and experimental guidance by two coupling strategies for the design of highly active molecular CoPc-based ORR electrocatalysts in the practical application.
基金Project supported by the Sichuan Science and Technology Program,China(Grant No.2019YFG0419)the National Natural Science Foundation of China(Grant No.61601312)
文摘The applications of magnetrons are greatly limited because of the poor output spectrum of the free-running magnetron.Currently, one of the best ways to solve this problem is injection locking. However, the injection locking theory which is widely used nowadays is based on the simplified oscillator, which does not include the frequency pushing effect of the magnetron. In this paper, the theory of injection locking magnetrons with frequency pushing effect is systematically studied.Analytical analysis shows that the locking bandwidth turns larger with the consideration of the pushing parameter(α), and the increase of locking bandwidth is expanded with α increasing. Experimental results show that the locking bandwidth is expanded by 0.3 MHz, 1 MHz, and 1.6 MHz compared with the locking bandwidth from the conventional locking theory under an injection ratio(ρ) of 0.05, 0.075, and 0.1, respectively. This research provides a more accurate prediction of the properties of the injection-locked magnetron.
