The effect of the internal magnetism of ferromagnetic catalysts on their catalytic activity toward oxygen reduction reaction under an external magnetic field

Abstract

In the oxygen reduction reaction (ORR), the oxygen transport rate plays an important role in the ORR on the cathode. An approach by applying magnetic fields on the cathode can effectively improve the oxygen transport. However, no work reports the effect of the magnetism of ferromagnetic catalysts on ORR under an external magnetic field. Herein, the catalytic performances of the ferromagnetic catalysts including Fe 3 O 4 , γ-Fe 2 O 3 , and Fe-N-C for ORR are studied under an external magnetic field. Linear sweep voltammetry (LSV) results indicate that the ORR current on the cathode increases with the strength of the external magnetic field due to the improved oxygen transfer. Meanwhile, the increase of the ORR current on Fe-N-C is larger than Fe 3 O 4 and γ-Fe 2 O 3 since some internal tiny magnetic fields generated by the Fe 3 O 4 and γ-Fe 2 O 3 catalysts are different from the magnetic direction of the external magnet. It is also found that the magnetic direction of the external magnet does not have any effect on the oxygen transfer.

Magnetic Field‐Enhanced 4‐Electron Pathway for Well‐Aligned Co3O4/Electrospun Carbon Nanofibers in the Oxygen Reduction Reaction

“…(4)] from the peak current position on the square root of the voltage scan rate (Figure c), the increased number of exchanged electrons was obtained for the Co 3 O 4 /ECNFs‐modified electrodes under magnetic fields of 0.22, 0.44, 0.66, 0.88 mT, 1.10 mT, 1.32 mT (Figure d, Table ). There is no measurable difference in the number of electrons exchanged on the bare GC electrode in absence (Figure S2) or presence (Figure S12) of an external magnetic field at 1.32 mT, suggesting that the external mT‐range magnetic field does not have a significant effect on oxygen diffusion/transfer due to the applied magnetic field strength . A small difference in this number was observed for the ECNFs‐modified electrode in the absence ( n ≈2.28; Figure S13 a) and presence ( n ≈2.35, 3.1 % increase; Figure S13 b) of an external magnetic field at 1.32 mT, indicating that the external mT‐range magnetic field may promote the transfer of paramagnetic peroxo radicals along the porous structure of the ECNFs as a result of the Lorentz force .…”

“…(3)] from ap lot of log (peak current) versus potential (Figure 5b)a nd slope 2[ Eq. [44,45] However,t he hybrid of Co 3 O 4 with ECNFsafforded much greater activity (n = 3.48 vs. 2.28 at 0mT). There is no measurable difference in the number of electrons exchanged on the bare GC electrode in absence ( Figure S2) or presence ( Figure S12) of an external magnetic field at 1.32 mT,s uggesting that the external mT-range magnetic field does not have as ignificant effect on oxygen diffusion/transfer duet ot he appliedm agnetic field strength.…”

“…According to slope 1[ Eq. [44,45] As mall differencei nt his number was observed for the ECNFs-modified electrode in the absence (n % 2.28;F igure S13 a) and presence (n % 2.35, 3.1 %i ncrease;F igure S13 b) of an externalm agnetic field at 1.32 mT,i ndicating that the external mT-rangem agnetic field may promote the transfer of paramagnetic peroxo radicals along the porous structure of the ECNFs as ar esult of the Lorentz force. (4)] from the peak current position on the square root of the voltage scan rate (Figure 5c), the increased number of exchanged electrons was obtainedf or the Co 3 O 4 /ECNFs-modified electrodes under magnetic fields of 0.22, 0.44, 0.66, 0.88 mT,1 .10 mT,1 .32 mT (Figure 5d,T able 1).…”

“…There is no measurable difference in the number of electrons exchanged on the bare GC electrode in absence ( Figure S2) or presence ( Figure S12) of an external magnetic field at 1.32 mT,s uggesting that the external mT-range magnetic field does not have as ignificant effect on oxygen diffusion/transfer duet ot he appliedm agnetic field strength. [44,45] As mall differencei nt his number was observed for the ECNFs-modified electrode in the absence (n % 2.28;F igure S13 a) and presence (n % 2.35, 3.1 %i ncrease;F igure S13 b) of an externalm agnetic field at 1.32 mT,i ndicating that the external mT-rangem agnetic field may promote the transfer of paramagnetic peroxo radicals along the porous structure of the ECNFs as ar esult of the Lorentz force. [44,45] However,t he hybrid of Co 3 O 4 with ECNFsafforded much greater activity (n = 3.48 vs. 2.28 at 0mT).…”

“…[44,45] As mall differencei nt his number was observed for the ECNFs-modified electrode in the absence (n % 2.28;F igure S13 a) and presence (n % 2.35, 3.1 %i ncrease;F igure S13 b) of an externalm agnetic field at 1.32 mT,i ndicating that the external mT-rangem agnetic field may promote the transfer of paramagnetic peroxo radicals along the porous structure of the ECNFs as ar esult of the Lorentz force. [44,45] However,t he hybrid of Co 3 O 4 with ECNFsafforded much greater activity (n = 3.48 vs. 2.28 at 0mT). Similarr esults werer eported when Co 3 O 4 was supported on graphene [28] or carbonn anotubes.…”