Water splitting involves a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode, and OER has been considered as the major bottleneck for water splitting due to the sluggish reaction kinetics and high OO bond formation energy barrier caused by its four-electron coupling process. [2][3][4][5] Designing the external-and internal structure of electrocatalysts is fundamental to achieve high catalytic activities at low overpotential and equally important to the electrocatalysts themselves, the reaction efficiency also strongly depends on the mass transfer outside the electrode surface and electron transfer inside the electrode structure. [4][5][6] The mass transfer at the interfaces between the catalyst and electrolyte is responsible for the immediate supplying of electrolytes (and reactants) and associated with rapid release of bubbles generated by the reactions (O 2 gas, for the case of OER). [7] The kinetics of mass transfer as the rate-controlling step, therefore, govern the efficiency of the electrochemical reaction, by taking much larger time constant compared with that of the electron transfer. [8,9] For gas-evolving electrochemical system, bubbles may adhere to the catalyst's surface and block the active sites by forming bubble froth layers. This process
The promotion of magnetic field on catalytic performance has attracted extensive attention. However, little research has been reported on the performance of the oxygen evolution reaction (OER) for the modulating intrinsic magnetism of the catalyst under a magnetic field. Herein, we adjusted the intrinsic magnetism of the Co x Ni1–x Fe2O4-nanosheet by adjusting the ratio of Co and Ni, and researched the relationship between the OER activity and the intrinsic magnetism. The results indicate that the CoFe2O4-nanosheet has the most OER activity increases in the magnetic field due to the optimal intrinsic magnetism. The required overpotential of CoFe2O4-nanosheet@NF to reach a current density of 10 mA cm–2 was reduced by 21 mV under about 100 mT magnetic field compared with no magnetic field, and the degree of improvement of OER activity of different magnetic catalysts in the same magnetic field is positively correlated with the intrinsic magnetism of the catalyst. Therefore, magnetic field assistance provides a new, effective, and general strategy to improve the activity of electrodes for water splitting.
The slow oxygen evolution reaction (OER) limits water splitting, and external fields can help improve it. However, the effect of a single external field on OER is limited and unsatisfactory. Furthermore, the mechanism by which external fields improve OER is unclear, particularly in the presence of multiple fields. Herein, we propose a strategy for enhancing the OER activity of a catalyst using the combined effect of an optical‐magnetic field and study the mechanism of catalytic activity enhancement. Under the optical‐magnetic field, Co3O4 reduces the resistance by increasing the catalyst temperature. Meanwhile, CoFe2O4 further reduces the resistance via the negative magnetoresistance effect, thus decreasing the resistance from 16 Ω to 7.0 Ω. Additionally, CoFe2O4 acts as a spin polarizer, and electron polarization results in a parallel arrangement of oxygen atoms, which increases the kinetics of the OER under the magnetic field. Benefiting from the optical and magnetic response design, Co3O4/CoFe2O4@Ni foam requires an overpotential of 172.4 mV to reach a current density of 10 mA·cm−2 under an optical‐magnetic field, which is significantly higher than those of recently reported state‐of‐the‐art transition‐metal‐based catalysts.This article is protected by copyright. All rights reserved
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