Electrochemical Reconstruction Of NiFe/NiFeOOH Core-shell Nanoparticles For Magnetic Heating Enhancement Of Oxygen Evolution Reaction

Transition metal catalysts undergo electrochemical reconstruction during the oxygen evolution reaction(OER)process.The resulting transition metal(oxy)hydroxides(MOOH,M = transition metal)have high catalytic activity and low cost,making them an emerging substitute for noble-metal-based catalysts such as Ir/Ru.However,the amorphous nature of the electrochemically reconstructed(oxy)hydroxides impedes the electrochemical kinetics due to poor electrical conductivity.One effective approach to addressing this issue is by constructing spaceconfined structures that enable contact between the amorphous materials and highly conductive confined matrices.Recent studies have shown that ferromagnetic nanoparticles catalysts exhibit magnetic heating effects under alternating magnetic fields,which can improve their catalytic performance.The magnetic heating effect of ferromagnetic nanoparticles(NPs)is mainly determined by two mechanisms: Brownian relaxation and Néel relaxation.Brownian relaxation related heating effects result from the physical rotation of the NPs,which may lead to disengagement or changes in microscopic arrangement,resulting in decreased catalytic performance.In constant,Néel relaxation related heating effect is caused by the flip of magnetic moment direction along with the external AMF and is independent of the physical rotation of NPs.Therefore,stable catalytic performance improvement can be achieved by utilizing the magnetic heating effect associated with Néel relaxation.In this paper,we have carried out the following research on the basis of the successful preparation of NiFeNPs in highly conductive carbon matrix by pulsed laser deposition(PLD)(1)NiFe/NiFeOOH core-shell heterojunction NPs catalyst was successfully prepared by electrochemical reconstruction.Electrochemical tests showed that the NiFe/NiFeOOH core-shell heterogeneous NPs catalyst had excellent OER catalytic activity and stability.The density functional theory analysis explained that after the formation of NiFe/NiFeOOH heterostructure,the strong electronic interaction between NiFeand NiFeOOH reduced the binding strength of the reaction intermediate,enhanced the charge transfer and improved the OER kinetics.(2)Based on the preparation of NiFe/NiFeOOH core-shell heterojunction NPs,we have successfully obtained superparamagnetic NiFe/NiFeOOH core-shell heterojunction NPs through magnetic measurement.Through the application of AMF,benefiting to the magnetic heating effect related to the Néel relaxation,the superparamagnetic NiFe/NiFeOOH core-shell heterojunction NPs catalyst can significantly improve the OER performance under the AMF.This work not only demonstrates that construction of spatial confinment structures is an effective way to address the poor conductivity issue of amorphous transition metal hydroxy oxides,but also reveals that the magnetic heating effect related to the Néel relaxation is an effective approach to achieve stable performance improvement of ferromagnetic NP catalysts.