Enhancing Electrocatalytic Hydrogen Evolution Reaction Performance Of Confined NiSe_2-x Nanoparticles By Alternating Magnetic Fields

Driven by the goal of carbon peaking and carbon neutrality,hydrogen energy is considered the best secondary energy source to replace traditional fossil fuels due to its clean,non-polluting,efficient and sustainable characteristics.While conventional fossil fuel-based hydrogen production is very well established,the consequent problem of large carbon emissions indicates that this technology is ultimately undesirable.Therefore,clean and efficient hydrogen production technologies need to be developed.Alkaline electrolytic water hydrogen production technology is widely used for industrial-scale hydrogen production due to the high purity of the hydrogen produced and the simplicity as well as the reliability of the process.However,the high cost of alkaline electrolytic hydrogen production compared to conventional hydrogen production techniques has prompted researchers to develop cheaper and more efficient electrocatalysts.Transition-metal dichalcogenides（TMDs）represented by NiSe₂ have received a lot of attention from researchers because of their low cost,abundant reserves and good stability in alkaline media.The preparation of NiSe₂ into ultra-small monodispersed nanoparticles（NPs）can greatly utilize its catalysis active site,however,its hydrogen evolution reaction（HER）activity is still unsatisfactory.The conventional modulation strategies have limited scope for enhancing the HER activity,and how to break the bottleneck of HER activity increase for TMDs materials has become one of the most challenging tasks at present.Besides the conventional strategy of modulating the catalyst itself,the introduction of external fields in the HER process has become a promising new strategy in electrocatalysis.It has been shown that an external alternating magnetic field（AMF）can significantly enhance the catalytic performance of magnetic NPs electrocatalysts through the magnetic heating effect.However,there are still two pressing issues when applying this strategy to alkaline electrolytic hydrogen production by TMDs materials.（1）The magnetic heating effect at the nanoscale under AMF is limited to room temperature ferromagnetic materials,whereas most TMDs materials are paramagnetic at room temperature and have a negligible response to external AMF.（2）Localised heating of the electrocatalyst may lead to agglomeration or even falloff of the magnetic NPs,resulting in performance degradation.To address these two issues,four methods to modulate the magnetic properties of TMDs are exemplified in this work,and the paramagnetic NiSe₂ at room temperature is successfully modulated to the ferromagnetic NiSe_2-X by simple vacancy engineering.Subsequently,according to the heating mechanism of magnetic NPs under AMF,we proposed a feasible design method to confine ultra-small monodisperse NiSe_2-X NPs in an amorphous carbon substrate,and successfully prepared them by pulsed laser deposition combined with rapid thermal annealing treatment.Under the AMF,the spin-flip of the magnetic domains of the confined NiSe_2-X NPs generates magnetic heating associated with Néel relaxation,which achieves rapid local heating of NiSe_2-X NPs electrocatalysts and greatly enhances the HER activity（the current density under the AMF increases significantly by about400%in the j-t test at-180 m V）,and the confined structure of NiSe_2-X NPs ensures their ultra-high stability under the AMF.This paper provides a new idea for the preparation of ultra-small monodispersed NPs electrocatalysts that can be used to rapidly increase the activity by AMF,which is important for accelerating the production of hydrogen energy.