Exploring the role of iron in Fe_(5)Ni_(4)S_(8)toward oxygen evolution through modulation of electronic orbital occupancy

Ni-Fe-based catalysts are considered to be among the most active catalysts for the oxygen evolution reaction(OER)under alkaline conditions,with Fe playing a crucial role.However,Fe leaching occurs during the reaction due to thermodynamic instability,which has resulted in conflicting reports within the literature regarding its role.To clarify this point,we propose a strategy consisting of modulating the electronic orbital occupancy to suppress the extensive loss of Fe atoms during the OER process.Theoretical calculations,in-situ X-ray photoelectron spectroscopy,molecular dynamics simulations,and a series of characterization showed that the stable presence of Fe not only accelerates the electron transfer process but also optimizes the reaction barriers of the oxygen evolution intermediates,promoting the phase transition of Fe_(5)Ni_(4)S_(8)to highly active catalytic species.The modulated Fe_(5)Ni_(4)S_(8)-based pre-catalysts exhibit improved OER activity and long-term durability.This study provides a novel perspective for understanding the role of Fe in the OER process.

Structure-catalytic functionality of size-facet-performance in pentlandite nanoparticles

As one of the pentlandites,Fe5Ni4S8(FNS) based materials have attracted increasing attention due to their excellent catalytic properties and promising applicability.The control over the catalyst surface structure often benefits its heterogeneous catalytic activity.However,this has not been investigated for FNS materials at the nanoscale regarding the catalytic activity related to high-index facets.Herein,FNS nanoparticles(FNSNPs) with enclosed continuous tunable high-index facets were prepared and studied to clarify the relationship between the structure and catalytic functionality.The results suggested strong dependence between exposed facets of FNSNPs and their sizes.The decline in the average size to5.8 nm led to enclosing by high-index facets(422) and(511) to yield optimal electrocatalytic activities toward the hydrogen evolution reaction.The catalytic activity of FNSNPs was closely related to the surface energy of the main exposed facets.These findings clarified the relationship between high-index-facet and high-surface-energy FNSNPs,as promising approaches in crystal surface control engineering.

Enhanced reconstruction of Fe_(5)Ni_(4)S_(8) by implanting pyrrolidone to unlock efficient oxygen evolution

During oxygen evolution reaction(OER),complex changes have been reported on surfaces of bimetallic Fe-Ni-based catalysts,and regulating the dynamic evolution could improve their electrocatalytic performances.Herein,a pyrrolidone-promoted reconstruction of pentlandite was investigated to uncover the correlation between the reconstructed surface and the OER performance.The theoretical calculations indicated the preferential implantation of pyrrolidone at Fe atoms,useful for regulating the electronic structures of pentlandite.The vale nce state of Ni increased,suggesting the promotion of the in-situ reconstruction of pentlandite via strengthening hydroxyl adsorption to generate highly active NiOOH.The electron-rich pentlandite was also found conducive to charge transfer under applied voltages.The Operando Raman and various quasi-in-situ characterizations confirmed the realization of more delocalized electronic structures of pentlandite by introducing pyrrolidone.This,in turn,promoted the accumulation of hydroxyl groups on the pentlandite surface,thereby boosting the formation of highly active NiOOH at lower OER potentials.Consequently,the adsorption energies of intermediates were optimized,conducive to enhanced OER reaction kinetics.As a proof of concept,the pentlandite decorated by pyrrolidone exhibited an overpotential as low as 265 mV at 10 mA cm^(-2) coupled with stable catalysis for 1000 hours at a high current density of 100 mA cm^(-2).In sum,new insights into unlocking the high catalytic activity of bimetallic Fe-Ni-based catalysts were provided,promising for future synthesis of advanced catalysts.