Morphological Modulation Of NiFe-based Catalyts With A Hollow Structure And Their Enhanced Performance In Oxygen Evolution Reaction

Renewable energy,such as wind and solar energy,is difficult to meet the urgent needs of the world for energy because of its intermittent shortcomings.People need to find effective solutions to solve the problem of energy shortage.Electrochemical water splitting into oxygen and hydrogen is an attractive and competitive approach due to its advantage of the acknowledged ecofriendly process with high pure hydrogen.The water splitting contains two half reactions:hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,both show high overpotential and low reaction rate because of sluggish reaction kinetics To promote the overall efficiency,noble metals（Pt）and precious metal oxides（RuO₂ and IrO₂）have been employed as the benchmark catalysts in HER and OER,respectively^[3].Despite their good performance for the water splitting,the large-scale applications face hurdles due to the scarcity and high cost.Therefore,it is of great desirable to develop highly effective non-precious metal-based catalysts for overall water splitting.In basic and near netural conditions,transition metals（Mn,Fe,Co,Ni）oxides and hydroxides display excellent performance.In particular,both Ni-and Fe-based hydroxides reveal very low overpotentials for OER.Recent studies have shown that NiFe-based oxides,nitrides and sulfides derived from NiFe hydroxides have very high activity for overall water splitting.In this paper,our research is mainly fouce on the design of NiFe-based oxides and sulfides.The wall of hollow polyhedron is composed of NiFe sulfides,NiFe oxides and NiFe alloy,which are wrapped into carbonitride shells.Importantly,the Ni_0.5Fe_0.5-HP and 23-S-FeNi@NC-3 hollow cuboctahedron show superior electrochemical OER activity in alkaline.Herein,a facile strategy by Fe-doping for tuning the growth rates of{111}and{100}facets was first proposed to modulate the morphologies of semi-crystalline Ni-coordinated complexes,and further template-engaged pyrolysis to build the unique hollow polyhedron with mesoporous wall,consisting of dominant metal（/alloys）,a small fraction of metal oxide and few-layer N-graphene shell(Ni_1-xFe_x-HP).Thanks to the structural and compositional features,Ni_1-xFe_x-HP present superior bifunctional properties for both HER and OER under alkaline conditions.In addition,the Ni_0.5Fe_0.5-HP are highly active for OER,which reaches the current density of 10 mA cm^-2 at a low overpotential of 280 mV.This work offers a new and time-saving strategy using semi-crystalline Ni-coordinated complexes instead of highly crystallized metal-organic frameworks as precursors to fabricate hollow and nanostructured hybrids.Despite the significant progress in the preparation of hollow structures,it is a challenge to build high-quality complex hollow structures with controllable morphology,particularly for multicomponent materials.Herein,a facile strategy wasfirst developed to tune the morphology of coordinated transition bimetal complexes via controlling the growth rates of{111}and{100}facets using sulfur as a morphological modulator and template-engaged pyrolysis to form a unique hollow polyhedron（S-FeNi@NC）.By virtue of the structural and compositional features,the optimized S-FeNi@NC hollow cuboctahedron shows excellent activities with a remarkably small overpotential of 272mV to reach 20 mA cm^-2,a lower Tafel slope with 84 mA dec^-1,and an excellent durability without degradation after 5000 CV cycles toward oxygen evolution reaction（OER）in an alkaline medium.The strategy developed here provides a new path to prepare hollow transition metal hybrids with a tunable polyhedral structure for catalysis and energy conversion.