Research On The Microstructures And Activities Of Fe/Ni Sulfide OER Electrocatalysts

Electrocatalysts can convert electrical energy into hydrogen energy at a low overpotential,leading to the possibility of green preparation of hydrogen using renewable energy electricity.Due to the four electron transfer processes and a variety of intermediates involved,the anode oxygen evolution reaction(OER)is considered to be the decisive factor affecting the voltage required for electrocatalytic water splitting.At present,except for the commercial expensive noble-metal-based OER catalysts,transition metal-based OER catalysts are generally faced with problems such as insufficient stability and unclear performance attribution.In this thesis,with iron-nickel sulfide as the main research object,aiming at an overall optimization of the catalytic activity and stability,nickel disulfide/iron disulfide systems with different microstructures were constructed,and the effects of heterogeneous doping,crystal facet exposure and heterogeneous interface on catalytic properties were well studied,thus obtaining high-performance catalysts as well as achieving accurate attribution of the OER activities.The cubic crystals of nickel disulfide,which have surface iron doping and low-indexfacet exposure were constructed,realizing the dual regulation of electrocatalytic activity and stability.With Fe3+ as both the facet-controlling agent and the dopant,the Fe doped NiS2 cubes with exposed {001} facets were synthesized by a one-step hydrothermal method.Under OER conditions,the Fe-rich surface is converted in situ into active Fe/NiOOH,while the low-index crystal facets remained from the bulk by further oxidation results in high OER activity and stability of the catalyst.With current density of 10 mA/cm2,the overpotential required is only 277 mV and can be maintained for over 20 h.This work focuses on the effects of the spatial distribution of iron dopants and the specific lattice orientation on the activity and stability of iron-nickel sulfides,and provides a method without specific capping agents.The gradient core-shell FeS2@NiS2 was designed and prepared,realizing the vector distribution and efficient synergy of different active sites.Generally,different OER intermediates have special requirements for the reaction sites.Based on the different nucleus dynamics of FeS2 and NiS2,the FeS2@NiS2 core shell structure was obtained by controlling the concentration of precursors,in which the iron content decreases and the nickel content inversely increases from the interior to the surface,respectively.With the current density of 10 mAcm-2,the required overpotential is only 238 mV and a long-term stability test over 80 h was realized.By comparing the catalytic properties of the FeS2@NiS2 core-shell structure,NiS2@FeS2 core-shell structure and FeS2&NiS2 hybrid structure,the relationship between the elemental gradient and the catalytic properties was demonstrated.Mesoporous single crystal NiS2 with FeS on the pore walls was constructed to expose sufficient active heterogeneous interfaces.By introducing FeS clusters and NiSx crystalline nucleus sites on the silica template,and using Fe3+ as both the morphology controlling-agent and the dopant,the mesoporous single crystal NiS2 with FeS modified pores was obtained.This leads to the iron doping,and the exposure of both low indexfacets and a large number of FeS-NiS2 heterogeneous interfaces.With the current density of 10 mAcm-2,the required overpotential was only 236 mV and could be maintained for over 20 h.By comparing the catalytic properties of the resulting catalyst with other reference samples,the unique advantages of heterogeneous interfaces in promoting OER activity were demonstrated.