Preparation And Electrocatalytic Properties Of MOF And Its Derived Sulfides And Phosphates

Electrocatalytic water splitting is an international frontier and hotspot in the field of green hydrogen energy.The hydrogen evolution reaction and oxygen evolution reaction of commercial electrocatalytic water splitting are catalyzed by precious metals such as Pt,RuO₂ and IrO₂.The high cost,high overpotential and low efficiency of catalyst have become the technical bottleneck restricting electrocatalytic hydrogen production.The development of efficient and low-cost non-noble metal based electrocatalysts has scientific significance and engineering value.To solve these problems,this thesis takes metal organic framework materials（MOFs）and their derived sulfide and phosphides as the research object.Through the regulation of their microstructure and electronic structure,transition metal sulfide and phosphide catalysts with unique nanostructure and high catalytic activity are prepared.The main research contents and conclusions are as follows.1.Chromium-doped nickel based MOF was sybthesized by simple hydrothermal method,and chromium-doped nickel disulfide particles（Cr-NiS₂/C）were prepared by subsequent dry-sulfidation.The Cr doped nickel disulfide particals composited with carbon nanotubes（Cr-NiS₂/C@CNT）and chromium doped nickel disulfide nanosheet arrays grown on nickel foam（Cr-NiS₂/C@NF）were also prepared.The results show that compared with Cr-NiS₂/C,the performance of Cr-NiS₂/C@CNT and Cr-NiS₂/C@NF have been significantly improved.Among them,Cr-NiS₂/C@NF is the most excellent.At the current density of 10 mA/cm~2,the overpotential of Cr-NiS₂/C@NF is 207 mV,while the Tafel slope is 43 mV/dec.In addition,the specially designed non in-suit Raman spectroscopy method was used to reveal the surface evolution in different reaction stages.An irreversible self-reconstruction from Cr-doped NiS₂ to Cr,S co-doped Ni（OH）₂followed by a reversible transformation into NiOOH is observed in cyclic voltammetry processes,indicating that NiS₂ plays a key role as pre-catalyst to generate highly active sites for electrocatalytic water oxidation.2.Using MIL-88（FeNi）MOF and carbon nanotubes as precursors,carbon nanotubes-interconnected heterostructural FeP/Ni₂P nanospindles was prepared by hydrothermal,annealing and phosphating treatment.Rearch shows that P-Ni Fe@CNT showed excellent OER performance in alkaline electrolyte.At a current density of 10mA/cm~2,the overpotential is 240 mV and the Tafel slope is 69.96 mV/dec,which is better than most transition metal phosphide catalysts reported.At the same time,there was no significant performance degradation in the 40-hours stability test.Its excellent OER performance is mainly due to the effective charge transfer via electronic structure modulation in FeP/Ni₂P heterostructure,superior electrical conductivity of existing CNTs network,inevitable active catalytic sites exposure by ultrafine FeP/Ni₂P heterostructural-nanoparticles（～10 nm）,and the porous nanostructure facilitated gas bubbles release.3.Using MIL-88（FeNi）MOF and graphene oxide nanosheets as precursor,double-shelled hollow bimetallic phosphide nanospheres anchored on nitrogen-doped graphene（Ni Fe-P@GNS）was prepared by hydrothermal and phosphating processes.Then HER and OER performances in 1 MKOH solution were investigated.Research shows the overpotential at 10 mA/cm~2 for OER and HER of Ni Fe-P@GNS are only 211 mV and175 mV repectively,and the Tafel slope are 43 mV/dec and 57 mV/dec respectively.The overall performance is better than that of single metal samples,and it is also better than benchmark catalyst RuO₂ in OER.In terms of overall water splitting,NiFe-P@GNS only required 1.578 V to drive a current density of 10 mA/cm~2.The excellent electrocatalytic performance is mainly due to the stable double shell hollow structure,the electronic structure advantages of bimetallic phosphides,and the nitrogen doped graphene nanosheets promote the charge transfer.