Synthesis Of Ni-based Electrocatalysts And Its Application In Water Splitting

Insufficient fossil fuel reserves coupled with environmental pollution have stimulated a large number of efforts to find renewable energy to replace traditional fossil fuels.Hydrogen with high gravimetric energy density,environmental friendliness,and renewability features,has gained much attention for future renewable energy demands.Industrially profitable water electrolysis is one of the most promising technologies for the large-scale production of high purity hydrogen.The full water splitting reaction contains two half-reactions:hydrogen evolution reaction(HER)on the cathode and oxygen evolution reaction(OER)on the anode,both OER and HER are thermodynamically uphill reactions.Furthermore,the OER involves a complicated four-electron transfer process,which is restricted by intrinsically sluggish kinetics.Consequently,it is essential to develop high-performance catalysts with long-term durability for HER,OER,and overall water splitting(OWS).In this thesis,Ni-based electrocatalysts were selected as study subjects,several synthesis strategies has been successfully designed for improve and optimize its performance.The main contents in this thesis are listed as follows:(1)Ru-NiFe-MOF/NF was prepared by a simple hydrothermal method,the as-prepared Ru-NiFe-MOF/NF electrode shows excellent OER activities at 10 m A·cm^-2with an overpotential of 205 m V,an ultralow Tafel slope of 50 m V·dec^-1,and excellent electrochemical stability over 100 h in 1.0 M KOH electrolyte.(2)Ru doped NiFe bimetallic phosphide derived from 2D MOF nanosheets was developed via a continuous two-step hydrothermal followed by phosphorization process.The as-prepared Ru-NiFe P/NF exhibits excellent catalytic for HER,which only requires overpotentials of 29,105,and 56 m V to afford current density of 10 m A·cm^-2in acid,neutral,and alkaline media,respectively.For the OER,Ru-NiFe P/NF exhibits an ultra low overpotential of 179 m V at 10 m A·cm^-2in alkaline solutions.Specifically,when assembled as anode and cathode simultaneously,the water electrolyzer requires a cell voltage of 1.47 V to achieve the current density of 10 m A·cm^-2with 100%faradic efficiency.(3)A series of vanadium doped NiCo bimetallic phosphides were in situ grown on carbon fiber paper substrate via a successive hydrothermal and phosphorization treatment,which were denoted as V_x-NiCo P/CFP(x=0,10,15,20%).The resulting V₁₅-NiCo P/CFP exhibits excellent HER electroactivity over a wide p H range.The optimized V₁₅-NiCo P/CFP electrode exhibits super low overpotentials of 52.4?85.3,and 46.5m V to achieve a cathodic current density of 10 m A·cm^-2in acid,neutral,and alkaline conditions,respectively.(4)A facile two-step hydrothermal reaction followed by electrodeposition method were designed for the synthetise of NiFe-LDH integration with Co Fe chalcogenides to construct heterostructures.The resulting NiFe-Co Fe₂O₄@Co₃S₄/CFP(denoted as NiFe-CFS/CFP)exhibits admirable OER catalytic activity,which only needs overpotential of 233.3 and 244.0m V to reach the current density of 50 and 100 m A·cm^-2,respectively.When employed as both the cathode and anode for overall water splitting,the NiFe-CFS/CFP electrolyzer only needs a cell voltage as low as 1.53 V to reach a current density of 10 m A·cm^-2.