Study Of Nickel Selenides And Tellurides As Electrocatalysts For Oxygen Evolution Reaction

Hydrogen is regarded as one of the most potential candidates of clean and renewable energy to replace traditional fuels.Water electrolysis for hydrogen production technology is the most effective way for converting electricity into hydrogen carrier for storage.However,the efficiency of water electrolysis is greatly limited by the slow kinetics of the oxygen evolution reaction（OER）because it involves a multistep four-electron process leading to high overpotential for the whole water splitting.Up to date,precious metal oxides（RuO₂ and IrO₂）exhibit benchmark electrocatalytic activity toward OER to overcome the large overpotential.But the low abundance,expensive prices,and poor stability hinder their widespread practical applications.Consequently,the investigation for efficient and inexpensive earth-abundant transition metal electrocatalysts for OER is still urgently required.In this work,Ni-based selenides and tellurides and their composites are studied as electrocatalysts for OER.One-step hydrothermal method was developed for the synthesis of a series of nickel selenides（NiSe,NiSe₂ and Ni₃Se₂）and their multiwalled carbon nanotubes（MWCNTs）nanocomposites.The NiTe grown on nickel-foam were also prepared by hydrothermal method.The structure-related oxygen evolution performance of the catalysts was systematically studied.The thesis mainly studies the following three aspects:（1）NiSe,NiSe₂ and Ni₃Se₂ catalysts were prepared by a simple one-step hydrothermal method.The influence of the chemical composition,crystal structure,particle size and distribution on the electrocatalytic activity were investigated.The results show that among the NiSe,NiSe₂ and Ni₃Se₂ catalysts,NiSe has the highest activity,exhibiting an overpotential of 389 mV to reach 10 mA/cm².The Tafel slope of electrocatalyst is only 93 mV/dec.The better electrocatalytic activity of NiSe should be ascribed to the increased number of active sites due to the smaller grain size and the enhanced cumulative 3d-2p repulsion.（2）In order to further improve the performance of NiSe catalyst,NiSe/MWCNTs nanocomposites were synthesized by a simple one-step hydrothermal synthesis where MWCNTs were added during the synthesis.The effect of MWCNTs content on the OER performance of NiSe/MWCNTs was studied.The results show that the OER performance of the NiSe/MWCNTs composites is significantly improved compared with the NiSe sample and the sample of the physical mixed NiSe and MWCNTTs.NiSe/MWCNTs with 20 wt%MWCNTs exhibits the best OER activity with an overpotential of 336 mV to reach 10 mA/cm².The Tafel slope of electrocatalyst is only 78 mV/dec.The addition of MWCNTs not only introduces an abundance of nucleation sites resulting in small particle sizes of NiSe crystals,but also improves the dispersion of NiSe nanoparticles.In addition,the porous and conductive MWCNTs facilitate the electronic transmission and electrolyte penetration.（3）A new strategy for the construction of a three-dimensional nanostructured NiTe and nickel-foam（NiTe/NF）composites was developed.The morphology of NiTe was controlled by adjusting the reaction temperature of hydrothermal synthesis.The NiTe/NF composites with NiTe particles,rods,and plates were synthesized.The effects of different structures and morphologies on the catalytic performance were investigated.The results show that the NiTe/NF composites with the presence of NiTe and Ni_10.35Te_7.79 mixed phases synthesized at 210°C has the best catalytic performance with an overpotential of 295 mV to achieve 50 mA/cm².This 3D porous structure has good electrical conductivity and provides abundant active sites.This unique structure is responsible for the superior catalytic activity toward OER.