Synthesis Of Fe-based Nanostructures And Ni₃Se₂ For Water Electrolysis

The ever-growing global energy demand,accompanied by the exhaustion of traditional fossil fuels and infamous air pollution,has motivated researchers to seek sustainable,renewable,and effective clean energy and energy conversion technology.Hydrogen energy is widely considered as an ultimate form of green energy for its zero-emission and recyclable utilization.During the past decades,water electrolysis and photoelectrochemical water splitting for hydrogen production have achieved rapid development and made great progress.In this dissertation,by the design of efficient catalyst materials for hydrogen production technology as the starting point,we study the synthesis of several iron-based nanostructures and Ni₃Se₂ catalysts and the strategies to modulate their phase structure,morphology,and performance,to exploit their performances in the field of water photoelectrolysis and electrolysis.The research in this dissertation include the following parts:1.Dodecahedral α-Fe₂O₃ nanocrystals have been successfully prepared via a simple,cost-effective and diethylenetriamine-assisted chemical transformation strategy using the inorganic-organic hybrid Fe S-diethylenetriamine two dimensional（2D）nanosheets as the starting precursors.It is found that the presence of diethylenetriamine is mainly responsible for the formation of the dodecahedral α-Fe₂O₃.The dodecahedral α-Fe₂O₃ has good crystallinity,and provides {110} facets with relatively high photocatalytic activity.It displays the photocurrent density of 3.06 m A cm-2 at 1.600 V vs.RHE in 1.0 M KOH,which is four times of commercial α-Fe₂O₃（0.77 mA cm-2）.Moreover,the photocurrent density remains over a 10-h test.2.Two simple and effective solution-chemical methods have been developed to synthesized 2D porous γ-FeOOH nanosheets and 1D β-FeOOH nanorods.β-FeOOH/Ni shows better oxygen evolution reaction（OER）activity than γ-FeOOH/Ni owing to its unique tunnels.The overpotential of β-FeOOH/Ni is only 270 mV at 10 mA cm-2.And the overpotential is almost the same at 150 mA cm-2 for both β-FeOOH/Ni and Ru O2/Ni.The current density of 50 mA cm-2 remains more than 10 h for β-FeOOH/Ni.3.3D hierarchical Ni₃Se₂ nanoforest has been successfully grown on Ni foam via a facile one-step and cost-effective solution-chemical route.This handy strategy endues the product with three characteristics: metallic Ni₃Se₂,hydrophilic and aerophobic surface,as well as self-support on highly conductive substrate.The as-synthesized 3D hierarchical Ni₃Se₂ nanoforest/Ni foam shows excellent electrocatalytic activity and stability for both hydrogen evolution reaction（HER）and OER.The current density of 10 mA cm-2 only require 1.612 V for overall water electrolysis.It is stable for at least 140 h at 1.700 V vs.RHE.These results indicate it a promising bifunctional electrocatalyst for overall water splitting.