Preparation Of Transition Metal Sulfide Composites And Their Performance For Water Electrolysis

The large amount of greenhouse gas emissions caused by over-exploitation and utilization of fossil energy has become the main cause of global warming.From the perspective of energy evolution,it is a general trend to replace traditional energy with new and clean energy.Hydrogen is a promising renewable energy source.So far,the output of electrochemical water splitting to produce hydrogen has only accounted for 4%of the total global output.This is mainly because electrochemical water splitting requires sufficient electric potential to promote the reaction.At present,the most effective catalysts for electrochemical water splitting are the noble metals Pt,Ir O₂ and Ru O₂.However,due to scarcity and high cost,the large-scale application of these precious metals has been severely restricted.Therefore,it is necessary to find high-performance catalysts to improve the efficiency of electrochemical water splitting to produce hydrogen.Due to its superior performance and low price,nickel-based composite materials have become a hot object of extensive research by scientific researchers.In this thesis,iron-doped rod-shaped nickel sulfide(Fe-Ni₃S₂@Fe Ni₃)was prepared on Fe Ni₃ foam substrate by one-step hydrothermal method for electrolysis of urea and electrocatalytic water splitting in electrolyte solutions of different p H.Fe Ni₃ foam not only provides a strong 3D framework structure,but also provides Fe elements for the preparation of the catalyst,reducing the use of reagents,thereby avoiding environmental pollution.Fe-Ni₃S₂@Fe Ni₃has excellent catalytic activity in acidic,alkaline and neutral solutions.It can promote the hydrogen evolution reaction and oxygen evolution reaction with a small overpotential,and has a catalytic activity comparable to precious metal catalysts.In addition,Fe-Ni₃S₂@Fe Ni₃also has excellent catalytic stability and can stably carry out a 40-hour catalytic reaction in different electrolyte solutions.Among them,the Fe-Ni₃S₂ nanorods are closely connected to each other,which greatly promotes the rapid transfer of electrons;the regular rod-shaped array exposes a large number of active sites,thereby improving the catalytic activity of catalyst;the doping of a small amount of Fe has a great contribution to the catalytic performance;a small amount of Fe doping adjusts the electronic structure of Ni₃S₂,improves the conductivity of the catalyst,and generates more active sites;Fe-Ni₃S₂ grows directly on the Fe Ni₃ foam and completely covers the Fe Ni₃ foam,which can prevent the3D framework from being corroded during the catalysis process,thereby prolonging the service life of the catalyst.In addition,cobalt-based composite materials are also the potential hotspot materials for electrocatalysis.In this paper,flower-like molybdenum sulfide and cobalt sulfide composite nanosheet arrays(Mo₃S₄/Co_1-xS@CF)was synthesized on cobalt foil(CF)by one-step hydrothermal method.Mo₃S₄/Co_1-xS@CF has excellent catalytic activity and catalytic stability in acidic,neutral and alkaline electrolyte solutions.The three-dimensional network thin layer structure of Mo₃S₄/Co_1-xS not only promotes the rapid transmission of electrons,but also provides a large number of active sites.In addition,the flower-like nanosheet array gives it high hydrophilicity,which not only increases the contact area of the catalyst but also promotes the release of gas,thereby improving the performance of the catalyst.