Electronic Structure Regulation and Hydrogen Evolution Kinetic Study of Two-Dimensional Nanomaterials

Author:Zhou Gang

Supervisor:wu xing long


Degree Year:2019





Two-dimensional nanomaterials have been extensively applied in catalytic production of hydrogen energy due to their unique physical properties.However,the low intrinsic catalytic efficiencies limit the practical applications of these nanomaterials.In this thesis,half-metallicity,semiconductor-metal phase transition and specific vacancy introduction were utilized to regulate the electronic band structures of two-dimensional nanomaterials in aim to improve the electron transmission rate,increase the active sites and reduce the activation energy,finally resulting in the excellent catalytic activity for hydrogen evolution.The results obtained are described as follows:1.Photocatalytic hydrogen evolution from water has triggered intensive research interests for metal-free semiconducting photocatalysts.However,traditional semiconducting materials suffer from limited hydrogen evolution efficiency due to low intrinsic electron mobility,rapid recombination of photogenerated carriers and lack of artificial microstructure design.We design and prepare a metal-free half-metallic carbon nitride nanosheets for highly efficient photocatalytic hydrogen evolution.The introduced half-metallic features not only facilitate well carrier transfer but also provide more active sites for hydrogen evolution reaction.The nanosheets incorporated into a micro grid mode resonance structure via in-situ pyrolysis of ionic liquid,which show further enhanced photoelectronic coupling and entire solar energy exploitation,boosts the hydrogen evolution rate up to 1009μmol g-1h-1.Our findings propose a strategy for micro-structural regulations of half-metallic carbon nitride material and meanwhile provide inspirations for the steering of electron transfer and solar energy absorption in electrocatalysis,photoelectrocatalysis and photovoltaic cells.2.Hydrogen production by water splitting with electrochemical/photoelectrochemical techniques relies mainly on fresh water which only represents 7%of the total water resource in the world.The difficulty with performing seawater splitting arises from the complex seawater composition and environment,but from the viewpoint of better utilization of natural resources,it is highly desirable to conduct the hydrogen evolution reaction(HER)in seawater.Herein,we design and prepare few-layer heterostructured ReS2 nanosheets with the lateral metallic T and semiconducting Td phase interface,in which cationic vacancies are intentionally introduced as active sites.The ReS2 nanosheets respond to the whole spectrum of visible light and produce hydrogen from seawater efficiently.Theoretical calculation and experiments indicate that the cationic vacancies are favorable to H+ adsorption because H+ has the lowest adsorption energy compared to other cations in seawater.The nanosheets show stable HER performance for over 12 h in a wide range of salinity.This effective strategy to produce hydrogen from seawater may be extended to other 2D materials to accomplish highly efficient hydrogen evolution from seawater.3.The exploitation of stable and earth-abundant electrocatalyst with high catalytic activity remains a significant challenge for hydrogen evolution reaction.Different from complex nanostructural design,this work focuses on a simple and feasible way to improve hydrogen evolution reaction performance via manipulation of intrinsic physical properties of the material.We present an interesting semiconductor-metal phase transition in ultrathin troilite FeS nanosheets triggered by near infrared radiation at near room temperature for the first time.The photogenerated metal-phase FeS nanosheets demonstrate intrinsically high catalytic activity and fast carrier transfer for hydrogen evolution reaction,leading to an overpotential of 142 mV at 10 mA cm-2 and a lower Tafel slope of 36.9 mV per decade.