Synthesis and Electro/photoelectrocatalytic Properties of Two-dimensional Tin-Based Nanomaterials

Author:Liu Guang Bo

Supervisor:li zhong hua hu ping an


Degree Year:2019





Recently,with the rise of two-dimensional(2D)nanomaterials,2D tin-based nanomaterials(e.g.SnS2 and SnO2 etc.)as an important branch of 2D nanomaterials family have attracted extensive attention due to their fascinating physicoche mical properties,earth-abundant resources and environmentally-friendly features.Nowadays,2D tin-based nanomaterials,especially SnS2 and SnO2 have gained substantial developments and showed great application prospect in the field of energy storage and conversion.Nonetheless,the current and electro/photoelectrocatal ytic performances of both 2D SnS2 and SnO2 nanomaterials are still not satisfactory.Also,the controlled synthesis and morphology or structure regulation of SnS2 and SnO2nanomaterials are confronted with great challenges.In this regard,to optimize their structure and performances,we target on the design and synthesis of 2D SnS2 and SnO2 nanomaterials with desired morphologies and structures based on the analysis of the key factors that restrict their electro/photoelectrocatalytic performances.By doing so,we aim to realize the morphology and structure regulation and performa nce optimization of 2D SnS2 and SnO2 nanomaterials,and thus further promote their applications in energy storage and conversion.As is known that for 2D nanomaterial based photoelectrodes fabricated by conventional methods,the poor light absorption and low photon-generated carrier separation/transfer efficiency are the main restricting factors on the photoelectrochemical(PEC)water splitting performances.To overcome such drawbacks,we successfully synthesized in large scale high quality vertically aligned2D SnS2 nanosheet arrays on FTO(SnS2⊥FTO)and CC(SnS2⊥CC)substrates with different densities through chemical vapor deposition(CVD)method.Such novel structures overcome the disadvantages within the conventional photoelectro des,through establishing good electrical contact with the conductive substrates,leading to much enhanced light absorption for the catalysts and large exposed surface area for the catalytic reactions.PEC tests show that these vertically aligned 2D SnS2 nanoshee t photoelectrodes exhibit a high photocurrent density of up to 1.73 mA/cm2 for SnS2⊥FTO and 1.92 mA/cm2 for SnS2⊥CC at 1.4 V vs.reversible hydrogen electrode(RHE),and a high incident photon to current conversion efficiency(IPCE)of up to36.76%for SnS2⊥FTO and 40.57%for SnS2⊥CC at 360 nm,much better than that of counterpart photoelectrode(SnS2//FTO)prepared by conventional spin-coating method.This strategy offers a versatile framework towards the design and fabrication of high performance PEC photoelectrodes based on 2D nanomaterials.The study of SnS2 for hydrogen evolution reaction(HER)has been progressing slowly due to the lack of active sites and poor conductivity up to now.To improve the electrocatalytic HER activites of 2D SnS2 nanosheets,we successfully design and fabricate defect-rich SnS2 nanosheets decorated with trace amount of Pt(0.37wt%)via in-situ electrochemical activation,and thus simultaneously optimizing both their active sites and conductivity.Electrocatalytic HER study shows that,compared with pristine SnS2 nanosheets,defect-rich SnS2 nanosheets decorated with trace amount(0.37 wt%)of Pt exhibit greatly enhanced HER activity due to the synergistic effect between the Pt nanoparticles and the defect-rich structures—low onset potential of32 mV and overpotential of 117 mV at 10 mA/cm2,small Tafel slope of 69 mV/dec,and large exchange current density of 394.46μA/cm2.This study offers new perspective and strategy for the design and fabrication of cheap and earth-abunda nt high performance HER electrocatalysts.In the field of electrocatalytic CO2 reduction reaction(CO2RR),increasing the electrical conductivity and the numbers of accessible activity sites of the catalyst are the basic principles for designing and preparing efficient CO2RR electrocatalys ts.However,how to increase the numbers of activity sites and retain the high conductivity for CO2RR electrocatalysts remains a great challenge.Here,pristine SnO2 and oxygen vacancies dominated SnO2(VO-SnO2)nanosheets are successfull y designed and synthesized by using SnS2 nanosheets as the precursor,which leads to the simultaneous regulation of both their structure and properties,and enhanced reaction kinetics for CO2RR.Electrochemical measurements demonstrate that,compared with pristine SnO2 nanosheets,VO-SnO2 nanosheets exhibit much superior CO2RR to formate performacnes with a high formate faradaic efficiency(FE)of 69.2%with the lowest overpotential of only 210 mV,a maximum formate FE value of 92.4%with an overpotential of 510 mV,and stable FE for formate of 90±2%in the large potential range of-0.6 to-1.1 V vs.RHE.Theoretical calculations show that oxyge n vacancies in the VO-SnO2 nanosheets lowered the free energy barrier by 0.12 eV during CO2RR,thus facilitating the electrocatalytic CO2RR and promoting the reaction activitiy and selectivity for formate.This work uncovers the correlation between oxygen vacancies and structure-activity relationship of electrocatalys ts,offering helpful guidances for designing high efficient and stable CO2RR electrocatalysts.