Study On The Optimization Strategy Of Molybdenum Disulfide Electrocatalysts For Hydrogen Evolution Reaction

Hydrogen is a critical chemical reagent and energy carrier,but it is currently produced using fossil fuels,which are scarce and release harmful CO2.The development of new,sustainable hydrogen production methods is a major scientific challenge.A potential method for producing renewable hydrogen is electrochemical water splitting,which converts H2O into H2 and O2.In order for this technology to be extensively used,efficient,low-cost,stable,and scalable electrochemical water splitting materials must be developed.Creating active catalysts with abundant active sites,and low kinetic energy barrier especially important barriers to overcome.In recent years,molybdenum disulfide(MoS2),a transition metal sulfide with excellent catalytic performance for hydrogen evolution reaction(HER)and the advantages of abundant supply and low cost,has become a research hotspot.However,because MoS2 has a small number of catalytically active sites and is a semiconductor with low conductivity,it still falls short of the Pt group in terms of performance.Electrocatalytic active sites along the Mo-terminated edge of MoS2 are responsible for the promising HER activity but poor electrical convey,and scarcity of active sites may inhibit its electrocatalytic performance.Therefore,enhancing the electronic conductivity and increasing the active sites in basal plane are required to realize more efficient HER activity for layered MoS2.In addition,sulfur vacancy(SV)engineering is an evolving approach to improve the performance of MoS2 and metal sulfides for HER;however,a simple and universal method for creating SV is still missing;thus,the catalytic role of SV in elemental steps of HER remains unclear.First,by the incorporation of heterophase(tin disulfide)SnS2 quantum dots into the basal plane to form atomic-level heterostructure,I report the enhanced HER activity from MoS2 with current density(i)of-10 mA·cm-2 at a lowered overpotential of 240 mV.Structural characterization and electrochemical studies reveal the incorporation of heterophase SnS2 quantum dots can efficaciously realize the disorder engineering in the atomic level to regulate the electronic structure,optimize the energy barrier of hydrogen adsorption/desorption,and proliferate the catalytic active sites density,thus activating the basal plane of MoS2 for HER.Density functional theory(DFT)calculation reveals the inception of the improved electrocatalytic activity stemmed from an astronomically immense reduction of the kinetic energy barrier of hydrogen adsorption on and desorption from sulfur sites and SVs in the basal plane upon SnS2 incorporation and Sn doping.My efforts next to develop a facial hydrothermal process employing hydrochloride acid as the sulfur etching agent to synthesize high-performance surface SVs engineered MoS2 electrocatalysts.Surface vacancy-engineered MoS2 shows a 32-fold enhancement in HER compared to pristine MoS2,owing to the promoted desorption of hydrogen atoms.This strategy is also applicable for the development of other metal sulfides.Vacancy-engineered CoMoS2 displays a η10mA of-0.23 V vs the reversible hydrogen electrode(RHE)and outperforms the Pt electrode at high current density owing to the optimized desorption of hydrogen.Furthermore,electrochemical impedance spectroscopy(EIS)is employed to investigate the promotional mechanisms of surface SVs in MoS2.The impedance determined data indicates that a low concentration of surface SV is enough to optimize the charge transfer process,whereas populated surface SV promotes the desorption of hydrogen atoms.My findings reveals that the SVs are effective even at low surface coverages of hydrogen atoms,thus preventing accumulation of hydrogen atoms and eventually the poisoning effect.Finally,challenges and prospects in electrochemistry have been presented on oxygen evolution reaction(OER),nitrogen reduction reaction(NRR)and lithium sulfur batteries(LiSBs)in the field energy conversion and storage.Noble metals are the best electrocatalysts,however,associated issues such as high cost and low abundance hinder the commercialization of technology.Although improvements have been made to reduce noble metal loading through the modification of material compositions and morphologies or through the replacement of noble metals with non-noble metal-based catalysts,significant progresses have been insufficient.In summary,this dissertation covers fundamental studies of MoS2-HER catalysts along with promotional HER mechanism through SVs and challenges and prospects in electrochemistry for OER,NRR and LiSBs.