Regulation Of Defects Trigger High-efficiency Hydrogen Evolution Of Molybdenum-based Electrocatalysts

“Green hydrogen energy”means no carbon emissions produced in the process of hydrogen energy production,transportation,and utilization.Among them,electrocatalytic hydrogen evolution plays a key role.Unfortunately,it is difficult to the large-scale implementation due to the scarcity of traditional platinum-based catalysts.Molybdenum sulfide（MoS₂）has attracted much attention for electrocatalytic hydrogen evolution reaction（HER）due to their active edge sites with adsorption free energy of hydrogen atom（ΔG_H）close to platinum（Pt）.Because of poor edge sites and insufficient electrical conductivity,efficient HER performance is hard to be obtained for MoS₂.Based on this fact,edge sites and basal plane sites of MoS₂can be fully employed for HER by defect engineering and heteroatoms doping strategy in this paper.The details are summarized as follows:In a first study,defect-rich O-MoS₂slabs densely-coated highly crystallized CoS₂microspheres(CoS₂@O-MoS_2-x/CC-0.13)by a one-pot hydrothermal strategy.Abundant S-vacancies can be modulated into the basal planes of MoS₂by a one-pot incorporating-assisted compositing strategy.Atomic disordered structure and abundant edge sites can be introduced on the surface of MoS₂nanosheets by O incorporating.Meanwhile,exposed Mo atoms（EMAs）from S-vacancies can be designed as newborn catalytic sites and activate the inert base plane of MoS₂.Therefore,compared with CoS₂/CC and O-MOS₂/CC,CoS₂@O-MoS_2-x-0.13 exhibits enhanced HER performance with an overpotential of 143 mV at 100 mA cm^-2.In a second study,to explore the relationship between the S vacancy concentration and the catalytic HER performance of MoS₂,the theoretical numbers of exposed Mo sites(N_EMAs)and their adsorption free energy of hydrogen atom（ΔG_H）were obtained at various C_S-vacanciesby DFT calculated.As a result,with the increase of C_S-vacancies,theΔG_Hdecreased significantly while N_EMAsincreased.Obviously,a balance between the intrinsic activity of EMAs and N_EMAscan be realized at the optimal C_S-vacancies.Subsequently,we have demonstrated a novel one-pot incorporating-assisted compositing strategy to realize fine-tuning S-vacancies concentration(C_S-vacancies)of MoS₂-based electrocatalysts with the range from 0%to21.54%.Thus,with C_S-vacanciesof 13.27%,CoS₂@O-MoS_2-x-0.15 exhibit superior HER activity with an overpotential of 154 mV at 100 mA cm^-2,owning to abundant and highly active EMAs.Based on the theoretical and experimental results,we explore the relationship of both CS-vacancies and HER performance of MoS₂ by EMAs.Boosting highly active EMAs is the key factor to unlock the potential of inert basal planes in MoS₂for efficient hydrogen evolution.In a third study,in order to explore the influence of doping and defect engineering on catalytic performance,Se doping and H₂O₂etching strategy were firstly carried out for MoS₂nanosheets,respectively.As a result,after Se doping,the lattice distortion degree and electron density can be enhanced for MoS₂,which facilitates the kinetics of hydrogen evolution.Meanwhile,the number of active sites on the basal plane can be slightly increased by H₂O₂etching strategy.Subsequently,after Se doping and H₂O₂,SeM-0.2-120 not only inherited the excellent hydrogen evolution kinetics but also possessed abundant catalytic active sites on the basal planes of MoS₂.Thus,SeM-0.2-120 exhibits excellent HER activity with an overpotential of 200 mV at 200 mA cm^-2.