Study On Single-Atom Defect Design And Electrocatalytic Water Splitting Performance Of Two-Dimensional MoS₂

With the traditional fossil fuel shortage and environmental pollution issues turning substantially serious,the development of advanced clean energy plays a key role in meeting the national major needs and realizing carbon neutrality goal.Electrocatalytic water splitting is recognized as the ideal technical route for large-scale acquisition of green hydrogen energy.To drastically alleviate the bottleneck issue of high cost towards water splitting commercialization,cheap and high-efficiency electrocatalysts are indispensable by substantially reducing electric power loss.Rational design,precise construction and flexible regulation of active sites by means of single-atom defect engineering represents as an effective approach to optimizing comprehensive electrocatalytic performance and deciphering electrocatalytic mechanism from the atomic level.However,the current application of single-atom defect engineering is still heavily plagued by the deficiency of theoretical guidance and systematic selection procedures.Moreover,the existence states of single-atom defects lack overall while precise regulation,and the mutual assembly together with their synergistic catalytic mechanism among diverse single-atom defects also remain to be further explored.Herein,advanced high throughput computational techniques and precise defect manufacturing strategies were developed and well leveraged to theoretically predict,rationally design and systematically construcut muti-type single-atom defect configurations and their complexes,from which diverse active sites were flexibly modulated and synergistically utilized.Furthermore,the strong correlations among local coordination configuration,electronic structure and overall electrocatalytic activity were revealed from multiple perspectives of thermodynamic energy barrier,intermolecular interaction,electronic orbital filling,and charge transfer.And the structural origin of functional superiorities for varied single-atom defects together with their inter-collaboration mechanism was deciphered as well.On this basis,the electrochemical performance of hydrogen evolution reaction(HER)was appreciably improved to prompt the advances of defect engineering in catalysts towards precise regulation of single-atomic level.Aimed at the bottlenecks of active site deficiency and electrical conductivity inferiority for two-dimensional transition metal based dichalcogenides,the concept of single-atom vacancy catalysis was proposed.Guided by the high throughput prediction,a facile and mild liquid etching strategy was developed to precisely regulate the concentration and distribution of single-atom sulfur(S)vacancies on the surface of MoS2 nanosheet arrays.Such defect configuration enabled sufficient exposure of metallic active sites and considerable enhancement of electronic delocalization effect there.On this basis,S vacancies and nitrogen(N)heteroatoms were further assembled to achieve the breakthrough of active site amount and per-site intrinsic activity in MoS2.The corresponding HER overpotential was continuously lowered to 85 mV,and the reduction ratio was up to～60%.In addition,the bi-anionic defects enabled substantial elevation of intrinsic electrocatalytic activity and charge transfer property was unraveled to originate from the synergistic optimization of local charge distribution,density of states near the Fermi level,and orbital hybrization of compositional atoms.This work,to some extent,bridges the gap between precise theoretical design and practical regulation effects of catalysts from the atomic level,thus rendering reference value to the exploration of atomic defect assembly and synergy.To further expand the defect assembly forms and their catalytic effects,a dual cationic-and-anionic defect strategy was developed to construct asymmetric coordination geometry.The functional features of single-atomic manganese(Mn)substitution and single-atomic S vacancy complexes were theoretically predicted in terms of wide-range activation of surface S sites,fully exposure of Mo sites,and synergistic optimization of per-site activity.Enlightened by this,facile in-situ doping and subsequent mild liquid etching were jointly utilized to finely regulate the distribution of as-predicted defect complexes in MoS2 nanosheet arrays.The HER overpotential and Tafel slope were thus reduced to 67 mV and 51 mV dec-1,respectively.According to theoretical calculations,asymmetric coordination geometry can effectively elevate the Mo-d band center,and induce new electronic states near the Fermi level in S-p orbitals.This work delivers reference value to the rational design and precise construction of complex yet interesting coordination geometries,contributing to better understanding of subtle structure-performance correlations between catalyst micro-environment and site activity.Towards alkaline HER characteristic of more complex mechanism,the research idea of single-atom defect based active motif structuring for synergistically optimizing sequential step kinetics was proposed.And machine learning assisted rational design strategy for dual single-atomic configurations was developed as well.Through initial systematic screening from a large sample library followed by second-round targeted selection,the combination of single-atomic ruthenium(Ru)protrusion and single-atomic cobalt(Co)substitution(Co-Ru)was precisely figured out as the most superior for alkaline HER in MoS2.Solvothermal in-stiu doping and wet-chemical impregnation were combined to systematically regulate the specific distribution of as-predicted Co-Ru configurations in MoS2 nanosheet arrays.On this basis,the bottleneck issues of insufficient single-atom anchoring stability and ultrahigh water molecule dissociation energy barrier were addressed to considerably lower the overpotential and Tafel slope down to 56 mV and 48 mV dec-1,respectively.Such decent performance could rank in the forefront among those of ever-reported heteroatom mediated MoS2-based electrocatalysts.Theoretical calculations demonstrate that,single Ru atoms can dramatically adsorb and activate water molecules,and single Co atoms facilitate to activate adjacent S atoms for decent adsorption of H*intermediates.The as-proposed idea of data-driven rational design of active multi-site configurations can be extended to the construction of other complex catalytic platforms,thus facilitating the concurrent acceleration of multi-step reactions.This dissertation sheds new light on the extensive application of single-atom defects in the catalytic field,contributes to in-depth understanding of the catalytic activity origin in two-dimensional materials from the atomic level,and renders with guiding principles on the rational selection,precise regulation as well as optimal matching of active multi-sites.