Theoretical Design And Simulation Of Highly Efficient Two-Dimensional Electrocatalytic Materials

The development of advanced and clean energy conversion and storage technologies is the key to the sustainable development of society.Electrocatalysis is considered one of the most promising strategies for green chemical synthesis because of its high efficiency,controllability,and reproducibility.Exploring high-performance electrocatalysts is crucial for improving energy conversion efficiency and reducing energy consumption.Conventional noble metals have been widely used as electrocatalysts because they exhibit high activity and selectivity for many reactions.However,it is difficult to achieve large-scale commercialization due to the limitation of high cost and scarcity.Fortunately,as two-dimensional material synthesis technologies become mature,the application of two-dimensional materials in electrocatalysis has also attracted considerable attention.Two-dimensional materials are very promising as alternatives to noble metals due to their ultra-high specific surface area,a large number of exposed active sites and feature-rich electronic properties.However,how to realize high activity,stability and selectivity in the same two-dimensional material is the bottleneck of the development of two-dimensional electrocatalysts.The theoretical study of two-dimensional electrocatalytic materials is of instructive significance for developing the ideal two-dimensional electrocatalysts in experiments.Our studies mainly focus on two aspects in this dissertation.The first one is about the study of structural engineering strategy in improving hydrogen evolution and oxygen catalytic performance of two-dimensional materials.We actively explore effective descriptors to reveal the complex interaction mechanism between adsorbates and catalysts surface and accurately demonstrate the structure-efficiency relationship,which is expected to achieve the maximized catalytic performance of materials and provide theoretical guidance to promote the application of two-dimensional materials in practical energy conversion devices.The second one is about the rational design and effective screening of high-effective electrocatalysts for ammonia synthesis and reveals the underlying physical and chemical mechanisms behind the reactions.The more specific research details are as follows:(1)MoS2 has been attracting tremendous attention as a promising alternative to noble metal catalysts for the hydrogen evolution reaction.However,its inert basal plane and poor electric conductivity hamper its application.In addition,the active sites for electrochemical reactions are limited to Mo-terminated edges,thus leading to inefficient utilization.As a result,improving the conductivity and increasing the density of active sites are highly desirable for enhancing the hydrogen evolution activity of the basal plane of MoS2.Here,experimentally accessible grain boundaries in MoS2 are simulated and their catalytic performance for hydrogen evolution reaction is examined.It is conclusive that grain boundaries engineering is a very efficient strategy to activate the basal plane of MoS2 for hydrogen evolution reaction.Grain boundaries in MoS2 behave as one-dimensional metallic quantum wires with high conductivity.S-4|8 grain boundary shows greatly enhanced catalytic HER performance with a much lower overpotential of-0.17 V than the unbroken MoS2 of 1.88 V.We also propose an effective descriptor Δεp→d that can unambiguously unravel the origin of the enhanced hydrogen evolution reaction activity of grain boundaries and verified its applicability in cases of other defects such as point defects and edges,which is expected to provide a theoretical guide for improving the electrochemical hydrogen evolution reaction activity of transition metal chalcogenides in general.(2)The oxygen evolution reaction is a half-reaction of water electrolysis involving four-step proton-electron coupling.Its slow reaction kinetics usually requires a much higher electrode potential than the equilibrium potential to drive the reaction,which severely limits the efficiency of water electrolysis.Additionally,in the conventional adsorbate evolution mechanism,the inherent scaling relationship between the adsorption strength of oxygencontaining intermediates further limits its theoretical overpotential to no less than 0.37 V.Here,we design a series of iron-based single-atom catalysts with different coordination environments and find their stability,catalytic activity and selectivity of water electrolysis and oxygen reduction are highly correlated with the coordination microenvironment of iron atom center.Especially,we find that breaking the coordination shell symmetry breaks the well-accepted standard scaling relationship,and thus optimizes the oxygen evolution reaction activity,for example,to an extremely low overpotential of 0.17 V in FeC2N2-Ⅱ.In combination with ligand field theory,the dramatically improved oxygen evolution reaction activity can be well explained.we also highlight the pivotal role of spin configuration and orbital interactions in electrocatalysis.(3)We use the MoO3 monolayer as a model catalyst to further study the potential application of two-dimensional metal oxides in oxygen evolution reactions,and reveal the impact of structural engineering(oxygen vacancies,alkali metal modification and transition metal doping)for improving oxygen evolution activity.The results suggest that alkali metal(Li,Na,K and Cs)modification and transition metal(Fe,Co,Ni,Ru and Ir)doping are effective strategies to dislodge the inertia of MoO3 for accessing greatly reduced overpotentials.3d-TM(Fe,Co and Ni)doping transfers the reaction mechanism from the conventional adsorbate evolution mechanism to the lattice oxygen mechanism and successfully gets rid of the limitation of theoretical overpotential(0.37 V).We unravel the relationship between the transformation of the oxygen evolution reaction mechanism and the electronic structures of the catalysts,and confirm alkali metal modification can further improves the lattice oxygen reactivity by adjusting the p-band center.These findings emphasize the importance of structural regulation for improving catalyst activity and provide new theoretical insights for designing efficient catalytic materials.(4)Recently,electrochemical NH3 synthesis can be realized by reactions of nitrogen fixation and NOx reduction under mild conditions powered by renewable electricity,which has gained wide attention.Here,we design a series of single-atom catalysts in graphene-like carbon nitride and covalent-bonded carbon matrixes.W/g-CN and V-pyridine-G(aG,zaG)are screened as promising catalysts for nitrogen reduction reaction and nitrate reduction reaction,respectively.We demonstrate their stability from multiple aspects and explained the origin of their high activity from a theoretical view.These studies emphasize an important factor that an optimal match between active centers and ligands needs close attention,hinting at the future design of efficient catalysts for electrochemical NH3 synthesis.