Theoretical Study On Electronic And Electrocatalytic Properties Of Low-dimensional Materials

With the development of society,ever-increasing energy demand,depleting fossil-fuel resources and increasingly serious global warming urgently require us to find green,clean and sustainable energy alternatives,including renewable energy conversion and sustainable energy storage technologies.Electrocatalytic technology is considered to be one of the effective strategies to solve those challenges due to its high efficiency and pollution-free advantages.For electrocatalytic technology,electrocatalyst is critical for electrocatalytic performance.At present,high-efficiency electrocatalysts are usually based on noble metal or noble metal oxides.However,the high-cost and scarcity limit their large-scale commercial applications.In addition,they also face the problem of low-selectivity in practical applications.Therefore,finding stable,low-cost,high-activity and high-selectivity electrocatalysts is essential for the development of electrocatalytic technology.Low-dimensional materials have high specific surface area and unique electronic properties as compared with their bulk materials,providing them with high application potential in the fields of energy storage and conversion.In recent years,lowdimensional materials have been extensively studied theoretically and experimentally,and various low-dimensional materials have been successfully synthesized in experiments,which provides the foundation for the applications of low-dimensional materials in the field of electrocatalysis.In this dissertation,we study and design a series of novel low-dimensional materials,discussed their electronic structures and electrochemical properties,and explore their application potential in the fields of electrocatalytic hydrogen evolution reaction,battery electrodes,and electrocatalytic ammonia synthesis,and we reveal the intrinsic physical mechanism of their excellent catalytic performance.Those works provide theoretical guidance for the applications of low-dimensional materials in the field of electrocatalysis.This dissertation consists of six chapters.In the first chapter,we briefly summarize the research progress and application of low-dimensional materials.In the second chapter,we briefly introduce the theoretical basis of first-principles calculations and software package.In the third chapter,we introduce the design of two-dimensional electrocatalysts for hydrogen evolution reaction and the regulation of their properties.In the fourth chapter,we introduce the application potential of two-dimensional materials in battery electrodes.In the fifth chapter,we study the electrocatalytic properties for NH3 synthesis of low-dimensional materials.In the sixth chapter,we summarize the research contents and innovations of this dissertation,and discuss the future research directions of electrocatalytic technology.The main research contents and conclusions of this dissertation are as follows:(1)We explore the potential of A2BS4(A=Ag,Cu;B=Mo,W)monolayer as electrocatalysts for hydrogen evolution reaction and identify Cu2WS4 monolayer as a promising candidate.Our results indicate A2BS4 monolayer is dynamically and thermally stable,and they can be easily exfoliated from the layered bulks,with experimental feasibility.We find the basal plane of Cu2WS4 monolayer can reach excellent electrocatalytic activity toward hydrogen evolution reaction with small density of vacancies and applied strain.Through the exploration of the reaction mechanism,we further reveal the regulation of the catalytic activity is mainly achieved by regulating the the d-band center of the transition metal atoms.Our work enriches the research on electrocatalytic hydrogen evolution reaction.(2)We investigate the catalytic activity of group ⅣA monochalcogenide MX(M=Ge,Sn;X=S,Se)monolayer for hydrogen evolution reaction.Our results reveal that M vacancy can trigger the catalytic activities of the MX plane.Especially,SnSe with Sn vacancies and GeSe with Ge vacancies,they exhibit high catalytic activities for hydrogen evolution reaction at low defect concentrations,and the performances are comparable to,or even better than Pt.Furthermore,the detailed analysis of strain engineering and binding strength schematically unravel the mechanism of the boosted hydrogen evolution.This work expands the applications of group ⅣA monochalcogenides monolayers in electrocatalytic hydrogen evolution reaction.(3)We investigate the catalytic activities of single atom catalysts of transition metalporphyrin in Li-O2 batteries.Through fully exploring the possible reaction pathways,we reveal the reaction mechanism and chemical compositions of reaction products,and find that Fe/Co/Ni/Cu-porphyrins are promising cathode electrocatalysts for rechargeable Li-O2 batteries.Furthermore,the influences of various axial ligands on their catalytic activity are also studied.Based on the catalytic activities of free and axial ligand adsorbed Fe/Co/Ni/Cuporphyrin,the adsorption free energy of LiO2 is identified as an activity descriptor for these cathode electrocatalysts.We further show that such a descriptor is also applicable for the catalytic activities of Fe/Co/Ni/Cu-porphyrin in Na-O2 batteries.This work not only provides a series of highly efficient single atom catalysts for alkali oxygen batteries,but also presents a universal design principle.(4)We investigate the potential of transition metal-doped Janus MoSSe monolayer in oxygen reduction reaction,oxygen evolution reaction,and Na-O2 battery.We find that Ni-doped Janus monolayer MoSSe possess superior electrocatalytic performance toward oxygen reduction reaction for fuel cells and oxygen evolution reaction for water splitting.Both its oxygen reduction reaction and oxygen evolution reaction exhibit an ultralow overpotential,and the oxygen reduction reaction possesses a high selectivity.In addition,it also shows high performance of Na-O2 batteries with a low overpotential of 0.49/0.59 V for oxygen reduction reaction/oxygen evolution reaction,suggesting it is the excellent trifunctional catalyst.We reveal that the superior catalytic activity of Ni-doped Janus monolayer MoSSe are due to the synergistic effect of the built-in electric field and heteroatom doping.These findings not only gain deeper insight into the catalytic activity of Janus MoSSe but also guide for developing promising trifunctional electrocatalysts.(5)We investigate the electrocatalytic activity of molecular nanowires(i.e.,transition metal-phthalocyanine and transition metal-porphyrin nanowires)for hydrogen evolution and nitrogen reduction reaction.Among the 20 molecular nanowire systems,Cophthalocyanine/porphyrin nanowires are found to be the potential electrocatalysts for hydrogen evolution reaction,while Ti-porphyrin and Mo-phthalocyanine/porphyrin nanowires show superior electrocatalytic activity and selectivity for nitrogen reduction reaction.Such catalytic activities primarily correlate to the electronic occupation of their d orbitals.Our study not only extends the electrocatalysts to molecular nanowire systems for the first time but also provides a principle for designing high efficient molecular nanowire catalysts.(6)We design a metal-free electrocatalyst,namely,P atom doped single-layer C2N,as a promising candidate system for achieving the direct electroreduction of NO to NH3.Particularly,the double P doped C2N(2P@C2N)exhibits excellent catalytic activity and high selectivity,which correlates with the sp3 hybridization of the P atom.Moreover,our microkinetic modeling analysis of NO reduction reaction to NH3 on 2P@C2N exhibit that the turnover frequency is as large as 8.9×105 per s per site at 400 K,indicating an ultra-fast reaction rate.Our study not only provides the first metal-free electrocatalyst for NO removal,but also propose an effective alternative avenue for ammonia synthesis.(7)We investigate the properties of main group metal Mg,Al and Ga to form graphenebased single-atom catalysts for NO reduction reaction toward NH3,and find that the main group metal elements could be catalytic active centers.Through a rationally designed four-step process,from 51 single-atom catalysts candidates with different metal coordination environment,six single-atom catalysts are computationally screened with high catalytic activity and selectivity for NO reduction reaction toward NH3.The adsorption free energy of NO can be identified as efficient descriptor for such single-atom catalysts,and the catalytic performance is rationalized by the modulation of s/p-band filling of the main-group metals.The underlying physical mechanism is revealed and generally applicable to other main group metal single-atom catalysts.Our work extends single-atom catalysts to main-group metal elements.(8)We investigate the nitric oxide reduction reaction performance of transition-metal-atom decorated carbon nitride monolayer(g-C3N4).We find that the single Cu-atom decorated gC3N4(Cu@g-C3N4)could be a promising single-atom catalyst candidate for the NO reduction reaction toward NH3 with excellent catalytic activity,the limiting potential of 0.371 V.Moreover,Cu@g-C3N4 can efficiently suppress the competing hydrogen evolution reaction,with high Faradaic efficiency.Our work provides a potential single-atom catalyst candidate for NO reduction reaction to resolve environmental pollution and sustainable ammonia production.